CA1090630A - Plastic recording media for holography - Google Patents
Plastic recording media for holographyInfo
- Publication number
- CA1090630A CA1090630A CA316,939A CA316939A CA1090630A CA 1090630 A CA1090630 A CA 1090630A CA 316939 A CA316939 A CA 316939A CA 1090630 A CA1090630 A CA 1090630A
- Authority
- CA
- Canada
- Prior art keywords
- medium
- recording
- transparent plastic
- wavelength
- hologram
- 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
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
- B41M—PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
- B41M5/00—Duplicating or marking methods; Sheet materials for use therein
- B41M5/26—Thermography ; Marking by high energetic means, e.g. laser otherwise than by burning, and characterised by the material used
- B41M5/36—Thermography ; Marking by high energetic means, e.g. laser otherwise than by burning, and characterised by the material used using a polymeric layer, which may be particulate and which is deformed or structurally changed with modification of its' properties, e.g. of its' optical hydrophobic-hydrophilic, solubility or permeability properties
Landscapes
- Physics & Mathematics (AREA)
- Optics & Photonics (AREA)
- Holo Graphy (AREA)
Abstract
Abstract of the Disclosure The invention disclosed relates to an improved recording media for use in recording holograms in the IR region at wavelengths of about 10.6 µm i.e. the wavelength of a CO2 laser. The improved recording medium is a trans-parent plastic medium having high light absorption at that wavelength, selected from the group consisting of polyvinylidene chloride resins and acrylic resins.
Description
lO9U~30 This invention relates to recording media, and in particular to recording media suitable for holography at wavelengths comparable to the 10.6 ~m of a CO2 laser.
Numerous applications of holography using wavelengths in the visible spectrum have been published in recent years. In some cases, the potential advantages of using longer wavelengths, such as the 10.6-~m beam of a CO2 laser, justify the search for a good recording medium at these wavelengths.
Among applications of holography at a wavelength of 10.6 pm, one can expect a considerable increase of sensitivity in plasma diagnostic by interferometry, as compared to the techniques used presently. On the other hand, the use of such a long wavelength in the interferometric study of solids and their surfaces will allow the observation of much larger displacements or deforma-tions in comparison to similar experiments in the visible spectrum.
This search for recording media in the IR region at 10.6 pm has given rise to many experiments with thermochromic materials, liquid crystals, bismuth films, wax gelatins, etc.
Further~ certain transparent thin plastic films, in partlcular, those whose trade ~ark~ are Saran Wrap manufactured by the Dow Chemical Company and Stretch'n Seal manufactured by the Colgate Palmolive Company, have been investigated by D.T. Rampton and R.W. Grow, Appl. Opt. 15, 1034 (1976), for use as IR polarizers by vlrtue of their good light transmlssion at wavelengths of the order of 10.6 um.
According to one aspect of the invention, an improved method for recording a hologram on a recording medium at a wave length in the IR region at about 10.6 ~m is contemplated, the improvement comprising employing as recording medium a transparent plastic medium having high light absorption at said wavelengthO
According to another aspect of the invention a medium for recording a hologram at a wavelength in the IR region at about 10.6 ~m, and re-con-structing the recorded image by reflection, in the IR region, is contemplated, the medium comprising a transparent plastic medium having hi8h light absorption at said wavelength and a thin coating of silver deposited on at least one ma~or surface of said transparent plastic medium.
1090~i30 In the drawings which serve to illustrate embodiments of the inventlon, Figure 1 is a schematic illustration of the experimental arrange-ment for recording a hologram on a recording medium according to the inven-tion, and Figure 2 is a graph illustrating the diffraction efficiency at 632.8-nm of various recording media according to the invention. The holograms were produced by a 10.6 ~m laser beam on (a) a 603 mm thick acrylic sheet and ~b) a 8aran Wrap film, and Figure 3 is a graph illustrating diffraction efficiency with a 632.8-nm reconstructing beam reflected on the surface of an exposed Saran Wrap film. Circles represent reconstruction from the side opposite to that of the recording, while squares represent reconstruction from the recording side.
