CA1275588C - Apparatus and process for object analysis by pertrubation of interference fringes - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

Objects to be examined, such as tissue or any cellular or crystalline material, e.g. semiconductor wafers, are placed in a region of confluence of two interfering coherent beams of radiation which are at the same frequency and phase and at a frequency to which the object is semitransparent. The beams are produced by separate sources or by refraction by a Fresnel biprism or any other interferometer structure. An off-axis parabolic reflection system is also disclosed. The interference fringe phase and amplitude perturbation produced by the object is detached and examined to derive information regarding physical properties of the object or abnormalities in its structure. Such abnormalities, as fractures or latent stresses in a semiconductor wafer or the presence of tumors in biological tissue can be determined. Chemical characteristics of living tissue is determined by sweeping the frequency of the coherent radiation over a band which includes the absorption bands of given chemicals such as hydrogen, oxygen, sodium, and other materials which are representative of the structure of living tissue. The frequencies employed may be in the microwave band millimeter band or higher.

Description

lZ755~38 This invention relates to the analysis of ob~ects, including living tissue, by observing the perturbation of interference fringes betweell two interfering coherent beams of radiation in the object space.

Instruments for the non-invasive analysis of the in-terio~s of bodles, particularly biological tlssue, are well kno~n. By biologic tissue is meant living or dead tissue and the like. For example, x-ray apparatus is commonly used for the examination of hoth living tissue and inert materials. The use of x-rays for examination of llving tissue, particularly human beings, is hazardous because x-rays are ionizing radiation. Therefore, the use of x-ray examination is limited and the resolution which can be obtained through x-ray examination is limited because of dosage considerations.

The use of radioactive material is also fairly common for the examination of living tissue where the material is in~ected or ingested or otherwise applied to the living tissue. The tissue is then scanned to determine the concentration pattern o the radloactive material. The use of such diagnostic techniques again involves the use of ionizing radiation and the use and resolution obtain~d by the measurement is limited.

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Many other systems are known for the non-invasive testing of human tissues, such as nuclear magnetic reso-nance techniques (NMR). Nuclear magnetic reso-nance tech-niques are in growing use but the apparatus is extreme~y expensive and requires very long exposure times, for exam-ple 8-10 seconds, during which a patient can not move.
Furthermore, the use of NMR equipment requires the patient to be placed in a long tunnel defining the magnet which has adverse psychological attributes.
0 Many other non-invasive e~amination mechanismsincluding those employing ultrasound are also known, each having well known disadvantages.
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BRIEF DESCRIP~ION OF rHE INVEN~ION
In accordance with the present invention, non-ion-izing radiation is employed for the examination of the in-terior of objects to be analyzed. More particularly, and in accordance with the invention, two coherent beams of radiation are produced and are directed relative to one another such that their wavefronts interact in a region of confluence of the beams wherein an interference fringe pat-tern is produced. ~he frequency employed for the coherent radiation can be from microwave range through the millime-- ter range and higher into the optical range. ~he frequency selected is one at which the object to be analyzed is at least partly transparent. rhe object to be analyzed is then placed in the region of confluence of the two beams so that the object will distort the interference fringe pat-tern which is produced by the interfering wave fronts of the two beams. In effect, the interference field is em-ployed as an active grating with an adjustable period whichprovides an adjustment for the limiting spatial resolution for the system.
~e ~r~ ~he nature of the interference pattern change or ~crtub&-tio~ is related to particular selected characteris-tics of the object being examined. By way of example, in ~7~iS~

the analysis of biological tissue, the presence of a mass orregion of thickened tissue will produce a perturba~ion in the int~rference fringe pattern which would not occur in a normal tissue sample which does not include such a thickened region.

