CA1147182A

CA1147182A - Redirecting surface for desired light intensity profile

Info

Publication number: CA1147182A
Application number: CA000362822A
Authority: CA
Inventors: Albert Brunsting
Original assignee: Coulter Electronics Inc
Current assignee: Coulter Electronics Inc
Priority date: 1979-10-22
Filing date: 1980-10-20
Publication date: 1983-05-31
Also published as: US4327972A; DE3039496A1; GB2062282A

Abstract

ABSTRACT

REDIRECTING SURFACE FOR DESIRED LIGHT INTENSITY PROFILE

An optical device for redistributing incident radiation, such radiation having a non-uniform intensity distribution. The resultant redistributed radiation having a narrower desired intensity distribution in a predetermined region of an output plane. The optical device comprises a redirecting surface of a lens or reflector, for relocating at least a portion of the incident light. In one application, particles are illuminated in the output plane. The redirecting surface has a central portion and a peripheral portion, each said portion being disposed and configured to receive part of the incident radiation.
The central portion is constructed to permit the incident radiation to irradiate the predetermined region of the output plane, and the peripheral portion is constructed to redirect specific rays of the incident radiation to specific locations in the predetermined region of the output plane, whereby the specific locations are further irradiated so as to create the desired intensity distribution within the predetermined area.

Description

187,551 Disclosed is an optical device which relates to the redistribution of an incident intensity profile of light to yield a new desired intensity profile and, in one application, the concen~ration of the light into a new desired intensity profile for irradiating particles~

Many prior art flow cytometers utilize a laser beam for irradiating particles, suspended in a fluid flow, to produce detectably optical signals. These flow cytometers w~ste much of the high cost, high grade incident light. Typically, beam shaping optics focus collimated light from the laser into a slit-like ellipse at the location where the particles are illuminated. In that it is necessary to lrradiate the particles with a relatively uniform high intensity llght across the range of possible particle tra~ectories, only a relatlvely small center portion of this incident light usually is used, as shown in FIGURE 5, by the range of (-a<x<~a), wherein a equals the limiting x coordinate value for a particle trajectory. The unused energy (i.e., wasted) in the wings of this slit can be 84% of the total energy for a 2% variation in intensity across the possible particle trajectories, assuming a Gaussian intensity profile along the x direction of FIGURE 5. If a smaller amoun~ of variation in intensity is required (e~., 1%), a higher percentage of incident energy is not used.
Accordingly, it can readily be seen that there is a need in the art of cytology for a cytometer that utilizes more of the available radiant energy, while at the same time, maintains negligible or low intensity variations across the possible particle trajectories.
For more generalized usage, there is a need in the optical arts for transforming organized incident radiation into radiation having a desired intensity profile.
Relevant prior art is disclosed in U.S. Patent No.
3,476,463 to Kreuzer; U.S. Patent No. 4,128,303 to McNaney; Data Sheet No. 512, January, 1978, of Spawr Optical Research, Inc.; and Fluorescence Techniques in Cell Biology, A.A. Thaer and M. Sernetz, Springer-Verlag, 1973, p. 80.

7~Z
--b,_ According to a ~irst aspect of the invention there -ls provided: an optical device for redistributing incident radiation, hav~ng a non-uniform intensity distribution, to resultant radiation, having a deslred intensity distribution in a predetermined region of an output plane, said optical device comprising redirecting means having a central portion and a peripheral portion, each said portion being disposed and configured to receive part of the incident radiation;
said central portion being adapted to permit the incident radiation to irradiate the predetermined region of the output plane; and said peripheral portion being adapted to redirect specific rays of the incident radiation to specific locations in the predetermined region of the output plane, whereby the specific locations are further irradiated so as to create the desired intensity distribution within the predetermined area.
According to a second aspect of the invention there is provided: an illumination system for a particle analyzer, wherein particles are illuminated to produce detectable signals, said illumination system including a radiation source for providing incident radiation having a non-uniform intensity distribution, wherein the improvement comprises redirecting means for receiving and redistributing the incident radiation, to resultant radiation having a substantially uniform intensity distribution at an output plane; and said output plane being positioned to have the particles therein, and whereby the particles are illuminated by the resultant radiation.

~73 8Z

The invention ls directed toward an optlcal device and a metllod for redistribut~ng incident, organized radiation, having a non-uniform intensity distribution; to resultant radiation, having a desired intensity distribution. The optical device includes a redirecting surEace, in the form of a reflecting mirror or refracting lens surface, which redirects speciEic rays of the incident radiation to specific locations on an output plane for irradiation of the output plane. The amount of optical modification of the incident radiation by the redirecting surface is a function of the direction, dimensions, energy, and location of the incident radiation profile and ~he desired resultant radiation proEile~ In some embodiments of the invention, rays strike a peripheral portlon of the redirecting surface and are pointed toward specific points of the output plane. These sa~e points are also irradiated by specific rays which strike or pass through a central portion of the redirecting surface. The overlapping of radiation from the peripheral portion and the central portion concentrates the incident radiation to produce the resultant radiation, having the desired intensity distribution at the output plane. In other embodiments, most or all of the rays which strike the redirecting surface are optically modified to concentrate them, without overlapping, into the resultant radiation, having the desired intensity distribution at the output plane.
The above described invention has a particularly novel application in prior art particle analyzers wherein particles are illuminated to produce detectable optical signals. The prior art particle analyzers waste much of the high cost, high grade incident light, such light having a non-uniform intensity distribution. The optical system embodying the invention redistributes the incident light to provide a substantially uniform, high intensity light 7~L~2 distribution at the output plane, which contains the partlcles to be illuminated. The optical device embodying the inventlon eliminates the wasting of most of the energy, while at the same time, maintains low intensity variations across possible particle trajectories. The S optical device embodying the invention may be readily adapted for other useful purposes.

