GB2044445A - Measuring scatter distribution - Google Patents

Abstract

In an apparatus in which particles which may include biological cells are passed through an optical sensing zone to measure the spatial distribution of radiant energy scattered from them, a structure and method are provided for increasing the angle of capture of the scattered radiation for a planar assembly of photovoltaic detectors (60). A flow cell (26) is situated at the principal focus of an ellipsoid (29), paraboloid, hyperboloid or similar reflector which is symmetrical about its optical axis (20), along which a light beam is directed. The reflector is utilized to capture the radiant energy on angles which could include most forward and/or backward angles and all azimuthal angles and to deviate the same to the detector assembly (60). By moving the assembly of detectors along the optical axis (20) the optimum distance is established for obtaining the greatest amount of information. <IMAGE>

Description

SPECIFICATION Radiant energy reradiating flow cell systems and methods This invention is concerned generally with the measurement of the spatial distrubution of radiant energy such as that of reradiated light produced by scattering and fluorescence. More particularly, but not exclusively, the invention is concerned with the measurement of the energy and direction of light flux or rays produced and reradiated or distributed by particles passing through an optical sensing zone whereby to enable the identification of the particles and/or their characteristics.

The invention is applicable to improve the usefulness of a known integral planar geometric configuration of photovoltaic detectors whereby it is highly flexible and is rendered capable of measuring most forward or backward scattering angles and in all azimuths and the invention is not limited in its application to the subject matter of our co-pending patent applications based on U.S.

Serial Nos. 439 and 438 mentioned below.

A preferred embodiment of the invention will shortly be described in which there is substitution for an integral planar geometric configuration of photovoltaic detectors which enables the fabrication of a highly effective and economical device without the configuration. This preferred embodiment of the invention utilizes teachings of the following U.S. patent applications: "Apparatus and Method for Measuring the Distribution of Radiant Energy Produced in Particle Investigation Systems", Serial No. 000,439, filed January 2, 1 979 and "Apparatus and Method for Measuring Scattering of Light in Particle Detection Systems", Serial No. 000,438, filed January 2, 1979. We have included in the present specification passages and drawings taken from our co-pending patent applications based on U.S. Serial Nos. 439 and 438.

One problem with known measurement systems (not including measurement systems which are disclosed in the said copending applications) is that they are limited considerably in the range of polar angles that can be measured.

For the purposes of this discussion the optical axis of reradiation may be considered the line ofthe incident light beam projected at a sensing zone where a particle intersects the same. Using conventional definitions, the polar angles are those defined by the angles of the optical axis with lines centered at the sensing zone or point and radiating from that zone, while the azimuthal angles are those measured around the optical axis.

One attempt has been made to evolve an arrangement which can measure multiple angles by means of an integral, planar, geometric configuration of photovoltaic detectors, but the problem with this device is that it can only measure polar reradiating angles from about 1 " to somewhat less than 250. Any attempt to measure the energy distribution in most polar angles in the forward (00 to 900) and all angles in the backward direction relative to the sensing or scattering zone and the incident light direction including all azimuthal angles, fails because the sensitive area of the device is too small. This is because all of the photovoltaic elements which "see" the energy must be mounted on the same plane within the available space which is limited. Accordingly the utility of the device is limited.

The particular device which is referred to is in the form of a concentric ring and wedge photovoltaic detector. It is described in considerable detail in U.S. Patents 3,689,772; 4,070,1 13 and in two articles entitled "Light Scattering Patterns of Isolated Oligodendroglia" by R.A. Meyer, et al in The Journal of Histochemistry and Cytochemistry, Vol, 22, No. 7 pp. 594-597, 1 974 and a second article entitled "Gynecological Specimen Analysis by Multiangle Light Scattering in a Flow System" by G. C.

Salzman et al in the same journal, Vol. 24, No. 1, pp.308-314,1976. In these articles reference is made to the same or a similar detector device which is commercially available and which is identified as a Recognition Systems, Inc. detector (RSI).

The configuration of detectors which has been mentioned above will be referred to hereinafter as a planar configuration of detectors. As known at this time the one mentioned in the above references is expensive, difficult to manufacture, delicate, inefficient and slow-acting because of its relatively large area considering the number of detectors which it carries. The inefficient optical design results in a poor signal to noise ratio.

Notwithstanding these disadvantages, such a configuration and in general any radiant-toelectrical energy transducers configured in a geometric assemblage which is planar are and can be useful within the field they occupy, but according to the invention herein, this usefulness can be materially increased. The planar configuration of detectors at the minimum can serve the purpose of helping to find a location at which some desired set of polar6eradiating angles are the optimum for a given optical system and for a particular family or type of particles being studied.

Once an optimum position has been achieved in a given system, the planar configuration of photovoltaic detectors can be removed from the system and a more economical device substituted therefore, this latter device comprising a composite deviating lens or reflector which is formed of a large number o? elements such as prisms each oriented to deviate or reflect a certain geometric portion of the reradiated energy area being studied to different and spaced apart commonly available and highly economical photodetecting devices such as small photocells.

The measurements from all of the photocells give the information desired.

Prior art patents which may be of interest are: U.K. Patent 137,637 of 1920 to Pollard and Frommer U.S. Patent 3,248,551.

According to one aspect of the invention there is provided: A method of measuring the directional distributional properties of the radiant energy reradiated from a particle for characterization or the like of said particle and using a known integral configuration of photovoltaic detectors having a sensitive front planar surface which method comprises:: A. passing the particle through a sensing zone located on the interior of a concave reflector whose configuration is substantially defined be a geometric law, the reflector being symmetrical about an optical axis and having a first focal point also defined by said geometric law, the sensing zone being at said first focal point, B. directing a beam of incident radiant energy along said axis to said sensing zone, and C. intercepting the radiant energy which has been reradiated by said particle and emerging from the front of said reflector at said planar surface.

According to another aspect of the invention there is provided: Apparatus for measuring the distribution of radiant energy produced by particles for characterization or the like of said particles which comprises: A. a source of radiant energy arranged to project a beam of radiant energy along a first axis, B. a sensing zone on said first axis, C. means for moving particles through said sensing zone to produce reradiated radiant energy from said particles, D. means for collecting some of the radiant energy reradiated in angles substantially surrounding said sensing zone and projecting same as ray groups toward a measuring device spaced from said sensing zone along said axis, said collecting means comprising i. a concave reflector which is symmetrical about said axis, the opening of said reflector facing toward said measuring device, ii. the configuration of said reflector being defined by a predetermined geometric law which provides for a focal point on the interior of said reflector, iii. the sensing zone being coincident with said focal point, E. said measuring device comprising an integral configuration of photovoltaic detectors having a sensitive planar surface, said planar surface being normal to said axis and facing said opening of the concave reflector and adapted to receive the projected ray groups.

According to another aspect of the invention there is provided: A system for measuring reradiated radiant energy which has been scattered or reradiated by fluorescence which includes a flow cell in which a particle or a biological cell is passed through a sensing zone which additionally comprises the focus of a reflector on the interior thereof. The reflector can comprise a concave geometric shape symmetrical around its axis and adapted to capture reradiated light (e.g. scattered or fluorescent) from wide and narrow polar angles and all azimuthal angles and to project the same out of the reflector. The reflector is a shape of revolution of a geometric law about is optical axis.

As used herein light means any electromagnetic radiation which is capable of being detected by transducers of the type utilized in this art.

Means are provided for bringing the particles, cells or scatterers as they are often called herein, into the reflector as for example in a liquid flow, the reflector interior being enclosed and having a compatible liquid sealed therein.

The rays of light projected by the reflector can be either focussed or directed without focussing onto an integral, planar configuration of photovoltaic detectors of a construction known in the prior art thereby increasing the usefulness of that device.

One aspect of the invention provides for the configuration of detectors to be located at a place along the axis of the geometric reflector which provides the most favorable information in the particle system being investigated. Another aspect has the configuration moveable to find such a place. A third aspect teaches that one the best location has been found, a different structure is substituted for the configuration which comprises a composite lens or a composite reflector which captures the rays of reradiated light and either deviates them or reflects them in a plurality of different directions relative to the axis of the geometric reflector. An individual photocell of economical construction is then located to intercept each respective one of these rays and the investigation is carried out by monitoring all of the photocells.

The apparatus can be used for fluorescent light measurements by using filters to separate scattered and fluorescent light produced at the same sensing zone.

By way of example only, certain illustrative embodiments of the invention will now be described with reference to the accompanying drawings, in which: Figures 1 to 8H are taken from our co-pending patent application claiming priority from U.S.

Serial No. 439 and in which: Figure 1 is a diagrammatic view of the prior art environment in which apparatus shown in the other Figures is utilized; Figure 2 is a diagrammatic generally sectional view through a simplified form of apparatus showing the manner in which scattered light from a sensing zone is collected and thereafter deviated to photo responsive devices; Figure 2A is a front-on elevational view of a fresnelled lens assembly of Figure 2 showing one form thereof and Figure 2B is the same but showing another form thereof:: Figure 2C is a perspective view of several cylinders which can be assembled to produce a master for making a lens of the type shown in Figure 2; Figures 2D and 2E are diagrammatic generally sectional views of a structure used in apparatus such as shown in Figure 2 to enhance the operation thereof by purifying the beam of radiant energy reaching the photodetector; Figure 3 is a diagrammatic generally sectional view through one form of apparatus in which an ellipsoidal reflecting device is used to collect radiant energy and direct it to a fresnelled lens for deviation; Figure 3A is a generally front-on elevational view of an array of photodetecting devices of Figure 3 taken generally in the direction of the arrows 3A-3A of Figure 3;; Figure 3B is a generally front-on elevational view of the fresnelled lens of Figure 3 taken in the direction of the arrows 3B-3B; Figure 3C is a perspective view of several cylinders which can be assembled to produce a master for making a lens of the type shown in Figures 3 and 3B; Figure 4 is a view similar to that of Figure 3 but illustrating another form of apparatus in which narrow angle forward scattering measurements can be made; Figure 5 is another view similar to that of Figure 4 but illustrating the use of a television camera tube as a photodetecting device in place of conventional photocells; Figure 6 is a diagrammatic view of a system in which the beam of radiant energy is formed of at least two sources of light of different wavelengths;; Figure 6A is a front-on elevational view of the array of photodetecting devices of Figure 6 taken generally in the direction of the arrows of Figure 6; Figure 6B is a front-on elevational view of the fresnelled lens assembly of Figure 6 taken generally in the direction of the arrows 6B-6B of Figure 6; Figure 7 is a view similar to that of Figure 6 but showing a modified form of apparatus utilizing a plurality of wedges instead of fresnel prisms, all assembled as shown; Figure 7A is a sectional view through the same along the line 7A-7A and in the indicated direction; Figure 8 is a diagrammatic view of another system in which the scattered radiant energy is collected by a reflector of ellipsoidal configuration and deviated by a special composite reflector assembly;; Figures 8A, 8B, 8C and 8D are diagrams used to explain the operation and construction of the systems of Figure 8; and Figures 8E, 8F, 8G and 8H are photographic views in perspective of a model constructed to show how the mirror of Figure 8 is derived; Figures 9 to 1 3 are taken from our co-pending patent application claiming priority from U.S.

Serial No.438 and in which; Figure 9 is a diagrammatic generally sectional view through a simplified form of composite mirror showing the manner in which scattered light from a sensing zone is collected and deviated to photoresponsive devices; Figure 10 is a diagrammatic view similar to that of Figure 9 but showing the spherical mirror from which that form of Figure 9 is derived; Figures 11 and 12 are diagrammatic fragmentary generally sectional views of structures used in apparatus such as shown in Figure 9 to enhance the operation thereof by purifying the beams of radiant energy reaching the respective photodetectors; and Figure 13 is a view similar to that of Figure 9 but shows apparatus for measuring back scattering instead of forward scattering; Figure 14 is a diagrammatic view of a light reradiating flow cell system constructed in accordance with the invention and using as an element thereof an integral planar configuration of photovoltaic detectors; Figure 1 5 is a fragmentary view of the left hand portion of the system of Figure 14 but showing how a fresnel lens and individual photocells are substituted for the configuration of photovoltaic detectors of Figure 14.