In another use of the novel apparatus, still applied to the study of biological tissue, the frequency band o the coherent interfering beams is swept over a relatively narrow range to include one or more absorption ~ands of such elements and compounds such as hydrogen, water, salts, oxygen, calcium, iron lo and sodium. The presence of these elements and compounds will produce charact~ristic changes in the interference fringe perturbation when that particular frequency is reached during the sweep of the coherent beam frequency. This, in turn, will reveal physiochemical or physiological conditions representing an excess of or dimished quantities of the element in question due to certain pathological processes. Thus, the analysis of the content of hydrogenr water, oxygen, calcium, iron and sodium and other elements has a known relationship to pathological conditions in the use of NMR equipment and the same information can be obtained through the novel apparatus of the present invention.

When applied to human tissue, the frequencies used are preferably in the microwave to millimeter range, although higher frequencies may be used. Energy is applied for a short time to prevent excessive heating of the tissue. By way of example, the beam frequency can be varied. As by stepping or sweeping through a given frequency range which contains the absorption frequencies being investigated. As the frequency reaches a desired absorption frequency, it can dwell for a short time, for example, of the ~' .

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order of a millisecond, and is thereafter stepped or swept to the next absorption band of interest. One full cycle lasts less than about 20 milliseconds, whereby the measure-ment is unaffected by heart movement or body movement o~ a patient. A cycle time o~ less than about 30 millisecon~s is needed to display human heart readings without being affected by the contractions and expansions of the heart.
~he frequency range which is input is preferably from about 5 gigahertz to 500 gigahertz which will contain the rele-vant absorption bands presently known to us. A single cy-cle is believed to be sufficient to gather the data needed for an examination given an adequate source.
For examination of organic matter, the frequency sweep and dwell time can be adjusted, depending on the thermal sensitivity and absorption bands of interest in the sample. During th~ f~e~u~ency sweep, data can be gathered on the fringe ~a~u~t~ produced outside of the absorp-tion band being examined. ~hat data can then be "subtrac-ted" from the data obtained at an absorption band of inter-est, thereby to produce an enhanced picture of the distor-tion produced at one or more absorption bands of interest.
By pulsing the energy, undesired heating effects are re-duced.
Frequencies outside of the millimeter band can also be used for analysis of other objects. By way of ex-ample, internal stress or fractures in a wafer of monocrys-taline silicon can be determined by employing a source of coherent radiation having a frequency in the infrared ran~e, particularly an infrared laser source having a wave-30 length of greater than 1.2 microns. ~he 1.32 micron line of an ND-YAG laser is very useful for semiconductor analy-sis. A tunable dye laser could also be used; this would allow sweeping past the absorption bands. An ND-YAG laser would be useful as a pump for the dye laser, sweeping from the 1.064 um line to further into the infrared band. ~here are numerous inexpensive sources available. ~he interfer-~' : :.

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ence fringe patterns can then be imaged on a suitable infrared vidicon or the like. Other monocrystalline, polycrystalline or amorphous silicon ob;ects can also be examined by selection of appropriate frequencies. Obviously, ob~ects of other materials can similarly be examined.

Numerous radiation sources can be employed with the presen-t invention. For example, when employing microwave ~requencies, a single microwave generator can be employed. Its output is then split and delivered to spaced microwave antenna which produce converging coherent radiation beams which converge on the ob~ect to be examined. One leg preferably contains a precision phase matching apparatus.

Alternatively, the output of a single microwave radlation source can be applied to a Fresnel biprism implemented in a material of an appropriate refractive index for the frequency in use. The biprism will produce two output beams of coherent radiation which converge toward one another. Such Fresnel biprisms are known and have been used for educational demonstrations in the visible light range but have not been used nor any microwave, millimeter wave or infrared application. In a microwave or millimeter wave application, the biprism should be made of a material such as polytetrafluoroethylene (supplied under the trademark Teflon) which is semi-transparent and refractive at those frequencies.
Quartz Fresnel biprims can be used for an infrared, visible, or ultraviolet source of radiation.

Another useful source of the beams of coherent light which have a region of interfering confluence can be derived from an interferometer, for example, a Mach-Zehnder interferometer.