1~71~Z

By way of example only, illustrative embodiments of the invention now will be described with reference to the accompanying drawings, in which:
FIG~RE 1 is a view of the radiation redistribution in one plane of a reflector embodiment of the invention;
FIGURE 2 is a view of the radiation redistribution in one plane of a lens embodiment of the invention;
FIGURE 3 is a view of a variation of the embodiment illustrated in FIGURE 2;
: 10 FIGURE 4 is a view of the radiation redistribution in one plane of another lens embodiment of the invention;
FIGURE 5 is a cross-sect.lonal view of an elliptical radiation profile for illumina~ing a stream;
FIGURE 6 shows an ~ncident intensity distribution with a corresponding resultant distribution;
FIGURE 7 is a cross-sectional view oE the radiation profile after the incident radiation has been redistributed by the invention for illuminating a stream;
FIGUR~ 8 shows an incident intensity distribution with a corresponding resultant distribution;
FIGURE 9 shows yet another incident intensity distribution with a corresponding resultant distribution;
FIGURE 10 is a view of a variation to the embodiment illustrated in FIGU~ 2;
FIGURE 11 shows a plurality of sets of corresponding incident and resultant intensity distributions;
FIGURE 12 is a side plan view which illustrates a specific application for the embodiment illustrated in FIGURE 2;

~73~32 FIGURE 13 is a top plan view of the arrangement shown in FIGURE 12;
FIGURE 14 is a perspective view oE a lens embodiment incorporating the radiation redistribution of the lens of ~IGURE 2;
FIGURE 15 is a perspective view of a ref}ector embodiment which i~corporates the radiation redistribution oE the reflector of FIGURE l;
FIGURE 16 is a perspective view oE a lens embodiment whioh incorporates the radiation redistribution of the lens of FIGURE 4;
FIGURE 17 is a cross-sectional view oE a circular radiation profile for irradiating a stream;
FIGURE 18 is a cross-sectional vlew of a square radiation profile for irradiating a stream;
FIGURE l9 is a plan view of a lens embodiment which incorporates the radiation redistribution of the lens of FIGURE 2;
a~d FIGURE 20 is a plan view of a lens embodiment incorporating the radiation redistribution oE the lens oE FIGURE 2.

7~8Z

An optical system embodying the invention in FIGURE 1 has a light source 10 which produces an incident beam of light, usually having a non-uniform intensity distribution. A redirecting surface, in the form of a reflector 12, redistributes the light represented by this incident non-uniform intensity distribution so as to generate output light having a desired predetermined distribution at an output plane 14. The light source 10 can be, for example, a gas type laser, having associated beam shaping optical elements, which emits a continuous or intermittant beam 16 of light. Also, the light sol1rce 10 can be a high pressure mercury arc lamp, having conventional beam shaping optical elements. The reflector 12 is shown in cross section and centered on an optical axis 18. The reflector 12 has a central reflector portion 20 and an integrally adjacent concave peripheral reflector portion 22. The central reflector portion 20 is positioned at an angle, a , with respect to the optical axis 18. By virtue of this geometry, a center region 24 of light, substantially centered on the optical axis 18, reflects from the central reflector portion 20 and proceeds from the same. Hence, the center region 24 of light has its direction changed by 2a. The peripheral reflector portion 22 is concave with respect to incident light for the purpose of redistributlng the incident light in a peripheral region 26 of light with respect to the light in the center region 24. The peripheral reflector portion 22 is adjusted with respect to the output plane 14 so that the peripheral region 26 of light is superimposed over the center region 24 of light at the output plane 14. More specifically, the reflector 12 accomplishes a spatial redistribution of the peripheral region 26 of light onto the same area as the cen~er region 24 of light. In this manner, the redirection of peripheral light rays results in the formation of the desired intenslty profile, such as a ~7~32 uniform profile, in the output plane 14.
Another embodiment of the optical system embodying the invention is illustrated in FIGURE 2. In thls embodiment, the redirection surface 11 for light relocation comprises a lens 27 which produces the same results at the output plane 14 as the reflector 12 of FIGURE 1. ~he lens 27 has an aperture 28 formed therein, and the lens 27 and its aperture 28 are concentrically positioned on the optical axis 18. The aperture 28 is dimensioned and configured to have the center region 24 of light pass therethrough, whereby the direction of such light is not substantially modlfied optically. A
solid peripheral lens portion 29 of the lens 27 is configured and dimensioned to receive the peripheral region 26 of light and refracts such light to overlap with the center region 24 of light to create the desired dis~ribution in the output plane 14. The lens 27 has a planar outer surface 30, which is perpendicular to the optical axis 18 and does not substantially refract the light, and a curved outer surface 31, which refracts light in a manner to be described hereinafter. It should also be appreciated that, although the surface 30 is shown to be planar, the surface 30 could also be curved. Consequently, the surface 30, in combination with the surface 31, would give the desired refraction. A minor variation to the embodiment of FIGURX 2 is illustrated in FIGURE 3. The lens 27, instead of having the aperture 28, is provided with central lens portion 32 having a pair of planar, parallel boundaries 34 and 36. The central lens portion 32 provides the same function as the aperture 28, in that light passing therethrough is not substantially modified optically.
Yet another embodiment of the optical system embodying the invention is illustrated in FI~URE 4. The redirecting surface 11 of this embodiment comprises a lens 38 shown in cross section and centered on the optical axis 18. The lens 38 has a planar outer ~4~82 surface 40, which is perpendicular to ehe optical axis 1~, and a curved outer s~rface 42 for redistributing the incident light from the light source lO into a desired intensity profile at the output plane lfi. In the illustrative embodiment of FICURE 4, the rays are progressively refracted inward by the lens 38, with increasing amounts of light refraction proceedin~ from the center outward to the periphery of the lens 38.
Frequently in practice it is found that the light intensity across a laser beam is closely approximated by a Gaussian or normal distribution which may be mathematically described by the equation:

