Noncontact optical measurement methods are essential tools in many industrial and research domains. A family of new noncontact optical measurement methods based on the polarization states splitting technique and monochromatic light projection as a way to overcome ambient lighting for in-situ measurement has been developed. Recent works on a birefringent element, a Savart plate, allow one to build a more flexible and robust interferometer. This interferometer is a multipurpose metrological device. On one hand the interferometer can be set in front of a charge-coupled device (CCD) camera. This optical measurement system is called a shearography interferometer and allows one to measure microdisplacements between two states of the studied object under coherent lighting. On the other hand, by producing and shifting multiple sinusoidal Young’s interference patterns with this interferometer, and using a CCD camera, it is possible to build a three-dimensional structured light profilometer.
A profilometer which takes advantage of polarization states splitting technique and monochromatic light projection
method as a way to overcome ambient lighting for in-situ measurement is under development [1, 2]. Because of the
Savart plate which refracts two out of axis beams, the device suffers from aberrations (mostly coma and astigmatism).
These aberrations affect the quality of the sinusoidal fringe pattern. In fringe projection profilometry, the unwrapped
phase distribution map contains the sum of the object's shape-related phase and carrier-fringe-related phase. In order to
extract the 3D shape of the object, the carrier phase has to be removed [3, 4]. An easy way to remove both the fringe
carrier and the aberrations of the optical system is to measure the phases of the test object and to measure the phase of a
reference plane with the same set up and to subtract both phase maps. This time consuming technique is suitable for
laboratory but not for industry. We propose a method to numerically remove both the fringe carrier and the aberrations.
A first reference phase of a calibration plane is evaluated knowing the position of the different elements in the set up and
the orientation of the fringes. Then a fitting of the phase map by Zernike polynomials is computed [5]. As the
triangulation parameters are known during the calibration, the computation of Zernike coefficients has only to be made
once. The wavefront error can be adjusted by a scale factor which depends on the position of the test object.
Shearography is an interferometric technique suitable for detecting defects because they yield singular fringes and high phase values in wrapped and unwrapped phasemaps, respectively. We propose a methodology that leads to the defect size from unwrapped phasemap by extracting the size of the high phase values area. The area size is evaluated, thanks to a wavelet transform algorithm that enables the location of its borders. The performances of the methodology and of the algorithm have been tested by applying them on a defect where the size is known. An error less than 1.5% root mean square was reached. Our approach is independent of the shearing amount and of the phase profile, and it can be extended for other interferometric techniques.
Non-contact optical measurement methods are essential tools in many industrial and research domains. A family of new
non-contact optical measurement methods based on the polarization states splitting technique and monochromatic light
projection as a way to overcome ambient lighting for in-situ measurement has been developed1,2. Recent works3 on a
birefringent element, a Savart plate, allow to build a more flexible and robust interferometer. This interferometer is a
multipurpose metrological device. On one hand, the interferometer can be set in front of a CCD camera. This optical
measurement system is called a shearography interferometer and allows to measure micro displacement between two
states of the studied object under coherent lighting. On the other hand, by producing and shifting multiple sinusoidal
Young's interference patterns with this interferometer, and using a CCD camera, it is possible to build a 3D structured
light profilometer. After giving the behavior of the Savart plate, an overview of the two devices will be given as well as
their specifications and some applications.
We studied scars and wounds depths and surfaces thanks to our interferometric fringes projector 3D scanner1, 2. Color
information of a wound indicates its deterioration level. That's why the visual color restitution, as realistic as possible, is
a highly important parameter. Firstly our acquired 3D pictures were color mapped with an image recorded by a RGB
camera. The results were not efficient enough. In order to improve our technique and provide more precise information,
we add a spectral characterization to the set-up. Before adding the spectral information and a realistic color mapping to
the 3D measurements, we evaluate the performances of colorimetric measurements. The tests have been made on mice
with scars on their back.
Shearography is a growing optical technique in the field of non-destructive testing (NDT)[1],[2]. Hololab developed an
out of plane, in line and almost common path interferometer based on polarization states separation using a coated prism
for digital phase-shifting shearography[3]. This setup is efficient but does not allow varying the shearing direction that is
an important parameter for defects detection[1]and quantification[2].
To overcome this disadvantage, the coated prism is substituted by a Savart plate device that allows scanning several
shearing directions by rotating the device around the light propagation axis. The behaviour of the Savart plate as a
shearing device is experimentally analyzed to optimize its integration within the interferometer. Recorded phasemaps in
NDT for different shearing directions are presented.
