EP1238258A1

EP1238258A1 - An apparatus and a method for providing information relating to two or more particles, bubbles, and/or droplets

Info

Publication number: EP1238258A1
Application number: EP00974355A
Authority: EP
Inventors: Nils Damaschke; Cameron Tropea; Manfred Steiglmeier
Original assignee: Dantec Dynamics AS
Current assignee: Dantec Dynamics AS
Priority date: 1999-11-13
Filing date: 2000-11-13
Publication date: 2002-09-11
Also published as: AU1270001A; WO2001036937A1

Abstract

Providing information relating to two or more illuminated particles, bubbles, and/or droplets where the light providers are positioned so, relatively to the two or more particles, bubbles, and/or droplets and the detecting means, that at least two waves are reflected or refracted by the two or more particles, bubbles, and/or droplets toward the detector, the waves all having been either reflected by the two or more particles, bubbles, and/or droplets or all having been refracted a predetermined number of times within the two or more particles, bubbles, and/or droplets, the information being derived from spatial information from interfering waves generated when the waves from each of the two or more particles, bubbles, and/or droplets interfere on different parts of a sensitive area of the area detector or the line detector. Also, when more than one interfering pattern is used, the light waves from the particles may be refracted to reflected any number of times.

Description

AN APPARATUS AND A METHOD FOR PROVIDING INFORMATION RELATING TO TWO OR MORE PARTICLES, BUBBLES, AND/OR DROPLETS

The present invention relates to an apparatus and a method for providing information relating to two or more particles, bubbles, and/or droplets and more particularly to an apparatus and a method where one or more waves, such as light, is provided toward the particles, bubbles, and/or droplets and where waves are reflected or refracted by each particle, bubble, and/or droplet and is detected by a detector.

These detected waves then provide sufficient information to provide information relating to the particles, bubbles, and/or droplets.

An example of a particle counting technique is the phase Doppler (PD) technique. The PD technique is an extension of the laser Doppler (LD) measuring technique. In the LD technique, two intersecting laser beams define a measurement volume in their crossing region. If a particle passes this measurement volume, two scattered waves, one belonging to each of the two laser beams, propagate into space and interfere with one another. A suitably positioned detector records the light intensity scattered into the space. Through the movement of the particle, the interference fringes will sweep across the detector. The frequency detected by this receiver is proportional to the velocity of the particle.

The extension of the LD technique to the PD technique involves adding a further detector positioned in a suitably chosen location. For each scattering particle, both detectors register the scattered interference field present in space. The fringe spacing in the interference pattern, which sweeps across the detectors, is dependent on the distance between the two exit glare points of light on the surface of the particle and thus, the fringe spacing can be related to the particle size. The velocity and particle diameter can therefore be determined by a frequency and phase difference measurement between the signals on the two detectors. Furthermore, if one scattering order dominates the intensity of light on the detectors, the relationship between the measured phase difference and the particle diameter is linear.

In a first aspect, the invention relates to an apparatus for providing information relating to two or more particles, bubbles, and/or droplets, the apparatus comprising: means for providing light directed toward the two or more particles, bubbles, and/or droplets,

- means for detecting light refracted or reflected by the two or more particles, bubbles, and/or droplets, the detecting means comprising an area detector or a line detector, and

means for receiving information from the detecting means and for deriving therefrom the information relating to the two or more particles, bubbles, and/or droplets,

the wave providing means being positioned so, relatively to the two or more particles, bubbles, and/or droplets and the detecting means, that at least two waves are reflected or refracted by the two or more particles, bubbles, and/or droplets toward the detector, the waves all having been either reflected by the two or more particles, bubbles, and/or droplets or all having been refracted a predetermined number of times within the two or more particles, bubbles, and/or droplets,

the detecting means being adapted to have the waves from each of the two or more particles, bubbles, and/or droplets interfere on different parts of a sensitive area of the area detector or the line detector,

the detecting means being adapted to detect the interfering waves on the area or line detector and to provide spatial information relating thereto to the deriving means.

In the present context, particles, bubbles, and/or droplets are meant to cover all locally inhomogeneous structure s in a medium affecting the wave propagation, such as small items of fluid or solid matter in a gas, fluid or a solid medium or any combination of gas, fluid and/solid structures in a gas, fluid or solid medium.

Also, in the present context, e.g. light refracted by e.g. a particle will be directed toward the particle, enter the particle, may be internally reflected therein any number of times and will finally exit the particle. Thus, a light beam having been refracted within a particle twice will have entered the particle, been internally reflected therein twice and finally exited the particle. This will mean that the light reflected or refracted will be of the same scattered light order.