Figure 16 is a view similar to that of Figure 14 but illustrating an embodiment of the invention using a hyperboloidal reflector instead of an ellipsoidal reflector for certain specific measurements; Figure 1 7 is a simplified diagram of a modified form of the embodiment illustrated in Figure 1 6; Figure 18 is a simplified diagram of another embodiment of the invention using a paraboloid; Figure 19 is a simplified diagram of an embodiment of the invention for additionally measuring fluorescence; and Figure 20 is a simplified diagram of another embodiment of the invention which is the same as Figure 1 9 but symmetrically reversed about a dichroic mirror in order to permit the use of commercially more available mirrors.

Referring to Figures 1 to 8H a method of examining particles comprises providing a sensing zone and passing the particles through this sensing zone to sense their presence and to direct radiant energy thereon. The particle scatters the radiant energy and this scattered radiant energy is collected by suitable optical means and focussed or confluenced towards a point in space, but it is intercepted by an assembly of elements which causes the energy in the different angles or paths or geometric parts to be deviated for the convenience of measuring them. The measurement is effected by an array of photodetecting devices or elements which respond respectively to the intensity of energy present in the particular angle, path or part. This array may be a television vidicon surface.From this data, by reason of information which is known from previous studies, one can identify and/or determine the character of the particle which produced the scattering.

Apparatus shown in Figures 2 to 8H is believed to provide a greater quantity and more accurate scattering data than known methods and apparatus as a result of which it is useful for the establishment of information related to specific types of particles by passing known particles into the sensing zone in order to learn the scattering effects of such particles for use in other work where unknown particles are being identified.

In a specific sense, the scattered energy can be thought of as hollow or solid cones of light or radiant energy each of which is brought to a focus at the location of the photo-responsive device or element which is intended to make the measurement for that specific cone. The scattered energy can also be measured as part cones for additional information, as for example when the energy may not be in symmetrical geometric form, although this is unusual.

According to Figures 2 to 8H a lens or a mirror is formed out of a plurality of optical elements, usually annular in form, which "point" or are focussed in specific directions to enable the energy deviated thereby to be confluenced and measured. The elements can be assembled in a single integrated member such as a linear fresnel lens whereby the practical thickness of the resulting equivalent prismatic element is much less than it would be if actual prisms were used. In the case of a lens, the same is normally formed of generally annular prism elements but could be synthesized from a plurality of small prisms assembled to provide a lens which can produce a large number of beams to be directed onto the incremental elements of a television camera tube for measurement. This could be done as well for a mirror whose elements are rings or arcuate parts of rings assembled together.

Figure 1 illustrates a prior art system which shows the environment in which the apparatus of the other Figures is utilized. Here a source of particles 10 is provided which can feed, for example, white blood cells, exfoliated cells or the like in a diluent by way of the path 12 to the flow through element 1 6. This can be effected in this simple flow or with some additional second diluent which produces a particular form of geometric cross section of fluid in a sensing zone.

The additional diluent can comprise a stream of liquid under pressure surrounding the main flow to produce sheath flow conditions through the body of the liquid whereby to confine the particle stream. The basic stream itself can form a fiat planar stream through the sensing zone.

From the flow-through element 16, the fluid that has been passed through moves along the path 1 8 to a suitable receptor 20 which can be waste, another system or an accumulator.

The source of radiant energy is here shown as a laser 22 but can be any suitable source of light or the like. Apparatus according to Figures 2 to 8H provides an efficiency which enables the laser used to be of low power with very little heat generation. The resulting beam is passed along the optical axis 24 to an optical system or train represented by the lens 26 which shapes and focusses the incident radiant energy onto the sensing zone of the flow-through element 16, the emergent light being scattered and providing a plurality of radiating beams indicated at 30. Only three such beams are shown as representative, there being a continuous spread of the energy, the amount of radiant energy at any diverging angle and in any sector being dependent upon the size, shape, orientation and morphology of the scatterer (particle) plus characteristics of the incident light.

A detector 32 is provided which if ideally constructed would respond differently at its different geometric aspects facing the beams 30 so that at incremental locations over the area of its frontal aspect it will produce different indentifiable signals, notably, signals of different intensities.

These signals are passed through the channels 34 to some form of data processor 36. From the signals and their relationship to one another, both as to intensity and geometric location, the particle which produced the signals can be identified or at least characterized.

The detector 32 of the prior art has several optical disadvantages which are overcome in whole or in part by apparatus according to Figures 2 to 8H. The detector 32 has a large number of photoresponsive elements in its array because it was designed for many types of distributions of radiant energy. However in particle investigating systems, different populations of particles have different, optimal detection areas for the photoresponsive elements in general. By using different radiation redirecting means, such as a fresnel refracting device, the different optimal detection areas are easily and inexpensively obtained.

Although a large percentage of the radiant power scattered by a particle proceeds in the near-forward direction, the information carried by the scattered light is contained throughout the 4x steradians total solid angle centered at the particle. It is information which is sought; power perse is useful only as it increases signal-tonoise ratio. Using the detector 32 without optical elements between it and the particle, appreciably less than half of the total radiant information can be made to fall on the detector. By using a reflector as described herein, most of the total solid angle is available, and it can be easily subdivided into regions for optimal collection of information.

A combined radiant energy deviating means and array of photodetectors according to Figures 2 to 8H is usable as a replacement for the element identified as 32 in Figure 1.

In Figure 2 there is illustrated a simple form of apparatus. The point 40 represents the location of what may be termed the scattering point, this being, for example, a sensing zone through which particles are flowed. Although not here illustrated in can be assurned that these particles enter the sensing zone laterally of the optical axis 42 and cross the axis at said point 40 one at a time. Light or other radiant energy is directed from the left in the view toward the scattering point 40 along the optical axis 42 with the central or main portion of the beam being captured by an axially located angled mirror 44 directing the central portion of the beam to a laterally located absorbing device 46 which is known in the art as a light dump.

The scattered rays of radiant energy from the scattering point 40 are concentrated or collected by a lens 90 which for convenience is in fresenei form. It should be understood that any optical or lens system could be used for the same purpose, that is, the prevention of the spreading of the scattered rays 48 and concentrating them towards a point such as for example, the point 92.

The distances from the scattering point 40 to the lens 90 and from the lens 90 to the point 92 are equal and will determine whether there is any "magnification" of the scattered light by the lens 90 or an equivalent optical system. If the distances are both equal to twice the focal length of the lens 90, magnification will be unity, but this can be adjusted to other values if desired.

Immediåtely following the lens 90 to the right as viewed in Figure 3 there is an element 94 which is an optical assembly whose construction and function will be described.

The function of the element 94 is to capture radiant energy from a specifically defined geometric frontal area of the combined scattered beams 48 and to deviate the same as the energy or light passes through a particular portion of the element 94 from rear to front so that the radiant energy collected by the lens 90 will not tend to be directed to the focal point 92 as physically demanded by the action of the lens 90, but instead will be redirected to a point laterally of the axis 92. As indicated in Figure 2, one set of transmitted rays 50 which can be assumed to have a hollow conical configuration is shown being deviated to and confluenced upon a photodetector 96 while a second set of transmitted rays 52 of the same general configuration is shown being deviated to and confluenced upon a photodetector 98.These photodetectors are only examplary of a plurality which together receive many sets of rays, but each detector receiving only rays from a specific geometric portion of the scattered radiation. Their placement is at locations which will be convenient and can be widespread so that there is a practical distance between them. The location is controlled by the angle of deviation of the transmitted rays and the distance from the lens 90.

An advantage of this arrangement is that the photo-detectors can be standard photocells which are readily available. The radiant energy from the different portions of the element 94 is confluenced on these photocells which can now be quite small and hence provide a better signal to noise ratio, lower capacitance in the circuits used and reduced costs. Replacement of defective or damaged photocells is readily effected without discarding a substantial and expensive part of the apparatus.

Only two sets of rays 50 and 52 are shown in Figure 2 along with their companion photodetectors 96 and 98 but it should be understood that there will be a separate set of rays and an individual additional photodetector for each predetermined segment of frontal geometric area of the element 94.

In Figure 2A there is illustrated one form of the element 94 in which the element is made out of a series of annularfresnelled prisms 100,102,104, 106 and 108. The number of prisms here shown is five for convenience, but any suitable other number could be used. It is understood that their respective analogs are five conventional prisms.

The ridges due to the sawtooth cross sections of the various parts are indicated by cross hatching.

Radiant energy is devicated by an angle which depends upon the slope of the ridge surfaces and in directions perpendicular respectively to these ridges. The solid angles of radiant energy captured in this case will form in effect five conical composite beams of which the beams 50 and 52 comprise those provided by the outer two annular prisms 100 and 102, respectively. Generally for the identification and study of biological particles the prismatic elements of the assembly 94 will be symmetrical about the center of the element 94.

There will be a separate photodetector for each set of beams or solid angle geometric portion of the total radiant energy.

In Figure ZB an arrangement of elements composing the assembly 94' is illustrated in which the upper half of the element 94' is made out of annular fresnell prisms similar to those of Figure 2A but only half of each annular prism element is used. Using only halfis usually acceptable because of the normally symmetrical configuration of scatter patterns. Thus, there are four such semiannular prismatic elements 100', 102', 104' and 106'. The center element 108' may be cylindrical for convenience of construction. In addition there are wedge shaped prismatic elements 110, 112, 1 14, 1 16 and 1 18 which collect and concentrate or confluence rays of the scattered radiant energy of a different geometric area than annular.In this case the wedge shaped prismatic elements may be used to identify the presence of elongate constituents in certain particles. There will be a separate photodetector for each of the wedge shaped prismatic elements 110 to 118.

In the use of the apparatus, the electrical signals from the photodetectors 96 and 98 as well as all of the others which are not illustrated will be channeled to a suitable electrical system where the data will be processed. The analog signals can first be converted into digital if needed for the processing. For example, a computer can have a series of characteristics identified in its memory against which the signals are compared to ascertain the identification of the particle which caused the scattering. Scattering could have been caused by different kinds of structures and/or constituents within the particle, as for example, the organelles and their different densities, configurations and numbers.

Attention is now invited to the composition of the element 94 in Figure 2. As seen from Figure 2A the assembly is formed of five annular parts 100 to 108 each of which is prismatic in form although annular. Each annulus has the same prismatics cross sectional angles as though formed from the same prism but with different diameters.

This element 94 is made out of some suitable material which will refract the particular wavelength of radiant energy being scattered. It can be glass or some form of synthetic resin, which as explained below, can be molded readily.

It is thus dielectric normally and can be described as such. What follows is an explanation of the construction and operation of element 94.

It is only necessary to have the two faces of the element 94 where the rays of radiant energy enter and exit in the form of two planes which are at an angle to each other. The direction of any ray or assembly of rays entering the dielectric material of the element 94 will be rotated about an axis which is parallel to the intersection of these two planes.

The distances the ray travels in the dielectric material per se is immaterial; hence, in the circumstances that optical resolution is of secondary importance, it makes no difference whether the front and rear surfaces of the element 94 consist of two single planes or whether one or both are broken up into-many small planes all having the same angle with respect to its opposite face. This is the principle which makes fresnel prisms and lenses practical and which enables them to be made lightweight and thin.

One direct way to make the element 94 is to take a large fresnel prism and cut as by sawing along concentric circles to divide it into a set of annuli. Once cut, the annuli are all rotated with respect to one another so that the ridges of the fresnel lens are at different angles with respect to some reference and cemented together in a disc with suitable cement. This is illustrated in Figure 2 where the annular parts are 100, 102, 104, 106 and 108. The cross hatching is intended only to show different directions of prismatic ridges; This procedure readily produces a useful device, albeit somewhat expensive because of the labor involved.A problem with this technique is that when high resolution is needed or if, as frequently desired, the radial thickness of inner annuli become progressively smaller, the procedure becomes difficult because of the finite size of the tools which are available. Further, the orientation and adjustment of the individual annuli are delicate procedures.