exp [- (r/a) ~

~ .
where I(r) is the intensity at a dis~tance r(units of meters) from the optical axis 18 with units of watts¦meter2 and "a" is a scale factor ~ (units of meters). Moreover, in the art of flow cytology, wherein - particles in a flow stream are illuminated by a Gaussian laser beam, it is particularily advantagous to have uniform intensity illumination at an output plane which passes through the flow stream with a minimum of wasted light and a maximum intensity. For example, referring to FIGURE
-~ 5, t~e beam 16 of light, which is perpendicular to the plane of the drawing, has a Ga'ussian distribution and is superimposed over a typical flow stream 44, such as illustrated in the article entitled "Quantitative Single Cell Analysis and Sorting", published in "Science"
magazine, Volume 198, No. 4313. Typically, in a conventional flow stream arrangement, such as the flow stream 44, cells en~er a flow chamber under pressure through an introduction tube which is surrounded by a sheath fluid. Well known laminar sheath-flow techniques allow for the cells to be confined to ~he center of the 10w stream close to and along the y-axis. The flow stream 44 is normally a liquid jet with the particles suspended therein and surrounded by a quiescent liquid or gas.
Also1 the flow stream 44 could be a gas jet with another gas surroundlng it. Generally, the incident beam has a slit-like elliptical cross-sectional proflle 45. The magnitude of the light lnten~ity is illustrated by a plurality of intensity contour lines 46, such lines 46 illustrating the progressively increasing lntensity of the beam 16 with respect to movement toward the optical axis 18. Since the illustrated size relationships of the flow stream 44 and the beam 16 are those that commonly exist at the intersection of the two in the prior art cytometers, it is evident that a large amount of the light does not enter the flow stream 44 and therefore is wasted. ThUSJ according to the prior art, the intensity of light through which the particles flow is less than the intensity provided by the present inven~ion. Some overlapping of beam 16 with respect to the flow stream 44 ls necessary so as to allow for lateral movement of the flow stream 44. However, ! most of the overlapping is a function o the need to have uniform illumination of the flow stream 44. Hence, the prior art cytometric devices have only been able to use a small center area 47 of the beam 16. Accordingly, the invention will be descrlbed hereinaEter in connection with a specific embodiment in which an incident Gaussian distribution is used to illuminate the flow stream 44 of a conventional cytometer.
FIGURE 6 shows the incident distribution 48 of the light intensity as emitted from the light source 10 which, for the purposes of illustration, is a Gaussian distribution of a laser in a ~EMoo mode.
Here the intensity I(r) of the emitted light is considered to be a function of a distance r from an optical axis 18. Assuming that the Gaussian distribution 48, for example, is the incident intensity distribution of beam 16 in the embodiments of FIGURES 1, 2 and 4, then the desired resultant intensity distribution is illustrated by a uniform ~ -13-~ 7~

intensity distribution 50. When the present invention is applied to particle analysis, such a uniEonm distribution 50 is desirable Eor providing more uniform illu~ination of particles contained in the flow stream 44. The two distributions 48 and 50 are superimposed over each other in FIGURE 6 so as to show how the light is redistributed by the redirecting surface 11 of FIGURES 1, 2, and 4. The middle area 52 of the distributions 48 and 50, which extends from "b" to "-b" along the x - axis coincides with the incident width of the center region 24 of light.
~- A pair of opposed areas 54 and 56 of the distributions outside the range of "-b" to "b" coincide with the incident light in the peripheral region 26. In the incident distribution 48, the power (units of watts~ the opposed areas 54 and 56, Pl, and the middle area 5~, P2, are related to the total power PT, by:

F~ P2 PT
P2 is chosen so that a constant, or desired, intensity distribution ls obtained. Pl does not necessarily have to be equal to P2. After reflection from the reflector 12 or refraction of the lens 27 or 38, a uniform intensity distrlbution 50 is generated in whlch the peripheral region 26 of light, outside of the "-b" to "b" range, has been shifted to the center region 24 of light. With the uniform inten~ity distribution 50, the power of the middle area 52, P2, and the opposed areas 54 and 56, Pl are as follows:
(3) P2--PT AND Pl=O
Hence substantial light wastage in the opposed areas 54 and 56 is eliminated, a substantially uniform illumination of the flow stream 44 is maintained, and the intensity in the niddle area 52 is increased~

~73LB~

As a result, a less powerfu~ laser is required to acco~plish the same results achievable without the redirecting sur~ace 11 o~ the present invention. Hence, instead of the elongated light profile 45, as shown in FIGURE 5, a generally rectangular profile 58, as shown in FIGURE 7, is obtained, for example.
Using the lens 27 of FIGURE 2 or the reflector 12, the Gaussian distribution 48 can be converted to the uniform distribution 50, as shown in FIGURE 6, by a progressive fold-over relocation of the peripheral region 26 of light such that the most remote edge 60 of the Gaussian distributlon 48 is redistributed near the optical axis 18 and therefore near the peak of the Gaussian distribution. Each successively small segment 62 of the peripheral region 26 of light, which is disposed inward from the edge 60 is relocated progressively further out from the ~ optical axis 18. Although the light segments 62 do not have to be shifted in a strict progression of innermost to outermost, other arrangements of shifting segments, for these particular distributions 48 and 50, causes substantially greater lens discontinuities. The number of segments required for overlapping the peripheral region 26 of light over the center region 24 of light is a matter of design preEerence.
~0 Using the lens 38 of FIGURE 4, the Gaussian distribution 48can be converted to the uniform distribution 50, as illustrated in FIGURE
6, by progressively increasing the amount of refraction of the lens 38 from the optical axis 18, outward to the periphery of the lens 38.
Referring to FIGURE 8, a two peak intensi~y distribution 64 ~5 is shown which is illustrative of a light source 10 comprising a laser in the TEMo1 mode. With this distribution 64 as the inciden~
distribution, the skirts of the same would be relocated by the redirecting surface 11 of the present invention to Eill in the valley, so as to create the desired intensity distribution~ such as in the uniform intensity distribution 50.

8~

Referring to FIGURE 9, an intensity distribution 66 for a typical incoherent light sou~ce 10, such as a high pressure mercury arc lamp, is illustrated. The various embodiments of the invention, shown in FIGURES 1, 2, and 4, can be used to relocate the end portions of the distribu~ion 66 into a desired distribution~ such as the uniform intensity distribution 50.
In FIGURES 6, 8, and 9, the desired, resultant intensity distribution has been selected to be the uniform intensity distribution 50. As previously described, the uniEorm intensity distribution 50 in the output plane 14 is partic~larly useful in the art of cytology for irradiating particles. ~owever, it should be appreciated that the embodiments of this invention, as illustrated in FIGURES 1, 2, and 4, may be adapted to create desired intensity distributions, other than the uniform intensity distribution 50.
Also, it should be appreciated that central reflector portion 20 and the central lens portion 32 can be rnodified in dimensional size and configuration to accomplish the desired intensity distrlbution.
In the embodiments of FIGURES 1, 2, and 4, the light source 10 pro~ides the light beam 16 which, for the purposes of illustration, is collimated. However, it should be understood that any organized radiation, whether collimated, divergent or convergent~
may comprise the incident radiation for use with the embodiments of the invention. Merely for the purposes of illustration, one of ~any variations of the light beam 16 that is within the scope of this invention as defined in the appended claims, i5 illustrated in FIGURE
10. FIGURE 10 illustrates the use of a redlrecting surface 11 for a convergent beam 16. The lens 27 relocates light in a manner already explained. Likewise the output plane 14 is positioned between the lens 27 and a focus 70, but could be positioned on the other side of the focus 70. There are many variations of incident light organi~tion, with the corresponding modification to the redirecting surface 11, that will be obvious to those skilled in the art.
In FIGURES 1, 2, and 4, the optical systems have been viewed from a single cross sectional plane 7l, which is perpendicular to the plane of the drawings in FIGURES S and 7 and parallel to the x-axis.
ReEerring to FIGURE 5, it should be appreciated that there are an inEinite number of these planes 71 which perpendicularly intersect at the y-axis and have the Gaussian distrlbution 48~ In one application of the redirecting surface 11 of the invention, each of these planes 71 is modified in a manner illustrated in FIGURES 1, 2, and 4. In FIGURE 7, for example, the planes 71 more remotely disposed from the optical axis 18 intersect the elliptical profile 45 so as to have less power than those planes nearer the optical axis 18. Assuming that the range "-b" to "b" is maintained, for example, with the uniform intensity distribution 50, then the intensity I of the distribution 50 of a given plane 71 would be less relative to the intensity values of distributions 50 for planes 71 positioned nearer the optical axis 18~ As shown in FIGURE 11, a plurality of sets of corresponding Gaussian and uniform intensity distributions 48 and 50, respectively, are identified as 72, 74, 76 and 78. Hence, in FIGURE 7, as the particle trajectory deviates with respect to the x-axis, a given particle would be presented with a substantially uniform illumination, not considering refraction caused by the stream 44.
On the other hand, as particles traverse the beam profile 58 along the y-axis, there would be some variation in the intensity of the illumination. It should be understood that the range "-b" to "b" must be selected so that in any given set 72 or other set, the peak intensity of the Gaussian distribution 48 must not exceed the desired intensity of the uniform distribution 50. Otherwise, it would be necessary to shift light from the center region 24 of light. As will be seen in the three dimensional illustrations of the embodiments described hereinafter, the 7~