The present invention utilises the well-known technique where e.g. light is shone on the e.g. particle so that two glare points are formed thereon which emit light onto a detector.

Also, a line or an area detector is used. This type of detector is able to provide information relating to a fringe or interference pattern in a single determination. This information may be fringe separation, fringe intensity, fringe shape, and/or fringe deformation. According to the invention, the interference patterns or fringes will only be provided on a part of the sensitive area of the detector. The patterns of fringes of different e.g. particles are provided at different, potentially partly overlapping, areas of the detector in order to facilitate separation thereof.

At present, it is contemplated that the technique may be used with virtually any type of wave, such as acoustical waves, subsonic waves, visible light or any other type of electromagnetic wave.

In the present context, "spatial" information will mean information relating to the spatial interference pattern or fringe pattern on the detector. This information may be a frequency, a fringe shape, an intensity distribution or the like.

The present inventors have found that when using interfering waves from two glare points where the waves have been either reflected directly off the particle or have been refracted the same number of times, a number of advantages are obtained.

In one embodiment, the wave providing means are adapted to provide a single wave directed toward the two or more particles, bubbles, and/or droplets from a predetermined direction so that a wave is refracted along two or more paths within at least one of the two or more particles, bubbles, and/or droplets , the paths comprising the same number of refractions within the at least one of the two or more particles, bubbles, and/or droplets.

In this manner, only a single wave source illuminating the particle from a single direction is required. In this embodiment, the deriving means may be adapted to derive information relating to a refractive index and/or inhomogeneities and/or information relating to an internal structure of the at least one of the two or more particles, bubbles, and/or droplets. From the refracted wave which, naturally, has entered the particles, bubbles, and/or droplets, information relating to the interior or the surfaces where the wave has entered and exited may be derived in a standard manner.

In another embodiment, the light providing means comprise means for directing two or more waves toward the two or more particles, bubbles, and/or droplets.

In this manner, the waves interfering on the detecting means may be waves reflected or refracted.

This embodiment has the specific advantage that, e.g. in an optical measurement the fringe or interference pattern provided on the detecting means will, in a velocity measurement, alter in a manner different from that of prior art set-ups, which do not use glare point light beams of the same scatter wave order. In fact, due to this set-up, the fringe pattern will move faster than the particle, bubble and/or droplet. In this manner, even very small velocities and/or displacements may be determined.

The present apparatus may utilise both monochromatic and polychromatic light in any combination whereby the light providing means may be adapted to direct one or more polychromatic or monochromatic light beams toward the two or more particles, bubbles, and/or droplets.

Also, the apparatus may further comprise means for providing the two or more particles, bubbles, and/or droplets.

Preferably, the wave providing means are adapted to simultaneously provide one or more waves toward a plurality of particles, bubbles, and/or droplets, the detecting means are adapted to simultaneously receive waves reflected or refracted by the plurality of particles, bubbles, and/or droplets, and wherein the deriving means are adapted to provide information relating to each of the plurality of particles, bubbles, and/or droplets. In this manner, information relating to each particle, bubble, and/or droplet may be provided and/or combined information, such as mean velocity, mean direction of velocity, mean size or the like may be provided.

In a special embodiment, the wave providing means are adapted to provide two or more light beams and/or one or more light beams comprising two or more wavelengths toward the two or more particles, bubbles, and/or droplets.

When the wave providing means are adapted to provide one or more light beams comprising two or more wavelengths toward the two or more particles, bubbles, and/or droplets, the apparatus may further comprise means for selecting one or more predetermined wavelengths or wavelength regions, the selecting means then being positioned in a light path between the light providing means and the two or more particles, bubbles, and/or droplets or between the two or more particles, bubbles, and/or droplets and the detecting means. In this manner, wavelength dependent information may be derived as well as information relating to more than one wavelength.

As one example, the deriving means may then be adapted to provide information relating to a composition, such as material properties, refractive index, absorption, inhomogeneities, internal structure, and/or a shape, such as a size, a surface curvature/roughness, and/or sphericity, of the two or more particles, bubbles, and/or droplets. This information may be derived from two different fringe/interference detections - one relating to each wavelength where the selecting means may then be made to select between the two wavelengths - or the light providing means may be made to shift there between.

In a preferred embodiment, the wave providing means are adapted to provide wave(s) in the form of a measurement sheet or a measurement volume. One side length of this sheet or volume may be from 1μm to several meters, such as 10 meters depending on the actual measurement.