Referring to the drawings, in Figure 1 the experimental arrangement is seen to include an IR light source of a wave length of about 10.6 ~ , conveniently a stab~lized single mode continuous wave C02 laser, operating at a power output of 1 watt which produces a polarized laser beam of a wavelength of about 10.6 ~m and yielding incident intensities up to about 3.5 w/cm20 The incident laser beam was projected on the novel recording medium 1 through a conventional shutter 2 and then through a 50/50 germanium beam splitter 3. Any incident radiation reflected by the beam splitter 1 is directed to the recording medium 1 by a mirror 40 The recorded hologram thus comprises straight parallel fringes typical of the interference of two plane waves.
Simultaneous re-construction of the hologram in the visible spectrum may be achieved with a light source of a wavelength of about 632.8-nm, typically, a Helium-Neon laser. The reconstruction of 63208-nm is obtained by transmission through the hologram, i.eO in the direction opposite to the incident laser beams, the resulting waves being totally reflected at the germanium beam splitter toward the photographic plates 5, where visual
Numerous applications of holography using wavelengths in the visible spectrum have been published in recent years. In some cases, the potential advantages of using longer wavelengths, such as the 10.6-~m beam of a CO2 laser, justify the search for a good recording medium at these wavelengths.
Among applications of holography at a wavelength of 10.6 pm, one can expect a considerable increase of sensitivity in plasma diagnostic by interferometry, as compared to the techniques used presently. On the other hand, the use of such a long wavelength in the interferometric study of solids and their surfaces will allow the observation of much larger displacements or deforma-tions in comparison to similar experiments in the visible spectrum.
This search for recording media in the IR region at 10.6 pm has given rise to many experiments with thermochromic materials, liquid crystals, bismuth films, wax gelatins, etc.
Further~ certain transparent thin plastic films, in partlcular, those whose trade ~ark~ are Saran Wrap manufactured by the Dow Chemical Company and Stretch'n Seal manufactured by the Colgate Palmolive Company, have been investigated by D.T. Rampton and R.W. Grow, Appl. Opt. 15, 1034 (1976), for use as IR polarizers by vlrtue of their good light transmlssion at wavelengths of the order of 10.6 um.
According to one aspect of the invention, an improved method for recording a hologram on a recording medium at a wave length in the IR region at about 10.6 ~m is contemplated, the improvement comprising employing as recording medium a transparent plastic medium having high light absorption at said wavelengthO
According to another aspect of the invention a medium for recording a hologram at a wavelength in the IR region at about 10.6 ~m, and re-con-structing the recorded image by reflection, in the IR region, is contemplated, the medium comprising a transparent plastic medium having hi8h light absorption at said wavelength and a thin coating of silver deposited on at least one ma~or surface of said transparent plastic medium.
1090~i30 In the drawings which serve to illustrate embodiments of the inventlon, Figure 1 is a schematic illustration of the experimental arrange-ment for recording a hologram on a recording medium according to the inven-tion, and Figure 2 is a graph illustrating the diffraction efficiency at 632.8-nm of various recording media according to the invention. The holograms were produced by a 10.6 ~m laser beam on (a) a 603 mm thick acrylic sheet and ~b) a 8aran Wrap film, and Figure 3 is a graph illustrating diffraction efficiency with a 632.8-nm reconstructing beam reflected on the surface of an exposed Saran Wrap film. Circles represent reconstruction from the side opposite to that of the recording, while squares represent reconstruction from the recording side.
Referring to the drawings, in Figure 1 the experimental arrangement is seen to include an IR light source of a wave length of about 10.6 ~ , conveniently a stab~lized single mode continuous wave C02 laser, operating at a power output of 1 watt which produces a polarized laser beam of a wavelength of about 10.6 ~m and yielding incident intensities up to about 3.5 w/cm20 The incident laser beam was projected on the novel recording medium 1 through a conventional shutter 2 and then through a 50/50 germanium beam splitter 3. Any incident radiation reflected by the beam splitter 1 is directed to the recording medium 1 by a mirror 40 The recorded hologram thus comprises straight parallel fringes typical of the interference of two plane waves.