When the radial thicknesses of the annuli approach the dimensions of the linear pattern of a commercially available fresnel prism, it becomes practical and equally effective to form the element 94 from simple two-plane prisms. Thus an alternative exists between making cylinders from a simple prism or making prisms from simple cylinders. Obviously, the latter procedure is preferable. It is merely necessary to form an inner cylinder and as many pieces of tubing as the number of annuli needed out of the proper dielectric material such as glass or quartz. The pieces of tubing are assembled concentrically and secured to one another by a temporary cement such as wax, a short axial section piece cut off, polished and lapped to the desired prismatic angle.After polishing, the wax may be melted out and the rings as shown at 104, 106 and 108 in Figure 2C are rotated with respect to each other as desired and reassembled with suitable cement.

This small assembly would typically be substituted for the inner parts 108, 106 and 104 of Figure 2A if it is desired to have high resolution for the low angle scatter.

The above techniques are useful in producing individual or experimental devices 94 according to the invention. When building them in production quantities, once it has been determined what angles are to be observed by each of the several photocells 96, 98 etc, a master may be made of any suitable material. This may then be used to make inexpensive duplicates using known techniques such as disclosed in Alvarez U.S.

patent 3,827,798. The elements 94 can be molded in production. It is feasible to make the master from which the mold for element 94 is formed out of non-optical material such as brass or steel and assemble its parts by brazing or welding. The dimensions and angles are precisely computed and the parts cut on machinery that is responsive to computer data or tape.

Once the fresneiled element like 94 has been made for a given apparatus, the distance from the scattering point 40 to the element 94 must be the same in all duplicates of the apparatus. Likewise the placement of the photoresponsive device 96 and 98 and all others that may be used therewith must be the same as the respective positions for which the optical element 94 was designed.

Rather than being a disadvantage, this enables the apparatus to be built using tools, dies, jigs and fixtures which enable assembly line production methods.

It is feasible to combine the lenses 90 and prismatic element 94 into one integral unit and/or mounting.

In Figure 2D there is illustrated a portion of the structure of Figure 2 but enlarged and modified to show the effect of an arrangement which includes an iris. The scattered beams of light, scattering point and other parts of Figure 2 are for clarity not shown. The transmitted cone of radiant energy or beam 50 is here shown emerging from the annular element 100 on an optical axis 78 (which is not shown in Figure 2) in alignment with the photodetector 96. Where the angles of the optical axes of the respective parts of the beam such as 50, 52 and the others are disparate, it is likely that the photodetector elements will be arranged perfectly normal to the said optical axes, respectively, rather than normal to the optical axis 42 in Figure 2. The latter is only for illustration.

The cone of radiant energy represented by the beam 50 is substantially symmetrical around the axis 78. This cone is focussed on the central aperture 80 of an iris 82 instead of on the surface of the photodectector 96. This latter can include a photocell element or the element of a photomultiplier or the like where the focus normally takes place. The photodetector 96, as seen, is behind the iris 82 with respect to.the source of the beam 50. This arrangement prevents any radiant energy from reaching the photoresponsive device 96 except that which is being transmitted from the sensing zone 40 by means of the annular prismatic element 100. The center of the photocell can be sensitive to the extranseous light. say from the other parts of the fresnelled element 94 and from light which concentrates on the axis 42 after passing through the element 94 while getting past the mirror 44.

This center may be blocked off by a centrally located mask 84 as shown.

In Figure 2E there is another arrangement which, in addition to the iris 82 and its aperture 80, there is a small lens 86 between the aperture 80 and the front surface of the photocell 96. The mask 84 is then easily located on the central surface of the lens. This lens could be part of an integral'array of plastics material lenses serving all of the photoresponsive devices and suitably selectively masked by paint to provide the individual iris effect. The result would be to increase the signal to noise ratio of the photocells or other photo responsive devices.

Referring once more to Figure 2C, as mentioned above, the circular components of the element 94 are based upon the concept that the components have been individually formed out of cylinders. Acutally, in making the master, such cylinders conveniently can be cut from a single flat prism and reassembled with different orientations.

The thicker portions will be located around the exterior of the assembly 94 and the inner ones will be increasingly thinner with the result that each component will receive the scattered rays from an annular area and deviate the same to a focus spaced from the axis in a direction different from all others. Orienting the prisms so that they face in directions equally spaced around the axis 42 will place the foci equally distant around the axis as well. They can be located slightly spaced from one another along the axis, but this presents no problem in the manufacture of the element 94 as a fresnelled element. Nor does it produce any problem with respect to the location of the individual photoresponsive devices. The distance from the axis 42 will depend upon the original angle or deviation of the prism from which the parts are developed.

It is to be understood that the element 94 will be an integral molded member in production, the above-described master being- used to build such mold.

In Figure 3 there is illustrated a form of apparatus which utilizes. in addition to a fresnelled element 120 an ellipsoidal reflector 1 22. The apparatus is generally designated by the reference numeral 124. The sensing zone 126 in this case is located in the interior of the reflector 122 which, as will be explained, is filled with diluent 123 of the same index of refraction as that which carries the particles.

The advantage of the addition of an ellipsoidal reflector as used here is that since the reflector 122 surrounds the sensing zone 126, it can capture the scattered light for a polar scattering angle which occurs in the vicinity of 0 to, say 1350, depending on the eccentricity of the ellipse as well as in all aximuthal angles. (In Figure 3 the polar angles lie in the plane of the paper and the azimuthal angles lie in a plane perpendicular to the paper.) Back scattered light becomes increasingly important as the size of the particles to be measured decreases. For example, white cells and other biological cells may be of the order of 10 to 1 5 microns in diameter and their internal structure will normally be that which gives rise to the wider angles of scattering may have radii of curvature of the order of one micron and iess.

In Figure 3 the ellipsoidal reflector 122 has its forward opening closed off by a spherical transparent closure 128 that does not affect the direction of the collected radiant energy as it leaves the reflector 1 22. This closure has as its center of curvature the right hand focus of the ellipsoid. Radiant energy originating in the laser 22 passes along the axis 130 through an opening 132 in the element 120 to the sensing zone or scattering point 1 26. The particle source 134 pumps the particles in the diluent liquid into a central conduit 1 36 intb the interior of the ellipsoid 1 22 where it passes through the sensing zone 126 and into the discharge pipe 138 to a suitable reservoir 140 outside of the ellipsoid.In the meantime a second source of liquid 142 injects diluent through the concentric pipe 144 surrounding the conduit 1 36 so that there is a sheath flow confining the particles to the sensing zone 126.

The laser beam passes through the sensing zone 126, out through a transparent light port 146 in the rear of the ellipsoid and to a light beam dump 148 outside of the ellipsoid; (Theorectically the spherical closure 128 should be perfectly flat where the laser beam passes through to prevent spread, or alternatively beam shaping optics may be used. The effect on the laser beam, however, will normally be so small in most cases that it can be ignored.) Forward scattered and back scattered light is directed to the fresnelled element 1 20 and deviated in the manner which has been described to an array of photoresponsive devices 1 50 to 157 that the are arranged in a circle around the axis 130. In this case only several are shown in the side view of Figure 3 but it is intended by way of example that there be eight such photocells arranged as illustrated in Figure 3A. This results from the establishment of eight circular zones in the surface of the element 120 providing eight different annular prisms as shown in Figure 3B.

These are designated 1 58 to 165, each being of a different polar orientation to divert a different ring of forward scattered and back scattered light to one of the respective photoelectric cells 1 50 to 157.

In this case as in others described, the angle of deviation of the basic prism determines the radius of the ring defined by the proper placement of the photodetectors at points of beam focus.

The construction of the apparatus 124 which is illustrated is not the only one which can be adopted. In Figure 3 the ellipsoidal reflector 122 has a rim flange 131 to which is attached a bezel 133. The bezel carries the spherical transparent closure 128 and the fresenel element 132. The plugged openings 135 enable drainage and bubble removal.

In Figure 3B there is a frontal view of the element 120 with the individual annular prisms cross hatched to show their orientation relative to the axis. Arrows indicate the direction towards which the transmission of the radiant energy impinging on the rear surfaces thereof will be deviated. As seen, the arrows are at equal angles relative to one another so that the array of photoresponsive devices 1 50 to 1 57 can be arranged at equal angles about the axis 130.

The apparatus 124 of Figure 3 utilizes as its principal feature the fresnelled element 120 whose construction and operation do not differ materially from the construction and operation of the element 94. In addition to the use of the fresnelled radiant energy transmitting element in apparatus 124 there is a reflecting element comprising the ellipsoidal reflector 122 which collects the forward scattered radiant energy as well as back scattered energy, the latter being collected from much wider angles than would be achieved without the use of the ellipsoidal reflector 122.

Looking for the moment at the apparatus of Figure 2, it should be appreciated that the laser being on the left and the light collecting occurring on the right, the only radiant energy being measured is that of the forward scattered light In the case of the apparatus 124 of Figure 3, the laser 22 is on the right, the radiant energy which is represented by the beams 125 being typical of the back scattered light and being directed to one of the photocells. The radiant energy which is represented by the beams 127 reflecting from the portion of the ellipsoid 122 to the left of the sensing zone 1 26 is typical of the forward scattered light and is directed to another of the photocells.

The apparatus 124 of Figure 3 will give more data and information than the apparatus of Figure 2 because its radiant energy gathering characteristic is more efficient, using transmission of the light of deviation to predetermined locations and in addition, gathering the radiant energy through the use of an efficient reflector.

In connection with the structure 124 of Figure 3, it would be practical to have an ellipsoidal surface as shown which will capture all scattered light from about half a degree to 1400. The light is directed by the interior of the ellipsoid, that is, the left hand end as viewed in the figure, to the right hand focal point The interposed fresnel element 120 is shown to the left of the second focus in the view, but there could be a negative lens before the second focus or suitable positive lenses after the second focus to reduce the collection angle of the fresnel element 120 and any or all of the photocells to adjust for optimum collection results.

The lens would be small and have a very small focal length, but will thus be economical.

The structure of Figure 3 may have several practical disadvantages. The radial thickness or widths of the zones 158 to 165, if designed to subtend equal angles as viewed from the sensing zone become so small closer to the center of the element 1 20 that fabrication may present problems. Another disadvantage is that commercially available ellipsoidal mirrors generally have an access hole at the closed end which is quite large.

In the device which is illustrated in Figure 4, these problems to a large extent solve one another.

In Figure 4 there is illustrated a system 124' which takes advantage of the large opening the commercially available ellipsoidal reflectors for collecting forward scattered light. The reference characters are generally the same as in Figure 3.

The ellipsoid -122' has the same means for forming the sensing zone and the same type of fresnelled element 120. The light dump 148 is off to one side of the axis 130 and the center beam is directed there by a small reflector 1 74. The ellipsoid is drawn approximately full size. The ellipsoid 122' has the typical large hole 1 76 which is covered by a transparent spherical window centered on the sensing zone that will not adversely affect the operation of the device.

By using the hole 1 76 as a window, the collected light is split into two parts, each of which is subdivided by suitable fresnelled prism elements. The element 120 will subdivide the back scattered light while the fresnelled element 1 78 will subdivide forward scattered light which passes through the hole 176, this being generally the light that would normally have to be handled by the innermost rings of the element 120. Such light produces the beams 127 and the beams 129, for example. This forward scattered light 1 29 is collected and concentrated by the lenses 1 80 and 182 which are arranged in a classical assembly.

The lenses 180 and 182 focus the light at a point 186 along the axis 130 but before the light beams can converge to any great extent they are captured by the element 1 78 and their various parts deviated and focussed or confluenced on a series of photodetectors, two of which are shown at 188 and 190. Obviously, there will be a complete array of these around the axis 1 90 to the extent that is required by the parameters of the particles being studied.

This arrangement permits the light which would otherwise be reflected at the smaller inner angles of the ellipsoid 122' to be magnified and makes it unnecessary to have extremely small rings on the fresnelled element 120 with corresponding small radial widths for such rings. It also leaves room on the optical axis for mirror 1 74 and beam shaping optics (not shown).

Incidentally, any of the versions according to Figures 2 to 8H can have some form of beam shaping optics included.