The fact that an area or a line detector is used, provides an apparatus that may, in fact, receive waves from a number of particles, bubbles, and/or droplets, separate the contribution from each of these and thereby provide information from each individual particle, bubble, and/or droplet. Preferably, the detecting means are adapted to have the interfering waves from the two or more particles, bubbles, and/or droplets interfere on the area or line detector over an area being 50% or less, such as 25% or less, preferably 10% or less, such as 5% or less, preferably 2% or less, such as 1 % or less than a total light sensitive area of the area or line detector. In this manner, the waves from each particle, bubble, and/or droplet may be physically separated on the detecting means.

Where the wave providing means are adapted to provide the one or more waves in a first measuring sheet or volume, the apparatus may further comprise:

second means for providing one or more waves directed toward the two or more particles, bubbles, and/or droplets, the second wave providing means being adapted to provide the one or more waves in a second measuring sheet or volume being at an angle to the first measuring sheet, and

the second wave providing means being positioned so, relative to the two or more particles, bubbles, and/or droplets and the detecting means, that at least two waves are emitted from or reflected by the two or more particles, bubbles, and/or droplets toward the second detector, those light beams all having been either reflected by the two or more particles, bubbles, and/or droplets or all having been refracted a predetermined number of times within the two or more particles, bubbles, and/or droplets.

In this manner, two wave providing set-ups are used for the same detector.

Alternatively, the wave providing means may be adapted to provide the one or more waves in a first measuring sheet or volume, where the apparatus further comprises:

second means for detecting waves refracted or reflected by the two or more particles, bubbles, and/or droplets, the detecting means comprising a second area detector or line detector, wherein the receiving means are adapted to also receive information from the second detecting means and to derive therefrom the information relating to the two or more particles, bubbles, and/or droplets,

the second wave providing means being positioned so, relative to the two or more particles, bubbles, and/or droplets and the detecting means, that at least two waves are emitted from or reflected by the two or more particles, bubbles, and/or droplets toward the second detector, those light beams all having been either reflected by the two or more particles, bubbles, and/or droplets or all having been refracted a predetermined number of times within the two or more particles, bubbles, and/or droplets,

the second detecting means being adapted to have the waves, stemming from the second wave providing means, from each of the two or more particles, bubbles, and/or droplets interfere on different parts of a sensitive area of the second area detector or line detector,

the second detecting means being adapted to detect the interfering waves on the second area or line detector and to provide spatial information relating thereto to the deriving means.

Thus, two measuring set-ups are provided that may provide information from different directions, using different types of waves etc.

Preferably, the detecting means and the second detecting means are adapted to detect the interfering waves at least substantially simultaneously.

Also, preferably the first and second measuring sheets are at least substantially perpendicular to each other.

Providing information relating to two directions, the deriving means may be adapted to provide information relating to material properties, refractive index, absorption inhomogeneities, internal structure, and/or a shape, such as a size, a surface curvature/roughness, sphericity, of the two or more particles, bubbles, and/or droplets.

Also, especially if more than one detection is provided, the deriving means may be adapted to provide information relating to changes in composition, such as a mixing, chemical reaction, evaporation, particle internal movement, changes of shape, such as oscillation frequency and/or amplitude, size changes, surface curvature/roughness changes, and/or movement, such as displacement, orientation, position, direction of movement, velocity, rotation, rotational velocity and/or period, of the two or more particles, bubbles, and/or droplets.

Thus, the detecting means are preferably adapted to detect the interfering waves a plurality of times separated in time. Then, the deriving means are adapted to receive information from the detecting means each of the plurality of times and for deriving therefrom information relating to changes in composition, such as a mixing, chemical reaction, evaporation, particle internal movement, changes of shape, such as oscillation frequency and/or amplitude, size changes, surface curvature/roughness changes, and/or movement, such as displacement, orientation, position, direction of movement, velocity, rotation, rotational velocity and/or period, of the two or more particles, bubbles, and/or droplets.

In a second aspect, the invention relates to a method of providing information relating to two or more particles, bubbles, and/or droplets, the method comprising:

a) directing one or more waves toward the particles, bubbles, and/or droplets so as to provide, from at least two separate areas of a surface of each of the particles, bubbles, and/or droplets and in at least substantially the same direction, waves reflected from the two or more particles, bubbles, and/or droplets and/or having been refracted a, predetermined number of times thereby,

b) imaging waves from each of the at least two separate areas of each particles, bubbles, and/or droplets on an area or line wave detector in a manner so that waves from the at least two separate areas of each of the two or more particles, bubbles, and/or droplets interfere and provide an interference pattern on separate parts of a sensitive area of the area or line detector,

c) determining two or more spatial parameters relating to at least two interference patterns of the particles, bubbles, and/or droplets and d) deriving the information relating to the particles, bubbles, and/or droplets from the two or more parameters.

Part of the deriving step may be a step of separating the two or more interference pattern each generated by at least two separate areas on the surface of a particle (glare points) emitting reflected and/or refracted waves. A number of manners exist for performing this task.

