CA1131950A - Method and device for real-time infrared holography - Google Patents
Method and device for real-time infrared holographyInfo
- Publication number
- CA1131950A CA1131950A CA364,600A CA364600A CA1131950A CA 1131950 A CA1131950 A CA 1131950A CA 364600 A CA364600 A CA 364600A CA 1131950 A CA1131950 A CA 1131950A
- Authority
- CA
- Canada
- Prior art keywords
- hologram
- oil
- plate
- film
- real
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- 238000000034 method Methods 0.000 title claims description 17
- 238000001093 holography Methods 0.000 title description 7
- 238000001429 visible spectrum Methods 0.000 claims abstract description 9
- 239000011521 glass Substances 0.000 claims abstract description 8
- 239000003921 oil Substances 0.000 claims description 32
- 239000010408 film Substances 0.000 claims description 16
- 239000010409 thin film Substances 0.000 claims description 3
- 239000002480 mineral oil Substances 0.000 claims description 2
- 235000010446 mineral oil Nutrition 0.000 claims description 2
- 238000007689 inspection Methods 0.000 abstract description 5
- 235000019198 oils Nutrition 0.000 description 25
- 239000002609 medium Substances 0.000 description 8
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 2
- 238000010521 absorption reaction Methods 0.000 description 2
- 238000004458 analytical method Methods 0.000 description 2
- 239000000839 emulsion Substances 0.000 description 2
- 238000005305 interferometry Methods 0.000 description 2
- 230000005457 Black-body radiation Effects 0.000 description 1
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 1
- 229910052786 argon Inorganic materials 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 238000006731 degradation reaction Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000006073 displacement reaction Methods 0.000 description 1
- 238000003384 imaging method Methods 0.000 description 1
- 230000005855 radiation Effects 0.000 description 1
- 230000035945 sensitivity Effects 0.000 description 1
- 229910052710 silicon Inorganic materials 0.000 description 1
- 239000010703 silicon Substances 0.000 description 1
- 235000015112 vegetable and seed oil Nutrition 0.000 description 1
- 239000008158 vegetable oil Substances 0.000 description 1
Classifications
-
- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
- G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
- G03H1/04—Processes or apparatus for producing holograms
-
- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
- G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
- G03H1/04—Processes or apparatus for producing holograms
- G03H1/0402—Recording geometries or arrangements
- G03H2001/0413—Recording geometries or arrangements for recording transmission holograms
-
- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
- G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
- G03H1/04—Processes or apparatus for producing holograms
- G03H1/0402—Recording geometries or arrangements
- G03H2001/0441—Formation of interference pattern, not otherwise provided for
-
- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
- G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
- G03H1/22—Processes or apparatus for obtaining an optical image from holograms
- G03H1/2286—Particular reconstruction light ; Beam properties
- G03H2001/2289—Particular reconstruction light ; Beam properties when reconstruction wavelength differs form recording wavelength
-
- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
- G03H2222/00—Light sources or light beam properties
- G03H2222/10—Spectral composition
- G03H2222/16—Infra Red [IR]
-
- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
- G03H2260/00—Recording materials or recording processes
- G03H2260/30—Details of photosensitive recording material not otherwise provided for
- G03H2260/35—Rewritable material allowing several record and erase cycles
- G03H2260/36—Dynamic material where the lifetime of the recorded pattern is quasi instantaneous, the holobject is simultaneously reconstructed
Landscapes
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Holo Graphy (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A hologram is recorded at a wavelength of approximately 10.6 µm by dividing a CO2 laser beam having the desired wave-length, and causing the resulting two beams to interfere on an oil film on a glass plate, the flim having a thickness of 0.1 to 1.2 µm. The hologram is reconstructed in the visible spectrum using a He-Ne Laser, thus allowing Real-time holographic inspection in the infrared region.
A hologram is recorded at a wavelength of approximately 10.6 µm by dividing a CO2 laser beam having the desired wave-length, and causing the resulting two beams to interfere on an oil film on a glass plate, the flim having a thickness of 0.1 to 1.2 µm. The hologram is reconstructed in the visible spectrum using a He-Ne Laser, thus allowing Real-time holographic inspection in the infrared region.