In coordinating and collating the data from the photodetectors, it is preferred that the data be processed in a computer. The rings for the elements 120 and the other fresnelled elements of the drawings preferably subtend equal angles as viewed from the sensing zone, especially since the rings of a circular diffraction pattern are so spaced, but the computer can be programmed to compensate for rings of any varying width in the data being gathered. In Figure 4 the rays of light which are shown are for an element 120 intended to have each of the rings take care of 11.250 increment windows.

It is noted that the intensity of the back scattered light which is achieved by the apparatus 124' of Figure 4 is normally substantially less than that of the forward scattered light. Instead of photodetectors of the conventional type, photomultipliers could be used with advantage although this will increase the overall cost of the apparatus. The number of such photomultipliers needed for good resolution is another important factor in cost. The utilization of the economical elements 120 and 1 78 provides advantages over known detecting systems, even with the use of expensive photomultipliers.

In the structure of Figure 5, everything is substantially the same as that of Figure 4 with one important difference. Instead of an array of separate photoresponsive devices, a single television camera element or tube 192 is utilized.

The reference characters used in this view are generally the same as in Figure 4. The apparatus itself is designated 124". When a particle goes through the sensing zone, scattered light from each cone is focussed by the element 120 onto a discrete zone or increment of the target of the television camera element When the particle has passed through the sensing zone, which time can be sensed by detecting the trailing edge of one of the pulses from the forward scattered light, the array of charges on the target of the television camera tube can be scanned and transmitted to the computer.

The relatively intense forward scattered light can be directed to simple photocells 1 88 and 190, by photomultipliers or by another television camera tube.

It is clear that since the resolution of television camera tube target is much greater than that of ordinary photodetectors, the amount of information which can be obtained from any particle can be quite substantial, being limited only by the resolution capabilities of the fresnelled elements such as 120.

If the fresnelled prism element such as 120 is made out of parts or increments from the same prism, all focal points or spots of light will appear in a'circle whose radius is the distance from the fresnelled element to the reoeptor (the camera tube target or the surface of the photocell) multiplied by the tangent of the deviating angle of the original prism.

By using parts from prisms having different deviating angles, several rings of light spots (focussed light) of different radii can be formed.

Thus, the area occupied by the array of spots can be compressed for the purpose of concentrating all spots on a television camera tube target. The number of rings of spots will be the same as the number of different prisms used to form annuli.

In Figure 6 there is illustrated an apparatus 200 in which several rings of spots (as indicated in Figure 8A) can be achieved through the use of radiant energy of different wave lengths. Thus, there are two lasers 202 and 204 directing beams of different wave length light through a prism 206 which combines the beams and sends them both through a flow chamber of element 208 which has a sensing zone. The scattered light 210 is collected by the lens 212, the central energy being dumped at 214 by way of the central reflector 216. The light passing through the lens is now captured and deviated by the fresnelled prism element 218 but because there is radiant energy at two different wave lengths, the deviation will be different for each, and each color of light will be focussed at a different spacing from the axis 220.

The number of spots will be twice the number of component prism rings of the element 21 8. The refraction will be different on any dielectric material for different wave lengths.

Thus, in Figure 6B it is intended that the element 218 have five rings 222-226. Since this will produce an array of ten light spots, as shown in Figure 8A there will have to be ten photocells 227 to 231 receive the confluenced light of one wave length from the five rings 222 to 226 and the photocells 232 to 236 receive the confluenced light from the same respective rings but of the other wave length. The two rings of photocells will be in slightly different planes due to chromatic aberration of lens 212.

This type of information is readily processed by computers and is quite valuable for cell identificaiton. Inasmuch as the size, shape and orientation of constituents information romany particle which passes through the sensing zone is detected by all of the photocells and is common to both scatter patterns of different wave length, any differences between these patterns which can be measured is due to the change in refractive index of the different parts of the particle from one wave length to the other. The change of refractive index relative to wavelength is different for different materials, Since particle information which has been stored can include such data this increases the usefulness of the apparatus and the positiveness of identification of the particle.

The construction of a so-called fresnel element which is identified as 94 in Figure 2, 120 in Figure 3 and in Figure 4, 178 in Figure 4, 120 and 1 78 in Figure 5 and 218 in Figure 6 practically all cases will be effected by the use of molding techniques where a master is made first out of glass or quartz, properly ground and polished and with the various components properly oriented. As mentioned, even non-optical materials may be used. In the making of the master the actual cutting of the annular rings from a single prism is practical for larger rings. Where the inner rings get smaller and smaller this becomes more difficult; however, it is feasible to have telescoping glass or quartz tubes of proper wall thickness ground off and polished at the proper prismatic angles and assembling these with larger cut rings to form an assembly for the master.The tubes would be held together by some cement such as wax while the proper angle is cut across all of them after which they would be released from the adhesive to orient them properly and re-fixed in such orientation.

One of the most important reasons for using fresnel elements is that they are much thinner than non-fresnel elements which have the same optical characteristics. Space economy is the most important benefit and it derives from the fact that only the useful portion of an optical member is reproduced rather than the entire member.

When the number of prism sections or components is increased materially it becomes practical to use simple wedges acting as prisms instead of forming the large fresnel prism of annular components. This is shown in Figure 7 and Figure 7A where the element 300 is formed of annular sections or components such as in the case of the element 218 of Figure 6B but there are more of such components and the radial dimension becomes less and less as the center is approached. In this case there are annular elements 302, 303, 304, 305, 306, 308, 310, 312,314 and 316 with the center 318 being cylindrical. The annuli are divided into segments by radial lines such as shown at 320. It is preferred that these segments have a roughly oneto-one aspect ratio, that is, their radial dimension is about the same as their circumferential dimension.In other words, such segments are more or less curvilinear squares whose corner angles are 900. One such curvilinear square close to the edge is shown at 322 formed of heavy lines for illustrative purposes.

If made from original prisms the master for this structure would require the making of many rings including very thin and small ones and their careful assembly and orientation. This is expensive and difficult. In the structure of Figure 7, the element 300 is made up of a large number of small wedges which have been assembled together. For example, a prism of the proper dimensions for any given ring is formed as an elongate "stick". The edges are ground off to form the cross section intended for the particular ring, that is, the cross section will have the appearance of the single component 322. The stick is then sliced into as many components as needed, which in this case will be twenty, arranged in a circle and cemented together.Each of the rings can be adjusted to direct transmitted light coming through its rear at suitable forward photoconductors which can be located generally in a circle about the axis of the element 300, but each sector such as 322 may be individually oriented to point to a single location on a television camera tube target or electrode, for example, to give substantially greater resolution of the scattered light.

The aspect ratio which is preferred gives the same amount of so-called smearing in circumferential and radial directions.

An apparatus which is constructed utilizing the element 300 could combine reflecting means such as shown in Figures 3, 4 and 5 with the light deviating element to achieve the added advantage of increased radiant energy through gathering both forward and back scattered light.

Figure 8 shows a system in which the collecting of the scattered radiant energy is effected by reflection and the deviation by reflection as well.

Only the basic elements of the system are illustrated in Figure 8 for simplicity.

The collecting element in the system 400 of Figure 8 comprises an ellipsoidai reflector 402 whose construction is not significantly different from the reflectors 122 and 122' previously described in detail in connection with Figures 3, 4 and 5. It may be assumed to be a vessel containing liquid, with the particles being investigated injected in sheath flow by way of the entrance pipe 404 and carried away by the discharge conduit 406. The optical axis of the system is at 408 and a suitable source of radiant energy such as a laser 410 is disposed to direct its fine beam along the axis 408 into the reflector 402 where it intersects the path of the sample particles at the left hand focal point of the eilipsoidal reflector.This point is identified in the diagram Figure 8A as fl and it comprises the sensing zone from which light scattering takes place.

In Figure 8 there is a small window at 412 through which direct radiant energy emerges to enter the dump 414. The scattered radiant energy is collected and directed forward from the reflector in a cone which has its greatest diameter at the reflector interior defined by the outermost extent thereof and its apex at the second focal point of the ellipsoidal reflector 402. In the practical device, the cone of radiant energy never reaches the focal point, but this point is seen at f2 in the diagram of Figure 8A. The focal points f1 and f2 and the axis of the cone all lie on the optical axis 408.

A composite reflector assembly is designated generally as 41 6 and it comprises a series of elliptical mirror rings, here shown as six at 418, 419, 420, 421,422 and 424 arranged in a particular manner. This will be described presently but for the moment it will be taken that radiant energy can't get past the- reflector assembly 416 from left to right in Figure 8, and only the laser beam from source of radiant energy 410 can pass through the reflector assembly 41 6 from right to left in Figure 8 by reason of the center hole 426 in the central elliptical ring 424. The assembly 416 will normally comprise an integral or unitary structure when made commercially and is called a composite mirror in the claims. Such a mirror as 416 will have multiple reflecting surfaces ,corresponding to the rings 418. 420,422 and 424 or parts of such rings. The mirror surFaces are all facing to the left as viewed in Figure 8 so that the radiant energy received against such surfaces is deviated from their direct paths by being reflected or returned toward the ellipsoidal reflector 402 but at different angles to locations laterally thereof.

All of the elliptical reflector ring surfaces 418, 420, 422 and 424 surround the point 428 on the axis 408. All have the same angle of tilt a with respect to the axis, this angle a being chosen to be of such degree that the reflected focal points of all ring surfaces will occur at locations conveniently outside of the ellipsoidal reflector 402 where photodetectors such as 430, 432. 434 and 436 may be positioned. Each ring 418. 420, 422 and 424 is intended to receive a different annular portion of the radiant energy cone projected from left to right in Figure 8 and each is required to reflect the radiant energy it receives to a different location. In effect, therefore, each ring is required to fold the cone axis to a different circumferential location and cause confluence of the radiant energy it has captured at such location.

To receive an annular portion of radiant energy while being in a disposition tilted relative to the axis 408 each ring surface must be elliptical. To reflect to a different circumferential location, each ring must have an angular position about the axis 408 different from all others while maintaining its angle a and its center 428.

In Figure 8C the assembly of rings of arcuate mirror surfaces, as they may be called, is viewed along the axis 408 of Figure 8 looking from left to right. The ellipsoidal reflector 402 and its attendant apparatus is not shown. The locations of the faces of the photocells 430, 432, 434 and 436 are indicated to illustrate the angular disposition around the axis 408 (which is normal to the paper in Figure 8C) of each elliptical ring. To enable visualizing the angular disposition, each elliptical ring has been marked with a bar in the view lying on its long axis. Thus, the ring 41 8 has the bar 438, the ring 419 has the bar 439 the ring 420 has the bar 440 the ring 421 has the bar 441 the ring 422 has the bar 442 and the ring 424 has the bar 444.The explanation should be considered while also looking at Figure 8D which is intended to be an axial end-on view from the left of the reflector 402 in Figure 8, looking to the right with nothing shown but the reflector outline and the folded back axis of each of the rings.

Starting with the outermost elliptical ring mirror surface 418, its major axis or diameter lying on the bar 438 is chosen to lie in a vertical plane defined by the axis 408 and the major axis or diameter of ring 418. It should be borne in mind that there is still an angle a between the plane of the ring 418 and the axis 408. The axis 408 is therefore folded back toward the.reflector 402 and is shown at 408-1 in Figures 8 and 8D at an identical angle al with axis 408 as a mirror image as indicated in Figure 8A which shortly will be described.Note that this angle al as well as the angle a will not be 900 because of the tilt of the mirror 41 6. The radiant energy cone captured by the reflective surface of ring 418 may be conceived of as a hollow cone which is entirely folded back, but on the oblique axis 408-1. Its focal point or point of confluence of that portion of radiant energy it has deviated is at the top of the reflector 402 spaced away by a practical distance and the photodetector 432 is located precisely at that point of confluence. This can be optionally an aperture as described above in connection with Figures 2D and 2E.

Now consider the next inner elliptical ring 420.

It is smaller than the ring 418, is tilted by the same angle a and centered on the same point 428. By examining the location of its bar 440, it is seen that the ring has been rotated about the axis 408 in a counterclockwise direction by the angular extent p1 which has been chosen to be about 300 in the view of Figure 8C. By the same explanation given above, the axis 408 and the portion of the radiant energy cone captured by the reflective surface of the ring 420 has been folded back along the axis 408-2 and comes to a focal point of confluence of radiant energy at the location of the photodetector 430 (shown staggered for convenience in Figure 8).