In a first embodiment, the step of directing wave(s) comprises directing a single wave toward the two or more particles, bubbles, and/or droplets from a predetermined direction so that wave is reflected and/or refracted along two or more paths within at least one of the two or more particles, bubbles, and/or droplets, the paths comprising the same number of refractions within the at least one of the two or more particles, bubbles, and/or droplets.

Then, the deriving step may comprise deriving information relating to a refractive index and/or inhomogeneities and/or information relating to a composition, such as material properties, refractive index, absorption inhomogeneities, internal structure, a shape, such as a size, surface curvature/roughness, sphericity, surface, changes of composition, such as a mixing, chemical reaction, evaporation, particle internal movement, changes of shape, such as oscillation frequency and/or amplitude, size changes, surface curvature/roughness changes, orientation, rotation and/or rotational velocity/period of the at least one of the two or more particles, bubbles, and/or droplets.

In a second embodiment, the wave-directing step comprises directing two or more waves toward the two or more particles, bubbles, and/or droplets.

The light directing step may comprise directing one or more polychromatic or monochromatic light beams toward the two or more particles, bubbles, and/or droplets.

Also, the method may further comprise the step of providing the two or more particles, bubbles, and/or droplets.

Preferably, the wave directing step comprises simultaneously providing wave(s) toward a plurality of particles, bubbles, and/or droplets, and the imaging step comprises simultaneously receiving waves reflected and/or refracted by the plurality of particles, bubbles, and/or droplets, and the deriving step comprises providing information relating to each of the plurality of particles, bubbles, and/or droplets.

As mentioned above, the light directing step may comprise directing two or more light beams and/or one or more light beams comprising two or more wavelengths toward the two or more particles, bubbles, and/or droplets.

Then, the deriving step may comprise deriving information relating to movement, such as position, direction of movement, velocity, displacement, of one or more particles by phase changes of one or more interference patterns for each particle, at least one of the one or more interference patterns being created by reflected and/or refracted waves from different waves toward the one or more particles.

Also, the wave directing step may comprise directing one or more light beams comprising two or more wavelengths toward the two or more particles, bubbles, and/or droplets, the method then further comprising the step of selecting one or more predetermined wavelengths or wavelength regions, and wherein the imaging step comprises imaging light of the selected wavelengths or wavelength regions. Then, the deriving step may comprise providing information relating to a refractive index of the two or more particles, bubbles, and/or droplets.

As mentioned above, the wave-directing step preferably comprises providing wave(s) toward a measuring sheet or a measuring volume.

When the directing step comprises providing wave(s) toward a measuring sheet or volume, the method may further comprise the steps of:

e) providing a second sheet of light by directing light toward the particles, bubbles, and/or droplets so as to provide, from at least two separate, second areas of a surface of each of the particles, bubbles, and/or droplets and in at least substantially the same, second direction, light reflected from the two or more particles, bubbles, and/or droplets and/or having been refracted a predetermined number of times thereby.

Furthermore, the method may further comprise the steps of: f) imaging waves from each of the at least two separate, second areas of each particles, bubbles, and/or droplets on a second area or line detector in a manner so that waves from the at least two separate, second areas of each particles, bubbles, and/or droplets interferes and provides an interference pattern on the second area or line detector,

g) determining one or more second parameters relating to the interference pattern(s) on the second area or line detector of the particles, bubbles, and/or droplets, and wherein

the deriving step d) comprises deriving the information relating to the particles, bubbles, and/or droplets from the one or more parameters and the one or more second parameters.

Preferably, the imaging steps b) and f) are performed at least substantially simultaneously. Then, the steps a) and e) may comprise providing the first and second measuring sheets at least substantially perpendicularly to each other.

Also, the deriving step d) may comprise deriving information relating to a size, surface curvature, non-sphericity, rotational velocity and/or period, an oscillation frequency and/or amplitude of the two or more particles, bubbles, and/or droplets.

In order to especially be able to derive parameters varying in time - also seen from a single direction - the imaging step(s) comprise imaging light beams a plurality of times separated in time. Parameters of this type may be an oscillation frequency or a rotational velocity.

In that situation, the deriving step may comprise performing steps b), c), f). and g) each of the plurality of times and step d) comprises deriving therefrom information relating to a composition, such as material properties, refractive index, absorption inhomogeneities, internal structure, a shape, such as a size, surface curvature/roughness, sphericity, surface, changes of composition, such as a mixing, chemical reaction, evaporation, particle internal movement, changes of shape, such as oscillation frequency and/or amplitude, size changes, surface curvature/roughness changes, orientation, rotation and/or rotational velocity/period of the at least one of the two or more particles, bubbles, and/or droplets.