Simultaneous re-construction of the hologram in the visible spectrum may be achieved with a light source of a wavelength of about 632.8-nm, typically, a Helium-Neon laser. The reconstruction of 63208-nm is obtained by transmission through the hologram, i.eO in the direction opposite to the incident laser beams, the resulting waves being totally reflected at the germanium beam splitter toward the photographic plates 5, where visual
- 2 -lO~t)~30 observation on a white sCreen i8 also possible.
Holographic reconstruction in the IR region i.e. at about 10.6 pm was also made possible by vacuum-depositing a 50-nm layer of silver on at least the front major surface of the recordlng medium after recording the hologramO
In the latter case, the hologram which is pre-recorded on the recording medium i8 then illuminated with a laser beam of wavelength of 10.6 pm to obtain an image by reflection in the infrared.
In order to measure the intensity of the holographic images reconstructed in the infrared by reflection using the latter method, the reflected beam is chopped and its intensity measured with a Molectron P~3 detector (not shown) located at the position of the re-constructed image.
"Chopping" is a technical term meaning that the laser beam is shut periodi-cally with a shutter. The measured reflectivity of the silver coating is lO~h at 10.6 pm and more than 9~Z at 63208 nmO
Various transparent plastic materials were investigated including those known by the trade name Saran Wrap which is a polyvinylidene chloride resin film and Stretch'n Seal, as well as a thick acrylic resin plate of a thickness of about 2-7 mmO e.gO a 603 mm (1/4 inch) thick Plexiglas plateO
20 Plexiglas is a trademark Bor thermoplastic poly(methyl methacrylate)-type polymers. These materials are characterized especially by their low price, by their ease of use, by the absence of need for development (as with emul-sions currently used in the visible spectrum), and consequently by their potential advantages for application to real-time holography.
It was found that absorption at 1006 ~m is nearly 1007o for the acrylic material~ Saran Wrap and Stretch'n Seal have a measured transmission of respectively, 7~h and 6~/oo After a few experiments, Stretch'n Seal films showed a surface optically improper for the purpose at hand, and this material was thus eliminated from our study.
Holographic reconstruction in the IR region i.e. at about 10.6 pm was also made possible by vacuum-depositing a 50-nm layer of silver on at least the front major surface of the recordlng medium after recording the hologramO
In the latter case, the hologram which is pre-recorded on the recording medium i8 then illuminated with a laser beam of wavelength of 10.6 pm to obtain an image by reflection in the infrared.
In order to measure the intensity of the holographic images reconstructed in the infrared by reflection using the latter method, the reflected beam is chopped and its intensity measured with a Molectron P~3 detector (not shown) located at the position of the re-constructed image.
"Chopping" is a technical term meaning that the laser beam is shut periodi-cally with a shutter. The measured reflectivity of the silver coating is lO~h at 10.6 pm and more than 9~Z at 63208 nmO
Various transparent plastic materials were investigated including those known by the trade name Saran Wrap which is a polyvinylidene chloride resin film and Stretch'n Seal, as well as a thick acrylic resin plate of a thickness of about 2-7 mmO e.gO a 603 mm (1/4 inch) thick Plexiglas plateO
20 Plexiglas is a trademark Bor thermoplastic poly(methyl methacrylate)-type polymers. These materials are characterized especially by their low price, by their ease of use, by the absence of need for development (as with emul-sions currently used in the visible spectrum), and consequently by their potential advantages for application to real-time holography.
It was found that absorption at 1006 ~m is nearly 1007o for the acrylic material~ Saran Wrap and Stretch'n Seal have a measured transmission of respectively, 7~h and 6~/oo After a few experiments, Stretch'n Seal films showed a surface optically improper for the purpose at hand, and this material was thus eliminated from our study.