The same explanation applies to the ring 422 which has been rotated by the angle 2 clockwise from vertical in Figure 8C and the ring 424 which has been rotated by the angle p3 clockwise from vertical. The equivalent folded back axes of deviation for these rings are 408-3 and 4084 respectively. The focal point of confluence are at the races of the photodetectors 454 and 436, respectively.

The diagram of Figures 8A and 8B may assist in understanding the bases for functioning of the system 400.

The ellipsoid of the elliptical reflector 402 is shown in Figure 8A by the broken line oval 450.

The focal point f1 would be the sensing zone, and all radiant energy collected by the ellipsoidal reflector 402 would focus and confluence at the focal point f2. This is a cone of radiant energy which is, for convenience, shown to be bounded by the lines 452 on the left, with typical interior rays shown at 454 and 456.

A plane mirror 416' has been interjected in the cone 452 at the point 428, tilted at angle a relative to the axis 408. The projected cone 452 is captured by this mirror416' and deviated. But for the mirror 41 6', the cone 452 would continue to project its radiant energy to the right of the mirror 416' along the paths indicated at 452', 454' and 456' to confluence ate2. Due to the mirror 416' the right hand part 452' of the cone 452 is folded back and this is effected along the folded axis 408-F at angle a, equal to angle a relative to the plane of the mirror 416' (left side in Figure 8A) so that the folded part of the cone 452 now has the configuration 452-F and the focus or point of confluence f2 has also been folded back and becomes the point f2-F. The photodetector 432' can now pick up the deviated radiant energy alongside of reflector 402.

If we considered that the cone 452 were made of a number of concentric nested right circular cones, an axial view at any point to the left of the mirror 416' toward reflector 402 would show a series of perfectly annular rings but their extensions onto the tilted mirror would produce a series of elliptical rings. Since we have chosen to locate the plane mirror 41 6' normal to the paper to the paper, the major axes or diameters of all elliptical rings 41 8', 420', 422' and 424' are vertical as indicated by the aligned bars 438', 440', 442' and 444'. Because all are in the same plane there is only one folded 408-F.

Now if we should cut the rings 418', 420', 422' and 424' from the integral mirror 416' and rotate them about the common axis 408 as explained in connection with Figures 8C and 8D, then join them together as an integral composite mirror, the result would be the mirror 416 of Figure 8. The confluent locations would then be spread circumferentially about the reflector 402 on the axes 408-1, 408-2, 408-3 and 408-4, respectively.

While it may seem that there would be interference physically between rings, it should be remembered that they are ellipses and will not be in the same planes, and even if parts may tend to shadow one another due to some choice of angles, these shadows may be minimized by keeping the angles a and p 2 etc small. It is even practical to use portion of rings and adjust the centers slightly along the axis 408 as well as have slightly different angles a for each ring to achieve the most practical alignment of the points of confluence or locations of the photodetectors.

In this manner the photodetectors need not be in a common circle as in Figure 8C but could be in a straight or arcuate line tangent to the outer circumference of the reflector 402; they could all be on one side or the other or both or on the bottom; they could be spaced evenly around the reflector or axially staggered in any of these locations.

As mentioned above, the use of apertures, or irises can be combined to purify the confluenced radiant energy falling on the respective photodetectors. Likewise, the technique used in achieving the multifacet structure which is described in the connection with Figures 7 and 7A may be applied to the construction of a mirror in the system 400. The angle of tilt a would be very nearly the same for all facets since the television receiving photodetector would be located at one point, there being only very fine variations.

In order to demonstrate the actual construction of the mirror 41 6 of Figure 8, a metal model was constructed and photographed in Figures 8E, 8F, 8G and 8H. In Figure 8E there is shown six conical members which are turned in metal and which nest, each member representing a conical beam, the ends being cut off on an angle. The cones would correspond generally to those generated at 452', 454', 456' etc in Figure 8A. In Figure 8F, these cones have all been assembled and connected to a base to hold them in assembly so that they could be photographed. Note that a line groove has been cut across each cone face as indicated at 438', 440', 442' and 444' in Figure 8B. All grooves are aligned in Figure 8F because the cones have not been rotated.Thus the assembly in Figure 8F is the equivalent of the rays and mirror 416' of Figure 8A.

Figures 8G and 8H are the equivalent of the rays and mirror 416 of Figure 8. The shifted grooves are readily seen in each view, having been strengthened by dark lines marked on the photographs.

In the claims, reference to refraction shall be taken to mean a deviation of light or radiant energy by a transmitting element such as a simple or fresnelled assembly of prisms each of which deviates an entrance ray by the same angle as any other ray.

Referring now to Figures to 9 to 13 a method of examining particles again comprises providing a sensing zone or scattering point and passing particles through this sensing zone to sense their presence and to direct radiant energy thereon for that purpose. Each particle scatters the radiant energy and this scattered radiant energy is collected and deviated by suitable optical means and focussed or conflenced towards point in space, but the deviation is effected by an assembly of elements which causes the energy in the different angles or paths or geometric parts to be deviated to different locations for the convenience of measuring them. The measurement is effected by an array of photodetecting devices or elements which respond respectively to the intensity of energy present in the particular angle, path or part.From this data, by reason of information which is known from previous studies, one can identify and/or determine the character of the particle which produced the scattering.

Apparatus shown in Figures 9 to 1 3 is believed to provide more scattering data and of higher definition than known methods and apparatus which use reflection only as a result of which it is useful for the establishment of information related to specific types of particles by passing known particles into the sensing zone in order to learn the scattering effects of such particles for use in other work where unknown particles are being identified.

In a specific sense, the scattered energy can be thought of as hollow or solid cones of light or radiant energy each of which is brought to a focus or point of confluence at the location of the photoresponsive device or element which is intended to make the measurement for that specific cone. The scattered energy can also be measured as part cones for additional information, as for example when the energy may not be in symmetrical geometric form, although this is unusual.

According to Figures 9 to 13 a spherical mirror is formed out of a plurality of annular optical elements or segments which "point" or are focussed in specific different directions to enable the energy deviated thereby to be confluenced and measured. The elements can be assembled in a single integrated member whereby the practical thickness of the resulting element is much less than it would be if complete individual elements were used.

The prior art system illustrated in Figure 1 is also the environment in which apparatus acccording to Figures 9 to 13 is utilized. The description of Figure 1 will not be repeated.

Like Figures 2 to 8H apparatus according to Figures 9 to 1 3 provides an efficiency which enables the laser 22 used to be of low power with very littie heat generation.

The detector 32 of the prior art of necessity had a limited number of photoresponsive elements in its array because the pattern of scattering was not controlled. The scattered light is diffused; the part of the total solid angle of available radiant energy represented by rays 30 is small. Special detectors such as mentioned hereinabove were complex and expensive. According to Figures 9 to 13, since the pattern of the scattered radiation is altered to almost any which is desired and the areas of such radiation can be well-defined, the limitations on number and size of the array of photodetectors are less stringent.

A combined radiant energy deviating means and array of photodetectors according to Figures 9 to 13 usable as a replacement for the element identified as 32 in Figure 1.

Figure 9 shows what may be termed the scattering point or sensing zone 40 through which particles can be moved from a lateral source (not shown) along the path 42. These particles would be entering the sensing zone 40 preferably one at a time and, as mentioned, for biological particles can be entrained in a liquid confined by sheath flow. Although not here illustrated, the entire structure including the sensing zone 40 and the shortly-to-be-described collecting and deviating device 44 can comprise a container for a body of liquid whose refractive index is identical to that of the liquid entraining the particles.

The source of radiant energy in the apparatus illustrated is a laser 46 whose fine beam is directed along a principal optical axis 48 intersecting the path 42 at the scattering point 40.

This axis will be used as a reference axis for the explanation and the parts of the device 44 are tilted relative thereto; hence the axis designated "CENTER AXIS" in Figure 9. It is an extension of the optical axis 48. Radiant energy not scattered but passing the point 40 is captured by a small angled mirror 50 and directed laterally along the path 52 to a light dump 54. The portion of the radiant energy which is scattered in all directions which is collected is that which is scattered forward (to the left of the scattering point in Figure 9) by a composite mirror 44 and deviated by being reflected back toward the scattering point 40, but on axes which are substantially deviated from the axis 48.

The radiant energy which is collected by the composite mirror 44 is selectively collected by the concentric rings 56, 58. 60 and 62 which comprise the mirror 44 and is caused to confluence at locations lateral of the axis 48.

Individual photodetectors located at the respective locations of confluence can measure the intensity of radiant energy at these points. and, since each photodetector is individual to a particular one of the rings, it furnishes information only related to that ring.

For simplicity, it is assumed that the mirror 44 is formed out of four individual annular rings 56, 58, 60 and 62 which are tilted relative to the axis 48 vertically only. Each annular ring collects only a ring of scattered energy impinging on its mirrored surface and deviates that geometric portion by twice the angle between its tilted optical axis andthe center axis 48 to a lateral point of confluence (up or down in this arrangement).

For this illustration and ease of understanding.

it has been assumed that the rings of the composite mirror 44 have been cut or otherwise formed from a complete mirror and that if put back together, the rings would produce a complete mirror as indicated in Figure 10 at 44', all rings having their rear surfaces lying in a common plane. Thus, each of the rings 56, 58. 60 and 62 has the plane of its rear surface identified in Figure 9 by a reference character with the suffix P. The view being a section, each plane is shown by a broken line. Prior to separation, the rings of the spherical mirror would have the appearance as at 56', 58', 60' and 62' but when separated and tilted they are as in Figure 9. (As mentioned hereinafter, they can also be rotated).

Each of the rings is tilted by a different angle. in the particular simplified form there being two rings tilted upward relative to the scattering point and two tilted downward. As indicated, the tilting is vertically for simplified explanation.

The center ring 56 is the smallest of the rings which are derived from the spherical mirror 44' and it has been tilted upward slightly relative to the center axis 48 and the scattering point 40. The plane of the rear surface of the ring 56 is identified at 56-P, and the plane 100 which is normal to the center axis 48 is identified at NP. This would coincide with the plane of the rear surface of the mirror 44' in Figure 10. The angle between the normal plane 1 00 and the rear plane 56-P of the ring 56 is shown at 102. The same angle obtains between the central axis 48 and the optical axis of the ring 56, the latter being identified as 56-OA.

The focus or point of confluence of the ring 56 will, however, be along an axis which makes an angle relative to the central axis 48 that is twice the angle of tilt 102, it being a reflective axis. This is identified as the axis 56-RA and the focal point is at 68. The distance from the ring 56 to the focal point or point of confluence 68 depends upon the curvature of the reflective surface of the ring. For the purpose of this simplified version, it is taken that all rings are derived from the same spherical mirror; hence all of the points of confluence or focal points will be at substantially the same distance from the mirror 44.

A first photodetector 70 is located to respond to the confluenced energy from the ring 56. The ring 56 has collected a cone of radiant energy from that scattered forward from the scatter point 40 and has deviated same in a solid angle cone whose outer extent is defined by the surface 64.

Since the angle of ring 56 is solid, the cone of radiant energy is also solid.

The next outer ring 58 is annular, has been slightly tilted downward relative to the scatter point 40 so that its rear plane 58-P makes an angle 104 with the normal plane 100, its optical axis 58-OA making the same angle with respect to the central axis 48. The reflective axis 58-RA of the ring 58 is at an angle with the central axis 48 that is twice the angle 104 and the focal point or point of confluence 76 occurs on that axis. The cone of radiant energy which is collected and deviated by the ring 58 is hollow, being defined by an inner conical surface (not shown) and the outer conical surface 72. The confluenced radiant energy from the ring 58 is focussed on the face of the second photodetector 78.