range "-b" to "b" can remain constant or can vary, depending upon th~
configuration of the center region 24. As will beco~e apparent, the three dimensional res~ltant distributlon is typically modified to be uni~orm with respect to only one axis. Ilowever, if the range '-b" to "b" is varied in a predetermined manner, or if light redistribution is undertaken with respect to both axes, then the three dimensional resultànt distribut~on can be made uniform with respect to both the x-axis and the y-axis, as will be described in more detail hereinafter. Varying the range "-b" to "b" is generally not desirable in that it requires nonlinear surfaces. Referring to FIGURES 5 and 7, although planes 79, which are perpendicular to the drawing and parallel to the y-axis, also contain Gaussian distributions, for the application oE particle analysis, the variation in illumination of the elliptical profile 45 with respect to the y-axis is so small, the incident light does not nèed to be modified with respect to the y-axis.
FIGURES 12 and 13 are specifically directed toward applying the lens 27 to the application of particle analysis i~ a conventional cytometer, wherein the prior art cytometer illumlnated the particles contained within the stream 44 with radiation having the slit-like elliptical profile 45, as illustrated in FIGURE 5.
Typically, the prior art uses a cylindrical lens 80 to line focus the beam 16 with respect to the y-axis. Referring to FIGURE 13, a second cylindrical lens (not shown) usually is positio~ed in prior art arrangements where the lens 27 is positioned, and is usqd to slightly converge the light with respect to the x-axis, such converging being illustrated by the outer boundary lines 82 and 84 of a typical beam in the prior art. In the embodiment illustrated in FIGURES 12 and 13, the lens 27, whlch comprises a modified cylindrical lens, is substituted Lor the second cylindrical lens. It should be appreciated -l8-~7~82 that the light beam 16 from the light source 10 has a substantially circular cross section prior to impingi~g upon the lens 27. In the embodiment o~ FIGURES 12 and 13, the lens 80 is interposed between the OUtpllt plane 14 and the lens 27. It should be understood that the positionlng of other optical sur~aces between the redirecting surface 11 and the o~tput plane 14 is within the scope of the invention as de~ined in the appended claims. Interposing such optical surfaces, such as the lens 80, results in correspondingly modifying the redirecting surface 11, so that the combination of the redirecting surface 11 and the interposed optical s~rface provides the desired intensity profile at the output plane 14. FIGURE 15 illustrates a perspective view o~ the reflector 12 which is equivalent to the lens 27 of FIGURE 14. FIGURE 16 illustrates ~he lens 38 in a perspective view, which can be used in the above described application. Each of the redirecting surfaces 11 in FIGURES
14, 15, and 16 optically modify the incident light in planes 71 with I respect to the x-axis. Such modification for the lens 27 of FIGURE 14 is illustrated in FIGURE 2, for the reflector 12, in FIGURE 1, and for the lens 38, is illustrated in FIGUR~. 4.
ReferriQg to FIGURE 17, there is illustrated the beam 16 with a 6ubstantially circular cross-sectional profile 86. With the elliptical proEile ~5 of FIGURE 59 typically created by two cylindrical lens in a manner previously described, there was no need for making the light more concentrated with respect to the y-axis. ~owever, this is not the case with FIGURE 17, which is illustrative of the need for ~odifications to the incident light in two dimensions, one with respect to the x-axis and the other with respect to the y-axi~. As one possibility, the incident beam lS of FIGURE 17 can be modified with respect to the y-axis in a manner similar to that accomplished by the lens 80 of FIGURES 12 and 13. Then, the incident beam 16 can be modified with respect to the x-axls in a manner shown in FIGURES 1, 2 and 4, to prod~lce the light intensity profile 58 of FIGURE 7. As ano~her possibility, ass~e for example, that the resulta~t inte~sity distribution in both directions is to be the uniform intensity distribution 50, shown in FIGURES 6, 8, and 9, then the incident light can be modified in two dimensions by the techniques of FIGURES 1, 2, and 4, to create a substantially rectangular light proEile 88, as illustrated in FIGURE 18. For accomplishing light redirection in the above described ways, ~he lens 279 the reflector 12, and the lens 38 would have the redirecting surface 11 with an aspherical shape. For example, FIGURE 19 illustrates such a variation for the lens 27.
Moreover, the aperture 28 has a rectangular configuration. With respect to one of the axes, the -b" to "b" range preferably remains constant.
As explained, the incident beam 16 can be redistributed in the ~ embodiment of FIGURE l9 using the techniques of FIGURE 2 to provide uniform light intensity in one dimension. Alternati~ely, the incident beam 16 can be rearranged in two dimensions by using conventional mathematical iterative procedures to redistribute the light with respect to both the x-ax~s and y-axis.
Referring to FIGURE 20, two dimensional intensity uniformity can be accomplished by incorporating the light redirecting techniques of FIGURES l, 2, and 4 to modify the radial planes 90 of the redirecting surface 11. As an illustrative example, the radial planes 90, passing through the optical axis 18, of the lens 27 are modified in each radial plane in a manner illustrated in FIGURE 2. In this embodiment, the lens 27 has a radial symmetry with respect to the optical axis 18 wi~h the aperture 28 having a circular configuration. This produces a resultant circular intensity profile ~not shown) with substantially uniform intensity with respect to both the x-axis and the y-axis.
Referring to FIGURE 20, the circular light profile of uniform intensity, produced by the radially symmetric lens 27, as with the other embodiments, can be further modified by interposing other optical components between the radlally symmetric lens Z7 and the output plane 14. For example, the radially symmetric lens 27, shown in FIGURE 20, can bP substituted for the modified cylindrical lens 27 in the two optical element arrangement of FIGURES 12 and 13. In such a case, the resultant light profile would have a narrow elliptical configuration with the light being uniform with respect to ~he x-axis.
For the purposes of determining the scope of this invention as de~ined in the appended claims, it should be appreciated that the output plane 14 is shown as passing through the flow stream 44, and may have many light redirecting elements interposed between the output plane 14 and the light source 10, as illustrated in FIGURES 12 and 13.
In summary, one dimension beam concentration of the incident beam 16, wlthin a single plane, is illustrated in FIGURES 1,