- 3 -lU90~;3U
Table I. Effect of Exposure Time on Clear Acrylic Incident Exposure IR time lnten~ity (sec) (W/cm ) Remarks 3.5 2.2 Holographic recording threshold 3.5 2.2-402 Increase in diffraction efficiency; the recording is permanent after the shutter is closed 305 4.2 Deterioration of the recording begins 3.5 . 6.5 Holographic reconstruction disappears: the deterioration is complete Table II. Effect of Exposure Time on Saran Wrap Incident IR Exposure intensity time (W/cm2) (sec) Remarks 1.75 0.9 Holographic recording threshold 1.75 0.9-5 Diffraction efficiency increases up to a constant level 1.75 5-300 Diffraction efficiency remains constant The observations made are presented in three group~ of equal importance to the end-usersO These groups are the recording energy density, the linearity of recording, and the diffraction effeciency at reconstruction.
Energy Density at Recording i~
, The energy density is defined as the product of the exposure time by the power incident on themmedium per unit surface. Tables I and II
summarize the observations on the time behavion of t~e medium when exposed to a continuous IR laser beam interference in terms of the behavior of the real-time holographic reconstruction at 632.8 nm.
Table 1 indicates that for acrylic the initial exposure of 202 sec can be interpreted as the time required to provide the necessary energy to soften the surface material enough for a permanent deformation to occur. With more energy (exposure time greater than 4.2 sec), melting and/or heat conduc-tion probably is the agent that destroys the recordingO It is interesting to note that an exposure t~me between 2.2 sec and 4.2 sec, that is, an energy density between 8 ~/cm2 and 14 J/cm2, will allow a permanent recording 105~0~;30 of the hologram on the scrylic surface.
The case of thin plastic films, as reported in Table 1l, is some-what different: even with lower absorption at 10~6 ~m, recording is made with much lower incident energy. The threshold energy for holographic recor-ding on these films is about four times lower than on acrylic. Moreover, no deterioration of the recording was observed even for a very long exposure time. This behavior suggests that after a period of 5 sec, the film temper-ature stabilizes as a result of an equilibrium between the energy input and the heat exchange by conduction through the plastic and to the surrounding atmosphere.
Linearity of the Recording We have chosen to characterize a good linearity of the recording by a high ratio of the intensity of the reconstructed first order image to that of the higher orders.
A typical reconstruction at 632~8 nm showed that the recording on acrylic cannot be characterized as linear since the intensity of the second order reconstruction is appreciable. Experimental measurements of the intensity in both orders give l~/o for the first order and 27/o for the second order. However, it was found that the recording on saran films has a better 20 linearity since there are no apparent high order images: less than Q.0570 of the intensity is diffracted in thessedond order as compared to 4% in the first order.
Diffraction Efficiency The diffraction efficiency at reconstruction is defined as the ratio of the intensity of reconstructed first order image to that of the incident reconstructing beam. Measurements of the diffraction efficiency transmission with a wavelength of 632~8 nm are shown in Figo 2~ We observe a maximum efficiency of ~2~h for acrylic LFig. 2(a~ and of~ 4.5% for plastic films rFig. 2(b~ : these values are compared tentatively to the value 30 of 33~/o suggested in the literature for a sinusoidal phase grating. The maxim~m diffraction efficiency measured when using a wavelength of 10.6 ~rn reflected from the silver-coated suri!ace of the hologram is ~0.5% for acrylic and lower than our detection means (~0.17~ for the saran filmsO The important lO90~j30 discrepancy between the two wavelength measurements is attributed to the lower phase shift induced by the same hologram on longer wavelengths, this phase shift depending on the ratio of the depth of the recording to the wavelength.
After having recorded a hologram on a sample of Saran Wrap film which was subsequently coated on both sides with silicon, it is observed that holographic reconstruction at 63208 nm occurs on each surface, as shown by the values of diffraction efficiencies in Figure 30 This observation indicates that the deformation of the plastic film does not seem to occur on the surface only but through its whole thicknessO
The low diffraction efficiencies observed at 1006 pm, both for silver coated acrylic and for silver coated saran films, are attributed to thermal conduction and/or melting which prevent obtaining a deep enough surface modulation pattern. It is thus proposed that a pulsed C02 laser instead of the cw laser be used to eliminate the conduction effects. The number of pulses (at low repetition rates) may then become the determining `~`
factor in obtaining the deformation magnitude that corresponds to the maximum diffraction efficiency.