The next outer ring 60 is also annular, has been tilted upward relative to the scatter point 40 so that its rear plane 60-P makes an angle of tilt 106 with the normal plane 100, its optical axis 60-OA making the same angle with respect to the central axis 48. The reflective axis 60-RA of the ring 60 is at an angle with the central axis 48 that is twice the angle 106 and the focal point or point of confluence 84 occurs on that axis. The cone of radiant energy which is collected and deviated by the ring 60 is hollow, being defined by an inner conical surface (not shown) and the outer conical surface 80. The confluenced radiant energy from the ring 60 is focussed on the face of the third photodetector 86.It will be noted that in the view, the reflective axis 56-RA and the optical axis 60-OA happen to coincide because of the particular choice of angles. It should be understood that there are two lines representing axes one on top of another.

The outermost ring 62 is also annular, has been tilted slightly downward relative to the scatter point 40 so that its rear plane 62-P makes an angle of tilt 108 with the normal plane 100, its optical axis 62-OA making the same angle with respect to the central axis 48. The reflective 62-RA of the ring 62 is at an angle with the central axis 48 that is twice the angle 108 and the focal point or point of confluence 94 occurs on that axis. The cone of radiant energy which is collected and deviated is hollow, being defined by an inner conical surface 90 (Figure 11) and an outer conical surface 88. The confluenced radiant energy from the ring 62 is focussed on the face of the fourth photodetector 96.It will be noted that in the view, the reflective axis 62-RA and the optical axis 58-OA happen to coincide because of the particular choice of angles. It should be understood that there are two lines representing ,axes one on top of another.

All of the photodetectors 70, 78, 86 and 96 are coupled to a computer and/or readout device 99 which provides identification of the particles through comparison of the received data with previously stored or recorded data.

The mirror 44 has been described thus far as made up of four rings which have been described individually. Also the spherical mirror 44' from which this mirror 44 has been derived is described in connection with Figure 10. Inviting attention to Figure 10 there is illustrated a scattering point 40, a particle stream 42 and the laser beam path 48 which coincides with the center optical axis of the mirror 44', being directed at the optical center of the spherical mirror 44'. The front surface 110 of the spherical mirror 44' which faces the scattering point 40 is presumed to be reflective. The rear base plane 100 is the same as in Figure 9 except that in this case there is actually an integral surface defining this rear or normal plane as it is referred to in connection with Figure 9.

The mirror 44' is shown divided into four annular rings 56', 58', 60' and 63' by the cylindrical dividing interfaces 11 2, 114 and 11 6 that are coaxial with the axis 48.

Until and unless the mirror 44' is separated into the annular rings 56'. 58', 60' and 62' and these rings are re-oriented relative to the axis 48, all radiant energy collected by the surface 110 will focus at a point 1 20 on the axis 48. The points 40 and 120 can be coincident or spaced from one another, but the further the point 120 is from the mirror 44', the less degree of tilt is required of the rings to achieve any desired lateral spacing of the points 68,76, 84 and 94 (Figure 9). If the mirror 44' is cut into the four rings described along the interfaces 112, 114 and 116 and the individual rings tilted as described in Figure 9, the mirror 44 will result.For purposes of illustration, the focal point 120 is also indicated in Figure 9, but it is understood that note of the rings will be tilted to focus at this point since the laser beam would thereby be blocked.

To make mirrors such as 44 on a commercial scale, a master can be made by actually forming the mirror 44', cutting it into individual rings, tilting the rings, fixing them in their tilted positions by suitable cement and shaving the rear surface to a plane generally parallel with the normal plane 100 in order to render the composite assembly as thin as possible and with a flat rear surface. This master can then be used to mold many composite lenses similar to 44 out of suitable plastic or other material which is amenable to having its front surface silvered.

There can be many more rings than four and the orientation can include rotation to achieve circumferential spacing around the axis 48 relative to one another to establish and space the points of confluence and hence the locations of the photodetectors in any desired configuration. The configuration can be in a vertical or horizontal line, in arcs, in a circle around the axis, etc. This provides almost universal flexibility in the placement of the photodetectors which can be convention in their construction and hence quite ,economical and individually replaceable.

Figure 11 shows a part of the system of Figure 9 in which purification of the radiant energy collected and deviated by one ring is effected. The only ring shown is the outermost one, namely, 62, and in the view one can see the central inner surface 120, the reflective front surface 122, the rear surface 124, the optical axis 62-OA of the ring 62 and its reflective axis 62-RA. The center axis 48 is shown, this being the axis of reference.

In this view, the manner in which the radiant energy is deviated is clearly illustrated. The tilt downward of the ring 62 is here shown at 108', this being identical to the angle 108 of Figure 9.

Note that this angle 108' is measured between the center axis 48 and the optical axis 62-OA of the ring 62. Since the radiant energy enters the mirror surface 122 already at an angle, there will be an angle of reflection equal to the angle of incidence, hence the total angle of deviaiton relative to the axis 48 is twice the angle 108' and is designated in the view as 92. The hollow cone of deviated radiant energy which is defined by the surface of revolution 88 and 90 will be centered on the axis 62-RA and, as shown in Figure 9, would come to a focus or point of confluence 94.

This is approximately the same distance from the center of the ring 62 as the point 120 along the axis 48.

In Figure 9, the photodetector 96 is arranged so that its sensitive surface is located right at the point 94. In Figure 11, which shows a modification, instead of focussing on the front face of a photodetector, the ring 62 is focusses on an aperture 126 formed in a suitable diaphragm or iris 128 and the photodetector 96 is spaced beyond the aperture 126. This prevents any radiant energy from reaching the photocell 96 except that from the mirror ring or segment 62.

The center of the ordinary photocell is most sensitive and would respond to light from the center of the mirror assembly. Accordingly it could be blocked by a small central mask 130 in an arrangement of this kind.

All of the rings of segments of the mirror 44 would be so treated as shown for the single ring 62 in Figure 11.

In Figure 12 only a fragment of the cone of radiant energy is shown at 88 focussed on the aperture 126 of an iris 128. Instead of placing the photocell 96 in position to receive the light directly from the aperture 126, a lens 1 32 is interposed, the emergent light being focussed on the face of the photocell. Thus, very small efficient photocells may be used. The mask 130 is now applied as opaque paint to the lens faces. As assembly of such lenses for all of the photocells can be molded of economical synthetic resin with areas that are not required for light transmission blocked off with opaque coating material.

In Figure 13 there is illustrated a view similar to that of Figure 9 but in this case the apparatus is intended for measuring back scattered radiant energy. Additionally, the collecting and deviating device 244 is shown embodying the technique mentioned above for making a practical device.

The composite mirror 244 has been molded from an integral member of synthetic resin, for example, and is quite thin and economical to make.

The composite mirror 244 of Figure 13.has four annular segments or rings 256, 258, 260 and 262 which are formed on the front surface, the mirror being otherwise an integral member of plastic or the like. Each of these rings has a silvered coating to render the same reflective. The rear surface of the mirror 244 is flat and lies in the-plane 200.

Again in this embodiment, all of the surfaces 256, 258, 260 and 262 have been derived from a common spherical mirror surface and the number of rings is small for simplification of the view and the explanation, but this is not essential. The radius of curvature of the principal spherical mirror surface has been increased so that the resulting composite mirror need not be as thick as in the case of the mirror 44 of Figure 9, but of course this is a matter of the space and requirements of the apparatus. Increasing the radius of curvature will extend the points of confluence of the ring surfaces 256, 258, 260 and 262 beyond the distance of those equivalent of Figure 9.

The sensing zone or scatter point is shown at 240, being the intersection of a stream of particles 242 with the axis 248. Since this apparatus is intended primarily for the measurement of back scattering, there is a small aperture 282 in the center of the mirror 244 which is also centered in the spherically concave surface 256 and there is a beam of radiant energy directed through this aperture from the left hand side or rear of the mirror 244. This beam is coincident with the optical or central axis of the mirror 244 and originates for example in a low powered laser 246.

The beam of light is a fine pencil and intersects the particle stream 242 at the scatter point 240. Any light or radiant energy which continues along the axis 248 to the right of the scatter point or sensing zone 240, as for example during periods when there is no particle in the stream 242, will be collected by the small angled mirror 250 and reflected laterally along the line 252 to the light dump 254.

Light striking particles will be scattered backward toward the mirror 244 and be captured or collected by the ring surfaces 256, 258,260 and 262, each ring being effective to collect only a specific geometric area of radiant energy of the back scattered light. As in the case of the apparatus of Figure 9, the several rings are tilted slightly up and down with respect to the axis 248, but in this view none of optical or reflective axes of these rings is shown. The tilted angles are chosen to be approximately the same as the angles of Figure 9 for the rings having the same reference numerals but without the prefix "2". The cones of radiant energy for the rings 256, 258, 260 and 262 are illustrated in Figure 6 and these comprise the solid cone defined by the outer surface 264, the hollow cone defined by the outer surface 272, the hollow cone defined by the outer surface 280 and the hollow cone defined by the outer surface 288. The inner surfaces of the respective hollow cones are not shown but can readily be provided in the drawing by extending lines from the inner boundaries of the respective rings to the points of confluence of the radiant energy deviated by them.

The points of confluence of the respective rings are at 268, 276, 284 and 294 for the respective rings 256,258, 260 and 262. These are located generally about the same distance from the center of the mirror 244 as the point of focus 320 on the axis 248 would be if the mirror 244 were a complete unbroken surface spherical mirror whose radius of curvature was the same all over its said surface. The confluence points are laterally spaced from the axis 248 for the same reason as the points of confluence 68, 76, 84 and 94 are spaced from the axis 48. Since the radius of curvature of the mirror 244 is greater than that of the mirror 44 in the illustrations, the distance of the focal point 320 from its mirror 244 is greater than the distance of the focal point 1 20 from its mirror 44.

There is-a photodetector at each of the confluence points of the structure of Figure 13, these being 270, 278, 286 and 296, all being coupled to some type of measuring device through suitable connections in the same manner as the photodetectors of Figure 9. The same purifying means can be used in this case in the case of Figures 11 and 1 2 for each of the cones of radiant energy.

Reference has been made above to the rings 56, 58, 60 and 62 as segments. Likewise the ring surface 256, 258, 260 and 262 could be referred to as segments or arcuate elements. It is feasible and practical to use partial rings instead of full rings in forming the composite mirror. Likewise, all of the rings of a given composite mirror need not be derived from the same spherical mirror but could be derived from plural mirrors having different curvatures so that the locations of the points of confluence can be spaced axially relative to axis 48. These points can thus be chosen according to the maximum of convenience for any given apparatus.

The word "confluence" is used herein as a noun according to its normal use and additionally as a verb to signify the tapered directing of a cone of radiant energy toward its apex.

Basically the embodiments of the invention comprise a flow cell in which there are means for collecting radiant energy around the first focal zone where a particle or other small body, hereinafter called a scatterer, passes through a beam of light and causes secondary radiation from said particle; the collecting means causes a reflection of said secondary radiant energy to a second focal zone and to detector means capable of responding to at least one of several multiple angles of projected radiation. In one embodiment, the detector means comprises a known concentric ring photovoltaic detector and it is adjusted along an axis which passes through both the first and second focal zones. The optimum position for detecting the desired information from the scatterer is used.In an improved form, the detector means comprisea fresnel prismatic lens or other optical element of a composite nature which deviates or reflects the incident radiant energy flux in accordance with a plurality of different geometric areas to different, spaced apart, independent, small, photodetector devices, in a highly economical manner.

Other embodiments of the invention provide for back scattering.

In Figure 14 there is illustrated a flow cell system in which is there is a source of light 12 which projects a beam 14 through a suitable optical train which is called optics 1 6 to a partial reflector 1 8 on the optical axis 20. The partial reflector or beam splitter projects the incident light along axis 20 at a reduced intensity, now designated 22, through the spherical closure window 24 of the flow cell 26 to the sensing zone 28. Transmitted light passes undeflected through the beam splitter 1 8 as shown at 1 9 to other uses.