Description
``` 1131~;0 This invention relates to a holographic method and to a device for carrying out such method.
The inspection of articles using holography has hereto-fore been carried out at wavelengths of the visible spectrum and with accoustic waves. However, holographic inspection has not been effected in a satisfactory way at wavelengths in the infrared range, i.e., 10 ,um. The present inventors have discovered a method of effecting infrared holographic nondestructive inspection at a wavelength of 10.6 ,um, and have found a medium for effecting such method. Actually, it is the medium and its support which permit holographic inspection at the wavelength in question.
Amongst the various applications of holography in the visible spectrum, those of interferometry, imagery and Schlieren analysis are particularly interesting. The application of such techniques to wavelengths near that of the CO2 laser, i.e., 10.6 ~m is practical in certain circumstances. Because the wavelength of the CO2 laser is much longer than visible spectrum wavelengths, larger deformations or displacements of surfaces can be observed.
Moreover, the necessity o absolutely avoiding vibration, i.e., of having a good anti-vibration system is less stringent at longer wavelengths.
When considering the possibility of effecting holography at the longer wavelengths, the inventors encountered the problem of the lack of an acceptable recording medium. Because of the low energy of inrared photons, photographic emulsions cannot be used.
Even if a plate using a photographic emulsion for infrared holo-graphy was available, it would be necessary to store the plate at a very low temperature, since the plate would be exposed eve~ in the dark by blackbody radiation at room temperature.
' .
; ~ 1 !
` li31950 The object of the present invention is to overcome the problems that would be encountered in infrared holography using presently available media by providing a holographic method and a readily available medium for use in such method.
Accordingly, the present invention relates to a method of recording a hologram at a wavelength in the infrared region comprising dividing a beam having a suitable wavelength; and causing the resulting two beams to interfere on a thin oil film on a plate, and reconstructing the hologram in Real-time using wavelengths in visible spectrum.
The invention also relates to a device for recording an infrared hologram comprising a plate; a thin film of oil on said plate, and means for reconstructing the hologram in Real-time using wavelengths in the visible spectrum.
The invention will now be described in greater detail with reference to the accompanying drawing, the single figure of which is a schematic block diagram of an experimental device for carrying out the method of the present invention.
With reference to the drawing, a hologram is recorded using an apparatus which includes a CO2 laser 1 stabilized in the fundamental mode. A beam 2 from the laser 1 passes through a shutter 3 in the direction of arrow 4. The beam is divided in two using a beamsplitter 5. The beamsplitter 5 divides the beam 2 in such manner that the two resulting beams 6 and 7 have approximately the same power. Using a mirror 8, the beams 6 and 7 are caused to travel in the direction of arrows 9 and 10, re-spectively, and are made to interfere on a thin film of oil on a surface 11 of a plate, in this case a glass plate 12. When the plane of the glass plate is such that the two beams 6 and 7 sustend the same angle 0 with the normal of the plate, the hologram obtained is a series of straight, parallel interference fringes spaced apart by ~/2 sin ~. The hologram of an actual object (which is not shown) is obtained by placing the ob~ect in the object beam 7.
As the hologram is recorded, the reconstruction is achieved in Real-time by shining a He-Ne (or argon) laser beam 13 from laser 14 through the oil on the plate 12 in the direction of arrows 15. A l~ns 16 (which is optional) and a spatial filter (not shown) are used to separate the +l order of diffraction from the O and the -1 order. In any event, the reconstruction can be recorded on a magnetoscopic tape using a vidicon camera (not shown) and, at the same time, the response time of the oil film can be studied by means of a photodiode detector.
When preparing the plate 12, the surface 11 of the plate is painted with oil to a thickness of approximately 100 ~m.