This paper describes a new concept related to the micromechanical sensors for detecting the presence and concentration of chemical substances and/or biological organisms. We believe that this concept allow for a low cost and ease of fabrication of a large bi-dimensional array of sensors with an enhanced signal-to-noise ratio. A bi-dimensional array of micro-cantilever coated with different types of sensing layer enables to identify a characteristic chemical composition of the gas in real-time mode. The selective molecular absorption by cantilever sensing layer will produce cantilever bending proportional to the concentration of molecules. To increase the gas sensor sensitivity, the SPR phenomenon is used for cantilever deflection monitoring.
This paper describes a new concept related to the bolometric micromechanical sensors for detecting far IR and THz radiation. We believe that this concept permits a low cost and ease of fabrication of large bi-dimensional array of sensors with an enhanced signal-to-noise ratio. The micromechanical sensor comprises a thermo-sensitive bi-material (multi-material) micro-cantilever beam with a selective absorber dedicated to far IR and THz radiation energy, and optical readout system based on surface plasmon resonance for detecting the bending of the micro-cantilever element. To increase the radiation detector sensitivity, the SPR phenomenon is used for cantilever deflection monitoring.
The direct simultaneous acquisition of coherent imaging and strain information is of particular importance in the biomechanical characterization of biological tissue. This type of simultaneous information acquisition can be accomplished using a coupled photorefractive holography and shearography system for imaging and strain measurements, respectively. Optical scattering in a conventional speckle shearing interferometer rapidly reduces the contrast of the shearing fringes, thereby limiting the use of such interferometers with opaque surfaces. By coupling photorefractive holography with speckle shearing interferometry, properties of the photorefractive effect (spatial high-pass filtering and temporal low-pass filtering) combine to restore the shearing fringe contrast and enable strain imaging in diffusing media. This effect is demonstrated using synthetic scattering phantoms built from suspensions of silica spheres in water.
An original experimental setup for shearography with metrological applications is presented. The simplicity and the efficiency of the setup are provided by a shearing device, a prism that separates the TE and TM polarization modes with a coating and a thin glass plate placed on its face. The use of this shearing device enables an in-line and almost-common path configuration for the shearing interferometer, a path that leads to high stability and a low sensitivity to external disturbances. Moreover, the sensitivity of the interferometer can be easily adjusted for different applications by varying the shearing amount with glass plates of different thicknesses or by moving the shearing device between two lenses along the optical axis. The temporal phase-shifting method is applied through the use of a liquid crystal variable retarder.
An original experimental setup for shearography with metrological applications is presented herein. The
simplicity and the efficiency of the setup are provided by a shearing device, a prism that separates the TE and TM
polarization modes with a coating and a thin glass plate attached on its face. The use of this shearing device enables an
in-line and almost-common path configuration for the shearing interferometer, a path that leads to high stability of the
interferometer and a low sensitivity to external disturbances. Moreover the sensitivity of the interferometer can be easily
adjusted for different applications. The temporal phase shifting method is applied through the use of a liquid crystal
variable retarder.
An original experimental setup for shearography with metrological applications is presented herein. The
simplicity and the efficiency of the setup are provided by a shearing device, a prism that separates the TE and TM
polarization modes with a coating and a thin glass plate attached on its face. The temporal phase shifting method is
applied through the use of a liquid crystal variable retarder. The use of this shearing device enables an in-line and almostcommon
path configuration for the shearing interferometer, a path that leads to high stability of the interferometer and a
low sensitivity to external disturbances. In order to prove the efficiency and the accuracy of this speckle shearing
interferometer, the out-of-plane displacement derivative relative to the shearing interferometry direction of a centrally
loaded steel plate has been measured by the shearographic interferometer and then compared with the out-of-plane
displacement derivative computed from the displacement field provided by the finite element method. The results are in
good agreement.
The goal of this work is to develop a simple and systematic method to highlight the properties of filters for their application in temporal phase shifting interferometry. In this study, the effects of elementary filters (mean, gaussian and median masks) are analyzed. In order to compare those filters, correlation fringes were numerically synthesized and a Gaussian noise has been added. The advantages and the failures of each studied filtering mask have been enhanced thanks to the comparison of different profiles and fidelity functions. Finally, this study is applied to the filtering of a shearogram recorded in our laboratory.