A useful source of input radiation is provided when a microwave 30 source is directed toward an off-axis parabola which transforms the spherical wavefronts of the source output into parallel .
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wavefronts. The parallel wave-fronts are then applied to a Fresnel biprism which develops - 5a -,~i - : - .. .

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the convergent beams of coherent radiation which converge - in ~n interference region containing the ob~ec~ to be e~am-ined. ~his is the preferred eMbodiment of the in~ention for medical applications since it enables use of equipment 5 which is compatible in size with existing x ray equlpment and peripherals, and x-ray rooms in hospitals.
While a significant advantage of the invention is to avoid the use o~ ionizing radiation, sources o~ ionizing radiation (up to about 10 KEV~ can, if desired, be employed Y 10 in the manner disclosed for the present invention. A mono-crystalline interferometer or a Wolter type grazing inci-dence mirror system may be employed to produce the inter-ference fringe pattern.
~he detectors for detecting the signal containing 15 the perturbed interference fringes can be any desired known infrared, visible, ultraviolet~ microwave, or millimeter , wave detector. By way of example, microwave interference fringes can be measured by appropriate modification of known traveling wave modulators to produce a traveling wave 20 detector in which microwave radiation modulates a light beam. It is also possible to use phased array receptor systems.
Other receivers can consist simply of a film hav-ing a silver halide modified to be responsive to the micro-25 wave radiation or to the particular radiation frequency employed. Solid state detectors and liquid crystal detec-tors can also be used.
he~ information can be compiled and analyzed by any desired well known process for analyzing and pre-30 senting such information. By way of example, the informa-tion produced can be scanned and applied, element by ele-ment, to a computer to process the information and to pro-duce an output image of the fringe pattern pertubations.
Image subtraction techniques can be used. ~hese may be 35 obtained by comparing the fringe pattern which is produced without the object in the object space to the perturbed ~7~S8~

pattern or by comparing the perturbation of the sample to the perturbation caused by a standard sample of the sub~ect or by comparing (subtracting) the perturbations at different frequencies. The perturbation patterns can then be presented in two-dimensional or three-dimension form. Thus, it is possible, for example, to employ techniques similar to those usad in CAT
Scans or holographic reconstruc-tion to produce the efect o a planar x-ray with information ln two or three dimensions.

The perturbation of fringes as a result of interaction between the radiation waves and the ob;ect matter will consist of changes in fringe position and in light absorption.

The displacement of the fringe position for a given frequency will be covered by Snells' law:
n sin ~ = n' sin ~ ', where n and n' are the indices of refraction in a refracting region of changing index of refraction, and and ' are the angles of incidence in the medias having indices n and n', respectively. The index of refraction n may change to n' in step fashion, or in conti~uous matter at a constant or variable rate of change.

The fringe intensity perturbation is ~overned by the Lambert-Beer Law of Absorption:
I~Io = e c~L, where: I = Incidence intensity Io = Transmitted intensity ~X_= Linear absorption coefficient ~' .. -- ~, . - , - ' ' .
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,. , BRIEF DESCRIP~ION OF ~ E_DRAWINGS
Fig. 1 schematically illustrates a first embodi-- ment ot` the invention in which two microwave an~enna pro-duce interfering, convergent beams in an object area con-taining an object to be examined.
Fig. 2 shows the interference fringes which are produced in the apparatus of Fig. I when no object is pres-ent in the region of confluence of the two beams.
Fig, 3 shows the interference fringe pattern which is produced when an object is present in the object space of Fig. 1.
Fig. 4 is a schematic illustration of a second embodiment of the invention in which a Fresnel biprism beam separator is employed.
Fig. 5 is a schematic diagram of a third, and pre-ferred embodiment of the inven'ion in which an off-axis ~arabolic reflector and Fresnel biprism is employed.
Fig. 6 is a still further embodiment of the pres-ent invention in which an interferometer with a low compon-ent count is employed as the source of the two coherentradiation beams.
Fig. 7 is a schematic diagram of apparatus having a Mach-~ehnder interferometer which ~vas employed to test the concept of the present invention in which interference fringes with pertubations caused by an object were produced through the interference of two coherent beams.
Fig. 8 is a plan view of a circular plastic ball which was used in one experiment in the apparatus of Fig.
7.
Fig. 9 is a sectional view of Fig. 10, taken across section line 9-9 in Fig. 10, of an elongated cylin-der of plastic having two curved openings therein which was employed in another test of the apparatus of Fig. 7.
Fig. 10 is a c,ross-sectional view of the cylinder of Fig. 9 taken across section line 10-10 of Fig. 9.