For better results, a 10 ,um thick oil film is evaporated on the surface of the glass plate 12. With both methods, the oil film is ready only after being exposed for a few seconds to the CO2 laser radiation which reduces the thickness of the oil to approx-imately 1 ,um. If the CO2 laser beam is then stopped, there is ~ .
no degradation in the quality of the oil surface even though the plate 12 is held in the vertical position, i.e. with the oil coated surface 11 in a vertical plane. By causing the beams 6 and 7 to interfere at this time and by a thermal effect, a surface modu-lation of the oil film occurs, giving a phase hologram. Of course, many factors must be considered when attempting to explain the process. However, since at a wavelength of 10 ~m the absorption of a thin oil film is negligible and since the glass has a very high absorption coefficient, it is reasonable to state that first the plate is heated and then the heat is transferred to the oil by conduction, the second phenomenon probably being the factor ' , 1131950 ~
that limits the response time of the oil. The response time is the time for the diffraction efficiency at reconstruction to increase from 10 to 90% of its maximum value.
It has been found that the incident power on the oil film and the duty time of the oil are interrelated (duty time being the time interval between the beginning of reconstruction and the time at which the diffraction efficiency has fallen to 10%
of its maximum value). If the average power density is kept below 0.5Wjcm , the dutv time is very long. At such low energy densi-~10 ties, the diffraction efficiency is low and it is preferable towork in a chopped mode with higher peak power which gives both a high diffraction efficiency and a long duty time.
With respect to linearity, the oil film presents a good linearity for irradiances below 10 milijoules per square centimeter.
For irradiances higher than 10 mJ/cm2, higher diffraction orders become clearly visible. It has been found that the irradiance necessary to record a hologram is of the order of 10 mJ/cm , which is at least one order of magnitude lower than previously known ~j mediums.
~20 ~ ~ It has been found that any thickness of oil below 1.2 ~m remains adequate for recording a hologram even if the infrared irradiance is stopped. M~reover, if the power density afterwards remains below O.5W/cm2, the oil thickness will remain the same as well as the response time. A plot of the ratio of diffraction efficiency to response tlme versus oil thickness shows that the curve levels off above 1 ~m. At the same time, the diffraction efficiency goes down and stays constant for the same thickness.
The optimum thickness is found to be from 0.9 to 1.2 ~m, the diff-raction efficiency is approximately 5~ and the response time of ; 30 the order of 10 ms. Such an experimental condition is obtained "
j - 4 -1131950 `
using an irradiance of 12 mJ/cm2. For such conditions, the spatial resolution is approximately 20 cycles/mm. At the expense of diff-raction efficiency, the spatial resolution can go as high as 50 cycles/mm.
As mentioned hereinbefore, the oil film medium can be used and indeed has been used in recording holograms and imaging, in Schlieren analysis and in interferometry. The medium has been found (i) to meet the requirements of an adequate recording med-ium at 10.6 pm, (ii) to have good sensitivity and (iii) to respond rapidly. The recording is not permanent so that Real-time holo-graphy and reconstruction in the visible spectrum can be performed.
The medium has reasonably good resolution and is inexpensive. The best oils have been found to be Volt-Esso-35 (a trade mark for transformer oil) and/or any silicon oil. Any pure mineral oil is acceptalbe. For some unknown reason, the vegetable oils used did not function properly.
~ , , ',~ .
The inspection of articles using holography has hereto-fore been carried out at wavelengths of the visible spectrum and with accoustic waves. However, holographic inspection has not been effected in a satisfactory way at wavelengths in the infrared range, i.e., 10 ,um. The present inventors have discovered a method of effecting infrared holographic nondestructive inspection at a wavelength of 10.6 ,um, and have found a medium for effecting such method. Actually, it is the medium and its support which permit holographic inspection at the wavelength in question.
Amongst the various applications of holography in the visible spectrum, those of interferometry, imagery and Schlieren analysis are particularly interesting. The application of such techniques to wavelengths near that of the CO2 laser, i.e., 10.6 ~m is practical in certain circumstances. Because the wavelength of the CO2 laser is much longer than visible spectrum wavelengths, larger deformations or displacements of surfaces can be observed.