We present a new 3D full-frame profilometer based on structured laser light projection method. This device takes advantage of the polarization states splitting technique for producing and shifting multiple sinusoidal Young's interference patterns that are projected on the inspected surface. The principle of the technique is presented and we discuss the advantages of monochromatic light projection method as a mean to overcome ambient lighting for in-situ measurement. Some results that we obtained on objects from the Egyptian Department of the British Museum are presented to demonstrate that 3D laser profilometry is a worthwhile technique for epigraphic investigations where naked-eye inspections fail.
Simple resonant structures that permit holographic reflection filtering are studied. The filters under study work under a 45-deg incidence for a wavelength of =632.8 nm, a condition useful for future inclusion in substrate mode systems. First, the influence of the structural parameters of the grating and the waveguide on the position and the shape of the resonance peaks are studied by numerical computation. The numerical results, obtained within the rigorous coupled wave theory, are compared with the measured response of some filters. These filters contain a grating recorded by holography deposited on the substrate. In the case of the bilayer filter, a waveguide is introduced between the grating and the substrate. Second, the numerical results are used for the conception of an active substrate mode spectral filter built from electro-optic zinc oxide.
The third order nonlinear optical effect called the optical Kerr effect was studied in InP nanoparticles solutions. The synthesized InP nanoparticles have sizes ranging from 1.5 to 3.5 nm and each sample is characterized by its sizes distribution. The Z-scan technique was used to study nonlinear absorption and refraction. Different lasers were used, hence different nonlinear refraction effects were observed at different wavelengths (532, 633 and 1550 nm) and at different time scales (continuous and femtosecond).
We study the realization of simple resonant structures allowing to obtain holographic reflection filters under a 45° incidence for a wavelength of λ = 632.8 nm. In particular, we will be interested in the influence of the parameters of the structures on the position and the shape of the resonance peaks. The 45° incidence takes its origin in the will to include resonant components in substrate mode systems. In the second part of this paper, we use the obtained results to study the realization of an active substrate mode spectral filter by the use of an eletro-optic material: zinc oxide (ZnO). The presented results which obtained by an algorithm based on the Rigorous Coupled Wave Theory.
We describe an alternative design for the 4-quadrant phase mask coronagraph described recently by Rouan et al. 2000. Based on the same principle, i.e. producing a very efficient nulling by mutually destructive interferences of the coherent light from the main source, our mask realises the pi phase shift using some properties of ZOGs
(Zeroth Order Gratings) and according to an original scheme respecting the 4-quadrant symmetry. When the period of the one-dimension grating structure is smaller than the wavelength of the incident light, the structure becomes birefringent. The effective refractive indices depend on the wavelength. Using this feature, we can design a mask whose nulling e±ciency is maintained within a wide wavelength range. Numerical simulations were made according to the RCWT (Rigorous Coupled Wave Theory).
We investigate the recording dynamics of Omnidex photopolymer film
from DuPont. We use a reviewed version of the diffusion model
proposed by Zhao and Mouroulis in order to describe the recording response, that combine photopolymerization and free monomer diffusion process. Experiments are presented that lead to the determination of
material kinetic parameter. These values are introduced in a
numerical model to provide quantitative simulation of gratings
formation under various holographic exposures. We extend its
application to the investigation of film shrinkage influence on
refractive index distribution and spectral selectivity of
reflection gratings. This study improves the understanding of
recording process and consequently allows building more accurate
holographic components in this material.
Sol-gel derived silica glasses are well suited as host for molecular dopants that show specific optical properties, such as laser action (high second and third order nonlinear coefficients). Such materials are of interest in optical waveguide and switching for telecommunication networks. The material is prepared by sol-gel technique in which some nanocrystallites of semiconductor (II-VI) are included, specially CdTe. Nanocrystallites are prepared out of the host matrix and included in the sol-gel after. The nanoparticles are prepared by sono-electrochemical technique. Sono-electrochemistry, or pulsed electrodeposition in presence of high intensity ultrasound, is used to product powders. The nanoparticles are characterized by scanning and transmission microscopy, electron diffraction, and x-ray fluorescence. The nonlinear refractive index and absorption are measured by the Z-scan method at 532 nm (Nd-YAG pulsed laser).