, ~7SS~313 Fig. 11 shows the interference fringe pattern which was observed in the apparatus of Fig. 7 with no ob- -ject in the object analysis space.
Fig. 12 shows the manner in which the inter-ference fringe pattern of Fig. 11 was perturbed when the ob~ect of Fig. 8 was placed in the object analysis space in Fig. 7.
Fig. 13 shows the manner in which the fringe pat~
tern of Fig. 11 was perturbed when the object of Figs. 9 and 10 was placed in the object analysis space of Fig. 7.

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DE~AILED DESCRIP~ION OF ~HE DRAWINGS
Referring first to Fig. 1, there is shown therein a schematic top view of a treatment room 20 adapted for carrying out the present invention. ~he walls of the room may be microwave shielded by conventional microwave absorb-ing pyramids which line the surfaces thereof. A microwavegenerator 21 is disposed exteriorly of room 20 and is con-nected to a signal splitter 22 which connects the energy of generator 21 through appropriate wave guides, to microwave antenna 23 and 24. Appropriate microwave lenses 25 and 26 are disposed in front of the output of antenna 23 and 24, respectively. A suitable frequency sweep control circuit 2'7 is connected to the transmitter 21. In designing the antenna 23 and 24, a millimeter wave operating frequency is preferred. ~his will reduce room size and apparatus size.
According to the Nyquist criterion, a small wavelength is preferred for better spatial resolution so that for the millimeter band, it is preferred to employ a ~requency of from 5-500 gigahertz. Preferably, the room and apparatus is temperature stabilized t~ avoid frequency drift.
~he generator 21 and frequency sweep control 27, in a typical embodiment of the invention, produce a milli-meter wave output from antenna 23 and 24 at a frequency which can step from absorption band to absorption band over a range of 5 gigahertz to 500 gigahertz. ~ypical absorp-tion bands can be found in the literature, or can be exper-, .

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imentally determined. Oxygen (2), for example> has two well defined absorption peaks, one at 60 gigahertz and a second at 119 gigahertz. Wàter also has two absorption peaks, one at about 21 gigahertz and the other at 183 giga-hert~. Other absorption bands are well known ~or othermaterials. ~he output pulse at a given absorption band will have any desired shape and duration. ~he duration of a given pulse is preferably less than one millisecond with a sharp rise and fall shape. ~he duration of a fu11 cycle in which each of a plurality of absorption bands and/or - standard frequency samples are taken is less than about 30 milliseconds.
~ he antenna 23 and 24 are directed toward an ob-Ject 30, which can, for example, be a tissue sample or a human being, with the object 30 being located in an area of confluence of the wavefronts of the two beams coming from lenses 25 and 26. Consequently, the tissue 30, which is semi-transparent and refractive to the radiation of the converging beams from antenna 23 and 24, will cause pertu-` 20 bations in the interferenece pattern which is produced at this overlapping area. By way of example, in the absence of object 30, inter~erence fringes are produced, as shown in Fig. 2, whereas the object 30, when illuminated at a given frequency, causes the perturbed interference fringes shown in Fig. 3. ~he frequency of the radiation illuminat-ing the object 30 may then be varied, which includes step-ping or switching from standard frequencies and absorption frequencies with a single sweeping cycle.
~he interference fringes which are produced are detected by a conventional microwave detector 31, which can be any desired type of two-dimensional detector, such as a traveling wave detector or phased array receptor system.
It is also possible simply to use a film which is sensitive to the wavelength of the microwave radiation which is used or a solid state detector or liquid crystal detector.