2 and 4 using the redirecting surface 11, which can take different forms, such as the lens 27, the reflector 12 and the lens 3~. As will be obvious to one skilled in the art, one dimension beam concentration can be incorporated into numerous three dimensional refractor and reflector arrangements, such as the preferred modified cylindrical redirecting surface arrangement of FIGURES 12 and 13~ In this preferred arrangement, the modiEied cylindrical redirecting surface 11, as illustrated in FIGURE 14, has the aperture 28 with a uniform width that preferably modifies the incident beam so that the resultant intensity profile is unifor~ with respect to one of the axes of the output plane 14. Other less desirable reflector and refractor arrangements can incorporate the beam concentrating modifications of FIGURES 1, 2, and 4, such as those illustrated in FIGURES 19 and 20.
~Ioreover,.a uniform intensi-ty profile can be created at the output plane 14 in which there is two dimensional intensity uniEormity w.ith respect to both axes.

~ 7~

Although the illumination of particles is illustrated as one possible application where the above described redistribution techniques are particularly useful, other applications of these techniques will be obvious to those skilled in the art. Although the term "light" is used in the description of the preferred embodiments, the redirecting surface 11 can be used with other types of radiant energy, and is not necessarily restricted to visible wavelengths.
The mathematics involved in redirecting the light rays for the lenses 27 and 38 of the embodiments of the inventions are described hereinafter. There are four basic cases:
1) the symmetric lens 27 with cross over rays, as illustrated in the embodiment of Figure 20j - -2) the asymmetric lens 27 with cross over rays, as illustrated in the embodiment of FIGURE l4,

3) the symmetric lens 38 without cross over rays, which is illustrated in radial cross section in FIGURE 4, and 4) the asymmetric lens 38 without cross over rays, as illustrated in the embodiment of FIGURE 16.
In all four above described cases, we have the following introductory formalism. Let R1 and R2 be the radiant fluxes of the incident beam onto any one of the lenses 27 or 38 and the output plane 14, in units of watts, respectively. Let Ml and M2 be ~he radiant excitance distributions of the incident beam and output plans (corresponding to Rl and R2) in units of watts/metsr2. I.et all the radiant energy falling on the lens be cylindrically sy~metric about the optical axis 18. In the analysis below, the effects due to reflection off the lens material-surrounding material and due to absorption of light in the lens material will be ignored for the sake of clarity.

~ -Z2-1~7~B~

By conservation of energy, the following equat~on.
results:

(4) R, = R2 and equivalently:

(5) J M,(~)~ da=J M2(r) da al a2 where a1 and a2 are the areas normal to the optical axis 18 of the incident radiant energy, having a radius "a"; and of the output plane 14, having a radius "b". The radial dlstance from the optical axis 18 ~ is "r".
lS . In cases 1 and 3 ~the symmetric lenses 27 and 38 with and without cross over rays, respectively), let M1 have a Gaussiall profile. (This formalism can be used for other proEile.s as well.) Accordingly:
- (6) M l(~) = M O eXp L- (r/ra) ~

where Mo is the radiant excitance of Ml at r - O and r~ is a constant with units of length. For a constant profile at the output plane 14 and equal to M2 we can solve for M2. Equation 5 becomes:

L8~
(7) J J M(3- exp [-(r/ra)l r d r d~--Jo JOM2- rdr d~) where ~ is the azimuthal angle. Thus, the following equation results with a ra: -(8) 2 Mz - (ra/b) Case 1 (symmetric lens 27 with cross over rays) will now be specifically considered.
- The incident rays located at distances from the optical axis of r'j, j=O, 1, ...~,N are selected so that these rays are reEracted to distances from the optical axis 18 in the output plane 14 of rj, j=O, l,... ,N, respectively. Our convention will be that t rO~= r'O = b and rN = Q and r'N - a~>ra- Let the r' values be equally spaced, i.e., ~ l~ r'J = r'J - r'J _ I , AND
l~r' -Qr' ~731 82 The corresponding rj values are co~puted from addin& ~he radiant fluxes betwe~n r'j and r'; 1 and between rj_1 and rj and dividing by the area in the output plane 14, ~ trj21 - rj2).
The result is set equal to P12 found in equat.ion (8):