Moreover, the necessity o absolutely avoiding vibration, i.e., of having a good anti-vibration system is less stringent at longer wavelengths.
When considering the possibility of effecting holography at the longer wavelengths, the inventors encountered the problem of the lack of an acceptable recording medium. Because of the low energy of inrared photons, photographic emulsions cannot be used.
Even if a plate using a photographic emulsion for infrared holo-graphy was available, it would be necessary to store the plate at a very low temperature, since the plate would be exposed eve~ in the dark by blackbody radiation at room temperature.
' .
; ~ 1 !
` li31950 The object of the present invention is to overcome the problems that would be encountered in infrared holography using presently available media by providing a holographic method and a readily available medium for use in such method.
Accordingly, the present invention relates to a method of recording a hologram at a wavelength in the infrared region comprising dividing a beam having a suitable wavelength; and causing the resulting two beams to interfere on a thin oil film on a plate, and reconstructing the hologram in Real-time using wavelengths in visible spectrum.
The invention also relates to a device for recording an infrared hologram comprising a plate; a thin film of oil on said plate, and means for reconstructing the hologram in Real-time using wavelengths in the visible spectrum.
The invention will now be described in greater detail with reference to the accompanying drawing, the single figure of which is a schematic block diagram of an experimental device for carrying out the method of the present invention.
With reference to the drawing, a hologram is recorded using an apparatus which includes a CO2 laser 1 stabilized in the fundamental mode. A beam 2 from the laser 1 passes through a shutter 3 in the direction of arrow 4. The beam is divided in two using a beamsplitter 5. The beamsplitter 5 divides the beam 2 in such manner that the two resulting beams 6 and 7 have approximately the same power. Using a mirror 8, the beams 6 and 7 are caused to travel in the direction of arrows 9 and 10, re-spectively, and are made to interfere on a thin film of oil on a surface 11 of a plate, in this case a glass plate 12. When the plane of the glass plate is such that the two beams 6 and 7 sustend the same angle 0 with the normal of the plate, the hologram obtained is a series of straight, parallel interference fringes spaced apart by ~/2 sin ~. The hologram of an actual object (which is not shown) is obtained by placing the ob~ect in the object beam 7.
As the hologram is recorded, the reconstruction is achieved in Real-time by shining a He-Ne (or argon) laser beam 13 from laser 14 through the oil on the plate 12 in the direction of arrows 15. A l~ns 16 (which is optional) and a spatial filter (not shown) are used to separate the +l order of diffraction from the O and the -1 order. In any event, the reconstruction can be recorded on a magnetoscopic tape using a vidicon camera (not shown) and, at the same time, the response time of the oil film can be studied by means of a photodiode detector.
When preparing the plate 12, the surface 11 of the plate is painted with oil to a thickness of approximately 100 ~m.
For better results, a 10 ,um thick oil film is evaporated on the surface of the glass plate 12. With both methods, the oil film is ready only after being exposed for a few seconds to the CO2 laser radiation which reduces the thickness of the oil to approx-imately 1 ,um. If the CO2 laser beam is then stopped, there is ~ .
no degradation in the quality of the oil surface even though the plate 12 is held in the vertical position, i.e. with the oil coated surface 11 in a vertical plane. By causing the beams 6 and 7 to interfere at this time and by a thermal effect, a surface modu-lation of the oil film occurs, giving a phase hologram. Of course, many factors must be considered when attempting to explain the process. However, since at a wavelength of 10 ~m the absorption of a thin oil film is negligible and since the glass has a very high absorption coefficient, it is reasonable to state that first the plate is heated and then the heat is transferred to the oil by conduction, the second phenomenon probably being the factor ' , 1131950 ~
that limits the response time of the oil. The response time is the time for the diffraction efficiency at reconstruction to increase from 10 to 90% of its maximum value.
It has been found that the incident power on the oil film and the duty time of the oil are interrelated (duty time being the time interval between the beginning of reconstruction and the time at which the diffraction efficiency has fallen to 10%
of its maximum value). If the average power density is kept below 0.5Wjcm , the dutv time is very long. At such low energy densi-~10 ties, the diffraction efficiency is low and it is preferable towork in a chopped mode with higher peak power which gives both a high diffraction efficiency and a long duty time.