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- ~.Z7SS88 ~ he output of detector 31 can be digitized by any appropriate digitizing system well~known in the art and the image produced c&n then be computer-processed in any de~
sired ma~n~r~ By way -of example, it is possible to display the ~ b~i-o~ caused by the presence of objeck 30 on the interference pattern at different illumination frequencies in an either two-dimensional or three-dimensional display.
~he display can also be a subtracted display in which only the p~tuba~ion caused at a given frequency is displayed in an enhanced manner.
As shown in Fig. 3, the interference fringes will - be perturbed diffe~rentl~ about the two sides of the center line 33. ~he ~pe~ubl~o~ will be related to the charac-teristics of the object 30 and will be related, for exam-ple, to the frequency at which the interference fringe pat-tern of Fig. 3 was measured. For example, a unique pertur-bance pattern (to the object) will be produced when the microwave frequency is in the frequency absorption band of given elements. ~his makes it then possible to plot the concentration of elements of the volume of the object being examined by superposition of several images, each at a dif-ferent frequency; the attenuated elements in each image - representing the desired information. ~his can produce ; useful information relatedr for example, to the presence of tumorous masses and the like which would be particularly defined by the concentrations of various elements or com-pounds. Such abnormal and normal patterns are known in NMR
processing techniques or can be derived experimentally.
In particular, the phase and amplitude and orien-tation information regarding the object 30 will be present in the fringe distortion, and this information can be de-rived from the fringe patterns in any desired manner. Note that the invention, in essence, employs the interference field as an active grating. Any interferometer can be used - 35 as a source of interference fringes.

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. ' . ~ . , .: ~ ' ' - - - ~ ' ' ' ` - ~2~5SB !3 Fig. 4 shows another embodiment of the invention in which the apparatus is simplified and is operated from an infrared laser, rather than a microwave source. Note, . .
however, that a maser or any other laser source can be used as well. ~hus, in Fig. 4, a conventional infrared laser 40 is shown, which produces an output through a spatial filter 41 which removes noise and produces a high quality signal for the output radiation. ~he coherent beam output of the spatial filter 41 is then applied to a beam e~pander 42, ~' lO which can be a suitable infrared lens, and is then applied to a quartz Fresnel biprism 43. Biprism 43 will produce two converging output beams 44 and 45 from the single input beam from the beam splitter 42. Note that prism 43 is shown in perspective view in Fig. 4 and is a rectangular prism. ~he prism angles are approximately 1, 178 and ~.
~hese angles can vary depending on the required field of view, de~th of field and size of object to be examined.
rhe two output beams ~4 and 45 converge toward one another and interfere with one another in an object space containing an object 46. Consequently, the presence of the object 46, which is semi-transparent and refractive to the infrared radiation produced by laser 40, will perturb the inter~erence ~ringe pattern due to hidden or latent or ap-parent discontinuities within the object 46 or on its sur-face. ~he radiation containing the perturbed interferencefringe pattern proceeds toward the detector 48. Detector 48 may consist of any desired means to convert the radia-tion pattern to visible light and may then apply the light to a ground glass screen which can be photographed. ~he perturbed light pattern can also be optoelectrically con-verted for display on a cathode ray tube. ~he perturbed fringe pattern, as monitored by detector 48, may also be processed as described in connection with Figs. 1, 2 and 3.
Note that a biprism such as biprism 43 could be - 35 used for processing energy in the microwave and millimeter - . . , - .
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~2~S588 ranges where the biprism would then be of polytetrafluorethylene (supplied under the trademark Teflon) which is semi-transparent and has a usable index of refraction at those frequencies.

