JPH10505426A - High efficiency compact lighting system - Google Patents

Abstract

Abstract: An improved illumination system using two concave mirrors (24, 26) and a non-imaging reflector (14) to more efficiently collect energy (light) is apparent. Is done. The use of the system in a novel spectroscopic analyzer is also demonstrated.

Description

Description: FIELD OF THE INVENTION The present invention is used in a wide range of instruments requiring an efficient light source, such as the spectroscopic analyzer disclosed in US patent application Ser. No. 08 / 224,655. Lighting system. In particular, the invention relates to an illumination system for imaging energy from a light source in a very efficient manner at the input aperture of a non-imaging reflector. BACKGROUND OF THE INVENTION U.S. Pat. No. 4,956,459, hereinafter referred to as the Philips patent, discloses a light source, a pair of concave mirrors positioned to collect substantially all of the light from the light source, and a device that collects substantially all of the light. Illustrates an illumination system with non-imaging optics having an input aperture positioned to redirect in a controlled manner. The second concave mirror is shaped such that a linear shape is rejected, as revealed in the Philips patent. Since the second concave reflector forms the image of the light source at a point distant from the light source, the center of curvature of the concave mirror and the light source can at best be on the same plane. Such an arrangement is disadvantageous for the following reasons. (1) This arrangement requires the incorporation of a large package (surround). (2) This arrangement requires a higher degree of complexity of the mechanism with higher costs. And (3) this arrangement shows greater sensitivity to alignment errors because it is away from the common center line. The ability to produce a small divergence angle illumination beam, i.e., the direct function of the non-imaging optics, changes the angle of light entering the input aperture to a smaller angle as it exits through the exit aperture due to several factors. That is. Generally, as the divergence angle entering the non-imaging optical system increases, the angle exiting the non-imaging optical system increases. Prior art illumination systems make a large angle of 90 ° to the center line of the non-imaging optics as it enters the aperture. In comparison, the objects of the arrangement of the present invention can enter the non-imaging optics at about 65 ° at the maximum divergence angle, and therefore have a more efficient energy concentration than prior art designs. It is. In addition, all the spheres of the design disclosed in the Philips patent make the energy distribution at the entrance aperture of the non-imaging optics asymmetric. In addition, the fabrication of all spherical versions of the design disclosed in the Philips patent (positioning the second concave reflector with minimal displacement, and thus minimal aberration, with respect to the light source and image) was extremely difficult. . It is an object of the present invention to provide a lighting system that has a more efficient energy concentration than prior art systems. Another object is to provide an illumination beam with a smaller divergence angle than the prior art. It is also an object of the present invention to provide a system that is relatively insensitive to alignment errors. It is a further object of the present invention to provide a system that has a minimum perimeter dimension as compared to conventional designs, and the complexity of the mechanism is reduced with a corresponding reduction in manufacturing costs. Yet another object is to provide a variety of instruments using light sources including, but not limited to, microscopes, slide projectors, surgical instruments, spectrometers, keratometers, and endoscopes, especially with high efficiency and small size improvements The present invention provides an illumination system for use in a light source for a spectroscopic analyzer. Such spectrometers are suitable for use with gas, solid and liquid samples. It can be used to analyze various components of a sample simultaneously, and is suitable for measuring diffuse and solid specular reflection. SUMMARY OF THE INVENTION These objects are directed to a light source, which collects light from a light source in a first hemispherical space and reflects or focuses the collected light at a point remote from the light source to form a first image of the light source. A first concave reflective surface or concave mirror positioned to collect light from a light source outside the boundaries of the first concave mirror to collect light in a second half space Wherein the second concave mirror reflects or images light in the second half-space to create a second image of the light source at a point proximate to the light source, wherein the first concave mirror is collected by the second concave mirror. A second concave reflective surface or mirror for reflecting or re-imaging the provided light to provide a third image of the light source at a remote point where the first image was created; and first and third of the light source. Illumination system with a non-imaging reflector having an input aperture positioned to receive substantially all of the light from the image of the It is achieved by. That is, these objects are achieved by a highly efficient compact lighting system. The first concave mirror is of a type that creates a first image of the light source at a location remote from the light source. The second concave reflective surface includes collecting light beyond the boundaries of the