It will be appreciated by those skilled in the art that the inven-tion has been described in terms of specific embodiments thereof and that -;
modifications and variations will be apparent, without departing from the spirit or central characteristics of the invention, and that such embodiments are to be considered as illustrative and by no means restrictiveO
Table I. Effect of Exposure Time on Clear Acrylic Incident Exposure IR time lnten~ity (sec) (W/cm ) Remarks 3.5 2.2 Holographic recording threshold 3.5 2.2-402 Increase in diffraction efficiency; the recording is permanent after the shutter is closed 305 4.2 Deterioration of the recording begins 3.5 . 6.5 Holographic reconstruction disappears: the deterioration is complete Table II. Effect of Exposure Time on Saran Wrap Incident IR Exposure intensity time (W/cm2) (sec) Remarks 1.75 0.9 Holographic recording threshold 1.75 0.9-5 Diffraction efficiency increases up to a constant level 1.75 5-300 Diffraction efficiency remains constant The observations made are presented in three group~ of equal importance to the end-usersO These groups are the recording energy density, the linearity of recording, and the diffraction effeciency at reconstruction.
Energy Density at Recording i~
, The energy density is defined as the product of the exposure time by the power incident on themmedium per unit surface. Tables I and II
summarize the observations on the time behavion of t~e medium when exposed to a continuous IR laser beam interference in terms of the behavior of the real-time holographic reconstruction at 632.8 nm.
Table 1 indicates that for acrylic the initial exposure of 202 sec can be interpreted as the time required to provide the necessary energy to soften the surface material enough for a permanent deformation to occur. With more energy (exposure time greater than 4.2 sec), melting and/or heat conduc-tion probably is the agent that destroys the recordingO It is interesting to note that an exposure t~me between 2.2 sec and 4.2 sec, that is, an energy density between 8 ~/cm2 and 14 J/cm2, will allow a permanent recording 105~0~;30 of the hologram on the scrylic surface.
The case of thin plastic films, as reported in Table 1l, is some-what different: even with lower absorption at 10~6 ~m, recording is made with much lower incident energy. The threshold energy for holographic recor-ding on these films is about four times lower than on acrylic. Moreover, no deterioration of the recording was observed even for a very long exposure time. This behavior suggests that after a period of 5 sec, the film temper-ature stabilizes as a result of an equilibrium between the energy input and the heat exchange by conduction through the plastic and to the surrounding atmosphere.
Linearity of the Recording We have chosen to characterize a good linearity of the recording by a high ratio of the intensity of the reconstructed first order image to that of the higher orders.
A typical reconstruction at 632~8 nm showed that the recording on acrylic cannot be characterized as linear since the intensity of the second order reconstruction is appreciable. Experimental measurements of the intensity in both orders give l~/o for the first order and 27/o for the second order. However, it was found that the recording on saran films has a better 20 linearity since there are no apparent high order images: less than Q.0570 of the intensity is diffracted in thessedond order as compared to 4% in the first order.
Diffraction Efficiency The diffraction efficiency at reconstruction is defined as the ratio of the intensity of reconstructed first order image to that of the incident reconstructing beam. Measurements of the diffraction efficiency transmission with a wavelength of 632~8 nm are shown in Figo 2~ We observe a maximum efficiency of ~2~h for acrylic LFig. 2(a~ and of~ 4.5% for plastic films rFig. 2(b~ : these values are compared tentatively to the value 30 of 33~/o suggested in the literature for a sinusoidal phase grating. The maxim~m diffraction efficiency measured when using a wavelength of 10.6 ~rn reflected from the silver-coated suri!ace of the hologram is ~0.5% for acrylic and lower than our detection means (~0.17~ for the saran filmsO The important lO90~j30 discrepancy between the two wavelength measurements is attributed to the lower phase shift induced by the same hologram on longer wavelengths, this phase shift depending on the ratio of the depth of the recording to the wavelength.