In the embodiment of Fig. 4, the ob~ect 46 being examined can be a material such as a monocrystaline silicon wafer belng examined for hidden fractures and latent stresses. The occurrence of a fracture or stress in the wafer would be revealed by a given perturbation from the pattern which would be produced from an unstressed and unfractured wafer. Thus, the invention makes possible a relatively inexpensive instrument for analyzing hidden or latent defects in silicon wafers. Obviously, other material samples can be suitably analyzed for stress, fracture or the like in the manner similar to that described above.

A further embodiment of the invention is disclosed ln Fig. 5 which shows an improved method for generating an interference field input coherent wave beam with parallel wavefronts. Thus, in F~g. 5, a microwave tmillimeter wave) source 50 of conventional form is provided with a driving power source 51.
Microwave source or antenna 50 can be operated in the frequency range described in Fig. 1. The output of microwave antenna 50 consists of spherical wave fronts which are applied to an off-axis parabolic microwave reflector 52. By appropriately designing the curvature of the parabolic reflector relative to its spacing from source 50, it is possible to produce planar parallel r~flected wave fronts moving in the direction of arrow 53 and toward the Teflon biprism beam separator 54. The converging beams produced by the b~prism 5~ are then perturbed by the ob~ect 55, as described previously. When ob~ect 55 can be organic tissue or the liXe, and the perturbed fringe pattern -then detected by detector 56. Note that detector 56 can include means for converting the radiation to visible light and that the perturbed image can then be applied to a ground glass screen and observed or photographed. Optoelectric imaging techniques can also be used.

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Fig. 6 shows another embodiment of the invention in which an interferometer of low part count is used as the source of the interference field. ~hus, in Fig. 7, the output o~ a laser 70 is applied to a beam splitter 71. rhe path through beam splitter 71 is applied to a diverging lens 72 and mirror 73, while the other path ~rom mirror 71 proceeds through diverging lens 74 to reflecting mirror 75.
~he path lengths from mirrors 73 and 74 are of the same length and the radiation from the two paths interfere in the object space, shown as containing an object 76. Detec-tor 77, which may be a camera senstive to the radiation of laser 70, can take a photograph of the interference fringe pattern which is produced with or without object 76 in the object space.
Fig. 7 shows still another embodiment of the in-vention in which the convergent beams of coherent radiation are produced by a Mach-Zehnder interferometer. ~hus, in Fig. 7, a laser source 60 directs an output beam of light toward beam splitter 61, which divides the beam into two paths which are directed toward reflecting mirrors 62 and 63. ~hese two paths are of identical length and are recom-bined in a second beam splitter 63. ~eam splitter 63 has an angle such that the light from mirror 62 is caused to converge at an angle which is less than about 1 relative to the light coming from mirror 63. ~hese two converging beams are a~plied to optical lens 64 which can, for exam-ple, be a 60 power microscope objective which produces sep-arate converging beams which interfere in the space con-taining object 76 which is to be examined. ~s before, the two beams coming from the path containing mirror 62 and from the path containing mirror 63, have their interference patterns perturbed by the object 76 to reveal interior structural characteristics of the object 76. ~he perturbed fringe pattern is then detected by the detector 66 which may be similar to the detector disclosed in Fig. 4.

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An alternate arrangement for Fig. 7 is shown in dotted lin0s in Fig. 7 where the laser 60a produces an output through an attenuator 68 to a reflector 69 which then produces the output light for use by the Mach-ZPhnder interferometer portion of the system.

The ob~ect 76, ln one experiment using the apparatus of E~ig. 7, was a simple spherical transparent plastic which was a polymethylmethacrylate (supplied under Lucite) ball 78 shown in Fig. 8. Laser 70 was a 4 milliwatt, unpolarized HeNe dsvice.
When the ball 78 was not in the obiect space 76 and the ob~ect space was clear, the fringe pattern ~onslsted of straight parallel fringes, as shown in Fig. 11. When, however, the spherical object 78, which was semi-transparent to the radiation of laser 70, was in place, the interference pattern of Fig. 12 was observed. In Fig. 12, the circular region 80 was simply the outline of the diameter of the ob~ect 78. Note that outs~de of this circular region, the same unperturbed parallel frlnges of Fig. 11 were observed. In the area within the outline 80, however, the fringe pattern consisted of arcuate fringes curving away from one another on the opposite sides of the center of region 80, disclosing the shape of the ob~ect and the lack of discontinuities within the ob;ect.