first concave mirror and creates an image of the light source at a point proximate to the light source. It is also a function of the first concave reflective surface to collect this light again imaged by means of a second concave mirror and to create a third image of the light source at a point remote from the light source. The input aperture of the non-imaging optic is positioned to collect substantially all of the light of the first and third image types created by the two concave mirrors and is further emitted from its exit aperture. It is operated to reduce and limit the divergence angle of the light. According to a preferred embodiment, the first and second concave mirrors are profiled such that the first and third images are accepted by the input aperture of the non-imaging optics. This embodiment includes an elliptical concave reflector having a first focal point at the light source location and a second focal point located at a distance from the light source and corresponding to the entrance aperture of a homogenizing element or non-imaging optics. With such a first concave mirror. The second concave mirror has a form in which its center of curvature is located in close proximity to the light source position, preferably a spherical form. In the most preferred system, the light source, the center of curvature of the concave mirror, the non-imaging optics, and all images are on a common line. Important applications of this illumination system are as high efficiency collectors in spectroscopic analyzers. For this purpose, the spectroscopic analyzer comprises a first concave reflecting part and a second concave reflecting part facing it and having a through outlet passage. A light source that emits light in a predetermined wavelength range is positioned in the collector such that the emitted light is collected by the reflective portion and directed to the exit passage. The sample holder is positioned adjacent the outlet passage of the collector and has an inlet end and an outlet end. At the exit end of the sample holder is the entrance end of the elongated reverse non-imaging optic. The optical element has a peripheral wall that reflects light rays entering through the exit window of the holder to reduce the angle of the light rays with respect to the optical axis of the optical element as they pass therethrough. At the exit end of the optical element is a detector assembly, which comprises at least one photodetector sensitive to light of a predetermined wavelength, and said predetermined wavelength located between the optical element and the detector. It has at least one filter that allows light to pass through. Advantageously, the first part of the collector is a concave spherical or elliptical surface. Although the non-imaging optical element has a compound hyperboloid shape, it may have a shape selected from a substantially conical, aspherical surface, and a spline. The window of the sample holder filters certain frequencies or passes frequencies in a predetermined wavelength range. The detector assembly includes a light collector between the filter and the light detector. The detector assembly may include a plurality of photodetectors and filters cooperating to respond to light in different wavelength ranges. The sample holder is a cylindrical member for containing gas or has means for supporting a translucent fixed sample, or comprises means for placing the surface of the sample at an angle with respect to the longitudinal axis of the holder. . The sample holder can also be a translucent solid light guide, which allows a slight absorption of the spectral energy at the interface with the sample placed around it. If desired, a chopper can be provided to pulse the light passing into the sample holder. Infrared light is generally preferred, but ultraviolet and visible light can also be used. In use, the light source is powered and emits light rays which are collected and reflected from the collector to the exit aperture and further into the sample holder containing the sample to be analyzed. The sample interacts with the light beam to provide a spectral representation of its components. The light beam then passes through the elongated non-imaging optic, whereupon the angle of the light beam with respect to the optical axis of the optic is reduced. The light rays emanating from the optical element then strike a photodetector, producing signals indicative of the components of the sample, and these signals from the photodetector are analyzed. Preferably, the light rays exiting the optical element are directed through a filter before hitting the light detector, and the light rays exiting the optical element are directed to the light concentrator before the light detector. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partially diagrammatic view of a gas and liquid spectrometer embodying the present invention. FIG. 2 is an exploded view of the analyzer of FIG. FIG. 3 is a schematic drawing of a light collector, a gas cell and a parabolic light collector showing the trajectory of a passing light beam. 4a and 4b are diagrammatic partial views of a light concentrator for a detector assembly for collecting light rays striking on a light detector. 5a-5d are diagrammatic views of different shapes of non-imaging optical elements that can be used in the present invention. 6a-6c are diagrammatic views of another type of sample holder that may be used. FIG. 7 is a diagrammatic drawing of a concentrator having parabolic and spherical reflecting surfaces. FIG. 8 is a schematic drawing of a light source, a concave mirror, a uniformizing element, and a non-imaging optical system showing the trajectory of a passing light beam. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring first to FIGS. 1 and 2, which in the analyzer embodying the illumination system of the present invention is illustrated diagrammatically. This is typically a light source and concentrator generally designated by the number 10, a sample holder generally designated by the number 12, a non-imaging optical element generally designated by the number 14, and an entirety designated by the number 16. A detector assembly is provided. Also shown is a chopper assembly generally designated by the numeral 18. The concentrator 10 typically comprises a pair of blocks 20 and 22 each having a spherical concave surface 24 and an opposing spherical surface 26. The block 22 is provided with a coaxial opposed opening 28. A light source 30 is coaxially disposed on the block 20 such that light rays produced by the light source are reflected from the surfaces 24, 26 and directed to the aperture 28. The light source or light emitter 30 is connected by a cable 32 to a power supply (not shown). The chopper assembly 18 includes a drive motor 34 having a joint 36 that transmits rotational motion to a drive shaft 38 having a chopper blade 40 extending across the opening 28. Power is supplied to the motor 34 via the cable 35. The sample holder 12 of this embodiment is provided with a block through which a gas or liquid is passed and having a coaxial recess 42 therein. An inlet port 44 and an outlet port 46 allow the passage of the gas or liquid to be analyzed, and windows 47, 48 at each end retain the gas or liquid therein. After passing through the sample in holder 12, the light beam exits through window 48 and enters non-imaging optic 14. As it passes therethrough, it is reflected at the wall defining the passageway 50 so as to exit at a smaller angle with respect to the optical axis of the passageway 50, ie, move closer to the optical axis. Upon exiting the optical element 14, the light passes into the detector assembly 16, where it passes through a filter 52 and enters a photodetector 54 where the intensity of the filtered light is measured. A signal is output to computer 56 via lead 55 to determine the light intensity and determine the concentration of the component being analyzed. More particularly, as shown in FIG. 2, an easier-to-use assembly is provided with several blocks and tubes connected by pins or dowels 57 seated in aligned recesses 58 and secured by gluing, friction or set screws. Is done. The flange of the chopper motor 34 is fixed to the block 20 by the screw fixture 60. A removable end cap 62 is secured to a block 66 by a fixture 64, which provides a housing for the detector assembly 16. The entire assembly is supported by a mounting 68, which can be secured to any suitable support (not shown). Referring now to FIG. 3, the trajectory of light rays emitted by light source 30 reflected by surfaces 24, 26 and reaching exit aperture 28 is shown schematically. This outlet opening extends into window 28 (see FIG. 1) and thus into sample holder 12. Light rays are reflected from the surface, pass through it, pass through the sample contained therein until exiting the holder 12, and pass into the non-imaging optical element 14. The light rays are reflected at the surface defining the path through the element 14, so that the light rays exit at a relatively small angle with respect to the optical axis 72 of the assembly. Although not essential, the effectiveness of the device can be increased by providing a light guide or concentrator in the detector assembly 16 to direct light rays onto the light detector 52. . As seen in FIGS. 4a and 4b, the detector housing 70 can incorporate a plurality (only one is shown) of converging passages 72 whose exit ends are aligned with the light detectors 52. Some of the shapes of the non-imaging optics to reduce the angle of the passing light rays as indicated by the ray trajectories are shown diagrammatically in FIGS. 5a-5d. 5a and 5b are another spherical form, FIG. 5c shows a conical surface, and FIG. 5d shows the use of a spline surface. As can be seen in FIGS. 6a-6c, the sample holder can have many structures depending on the type of material being analyzed and the nature of the effect of the sample on the light beam, such as absorption, reflection and attenuation. The embodiment shown in FIGS. 1 and 2 shows a sample holder where light is transmitted through the sample and is generally used with liquids and gases. FIG. 6a shows a sample holder 80 for an opaque solid, which has a V-shaped light guide 81, which supports a sample 82 at its apex such that light rays are reflected from the surface of the material. FIG. 6c shows a sample holder 84 in which a light guide 86 extends through a tube 88 containing a liquid sample 90 and attenuation occurs at the surface of the light guide 86. As mentioned above, light rays emanating from the non-imaging optics preferably pass through a filter that is associated with and cooperates with the photodetector. These filters may allow only light in a narrow wavelength range to pass through, or selectively filter out light in a narrow range, depending on the wavelength band measured by the detector. The light rays are directed at an angle close to normal to the filter due to directing by the optical system, and the spectroscopic filter can function more effectively to analyze the light energy after interacting with the sample. Filters are typically designed to allow passage through the filter for a particular wavelength bandwidth and reject other energies. Thus, if the filters have a bandwidth that closely matches the absorption band of the sample in the compartment, they will be able