After having recorded a hologram on a sample of Saran Wrap film which was subsequently coated on both sides with silicon, it is observed that holographic reconstruction at 63208 nm occurs on each surface, as shown by the values of diffraction efficiencies in Figure 30 This observation indicates that the deformation of the plastic film does not seem to occur on the surface only but through its whole thicknessO
The low diffraction efficiencies observed at 1006 pm, both for silver coated acrylic and for silver coated saran films, are attributed to thermal conduction and/or melting which prevent obtaining a deep enough surface modulation pattern. It is thus proposed that a pulsed C02 laser instead of the cw laser be used to eliminate the conduction effects. The number of pulses (at low repetition rates) may then become the determining `~`
factor in obtaining the deformation magnitude that corresponds to the maximum diffraction efficiency.
It will be appreciated by those skilled in the art that the inven-tion has been described in terms of specific embodiments thereof and that -;
modifications and variations will be apparent, without departing from the spirit or central characteristics of the invention, and that such embodiments are to be considered as illustrative and by no means restrictiveO
Claims (14)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In a method for recording a hologram on a recording medium at a wavelength in the IR region at about 10.6 µm, the improvement comprising employing as recording medium a transparent plastic medium having high light absorption at said wavelength, selected from the group consisting of acrylic resin and polyvinylidene chloride resins.
2. A method according to claim 1, wherein said hologram is recorded onto the recording medium using a laser beam.
3. A method according to claim 2, wherein the laser is a continuous wave CO2 laser beam.
4. A method according to claim 3, wherein the power output of the CO2 laser is 1 watt.
5. A method according to claim 4, wherein said transparent plastic medium is an acrylic sheet of thickness of about 2-7 mm.
6. A method according to claim 4, wherein said transparent plastic medium is thin polyvinylidene chloride film.
7. A method according to claim 5, wherein the exposure time is about 2.2 to 4.2 seconds.
8. A method according to claim 6, wherein the exposure time is about 0.9 to 5 seconds.
9. A method according to claim 1, 7 or 8, wherein the holographic image is simultaneously re-constructed in the visible spectrum at about 63208 nm by projecting an He-Ne laser beam through the transparent recording medium in the opposite direction to the incident projected image.
10. A method according to claim 1, 7 or 8, wherein a thin coating of silver is deposited on at least the front major surface of the transparent plastic recording medium, and wherein the holographic image is reconstructed in the infrared region by reflecting the incident laser beam at about 10.6 microns, off the silver coating.
11. A medium for recording a hologram at a wavelength in the infrared region at about 10.6 µm, and reconstructing the recorded holographic image by reflection, in the infrared region, comprising a transparent plastic medium having high light absorption at said wavelength, selected from the group consisting of acrylic resin and polyvinylidene chloride resins, and a thin coating of silver deposited on at least one major surface of said trans-parent plastic medium.
12. A medium according to claim 11, wherein said transparent plastic medium is acrylic sheet of a thickness of about 2-7 mm.
13. A medium according to claim 11, wherein said transparent plastic medium is thin polyvinylidene chloride film.
14. A medium according to claim 11, 12 or 13, wherein the thickness of the silver coating is about 50 nm.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA316,939A CA1090630A (en) | 1978-11-27 | 1978-11-27 | Plastic recording media for holography |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA316,939A CA1090630A (en) | 1978-11-27 | 1978-11-27 | Plastic recording media for holography |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1090630A true CA1090630A (en) | 1980-12-02 |
Family
ID=4113027
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA316,939A Expired CA1090630A (en) | 1978-11-27 | 1978-11-27 | Plastic recording media for holography |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1090630A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5208123A (en) * | 1989-05-18 | 1993-05-04 | Pilkington P.E. Limited | Hologram construction |
-
1978
- 1978-11-27 CA CA316,939A patent/CA1090630A/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5208123A (en) * | 1989-05-18 | 1993-05-04 | Pilkington P.E. Limited | Hologram construction |
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