In a second experiment, a Lucite ~a trademark) plastic cylinder 85 of Figs. 9 and 10 was used, in which the plastic cylinder 85 was semi-transparent to the laser radiation and was of the same material of the ball 78. The cylinder 85 contained two arcuat0 openings 86 and 87 therein which simulated the shape ~nd size or blood carrying vessels. Ob~ect 76 was placed in the ob~ect space of Fig. 7 with its axis extending parallel to the plane of detector 77. The fringe pattern obtained by placing the ob;ect 85 in the ob~ect space 76 is shown in Fig. 13. The fringe pattern is unperturbed outside of the outline of the cylinder 85.
Within the cylinder 85, however fringe discontinuities in the regions of the openlngs ~6 and 87 outlined the openings 86 and ~ 15 -. ~ - - ~ . - -' lZ7~5BB

87. A stress plane in the plastic which was not visible to the eye was also revealed at dotted line so.

In the processing of the information which is obtained in the perturbations in the interference pattern produced by the invention, any desired processing can be employed. In ls, ~or example, possible to use non-coherent fourier transform output techniques and then to process these to produce the output image.
similarly it is possible to employ holographic-like reconstruction of the lnformation to produce three-dlmensional stress perturbation lmages of the ob~ect being analyzed.

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558~3 ~hile the above disclosure preferably employs radiation outside of the range of ionizing radiation, it is also possible to employ ionizing radiation. By way of example, it is possible to incorporate an x-ray band using "K" edge absorption concep-ts.
This has been used in x-ray interferometry at energies less than about 10 KEV and can be extended to application with the presenk invention.

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Claims (13)

1. The process of examining an object comprising the steps of directing first and second beams of coherent radiation of a frequency at which said object is transparent toward said object so that said beams interfere with one another, whereby the interference pattern which is produced is distorted from the pattern which would be produced in the absence of said object, and thereafter deducing from the pattern at least one characteristic of said object.

2. The process of claim 1, wherein said object is a living organism.

3. The process of claim 1 which further includes the step of varying or sweeping the frequency of said coherent radiation through the absorption band frequency of at least one chemical element which is present in said object and analyzing the distortion produced at said absorption band frequency.

4. The process of claim 3, wherein said radiation is in the millimeter radiation band and wherein said radiation is produced in short, spaced pulses to avoid unnecessary heating of said object.

5. The process of claim 3, wherein said radiation frequency is one of microwave, visible, ultraviolet and x-ray frequencies.

6. The process of claim 1, wherein said object is a semiconductor silicon wafer.

7. The process of claim 1, wherein said radiation frequency is one of microwave, visible, ultraviolet and x-ray frequencies.

8. Apparatus for analyzing selected characteristics of a sample; said apparatus comprising: means for supporting said sample in an object space; means for producing two coherent interfering beams of radiation of the same frequency which pass through said specimen sample; said beams being of a frequency to which at least portions of said sample are semitransparent and refractive, whereby the interference fringes produced by said beam are perturbed; detector means positioned on the side of said sample at which said beams exit from said sample from which fringe information can be derived.

9. The apparatus of claim 8, wherein said beams have a wavelength in the millimeter range.

10. The apparatus of claim 8, wherein said beams have a wavelength in the range containing infrared, visible and ultraviolet light.

11. The apparatus of claim 8, which includes means for varying the frequency of said beams over a band which is greater than about 5 gigahertz and less than about 500 gigahertz.

12. The apparatus of claim 11, wherein said means for varying the frequency steps said frequency over a given number of different discrete frequencies.

13. The apparatus of claim 8 or 11 which further includes means for stabilizing the temperature of said apparatus.