to alert the system to the lack of light energy, which means the wavelength of a particular material. This confirms the presence of a known material in the sample compartment due to its absorption. Because of their efficiency and compactness, spectrometers can be made as small, battery-powered gas detectors that allow easy and economical atmospheric monitoring of a wide variety of gases. The components make this easy and relatively economical, so the cost of the user is relatively small compared to existing devices that are large, heavy and not actually portable. Two components such as non-imaging optics and a detector assembly can be combined as seen in FIG. 5d. The light collection and pointing properties of the system are highly efficient, and the components are modular and the three main components (light source / collector, sample holder, energy collector / redirector) are many Allow to assemble into shape. The efficiency of light collection and pointing of the system can be applied industrially to gas analysis, fluid analysis, fluorescence analysis, and generally any application that obtains spectral information by means of sample / light energy interaction. Further, as a result of this highly efficient assembly, by providing a series of different photodetectors and filters that cooperate therewith, each monitoring a different wavelength of light of a different component, four types of samples are provided. Or more different components can be monitored. In a concentrator, two reflecting surfaces cooperate with a light emitter located in between. In the optical system described above, the components are arranged to allow maximum solid angle radiation efficiency. The relationship between the focal point of the light collection shell and the overall shape determines its light collection efficiency. The vertex of the first half of the optical shell is located behind the center point of the light source. This particular portion can be one of two general shapes. The first is a simple sphere. The radius of the sphere is selected to create an image of the light source at the window to the sample holder. Another choice for the shape of the first block 20 portion is the ellipsoid 100 seen in FIG. In this case, the ellipse has one focus at D1 and the other focus at D2. The advantage of using an ellipse instead of a sphere is the reduction of aberrations such as spherical aberration encountered when using a sphere in this way. However, aberrations are ignored as long as the blur diameter can be obtained from the sample components. A major drawback of utilizing aspheric surfaces (ellipses or ellipses modified to allow aberration correction) is the associated high manufacturing costs. The second part of the concentrator should always be spherical. The spherical mirror is positioned with its center of curvature coaxial with the center of the light emitter. As a result of such an arrangement, as can be seen in FIG. 3, all of the energy outside the light receiving range of the first shell half is reflected from the second shell half back toward the first shell half, One shell half allows the energy to be focused into the sample holder. In the embodiment shown in FIG. 1, the light emitter can be an infrared (IR) energy source equivalent to a heating wire operating at 660-800 ° C. This gives a broadband IR radiation of 2-15 microns, which is collected by the reflective surface into a beam of narrow IR energy. As can be seen in FIG. 3, a collection of light from a finite light source with mirror segments up to NA (numerical aperture) of 1.0+ is focused into the entrance aperture of the sample holder. The light collection efficiency is increased beyond 1.0 + NA by the addition of a second concave light collection element that redirects energy from angles beyond the 1.0 + NA condition toward the focal point of the first mirror segment. Can be The first segment can then collect this energy again and direct it to the inlet opening of the sample holder. For this reason, this condensing optical system reliably collects energy from the light emitter at a high ratio. The sample will encode the incident light energy with information about its molecular physical properties. As is known, the light energy of a particular spectral characteristic is affected by the sample components, so the light energy from the sample holder will carry information indicative of the molecular properties of the sample. The window for the sample holder is desirably made of a material capable of transmitting light energy within the wavelength bandwidth of light of interest. For example, a window for an infrared detector would include barium fluoride. This material is chosen for its ability to transmit IR energy without absorption in the region of interest. As described above, the non-imaging optical element is shaped so as to reduce the angle of the incident light when the incident light moves. The concept of these optics can be described as a collection of points that define the tangent to the angle of light received at a smaller angle. As a result of determining the angular orientation of the optical system, the vertical angle between the light rays emerging from the non-imaging optics and the normal to the optical filter / photodetector increases. An optical filter having a narrow wavelength band is designed so as to transmit a relatively small wavelength range. This can be achieved by stacking different layers of transmission material. Energy striking the filter surface at an angle away from a right angle to that surface will have a path length in the media defined by an oblique path through a particular filter layer. As this angle increases, the