The flow cell 26 can be constructed using conventional techniques for sealing and the like and it comprises a reflector 29 that is a portion of an ellipsoid, having the window 24 sealed to its front and open end as at 30, having a rear window 32, an entering conduit 34 and a discharging conduit 36. The cell 26 is filled with a fluid 38 that is compatible with the liquid which carries the particles and has the same index of refraction as that liquid. The particle source 40 moves the scatterers in the fluid mentioned to the entering conduit 34 from which they pass through the sensing zone 28 into the entrance of the discharging conduit 36 and pass into the reservoir 42. By techniques known as sheath flow the fluid with scatterers may be caused to pass in a straight path across the sensing zone 28 and be discharged.

The beam of light 22 intersects the flow of scatterers at the sensing zone 28. That light not scattered plus that light scattered into small polar angles in the forward directions passes on through the window 32 into the light dump 44. Instead of such light dump there could be another detecting system as described with reference to Figures 2 to 13.

The sensing zone is chosen to be centered in the region of the first focal point of the ellipsoid of which the reflector 29 is a part. The interior surface 46 of the reflector 29 is polished or mirrored and all light or radiant energy which originates at its focal point 28 will be reflected from the surface 46 to the second focal point 48 of the ellipsoid of which the reflector 29 is a part.

A typical ray of light is designated 50 and its path can be traced from the first focal point 28 upward and to the left to reflect from the surface 46 and then directly to the second focal point 48.

All of the reflected rays of the reradiated energy from the reflector 29 are focussed at the focal point 48 and will thereafter (to the left of the point 48) diverge. An aperture 54, through which the radiant energy beams may pass and which eliminates most stray light, is located in opaque .barrier 52 and at the focal point 48. The plane of the opaque barrier 52 is designated 56, this bering a plane which is normal to the axis 20 and the beam 22. It will be noted that the radius 58 of the spherical transparent window 24 which can be of glass is centered at the focal point 48 to eliminate any refractive bending in the beam 50 or any others which emerge from the reflector 29.

At a distance dfrom the plane 56 there is provided the planar configuraiton of detectors 60 which has previously been mentioned. The planar face 62 of the configuration 60 has the photosensitive elements and this face 62 is parallel with the plane 56. Accordingly its several rings and wedges, if is has such wdges, will respond to the portions of the radiant energy which fall upon them, respectively. As will be noted, the angles which can be captured by the reflector surface 46 can be as large as 1400 for example. By itself, as previously mentioned, a device such as 60 has only been capable of collecting scattering angles to a maximum of 250 or so.Thus, the detector 60 has had its utility increased and it is made capable of responding to many more scattering angles and providing much more information than if it received the scattering light directly from the sensing zone 28 with no ellipsoidal reflector in place.

By moving the cqnfiguration 69 right and left through the medium of a motor 65 or the like as indicated by the double arrow 64 the optimum position can be obtained for determining the information desired. This, or course will depend upon the type of scatterers, what information is desired of them, etc. Actualiy, by moving the configuration of detectors 60 over a range of the dimension d information can be obtained from a variety of locations, keeping in mind, of course, that the largest' scattering angle falling on the detector will decrease as the distance d is increased.

Once a given course of investigation is to be followed and the optimum dopt has been ascertained and the corresponding scattering or reradiating angles have been calculated, instead of leaving the planar configuration of detectors 60 in place, fresnel lens elements 66 and 69 (Figure 15) made up of portions of prismatic wedges or segments or rings oriented in different directions relative to the axis 20 and/or tilted relative to said axis 20 may be substituted for the device 60. The fresnel prismatic lens deviates the converging rays of radiant energy to different spaced apart photocells such as shown at 68, 70, 72 and 74.

The latter are small, sensitive, economical elements easily obtained commercially and easily replaced. They can be separated by distances to prevent interference between them, often referred to as "crosstalk". The rays of radiant energy projected from the reflector surface 46 (Figure 14) are focussed again at the second focal point 48 of the aperture 54 (Figure 15) arid the typical ray 50 is directed at the fresnel prismatic lens 66. Just in front of this lens 66 a focussing lens 69 has been located for the purpose of converging the rays from the reflector 29 before they impinge on the prismatic elements of the lens 66. The focussing lens 69 can be a conventional ground of molded lens or could be a fresnel focussing lens as illustrated.

The concept of utilizing the type of prismatic lens 66 which has been described in connection with Figure 1 5 and the details and benefits thereof are described with reference to Figures 2 to 13.

Thus, an instrument can be built using the planar configuration 60 in which the detector is moved by some mechanical means 65 or even manually to provide flexibility; an instrument can be built in which the configuration 60 has been fixed in place after adjustment in the factory to a particular distance dfor a specific purpose; an instrument can be built of the latter type in which a very economical fresnel lens which has the equivalent function of the optimum arrangement has been substituted for the configuration 60 after the best location dopt has been determined.

The exact mechanical construction of the components of the system 10 is not described as those skilled in the art will understand from their ordinary knowledge that the structure for assembling the flow cell 26 and its parts provides for filling, bubble relief, etc.

It should be appreciated that the increased utility of the integral planar configuration of detectors 60 over that for which it is at the present used comes about by virtue of the fact that each ring of the device 60 can correspond to a large range of scattering angles, certainly larger than the range of angles that is represented by the present conventional way of using the said device 60.

Back scattering angles can be measured in the apparatus 10 simply by disposing the light dump 44 below the mirror 18 at the location occupied by the optics 16 and light source 12 and by disposing the optics 1 6 and light source 12 where the light dump 44 is located in Figure 14. In this way, the beam 22 will have its arrows reversed, light coming in by way of the window 32 and passing from right to left as viewed in Figure 14.

In all other respects the system 10 will not be altered.

The system admits of variations and uses in addition to the one described above. For example, the location of the light source 12, optics 1 6 and mirror 1 8 need not be where shown but could be at a location between the plane 56 and the detector 62. This location is indicated at 76 in Figure 14, this being the line along which the beam 14 would be projected toward the previous position of the mirror 18. The mirror 1 8 need not be fully reflecting but could be seim-transparent.

Fluorescent light reradiation can be measured with the apparatus 10 is slightly modified as explained hereinafter.

In Figure 1 6 there is illustrated a system 100 in which the object of the apparatus is to investigate scattering angles closer to the forward direction than can be obtained through the use of the ellipsoidal reflector 29 of Figure 14. The flow cell 126 in this instance is comprised of a hyperboloidal reflector 129 whose axis is designated 120 and having a first focal point 128 and its second or virtual focal point at 128'. As in the case of the cell 26, the interior of the cell 126 is provided with a fluid 1 38 which may be held in place by a glass or other material transparent spherical closure 124 whose radius of curvature 1 58 is centered on the virtual focal point 128'.

Particle source 140 provides the scatterers in a 'liquid which flows into the interior of the cell 1 26 by way of the entrance conduit 134 through the sensing zone-focal point 128 and out by way of the discharge conduit 1 36 to the reservoir 142.

Light from the source 11 2 is directed as a beam 114 to the beam shaping optics 11 6 and thence as the beam 122 to the foiding mirror 118 on the axis 120 through the front of the closure 124 to the sensing zone-focal point 128 and out the window 132 to the beam dump 144. Typical light rays or fluxes resulting from the scattering are shown at 150 and 151 and it will be noted that these diverge, rather than converge, giving information on the type of polar angles mentioned above, that is, smaller forward angles.

These beams, as the others which are not shown, are captured directly in Figure 1 6 by the configuration of detectors 1 60 which can be moved in the direction of the arrow 164 by a motor such as 165 or by manual means to find the best location along the axis 120 relative to the cell 126. When the optimum distance has been located, collecting optics, a fresnel lens and individual photocells may be substituted for the device 1 60. It will be noted that the direction along which the beams of scattered light 1 50 and 1 51 extend are extensions of lines 150' and 1 51' respectively from the virtual focal point 128'. In this case no stray-light suppressing aperture 54 is used.

In the system 200 of Figure 1 7, the light flux or rays emerging from the hyperboloidal reflector 229 are not used in their diverging form but are focussed so that they can be passed through an aperture for suppressing the stray light before being measured. Thus, the light rays 250 and 251 which are typical of scattered light reradiated from the sensing zone-focal point 228 are captured by the lens 280, focussed on the aperture 254 provided by the opaque barrier or iris 252 at the focal point 248 and then are brought to the device 260 which is the same integral geometric configuration of photovoltaic detectors which was described above. One good choice of the distances of the lens 280 from the focal point 228' on the axis 220 is twice the focal length of the lens.Then the aperture 254 will be located at the focal point 248, which is twice the focal length of the lens 280 from the lens.

Again, as in this structure, it is feasible to have the device 260 movable, to adjust it for optimum distance dOptfrom the aperture 254 and to substitute collection optics and a fresnel lens or a composite mirror in its place.

Instead of the lens 66, in which the light or radiant energy passes through the deviating means, it is feasible to use a composite mirror of multiple reflecting surfaces which receives the beams of light and reflects them to a plurality of spaced individual locations so that the separate photocells may be located thereat.

In Figure 19 there is illustrated a system 300 in which fluorescent reradiation is measured in addition to reradiation by scattering. In this case there is a flow cell 326 which is basically built out of an ellipsoidal reflector 346 but of course this could be any configuration of reflector of the types explained herein. The reflector 346 has a window 332 through which the light beam 322 from the light source 312 and optics 316 enters. The light source 312 could be a suitable laser and the beam 314 therefrom is applied to beam-shaping optics 316.

The beam 322 passes through the first local point 328 of the reflector 346 where it encounters particles or cells which are entering the reflector along the path 334 from the particle source 340.

At the first focal point 328 light will be reradiated in accordance with the character of the particle and this light will be reflected from the reflector 346 towards the second focal point 348 which lies in the plane 356 normal to the optical axis 320. A typical ray is indicated at 350 and this ray is shown striking the interior of the reflector 346 at the top thereof in the view and being deflected toward a mirror 318 which intercepts the ray.

The mirror 31 8 which is here chosen is a dichroic element in that light is transmitted or reflected according to the wavelength of that light.

The ray 350 includes components which are fluorescent and other components of visible light.

The dichroic mirror 31 8 is constructed to have substantially no effect upon light of the laser wavelength and hence those components of the beam 350 pass through the mirror 318 without deflection albeit somewhat diminished. These move toward the second focal point 348 as the ray 350' and impinge on the sensitive surface 362 of the integral planar configuration of photovoltaic detectors 360 which is the equivalent of the prior art device 60 previously described.

The direct rays of light at 322 pass into a light dump 344 after being reflected by small mirror 372.

The light rays which focus at the second focal point 348 are purified by the opaque barrier or iris 352 which lies in the plane 356 that is normal to the axis 320 and passes through the second focal point 348. Light passes the barrier 352 by way of a center aperture 354 in the barrier. Again the distance d between the plane 356 and the face 362 can be adjusted by suitable means to be optimum and when this achieved a collector and fresnel prism element with separate photodetectors substituted therefor as explained.

Those components of the ray 350 which have wavelengths to which the action of the dichroic mirror 31 8 will become effective are reflected by the mirror as the ray 350" to focus at the point 357 along the axis 320' which axis is shown perpendicular to the-axis 320. At the focal point 357 there is a purifying opaque barrier 353 with an aperture 355 so that the clear ray extends below the barrier. It is there intercepted by a suitable transducer such as a photomultiplier tube or element 361 so that measurements can be made and compared against known information to identify or characterize the particle.The combined information from the device 360 (or any system of fresnel lens and photodetectors substituted therefor) and the transducer 361 can be channeled to a computer 370 where previously known information is stored and against which the new information can be compared.

The rays such as 350' which pass through the dichroic mirror 31 8 will have less radiant energy than the original rays 350. Accordingly it is desired for maximum information to have as sensitive a detector at the position of the device 36Q as'feasible. This can be done by substituting a prismatic fresnel lens system and detectors as described earlier for the low sensitivity device 360.

Figure 19 has been included to illustrative apparatus based on the principle of collecting scattered and fluorescent light separately through the use of a dichroic mirror. To facilitate explanation, the version in which the scattered light is transmitted and the fluorescent light is reflected is shown. As a practical matter, however, due to manufacturing problems of the dichroic mirror, the inverse arrangement, in which fluorescent light is transmitted while the scattered light is reflected, is actually the preferred embodiment. This latter is illustrated in Figure 20 and is identical to Figure 1 9 except for the transposition of the respective elements.