J J exp(-r2).rdrd¢)+J J exp(-r2)rdrdp M2=
~ (r~ - r2) (9) . . exp(_r~2) -exp(-~J2 ~ exp(-~J!2l) -exp(-ri'2) ~ 2 ' 2 2 - rj Those rj values satisfying equation ~9) are needed, starting with rO ' b. This can be done with standard root finding techniques in numerical analysis.
At the refracting surface, N parabolas are pieced together, such that they and their first derivatives are constant across the r'j values. The jth parabola is of the form zj = aO ~ a1 r'j ~ a2r'j2. The distance paralIel to the optical axis 18 from the vertex of the lens 27 (where the refracti.ng surface crosses the optical axis.18~ to the refrac~ing surface is z, O>Zj, j = 0, 1, ...,N~ The slope is given by:

m. =dz I
dr' Ir'~
J

1~4~7182 All the r'j alld rj values are known. For a given j in the iteration process, the next z and m values are needed.
The coefficients-describing the next parabola, (aO, al, a2) are needed:
tlOa)Zj I ~ aO ~ al-rJtl~ a2 rJ!-(lOb)zj _ aO ~ al~r~l ~ a2-5 10 .
(loc)mj-l=al~2a2 ~J_I

(lQd)m; = al + 2 a2-rJ

Equation (lOa) indicates that the jth parabola must go thru the point (r'~ æj_l). Equation (lOb) indicates that the jth parabola goes thru (r~, z;). Equation tlOc) indicates that the jth parabola has the same slope, mj_l, at (r'~ Zj-l) as does the j-lst parabola. Equation (lOd) indicates that the jth parabola has the desired slope, mj, at (r'j, Zj).
There are four equations and five unknowns (Zj, mj, aO, al, a2); therefore another relation is needed.
This is obtained by considering the refraction of the incident ray, parallel to the optical axis 18, to the desired location in the output plane 14. Let ~j be the jth angle of incidence at ~r';, Zj).

-~6-Then:
(lL) ~j - Arctan tmj), ~J >

Let ~j be the jth angle of refraction at (r'j,zj), then by Snell's law, the following equatlon results:
(12) ~ =Arcsin (n-sln ~ >

The relative index of refraction of the lens 27 compared to the surrounding mediwm is n. Let ~j be the posi~ive angle between the light ray joining (r';, z;) to its location on the output plane (rj,B) and the optical axis 18. The distance between the vertex of the lens 27 and the output plane 18 is B. z is measured from the vertex and the positive direction is from the lens 27 to the output plane 18~ Then:
(13) ~j=Arctan (B---zJ) ~ J ~i Three more equations have been added (11-13) and two unkno~ns, ~j and ~'j, B and n are given r'j and rj are predetermined. Equation (13) can be rearranged for better use:

(14) r! - r.
. Z = ~ - J IJ
J tan(~

l~le following algorith&l can be ~Ised:
l. S~lect a trial m between ~ <m<mr~in, where mmin = tan ~c and where ac is the critical angle of incidence:

- ~c =Arcsir~ (I/n) Use equation (14) to compute Zj for this trial m.
2. Use equations tlOa) thru (10c) to compute the coefficients (aO, a1, a2).
3. Compute F - m; - a1 -2a2r'j from equation (lOd).
Go back to step 1 and find that m making F - O. Then m ~ mj.
4. Compute a z; corresponding to mj using equation (14). Use equations (lOa), (lOb) and (lOd) to compute the final (aO, a1, a2)-Now Case 2 (asymmetric lens 27 with cross over rays) will be specifically considered. Using the x-y coordinate system in FIGURE
7, in the output plane 14 the following relationship exists:

(15) M 2 = M o' C ' eXp [-( y /ra ~ '~

where ~ and ra are constantsO No matter which path the particle takes within the stream 44 of FIGURE 7, it is exposed to a radiant exitance distribution described by equation (15). Solve for c using equations (4), (5) and (15) to obtain the following equation:

~ -28-8~

(I6) ~ r 21 M~- 2b a MO exP (Y/ra)J

Express ~II (x,y) in an x-y coordinate system~ using ~2 ~ x2 ~ y2 and equation (6):

Ml (x, y) - Mo exp [-(X/lra)l exp L-(Y/ra) ~

Divide the x coordinates in a si~ilar way to which the r values were divided, x~, x~ 0, 1, ... N. Compute the radiant exitance over an elemental displacement in the y dimenslon, ~ y, setting the result in the output plane 14, equal to the incldent ra~iant exitance.

b Y+L~Y/
J J, M2 dydx Y-l~Y/2 ~Y

Xj I y~l~y~2 xJ y~l~y/~
f ,f Ml dy dx~ ~ J ~ Ml dy dx x) y l~Y~2 ~xJ I y-~Y/2 aY-(xi-~ -xj) ~ -29-~7~3Z