Substrate-mode gratings are used to couple and influence the signals that propagate in planar-integrated optical systems. Volume holograms are especially well suited for this role because they allow the recording of slanted fringe gratings. Photopolymer are among the best candidates for such applications due to easy handling, dry development process, high diffraction efficiency and replication possibilities. In this paper, we investigate the recording dynamics of OmnidexTM photopolymer from DuPont. We use the theoretical diffusion model proposed by Zhao and Mouroulis in order to simulate the recording process. Two different experiments are described that lead to the quantitative determination of kinetic parameters in this material. These values are introduced in the diffusion model and different recording procedures are simulated. The conclusion shows that it could be valuable to let the material in the dark for several minutes before develop it. This investigation should improve the understanding of recording process and consequently it should permit to build more efficient components.
Planar integration of various optical systems appears for some years as a way to reduce alignment problem and to build small size, robust and monolithic devices. An original planar integrated interferometric sensor is presented in this paper. It is based on the separation and control of polarization states in a substrate mode holographic system in order to obtain the optical path difference between two scanning spots. A unique planar system is used for projection of the spot and for recombination of probe beam reflected on the tested surface. The monolithicity and the differential nature of the element lead to a very good insensitivity to external vibrations. The sensor is a multilayered structure composed of a reflective polarizing holographic element sandwiched between two planar substrates. Probe beams are coupled in and out of the system by diffraction on a reflective Substrate Mode Hologram that constitutes a fourth layer. These two types of holographic elements are recorded in high index modulation photopolymer: OmnidexTM HFR-600 from DuPont. Design, realization and application are demonstrated and discussed.
Optical measurement methods and especially interferometric methods suffer from a great drawback. The beam that illuminates the investigated object travels through the air. When the air is moving due to thermal or other perturbation, the object beam propagates through a turbulent flow of air. It deviates from its expected optical path due to air refractive index changes produced by the turbulent flow. Those perturbations become very critical when interferometric measurements are achieved in industrial environment. We have developed an original solution to address that drawback of interferometers by introducing a phase conjugation mirror into the interferometer. First we record the shape of the perturbed object beam by means of interference with a reference (pump one) beam in a non- linear photosensitive polymer allowing phase conjugation. The object beam travels back and forth between the visualization part of the interferometric set-up and the object (perturbed zone). Then the interference pattern is read by another reference beam (pump two) antiparallel to the first pump beam to produce the phase conjugate of the object beam. The conjugate beam travels also back and forth the perturbed zone but in opposite direction in regard with the object beam. At the end of the perturbed zone the conjugate beam is unaffected by the optical path modifications due to refractive index changes. Finally the conjugate beam is used as object beam (in classical sense) and interferes with a reference beam (classical part of the interferometer). The complete interferometric set-up is only sensitive to optical path changes due to object displacements and not to optical path changes due to perturbed air.
We report on the characterization of some photopolymer recording materials based on DC-PVA films sensitized or non- sensitized by some xanthene dyes. The limit of the spatial resolution was determined for different sample preparation techniques. It is well known that the quality of the recorded hologram depends on the spatial resolution of the recording material. A bad resolution will reduce the visibility of the reconstructed wave and damages the reconstructed image. It is therefore important to characterize the spatial resolution of the holographic recording material. In this work we compare the result obtained with two different techniques for preparing the DC- PVA plates. Interference patterns with different spatial frequencies are recorded in the material and the modulation transfer function of each pattern is measured in order to get the limit of the spatial resolution of each material. By the way each sample is characterized by the MTF curve versus spatial frequency and the end-user can choose the well- suited material for this particular application taking into account other parameters such as exposure time, intensity, etc. After the characterization of the materials we test their ability for some applications.
The conversion of incoherent-to-incoherent images by spatial light modulators (SLMs) enables optical information processing and computing applications. The conversion consists of recording an incoherent image and an optical modulation on the same photosensitive element. The coherent readout of the photosensitive element is suitable for processing. DC-PVA is a well-adapted material for incoherent-to-incoherent conversion because of its wide sensitivity spectrum and because it is self developing. Optimization of incoherent and coherent intensities and exposure times is preformed. The spatial frequency of the optical modulation is also optimized. The conversion process is characterized by diffractive efficiency and fringe visibility analysis. Effects on phase and amplitude gratings in the material are investigated. Different recording modes are tested: the grating erasure, the grating writing and the simultaneous erasure/writing. In the grating erasure mode the photosensitive material is first impressed with the optical modulation and then with the incoherent image. The grating writing mode is the opposite process. In the simultaneous grating erasure/writing mode the incoherent image and the optical modulation are capture together continuously or with multiple exposures in the DC-PVA plates. Replacing the incoherent beam with the coherent beam in the same geometric configuration performs a comparative characterization. Another characterization consists of comparing the converted image properties with the properties of an image produced by a direct coherent readout of an incoherent slide. Comparisons between incoherent-to- incoherent conversion of incoherently illuminated slides with collimated or divergent beams or incoherently illuminated objects are shown.