Also, in order to be able to physically separate the interfering light from individual particles, bubbles, and/or droplets, the imaging step(s) may comprise having the interfering light beams interfere on the area or line detector over an area being 50% or less, such as 25% or less, preferably 10% or less, such as 5% or less, preferably 2% or less, such as 1% or less than a total light sensitive area of the area or line detector.

In the following, preferred embodiments of the invention, embodied as optical measurement methods, will be described in relation to the drawing wherein:

Fig. 1 illustrates a set-up using a single light beam illuminating the particles, where the rainbow region is used

Fig. 2 illustrates a set-up using two light beams stemming from a single source,

Fig. 3 illustrates a set-up using two recording electronics,

Fig. 4 illustrates an alternative set-up using two recording electronics now operated in the forward direction,

Fig. 5 illustrates a set-up using two illuminated sheets fed by one or different laser,

Fig. 6 illustrates a set-up as that of Fig. 5 where the rainbow region is used,

Fig. 7 illustrates a set-up for measuring a three-component velocity component, and

Fig. 8 illustrates a set-up using a multi colour light source.

Combination of Rainbow and new arrangement

For the proposed arrangement (Fig. 1), a single, double or multiple pulsed wave source (A) (e.g. Nd-YAG laser pair, copper vapor laser) is projected into the field as a sheet (C) through collimating and beam expansion optics (B). The area (J) is imaged via imaging optics (D) with the image plane (E). A camera (F) records an "out-of focus" image. The recording can be a one or multiple illumination recording or be two or more subsequent recordings synchronized with the illumination (G). These recordings are transferred to a PC (H) for further processing. The novelty of this arrangement is that several particles in the section (J) can be investigated simultaneously with the rainbow measuring technique (for the example water droplets in air, the rainbow scattering angle lies at 135 degrees), which uses two glare points of one scattering order per particle.

New arrangement with two laser light sheets

Differing from (Fig.1), a beam splitter (b) is now used (Fig.2) in order to generate two sheets (C1 ) and (C2) in the measuring region. The beam splitter (B) is used also to expand the laser sheets. The realization of the beam expansion can be performed using a single cylindrical lens before or after the beam splitter or using two cylindrical lenses after the beam splitter on each beam. The recording optics (D + E + F) are now positioned at any scattering angle. At least one interference fringe system follows from the interference of the two scattered waves of the same scattered light order, one from each of the two light sheets. The new evaluation method of the interference fringe pattern can be used to increase the accuracy of the particle size estimation as long as a double or multiple interference fringe systems are used.

New arrangement Pll method with two laser light sheets and stereoscopic recording

Based on Fig. 1 and Fig. 2, two recording optics are now used (Fig.3) in order to determine a third velocity component, as is common in the Particle Image Velocimetry (PIV) technique. While one optics receives in the forward direction, the second optics receives in the backward direction. An example of this is the measurement of water droplets in air (relative refractive index 1.33). In this case the first optics could receive refraction and, consequently, scatter waves of the first order glare points of both waves (C1) and (C2), the second optics receive two scattered waves of the glare points of both beams (C1) and (C2) due to reflection and/or four scattered waves of the glare points from second order refraction. The separation of the interference patterns through second order refraction can be performed e.g. through the spatial frequency and orientation of the fringe pattern.

A variation of this arrangement uses a mirror to return the second light sheet through the measurement plane. Thus both detectors would operate in forward scatter, for which the scattered intensity is generally higher than backscatter.

Stereoscopic recording in forward scattering

In the arrangement shown in Fig.4, both receiving optics are also operated in the forward direction and will still be able to record the third velocity component.

Arrangement with two fringe systems

In the arrangement shown in Fig. 5, two waves from different or the same source are separated into two partial beams through a beam splitter (K). With each of the partial beams, a sheet is generated as shown in the arrangement 1) to 4). The detector or detectors (D + E + F) record the scattered waves from each of two glare points of each scattered light order from both partial sections (C1A + C1 B) and (C2A + C2B). The separation of the scattered light on the detector from each of the laser light sheets can be carried out in different manners:

• through color separation in which case the beam splitter (K) is a color splitter

• through polarization, where the beam splitter (K) splits the beam into two beams and the polarization of the two light sheets is adjusted differently by (B1) and (B2) or already in the beam splitter (K)

• through a spatial frequency analysis of the image, i.e. through the orientation of the fringe pattern in the image, (K) in this case splits the incident wave into two beams.