Use equatio~ (16) and e~uation tl7) in equation (18), to obtain the following equation:

(19) er~ (Xi_l/ra) - er~ (Xj J r~) ~ e~f(XJ/r~)~erf(XJ_I/ra) X~

where the error function is defined by:

(~) e~ (z) =~ exp(-t2)-d ~

The x'; are set to equal increments just as the "r"~ were with x~0 = b and x'N - a ra. Using equation tl9), all the x~
values can be obtained and the surface of the lens can be generated using the formalism which led.to equations ~10) and ~14)~
. Now turning specifically to Cases 3 ana 4 ~the symmatrical and the asymmetrical lens 38 without cross over rays), the output plane 14 is divided into equal segments for r and x, similar to r'j and x~; above. Use the formalism which led to equations ~10) to (14) to define the surface of the lens.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An optical device for redistributing incident radiation, having a non-uniform intensity distribution, to resultant radiation, having a desired intensity distribution in a predetermined region of an output plane, said optical device comprising redirecting means having a central portion and a peripheral portion, each said portion being disposed and configured to receive part of the incident radiation;
said central portion being constructed to permit the incident radiation to irradiate the predetermined region of the output plane; said peripheral portion being constructed to redirect specific rays of the incident radiation to specific locations in the predetermined region of the output plane, whereby the specific locations are further irradiated so as to create the desired intensity distribution within the predetermined area;
and wherein the predetermined region of the output plane has a configuration with at least some smaller dimensions in at least one direction relative to the corresponding dimensions of the incident radiation; whereby the resultant radiation at the output plane has a smaller profile of higher intensity than the profile of the incident radiation.

2. The optical device according to claim 1, wherein the incident radiation comprises one of collimated radiation, convergent radiation, or divergent radiation.

3. The optical device according to claim 1 in combination with a particle analyzer for illuminating the particles to produce detectable signals, including means for moving a stream of the particles through a predetermined region of said output plane.

4. The optical device according to any one of claims 1, 2 or 3,wherein said redirecting means includes a lens having a redirecting surface for refracting the incident radiation over at least a major portion thereof and said lens is constructed to concentrate the incident radiation into the predetermined region at the output plane without overlapping of the individual rays.

5. The optical device according to any one of claims 1, 2 or 3, wherein said redirecting means comprises a lens having a peripheral lens portion and an aperture formed within the lens;
said peripheral portion of said redirecting means comprises said peripheral lens portion and has a curved outer surface for redirecting the incident radiation; and said central portio of said redirecting means comprises said aperture, whereby the incident radiation proceeds through said aperture without substantial optical modification.

6. The optical device according to any one of claims 1, 2 or 3, wherein said redirecting means comprises a lens having a peripheral lens portion and an integrally formed central lens portion; said peripheral portion of said redirecting means comprises said peripheral lens portion and has a curved outer surface for redistributing the incident radiation; and said central portion of said redirecting means comprises said central lens portion and has opposed planar surfaces, whereby the incident radiation proceeds through said central lens portion without substantial optical modification.

7. The optical device according to any one of claims 1, 2 or 3, wherein said redirecting means comprises a reflector having a central reflector portion and a peripheral reflector portion; said peripheral portion of said redirecting means comprises said peripheral reflector portion and has a concave configuration for redistributing the incident radiation; and said central portion of said redirecting means comprises said central reflector portion and has a planar configuration.

8. The optical device according to any one of claims 1, 2 or 3, wherein said redirecting means includes means for relocating peripherally disposed, incident radiation, represented by a pair of opposed skirts of the non-uniform intensity distribution, to be disposed in overlapping relationship with centrally disposed radiation, represented by the remaining center of the non-uniform intensity distribution, so as to produce resultant radiation having a substantially narrower, flatter desired distribution at the output plane.

9. The optical device according to any one of claims 1, 2 or 3, wherein said incident radiation has a Gaussian intensity distribution having a center area and a pair of opposed skirt areas, said skirt areas are defined to have successive segments of radiation; said central portion of said redirecting means is configured and dimensioned so that the incident radiation, represented by the center area of the Gaussian distribution, passes therethrough to the predetermined region of the output plane, the predetermined region having successive positions defined therein; said peripheral portion of said redirecting means is configured and dimensioned to progressively shift the successive segments of radiation to the successive portions at the output plane, with the most remote segment of each skirt being shifted to the nearest available position with respect to the center of the incident radiation passing through said center portion of said redirecting means; whereby the skirts of the incident intensity distribution are folded over to create the desired intensity distribution with a narrower width and flatter profile.

10. The optical device according to any one of claims 1, 2 or 3, wherein said peripheral portion of said redirecting means has a modified cylindrical configuration, a cylindrical lens is positioned between said peripheral portion of said redirecting means and the output plane, and said cylindrical lens is oriented to line focus the radiation in a direction substantially perpendicular to direction in which the radiation is modified by said redirecting means.

11. The optical device according to any one of claims 1, 2 or 3, wherein said peripheral portion of said redirecting means has radial symmetry and said central portion of said redirecting means has a circular outer boundary.