We present a transmission holographic element that spatially separates the Transverse Electric (TE) and Transverse Magnetic (TM) polarization modes. This element can be used as a polarizing beam-splitter as well as an optical switch. Its originality is that it is compared of two reflection holograms stacked together with index matching glue or liquid. The former hologram is a mirror called 'substrate- mode hologram' (SMH) because of its diffraction angle higher than the internal reflection angle in the substrate. The second hologram is a mirror that only reflects the TE mode in accordance with the coupled wave theory. The main advantages of associating two reflection elements rather than transmission usual ones are a wider angular selectivity peak, a greater wavelength selectivity and the possibility to reach high diffractive efficiency with the SMH for both polarization modes. The high index modulation amplitude in the DuPont Omnidex photopolymer enables the recording of elements with high performance and permits to take benefit of the dry process in order to save the accurate grating geometry associated with desired properties. We propose an original design and discuss theoretical and experimental behaviors for green and red reading wavelengths.
Vibration measurements by interferometry can be realized with continuous or pulsed lasers. A convenient and less expensive way to measure displacements relative to vibrating objects is to use an acousto-optic modulator in the object beam of an interferometer using a continuous laser. Stroboscopic illumination of vibrating objects can freeze moving speckle patterns when the stroboscopic and vibration frequencies are synchronous. This supposes a monofrequency excitation. We have developed a method for measuring the complex displacement response of vibrating objects at any frequency. The use of spatial phase-shifting and temporal phase-shifting allows consistent measurements of vibration amplitudes and phases without changing the phase of the excitation force. We call 'spatial phase-shifting' a method using the phase-shift of the reference beam in an interferometer and 'time phase-shifting' an original technique based on the relative change of phase between the stroboscopic illumination and the excitation force. Three spatial phase-shift steps and the impact of the choice of the phase-shift amounts in the developed algorithm is discussed. Recording of vibration amplitudes and phases at successive frequencies enabled us to measure the frequency response of objects and to analyze how eigenmodes appear.
Few conditions are absolutely necessary to improve the accuracy of quantitative measurements of displacements in an interferometer: the accurate calibration of the phase- shifter, the control and the suppression of the interferometers drift. Calibration consists in measuring phase shifts generated by piezoelectric transducers (PZT). We have developed an original in-line PZT calibration based on speckles intensity modulation. A new method to measure the phase drift versus time in the whole interferometer (reference and object arm) is presented. Two innovative methods to compensate phase drift in real time allow accurate displacements measurements. Both compensation methods do not use a feedback loop active control during DSPI measurements. So it allows us to avoid overshoot or oscillation problems linked to the feedback loop. All presented methods allow inexpensive data processing and were successfully applied to an out-of-plane sensitive interferometer. PZT calibration, drift measurements and real time compensation are automated.
A phase-shifting digital speckle pattern interferometer (DSPI) has been calibrated using a Michelson interferometer. Calibration consists in measuring phase shifts generated by piezoelectric transducers (PZTs) and also to determine drift of the phase with time in the interferometer arms. The calibration fringes are displayed live on the TV monitor and then processed slice by slice after recombination following their recording sequence (PZT voltage or time). Dark fringes are detected to compute the wavelength with good accuracy (λ/170 theoretical) and the optical path difference is stored in a datasheet for every slice. This leads to the measurements of the drift and the calibration of the phase shifters with an accuracy about λ/20. Out-of-plane and in-plane optical fiber DSPIs have been successfully characterized using the same algorithm. The method presented also enables inexpensive data processing. Moreover the real-time measurement of the interferometer drift enables feedback loop active control during DSPI measurements.
Among the different possibilities to generate a beam conjugated to an incident one, saturable absorption is presented as the most simple method. Recently, several authors have, however, described the use of Xanthene dyes (XD) as good candidates for degenerate four-wave mixing at low laser powers. This paper deals with the description of the systematic study of six XD compounds: Fluorescein and five of its halogenated derivatives. The rigid matrix in which the dyes are embedded is made of a poly(vinyl alcohol) film prepared from an aqueous solution. The measurements of the saturation intensities as well as reflectivities of phase conjugation mirrors are obtained by an original experimental set-up connected to a data acquisition system. Different parameters such as sample thickness, optical density or beam ratios are investigated. The results for the six dyes are presented and compared.