The advantage of this configuration is that the line connecting glare points from each scattered order are not parallel to one another, whereby the imaged fringe systems are also not orientated parallel to one another. Thus, curvatures of the particle surface are detected in different directions. Similar to the Dual-Mode phase Doppler system , a determination of non-sphericity is possible. The use of different light sources for both light sheets, instead of the beam splitter (K), the use of more than one camera, the additional irradiation of different light sections, and the non-perpendicular orientation of the two light sections in relation to one another are variations of this arrangement.

Arrangement with double combination of the new and the rainbow measurement technique

Contrary to the arrangement in Fig. 5, the use of two pairs of glare points arising from the same scattering order is shown in Fig. 6. Here multiple solutions of the scattered light (rainbows) are exploited. Again, the separation of the different fringe systems on the detector can be achieved using various techniques: the use of several cameras, several light sheets or separate light sources.

Recording of a volume region

In this arrangement (Fig. 7), a volume region (J) is illuminated with the light sheets (C1 + C2) and a section is imaged onto the detector using the detection optics. Thereby, a three velocity component measurement of the flow is possible, as opposed to the previous arrangements. The position of the particle across the width of the laser sheet can be determined through the size of the out-of-focus image. Variations of this method to achieve the third velocity component include: the use of more than one camera, the use of more than one pair of glare points from the same scattering order, by using additional light sheets or through the orientation of the laser light sheets.

Multicolor arrangement

All the arrangements described above can also be realized using a multicolor light source (A) (AR⁺ laser or white light) (Fig.8). In this case, several fringe systems will arise due to the refractive index dependency. Thereby, each fringe system or each image is assigned to a color. The images or fringe systems are, for the case of one dominant scattering order, formed by two glare points of the same order, as shown as an example in the upper sketch. The refractive index can be determined from the spatial frequency of the individual defocused images, separated by color. This arrangement can also be extended and modified, as described for the, previous arrangements.

Separation of images

The separation of the interference areas of the images may be performed in any desired manner. E. Hecht: "Optics", Addison-Wesley, 3rd ed., 1998 illustrates a number of such manners.

The interference fringe systems can be separated by: spatial frequency, phase, colour, orientation, polarisation and/or focussing.

Claims

1. An apparatus for providing information relating to two or more particles, bubbles, and/or droplets, the apparatus comprising:

means for providing one or more waves directed toward the two or more particles, bubbles, and/or droplets,

- means for detecting waves refracted or reflected by the two or more particles, bubbles, and/or droplets, the detecting means comprising an area detector or a line detector, and

the wave providing means being positioned so, relatively to the two or more particles, bubbles, and/or droplets and the detecting means, that at least two light beams are reflected or refracted by the two or more particles, bubbles, and/or droplets toward the detector, the waves all having been either reflected by the two or more particles, bubbles, and/or droplets or all having been refracted a predetermined number of times within the two or more particles, bubbles, and/or droplets,

2. An apparatus according to claim 1 , wherein the wave providing means are adapted to provide a single wave directed toward the two or more particles, bubbles, and/or droplets from a predetermined direction so that light is refracted along two or more paths within at least one of the two or more particles, bubbles, and/or droplets , the paths comprising the same number of refractions within the at least one of the two or more particles, bubbles, and/or droplets.

3. An apparatus according to claim 2, wherein the deriving means are adapted to derive information relating to a composition, such as material properties, a refractive index, wave absorption, inhomogeneities and/or internal structure and/or a shape, such as a size, surface curvature/roughness, sphericity, of the at least one of the two or more particles, bubbles, and/or droplets.

4. An apparatus according to claim 1 , wherein the wave providing means comprise means for directing two or more waves toward the two or more particles, bubbles, and/or droplets.

5. An apparatus according to claim 1 , wherein the wave providing means are adapted to direct one or more polychromatic or monochromatic light beams toward the two or more particles, bubbles, and/or droplets.

6. An apparatus according to claim 1 , further comprising means for providing the two or more particles, bubbles, and/or droplets.

7. An apparatus according to claim 1 , wherein the wave providing means are adapted to simultaneously provide one or more waves toward a plurality of particles, bubbles, and/or droplets, the detecting means are adapted to simultaneously receive waves reflected or refracted by the plurality of particles, bubbles, and/or droplets, and wherein the deriving means are adapted to provide information relating to each of the plurality of particles, bubbles, and/or droplets.

8. An apparatus according to claim 1 , wherein the wave providing means are adapted to provide two or more light beams and/or one or more light beams comprising two or more wavelengths toward the two or more particles, bubbles, and/or droplets.

9. An apparatus according to claim 1 , wherein the wave providing means are adapted to provide one or more light beams comprising two or more wavelengths toward the two or more particles, bubbles, and/or droplets, the apparatus further comprising means for selecting one or more predetermined wavelengths or wavelength regions, the selecting means being positioned in a light path between the light providing means and the two or more particles, bubbles, and/or droplets or between the two or more particles, bubbles, and/or droplets and the detecting means.