error increases. Filters allow the transmission of wavelengths that make up certain path lengths in the medium. Energy at shorter wavelengths where the angle of incidence on the filter is greater will appear to the filter as a wavelength with the proper path length. This phenomenon, known as the "blue transition", explains why lower angle (bluer) wavelengths can pass here. Therefore, non-imaging optical elements reduce the inherent error. A typical formula for "non-imaging" optics is to find it in "The Optics of Non-Imaging concentrators" by Welford and Winston, published by Academic Press. Can be. With reference to FIG. 8, it is schematically shown that the ray trajectory indicating the rays emitted from the light source 30 is reflected by the first concave mirror 24 and the second concave mirror 26 to the “selective” homogenizing element 12. . The light rays pass into non-imaging optics 14 that are positioned to collect substantially all of the light. Light rays are reflected from the surface defining the path through the element 14 and exit at a relatively shallow angle with respect to the optical axis 72 of the system shown in FIGS. 4a and 4b. As shown in FIG. 8, light from the light source 30 reflects off the first concave mirror 24 and creates a first image 91 at the entrance to the “selective” light guide 12. The second concave mirror 26 collects light from the light source 30 that is outside the boundary of the first concave mirror and forms a second image 92 immediately adjacent to the light source 30. The first concave mirror 24 forms an image of the light collected by the second concave mirror 26 and forms a third image 93 in the light guide 12 immediately adjacent to the first image 91. Non-imaging reflector 14, which may be a compound parabolic concentrator, receives images 91 and 93 through aperture 94 and collects light of these images along its length. This system collects light from light source 30 to 4 steradians. The lighting system of the present invention can be used for the following applications. Slide projectors, TV projectors, microscope illuminators, all types of "inspection" lamps, infrared / visible / ultraviolet filters, NIR spectrometers, Raman spectrometers, fluorescence spectrometers, refractometers, interferometers, general vehicles Lighting equipment, aircraft HUDs, Doran Jena fiber optic lighting, otoscopes, schlieren system equipment, searchlights, and general class laser resonators. In particular, the lighting system of the present invention is adapted to easily provide: 1. Enhanced infrared signal supply system for FTIR (Fourier transform IR) spectroscopy system. For an FTIR spectrometer bench, the system provides a significantly enhanced magnitude signal available for analysis, thus allowing a cooler light source for operation. The small, efficient design of the illumination system as a remote energy source for FTIR microscopes and in test systems that require a remote IR illumination source offers clear benefits. 2. In interstitial fiber optic endoscopes / borescopes that deliver significant energy into the optical fiber for illumination, to collect light from a white light source (eg, a halogen light source) and direct this light onto a microscope sample. A general visible illumination source for visible microscopes acting as a total reflection, low cost system for, and a white light illumination source for security systems, flashlights and floodlight type systems. The lighting system of the present invention is useful in any application where a limited amount of electromagnetic energy for lighting is available (e.g., UV fluorescence). In addition, the system can be used to create a system with the enhanced ability to deliver energy from almost 360 ° to the specimen, quite the contrary. This system has the ability to produce an illumination beam with a small divergence angle. The direct function of the non-imaging optics is to convert the angle of light entering the input aperture to a smaller angle as it exits the exit aperture due to several factors. Generally, as the angle of divergence upon entering the non-imaging optical system increases, the angle upon exiting the non-imaging optical system also increases. Prior art illumination systems make a large angle of 90 ° with respect to the center line of the non-imaging optics when entering the aperture. In comparison, the geometry of the system of the present invention allows even the most divergent rays to enter non-imaging optics at about 65 °. That is, energy concentration is more efficient than prior art designs. Since the divergence angle, sensitivity to alignment, size, and cost are major concerns in the production of an effective lighting system, the system of the present invention uses a total of 4 steradians (stereoscopic) of light emanating from the light source. Angle) and direct this energy in a manner that reduces the divergence angle to a size that significantly improves the operation of conventional optical systems. From the foregoing detailed description and accompanying drawings, a spectrometer using the illumination system of the present invention can be easily and economically manufactured, is highly efficient, and can be used like a laboratory or industrial device. In addition, it turns out to be small and light enough to provide many field portable devices. The analyzer can be used on gas, solid and liquid samples by means of easily exchangeable holders, and its efficiency makes it possible to use multiple light detectors to enable simultaneous analysis of multiple components in the sample. The light beam can be split across the sample holder to provide multiple beams to the instrument.