We present two types of polarizing holographic optical elements recorded in Du Pont's Omnidex film (reflection holograms). The first one takes benefit of the dry development process in order to respect the grating geometry associated with polarization properties. Thanks to that, we realized polarizing beam splitter with high diffraction efficiency and high polarization ratio. The second type of polarizer is an original polarizing mirror that is based on the polarization dependency of spectral and angular selectivities. The high index modulation of that polymer allows to record new holographic polarizers. Details about theoretical basis and experimental realization are given.
Recent work on an acrylamide-based photopolymer holographic recording medium is presented. The lifetime of recorded gratings is improved by the addition of cross-linking monomers. Shelf life is also improved. The effects of various constituents of the photosensitive material are studied to determine an optimum composition, and five xanthene dyes are compared as possible sensitizers for the system. With the most sensitive dye and optimum concentrations of the other constituents an improved formulation is presented with high sensitivity and very high diffraction efficiency. The new formulation also works well in reflection mode.
Small angle x-ray scattering (SAXS) technique has been employed to observe the microscopic structural changes at different stages of photocrosslinking in the holographic recording material: dichromated poly(vinyl alcohol). A detailed account of the SAXS technique is presented and results obtained with synchrotron radiation and Kratky Camera are discussed.
In our laboratories, we have performed many experimental investigations in order to characterize metal ion doped polymer materials, mainly Dichromated Poly(vinyl Alcohol) DC- PVA) and Dichromated Poly(acrylic acid) (DC-PAA), for their use in holography and nonlinear optics. These systems have been employed for recording volume transmission holograms and fabrication of holographic optical elements (HOEs). Moreover, they are attractive photosensitive materials because of their low cost, self-developing nature and high diffraction efficiency.
In the industrial applications of holography as well as in display holography, there is a need to adapt, in order to generate the specifically asked for effect, the type of the recording material or the processing of the emulsion after recording. Therefore, the search for new holographic materials as well as newly adapted processing techniques can lead to easier measurements or to better performances. This paper deals with a description of the techniques used for performance improvement of silver halide photographic emulsions. The study has shown that by the use of a fitted physical developer, the bandwidth of reflection holograms can be increased from 70 nm to 200 nm and diffraction efficiency can reach 14%. Using physical and chemical developments, the color of the hologram can be chosen depending on the composition of the development baths. Values of the efficiency of more than 40% were reported with selected chemical developers.
In this paper, we present a methodology for analyzing the characteristics of a photosensitive material for holography. When two Gaussian beams of equal intensities are exactly superimposed on the recording material, the modulation of the interference pattern is equal to unity. When they are no longer exactly superimposed, this modulation varies from one to zero depending on the analyzed point. On the other hand, the modulation is constant in a direction perpendicular to the incident plane. Therefore, it is possible to consider a complete analysis (point by point) of only one holographic grating in order to measure the diffraction efficiency (eta) at a given modulation versus exposure or for varying modulation for a given exposure. We present the results obtained with an experimental setup devised for that purpose. The tested recording material is a film of dichromated poly(-vinyl alcohol) (DC-PVA).
For some years, theoretical models have been worked out to describe the interaction between electromagnetic waves and a thick dielectric grating. Those models were developed for sinusoidal phase gratings illuminated with a plane wavefront. A method is proposed here to calculate the diffraction efficiencies of spherical and cylindrical holographic lenses and of spherical to cylindrical wavefront converters. Those calculations are based on the coupled wave theory of Kogelnik and on the work of Nishihara.
Many experimental investigations are performed to produce new optical recording materials for holography. They intend to improve applications such as the construction of holographic optical elements (HOEs), filters, aberration correctors, and nondestructive testing as well as optical data storage. All of these applications require materials with high optical performances. Because of their excellent ability to record high spatial frequency gratings, photopolymers are seen as promising holographic recording media. Indeed, one of the greatest photopolymers advantages is their high theoretical molecular resolving power. The addition of dichromate salts to a variety of water-soluble polymers such as gelatin, albumin and poly (-vinyl alcohol) (PVA) generally results in photosensitive materials which become insoluble in water after exposure to the action of light. This paper presents investigations on dichromated poly (-vinyl alcohol) emulsions (DC-PVA).
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