5 10. An apparatus according to claim 9, wherein the deriving means are adapted to provide information relating to a composition, such as material properties, refractive index, absorption, inhomogeneities, internal structure, and/or a shape, such as a size, a surface curvature/roughness, and/or sphericity, of the two or more particles, bubbles, and/or droplets. 10

11. An apparatus according to claim 1 , wherein the wave providing means are adapted to provide the one or more waves in a measuring sheet or a measuring volume.

12. An apparatus according to claim 11 , wherein the wave providing means are adapted 15 to provide the one or more waves in a first measuring sheet or volume, the apparatus further comprising:

second means for providing one or more waves directed toward the two or more particles, bubbles, and/or droplets, the second wave providing means being adapted to 20 provide the one or more waves in a second measuring sheet or volume being at an angle to the first measuring sheet, and

the second wave providing means being positioned so, relative to the two or more particles, bubbles, and/or droplets and the detecting means, that at least two waves are 25 emitted from or reflected by the two or more particles, bubbles, and/or droplets toward the second detector, those light beams all having been either reflected by the two or more particles, bubbles, and/or droplets or all having been refracted a predetermined number of times within the two or more particles, bubbles, and/or droplets.

30 13. An apparatus according to claim 11 , wherein the wave providing means are adapted to provide the one or more waves in a first measuring sheet or volume, the apparatus further comprising:

second means for providing one or more waves directed toward the two or more 35 particles, bubbles, and/or droplets, the second wave providing means being adapted to provide the one or more waves in a second measuring sheet or volume being at an angle to the first measuring sheet, and

second means for detecting waves refracted or reflected by the two or more particles, bubbles, and/or droplets, the detecting means comprising a second area detector or line detector,

wherein the receiving means are adapted to also receive information from the second detecting means and to derive therefrom the information relating to the two or more particles, bubbles, and/or droplets,

14. An apparatus according to claim 13, wherein the detecting means and the second detecting means are adapted to detect the interfering waves at least substantially simultaneously.

15. An apparatus according to claim 12 or 13, wherein the first and second measuring sheets are at least substantially perpendicular to each other.

16. An apparatus according to claim 12 or 13, wherein the deriving means are adapted to provide information relating to a composition, such as material properties, refractive index, absorption inhomogeneities, internal structure, and/or a shape, such as a size, a surface curvature/roughness, sphericity, of the two or more particles, bubbles, and/or droplets.

17. An apparatus according to claim 1 , wherein the detecting means are adapted to detect the interfering waves a plurality of times separated in time.

18. An apparatus according to claim 17, wherein the deriving means are adapted to receive information from the detecting means each of the plurality of times and for deriving therefrom information relating to changes in composition, such as a mixing, chemical reaction, evaporation, particle internal movement, changes of shape, such as oscillation frequency and/or amplitude, size changes, surface curvature/roughness changes, and/or movement, such as displacement, orientation, position, direction of movement, velocity, rotation, rotational velocity and/or period, of the two or more particles, bubbles, and/or droplets.

19. An apparatus according to claim 1 , wherein the detecting means are adapted to have the interfering light beams from the two or more particles, bubbles, and/or droplets interfere on the area or line detector over an area being 50% or less, such as 25% or less, preferably 10% or less, such as 5% or less, preferably 2% or less, such as 1% or less than a total light sensitive area of the area or line detector.

20. A method of providing information relating to two or more particles, bubbles, and/or droplets, the method comprising:

a) directing one or more waves toward the particles, bubbles and/or droplets so as to provide, from at least two separate areas of a surface of each of the particles, bubbles, and/or droplets and in at least substantially the same direction, waves reflected from the two or more particles, bubbles, and/or droplets and/or having been refracted a predetermined number of times thereby,

b) imaging waves from each of the at least two separate areas of each particles, bubbles, and/or droplets on an area or line light detector in a manner so that waves from the at least two separate areas of each of the two or more particles, bubbles, and/or droplets interfere and provides an interference pattern on separate parts of a sensitive area of the area or line detector, c) determining one or more spatial parameters relating to at least two the interference patterns of the particles, bubbles, and/or droplets, and

5 d) deriving the information relating to the particles, bubbles, and/or droplets from the one or more parameters.

21. A method according to claim 20, wherein the step of directing wave(s) comprises directing a single wave toward the two or more particles, bubbles, and/or droplets from a

10 predetermined direction so that light is reflected and/or refracted along two or more paths within at least one of the two or more particles, bubbles, and/or droplets ,.