In the course of the explanations given herein and in the claims, reference is made to focal points and to specific geometric configurations of reflectors such as ellipsoids, paraboloids, etc. The manufacture of instruments which embody and use all of the benefits and advantages of the embodiments of the invention would call for providing components which are formed with precision; however, for economy the configurations are certainly capable of being formed as approximations. Thus when specific configurations are mentioned it should be taken to mean that in addition to the precise geometric configurations substantial and/or approximate approaches to such configurations are intended to be included herein. Focal points may not always be precisely a point but may be a sort of zone but will still give the desired results.Reference to two focal points in the discussion and claims is not intended to exclude paraboloidal reflectors inasmuch as the second focal point thereof is considered to be at infinity.

Such a paraboloidal reflector is illustrated in connection with the apparatus 400 of Figure 18.

This apparatus includes a flow cell 426 which has a parabolic reflector 446 whose front opening is closed off by a suitable closure 424 which is planar because the reradiated radiant energy which emerges from the reflector 446 emanates along lines which are parallel to the optical axis 420. The light source 41 2 in this instance is behind the reflector 446 as shown and it projects a beam of incident radiant energy along the path 422 toward the folding mirror and onto the light dump 444, this beam of incident radiant energy passing through the sensing zone which coincides with the focal point 428 of the paraboloid 446.

Particles originating at the source 40 move along the path to the focal point 428 and at that point which comprises the sensing zone they intercept the beam 422 and reradiate some of the radiant energy of said beam. The rays move outward of the focal point 428 as for example along the line 450, engage the inner surface of the reflector 446 and thereafter are projected parallel to the axis 420, as stated above, toward what may be considered the second focal point of the reflector 446 at infinity.

In order to obtain benefits mentioned earlier, the groups of rays emerging from the front of the reflector 446 are captured by a focussing lens 469 which can be of conventional construction or fresnel construction and diverted along the lines such as 450' to another focal point at 448. This local point is located relative to the reflector 446 in accordance with the optical specifications of the lens 469 (or a lens system used in lieu thereof) rather than as a result of the geometric law which defines the paraboloid.

At this focal point 448 there is an opaque barrier or iris 452 having a central aperture 454, these both lying on plane 456 which is normal to the axis 420. At a distance dfrom the plane 456 there is located a measuring device which comprises an integral planar configuration of photovoltaic detectors 460 whose sensitive surface is in the front plane thereof at 462. The ray groups 450' emerging from the reflector 446 and focussed at the focal point 448 diverge after being purified of stray light at the focal point by the barrier 452 and impinge against the sensitive surface 462 of the measuring device 460. It will be recognized that this measuring device is the same as those which have been referred to herein and identified as 60, 160, 260 and 360.

Again in this case, the measuring device 460 may be moved back and forth parallel to the axis 420 but without charging its disposition relative to the axis to vary the distance d. Once the optimum distance and hence the optimum polar angles have been determined, the known measuring device 460 may be removed and the measuring devices which were described earlier for increased sensitivity and better data can be substituted for collecting light at these angles.

Many other variations are capable of the being made without departing from the scope of the invention as defined in the appended claims.

Claims (47)

1. A method of measuring the directional distributional properties of the radiant energy reradiated from a particle for characterization or the like of said particle and using integral configuration of photovoltaic detectors having a sensitive front planar surface which method comprises: A. passing the particle through a sensing zone located on the interior of a concave reflector whose configuration is substantially defined be a geometric law, the reflector being symmetrical about an optical axis and having a first focal point also defined by said geometric law, the sensing zone being at said first focal point.

B. directing a beam of incident radiant energy along said axis to said sensing zone, and C. intercepting the radiant energy which has been reradiated by said particle and emerging from the front of said reflector at said planar surface.

2. A method as claimed in claim 1 in which the configuration is adjusted along said axis while maintaining its disposition relative to the axis in order to find the location thereof along said axis providing substantially optimum response of said photovoltaic detectors due to said reradiated radiant energy from said particle.

3. A method as claimed in claim 2 further including, after said location of substantially optimum response has been found, removing the configuration from said location and substituting thereofor a composite optical member having the property of separating the received reradiated energy from said particles into plural individual ray groups and directing said ray groups along an equivalent plural number of respective paths, each group having a different direction relative to one another and a direction divergent from the said axis, and measuring the said individual ray groups separately by respective interception of said plural paths.

4. A method as claimed in claim 3 in which the separation is effected by deviation in transmission through said composite optical member.

5. A method as claimed in claim 3 in which the separation is effected by reflection from said composite optical member.

6. A method as claimed in any preceding claim in which the beam of incident radiant energy is directed from the rear of the reflector to said sensing zone whereby to provide information on reradiated energy initially directed primarily in the back directions.

7. A method as claimed in any of claims 1 to 5 in which the beam of incident radiant energy is directed from the front of the reflector to said sensing zone whereby to provide information on reradiated energy initially directed primiarily in the forward directions.

8. A method as claimed in any preceding claim in which the geometric law is that of an ellipsoid, the sensing zone being at said first focal point of said ellipsoid and including the step of passing the reradiated radiant energy from said particles through an aperture for the suppression of stray light at the second focal point of said ellipsoid before intercepting the same.

9. A method as claimed in any of claims 1 to 7 in which the geometric law is that of a paraboloid.

10. A method as claimed in any of claims 1 to 7 in which the geometric law is that of a hyperboloid.

11. A method as claimed in any preceding claim further including the step of focussing the reradiated energy.

12. A method as claimed in claim 11 further including the step of passing the focussed reradiated energy through an aperture.

13. A method as claimed in claim 12 in which the emerging reradiated radiant energy is focussed on the aperture before intercepting the same.

14. Apparatus for measuring the distribution of radiant energy produced by particles for characterization or the like of said particles which comprises: A. a source of radiant energy arranged to project a beam of radiant energy along a first axis, B. a sensing zone on said first axis, C. means for moving particles through said sensing zone to produce reradiated radiant energy from said particles, D. means for collecting some of the radiant energy reradiated in angles substantially surrounding said sensing zone and projecting same as ray groups toward a measuring device spaced from said sensing zone along said axis, said collecting means comprising i. a concave reflector which is symmetrical about said axis, the opening of said reflector facing toward said measuring device, ii. the configuration of said reflector being defined by a predetermined geometric law which provides for a focal point on the interior of said reflector, iii. the sensing zone being coincident with said focal point, E. said measuring device comprising an integral configuration of photovoltaic detectors having a sensitive planar surface, said planar surface being normal to said axis and facing said opening of the concave reflector and adapted to receive the projected ray groups.

1 5. Apparatus as claimed in claim 14 in which the geometric law is that of an ellipse and the reflector is a portion of an ellipsoid.

16. Apparatus as claimed in claim 15 in which the ellipsoid of which said reflector is a portion has a second focal point on said axis forward of said reflector opening, the projected ray groups being focussed at said second focal point, the apparatus including an iris defining an aperture at said second focal point, the said planar surface being spaced from the second focal point away from the reflector opening whereby the groups diverge from the aperture before impinging against said planar surface.

17. Apparatus as claimed in any of claims 14 to 1 6 in which the distance of the planar surface from said focal point is adjustable along said axis to enable determining an optimum distance from said aperture.

1 8. Apparatus as claimed in any of claims 14 to 1 7 in which the source is arranged to project its beam of radiant energy into the opening of said reflector from the front of the reflector.

19. Apparatus as claimed in any of claims 14 to 1 7 in which the rear normally closed portion of the reflector has a window and the source is arranged to project its beam of radiant energy to said focal point from the rear of the reflector through said window.

20. Apparatus as claimed in claim 4 in which the geometric law is that of hyperbola and the reflector is a portion of one branch of said hyperboloid.

21. Apparatus as claimed in claim 20 in which the hyperboloid has a virtual focal point spaced rearwardly of the normally closed rear portion of the reflector, the ray groups produced by reradiation at said sensing zone and projected out of the front opening of said reflector diverging along paths defined by straight lines extending from the virtual focal point through the points of reflection on the inner surface of said reflector, said apparatus including means to collect the diverging ray groups and redirect the same to said planar surface.

22. Apparatus as claimed in claim 21 in which the last mentioned collecting means comprise at least one focussing lens, the focussing lens being arranged to focus the ray groups to a third focal point on said axis, means defining an aperture at said third focal point, the ray groups being thereafter directed divergently to said planar surface.

23. Apparatus as claimed in any of claims 20 to 22 in which the position of the measuring device along said axis is adjustable whereby to enable determining the optimum distance of said planar surface from said third focal point.

24. Apparatus as claimed in claim 14 in which the geometric law is that of a parabola and the reflector is a paraboloid.

25. Apparatus as claimed in claim 24 in which means are provided to focus the parallel ray groups emerging from the opening of the reflector to a second focal point on said axis spaced from the reflector opening.

26. Apparatus as claimed in either claim 24 or 25 which includes means for movably positioning said measuring device along said axis on the side opposite the focussing means relative to said reflector.

27. Apparatus as claimed in claim 26 in which said measuring device is movably positioned along said axis at a distance further from said reflector than said second focal point, and means are included defining an aperture at said second focal point whereby stray radiant energy is rejected.

28. Apparatus as claimed in claim 25 in which said measuring device is located on the axis on the side of the focussing means opposite said reflector.

29. Apparatus as claimed in claim 28 in which said location of the measuring device is further from said reflector than said second focal point and in which means are provided defining an aperture disposed at said second focal point whereby to reject stray radiant energy.

30. A method as claimed in any of claims 1 to 1 3 in which prior to intercepting the radiant energy it is treated to separate the components at fluorescent wavelengths from all other components and in which the respective types of components are intercepted independently.

31. Apparatus as claimed in any of claims 14 to 29 in which there are means for separating the fluorescent components of said ray groups before they impinge against said measuring device, and diverting said fluorescent components to a second measuring device independent of the firstmentioned measuring device.

32. A method of measuring the directional distributional properties of the radiant energy reradiated from a particle for characterization or the like of said particle and using an integral configuration of photovoltaic detectors having a sensitive front planar surface, the method being substantially as herein described with reference to and as illustrated by Figures 14 to 20 of the accompanying drawings.

33. A method as claimed in claim 32 substantially as herein described with reference to and as illustrated by Figure 14 of the accompanying drawings.

34. A method as claimed in claim 33 modified substantially as herein described with reference to and as illustrated by Figure 1 5 of the accompanying drawings.

35. A method as claimed in claim 33 modified substantially as herein described with reference to and as illustrated by Figure 16 of the accompanying drawings.

36. A method as claimed in claim 35 modified substantially as herein described with reference to and as illustrated by Figure 17 of the accompanying drawings.

37. A method as claimed in claim 32 substantially as herein described with reference to and as illustrated by Figure 1 8 of the accompanying drawings.

38. A method as claimed in claim 32 substantially as herein described with reference to and as illustrated by Figure 19 of the accompanying drawings.

39. A method as claimed in claim 38 modified substantially as herein described with reference to and as illustrated by Figure 20 of the accompanying drawings.

40. Apparatus for measuring the distribution of radiant energy produced by particles for characterization or the like of said particles, the apparatus being substantially as herein described with reference to and as illustrated by Figures 14 to 20 of the accompanying drawings.

41. Apparatus as claimed in claim 40 substantially as herein described with reference to and as illustrated by Figure 14 of the accompanying drawings.

42. A method as claimed in claim 41 mddified substantially as herein described with reference to and as illustrated by Figure 1 5 of the accompanying drawings.

43. A method as claimed in claim 41 modified substantially as herein described with reference to and as illustrated by Figure 1 6 of the accompanying drawings.

44. A method as claimed in claim 43 modified substantially as herein described with reference to and as illustrated by Figure 1 7 of the accompanying drawings.

45. A method as claimed in claim 40 substantially as herein described with reference to and as illustrated by Figure 1 8 of the accompanying drawings.

46. A method as claimed in claim 40 substantially as herein described with reference to and as illustrated-by Figure 19 of the accompanying drawings.

47. A method as claimed in claim 46 modified substantially as herein described with reference to and as illustrated by Figure 20 of the accompanying drawings.