Claims (1)

[Claims]   1. light source,   Collecting light from the light source in a first hemispherical space at a point remote from the light source Positioned to reflect or image the light to create a first image of the light source. A first concave reflective surface or mirror,   From the light source outside the boundaries of the first concave mirror to collect light in a second half space A second concave reflecting surface or mirror for collecting light, wherein said second concave mirror is said second half mirror; Creating a second image of the light source at a point closest to the light source by reflecting or imaging light in space; The first concave mirror reflects or re-images the light collected by the second concave mirror The second providing a third image of the light source at a remote point where the first image was created; Concave mirror, and   Positioned to receive substantially all of the light from the first and third images of the light source. Non-imaging reflector with fixed input aperture Lighting system with.   2. 2. The illumination system of claim 1, wherein said second reflecting concave mirror is a spherical reflecting surface. .   3. A homogenizing element having an inlet opening and an outlet opening defines the inlet opening as the first and second openings. And positioned to collect substantially all of the light from the second concave mirror, and further comprising: Claims wherein an exit aperture is positioned to be positioned at the entrance to said non-imaging reflector Item 1. The lighting system according to Item 1.   4. 4. The illumination system according to claim 3, wherein said equalizing element is in the form of a reflective cylindrical mirror. .   5. 4. The illumination system according to claim 3, wherein said homogenizing element is in the form of a translucent refractive light guide. Stem.   6. The lighting system of claim 1, wherein the light source emits light of an infrared wavelength.   7. The light source, the center of curvature of the concave mirror and all of the image are substantially common The lighting system of claim 1 above.   8. (A) having a first concave reflective portion and a facing exit passage therethrough; A high efficiency concentrator having a second concave reflective portion, (B) radiation is collected by said reflective portion and directed to said exit passage; A light source that emits light in a predetermined wavelength range positioned in the light collector, (C) positioned adjacent the outlet passage of the collector and having an inlet end and an outlet end; Sample holder, (D) an elongate non-bonding having an inlet end at the outlet end of the sample holder and having an outlet end An image optical element, wherein a light ray passes through the image optical element with respect to an optical axis of the optical element. Rays entering through the exit end of the holder so as to reduce the angle of the rays Said element having a peripheral wall that reflects (E) at least one photodetector sensitive to light of a predetermined wavelength and said optical element And at least one optical filter disposed between the light source and the detector and transmitting the light of the predetermined wavelength. A detector assembly at the exit end of the optical element having a filter; With a spectroscopic analyzer.   9. (A) A light source having a predetermined wavelength range is provided in a light collector having a concave reflecting surface facing the light source. , (B) providing power to the light source to emit a light beam; (C) a sample holder for collecting the light beam and the outlet of the light collector and a sample to be analyzed. And the sample is reflected in the Interacts with the rays, (D) elongating the light beam to reduce the angle of the incoming light beam with respect to the optical axis of the element; Through the imaging optics, (E) transforming the light rays emerging from the optical element so as to produce a signal indicative of the components of the sample; Point on the light detector, (F) analyzing the signal from the light detector Spectroscopic analysis including various steps.