22. A method according to claim 21 , wherein the deriving step comprises deriving information relating to a composition, such as material properties, refractive index,

15 absorption inhomogeneities, internal structure, a shape, such as a size, surface curvature/roughness, sphericity, surface, changes of composition, such as a mixing, chemical reaction, evaporation, particle internal movement, changes of shape, such as oscillation frequency and/or amplitude, size changes, surface curvature/roughness changes, orientation, rotation and/or rotational velocity/period of the at least one of the

20 two or more particles, bubbles, and/or droplets.

23. A method according to claim 20, wherein the light directing step comprises directing two or more light beams toward the two or more particles, bubbles, and/or droplets.

25 24. A method according to claim 23, wherein the deriving step comprises deriving information relating to movement, such as position, direction of movement, velocity, displacement, of one or more particles by phase changes of one or more interference patterns for each particle, at least one of the one or more interference patterns being created by reflected and/or refracted waves from different waves toward the one or more

30 particles.

25. A method according to claim 20, wherein the wave directing step comprises directing one or more polychromatic or monochromatic light beams toward the two or more particles, bubbles, and/or droplets. 35

26. A method according to claim 20, the method further comprising the step of providing the two or more particles, bubbles, and/or droplets.

27. A method according to claim 20, wherein the wave directing step comprises

5 simultaneously providing the wave(s) toward a plurality of particles, bubbles, and/or droplets, and wherein the imaging step comprises simultaneously receiving waves reflected or refracted by the plurality of particles, bubbles, and/or droplets, and wherein the deriving step comprises providing information relating to each of the plurality of particles, bubbles, and/or droplets. 10

28 A method according to claim 20, wherein the wave directing step comprises directing two or more light beams and/or one or more light beams comprising two or more wavelengths toward the two or more particles, bubbles, and/or droplets.

15 29. A method according to claim 20, wherein the wave directing step comprises directing one or more light beams comprising two or more wavelengths toward the two or more particles, bubbles, and/or droplets, the method further comprising the step of selecting one or more predetermined wavelengths or wavelength regions, and wherein the imaging step comprises imaging light of the selected wavelengths or wavelength regions. 0

30. A method according to claim 29, wherein the deriving step comprises providing information relating to a refractive index of the two or more particles, bubbles, and/or droplets.

5 31. A method according to claim 20, wherein the wave directing step comprises providing wave(s) toward a measuring sheet or a measuring volume.

32. A method according to claim 31 , wherein the directing step comprises providing wave(s) toward a measuring sheet or volume, the method further comprising the steps of: 0 e) providing a second sheet of light by directing light toward the particles, bubbles, and/or droplets so as to provide, from at least two separate, second areas of a surface of each of the particles, bubbles, and/or droplets and in at least substantially the same, second direction, light reflected from the two or more particles, bubbles, and/or droplets 5 and/or having been refracted a predetermined number of times thereby,

33. A method according to claim 32, further comprising the steps of:

f) imaging waves from each of the at least two separate, second areas of each particles, bubbles, and/or droplets on a second area or line detector in a manner so that waves from the at least two separate, second areas of each particles, bubbles, and/or droplets interferes and provides an interference pattern on the second area or line detector,

34. A method according to claim 32, wherein the imaging steps b) and f) are performed at least substantially simultaneously.

35. A method according to claim 32, wherein the steps a) and e) comprise providing the first and second measuring sheets or volumes at least substantially perpendicularly to each other.

36. A method according to claim 32, wherein the deriving step d) comprises deriving information relating to a size, surface curvature, non-sphericity, rotational velocity and/or period, an oscillation frequency and/or amplitude of the two or more particles, bubbles, and/or droplets.

37. A method according to claim 20, wherein the imaging step(s) comprise imaging light beams a plurality of times separated in time.

38. A method according to claim 37, wherein the deriving step comprises performing steps b), c), f), and g) each of the plurality of times and wherein step d) comprises deriving therefrom information relating to a composition, such as material properties, refractive index, absorption inhomogeneities, internal structure, a shape, such as a size, surface curvature/roughness, sphericity, surface, changes of composition, such as a mixing, chemical reaction, evaporation, particle internal movement, changes of shape, such as oscillation frequency and/or amplitude, size changes, surface curvature/roughness changes, orientation, rotation and/or rotational velocity/period of the at least one of the two or more particles, bubbles, and/or droplets.

39. A method according to claim 20, wherein the imaging step(s) comprise having the interfering light beams interfere on the area or line detector over an area being 50% or less, such as 25% or less, preferably 10% or less, such as 5% or less, preferably 2% or less, such as 1% or less than a total light sensitive area of the area or line detector.