With respect to linearity, the oil film presents a good linearity for irradiances below 10 milijoules per square centimeter.
For irradiances higher than 10 mJ/cm2, higher diffraction orders become clearly visible. It has been found that the irradiance necessary to record a hologram is of the order of 10 mJ/cm , which is at least one order of magnitude lower than previously known ~j mediums.
~20 ~ ~ It has been found that any thickness of oil below 1.2 ~m remains adequate for recording a hologram even if the infrared irradiance is stopped. M~reover, if the power density afterwards remains below O.5W/cm2, the oil thickness will remain the same as well as the response time. A plot of the ratio of diffraction efficiency to response tlme versus oil thickness shows that the curve levels off above 1 ~m. At the same time, the diffraction efficiency goes down and stays constant for the same thickness.
The optimum thickness is found to be from 0.9 to 1.2 ~m, the diff-raction efficiency is approximately 5~ and the response time of ; 30 the order of 10 ms. Such an experimental condition is obtained "
j - 4 -1131950 `
using an irradiance of 12 mJ/cm2. For such conditions, the spatial resolution is approximately 20 cycles/mm. At the expense of diff-raction efficiency, the spatial resolution can go as high as 50 cycles/mm.
As mentioned hereinbefore, the oil film medium can be used and indeed has been used in recording holograms and imaging, in Schlieren analysis and in interferometry. The medium has been found (i) to meet the requirements of an adequate recording med-ium at 10.6 pm, (ii) to have good sensitivity and (iii) to respond rapidly. The recording is not permanent so that Real-time holo-graphy and reconstruction in the visible spectrum can be performed.
The medium has reasonably good resolution and is inexpensive. The best oils have been found to be Volt-Esso-35 (a trade mark for transformer oil) and/or any silicon oil. Any pure mineral oil is acceptalbe. For some unknown reason, the vegetable oils used did not function properly.
~ , , ',~ .
Claims (10)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method of recording a hologram at a wavelength in the infrared region comprising dividing a beam having a suitable wave-length; and causing the resulting two beams to interfere on a thin oil film on a plate; and reconstructing the hologram in Real-time using wavelengths in the visible spectrum.
2. A method according to claim 1, wherein said oil film is from 0.1-to 1.2 µm thick.
3. A method according to claim 1, wherein said oil film is from 0.9 to 1.2 µm thick.
4. A method according to claim 1, 2 or 3, wherein the hologram is recorded at a wavelength of approximately 10.6 µm using said oil film on a glass plate.
5. A method according to claim 1, 2 or 3, wherein said beam is a CO2 laser beam, and the hologram is recorded at a wavelength of approximately 10.6 µm using said oil film on a glass plate.
6. A device for recording an infrared hologram comprising a plate; a thin film of oil spread over at least part of one surface of said plate; and means for reconstructing the hologram in Real-time using wavelengths in the visible spectrum.
7. A device according to claim 6, wherein said film has a thickness of 0.1 to 12. µm.
8. A device according to claim 6, wherein said film has a thickness of 0.9 to 1.2 µm.
9. A device according to claim 6, 7 or 8, wherein said plate is a glass plate.
10. A device according to claim 6, 7 or 8, wherein said oil is a mineral oil.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA364,600A CA1131950A (en) | 1980-11-13 | 1980-11-13 | Method and device for real-time infrared holography |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA364,600A CA1131950A (en) | 1980-11-13 | 1980-11-13 | Method and device for real-time infrared holography |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1131950A true CA1131950A (en) | 1982-09-21 |
Family
ID=4118439
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA364,600A Expired CA1131950A (en) | 1980-11-13 | 1980-11-13 | Method and device for real-time infrared holography |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1131950A (en) |
-
1980
- 1980-11-13 CA CA364,600A patent/CA1131950A/en not_active Expired
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |