The paper presents the results of experimental demonstration of phase conjugation of weak laser radiation by means of two-stage dynamic holography in optically addressed liquid crystal spatial light modulator, implementing the TV-relay of the interferometery data for the record of hologram-corrector.
Vladimir Berenberg, Vladimir Venediktov, Natalia Ivanova, Michael Isaev, Elena Konshina, Arkady Onokhov, Michael Fedorov, Aleksandr Chaika, Nikolay Feoktistov
Presented are the results of investigations, directed onto creation of the OA LC SLM of reflective type with clear aperture diameter 100 mm for the record of holographic gratings with amplitude of up to 2π andasymmetrical fringe profile.
We discuss several schemes and methods, providing the possibility to extend the method of dynamic holographic correction of distortions by means of optically addressed liquid crystal spatial light modulators (OA LC SLMs) to IR spectral range. These are first of all the schemes with TV (computer) relay of interferogram to modulator and double-wavelength dynamic holography schemes. We consider also the performance of the first OA LC SLMs, specially developed for correction in 2.5-4 μm spectral range, providing diffraction efficiency of ~10% in traditional scheme and about 75% in the case of grating with asymmetric profile.
The results of experimental and theoretical studies are presented on the development of optically addressed liquid crystal spatial light modulators (OA LC SLM) with clear aperture up to 50 mm and phase modulation depth up more than 2π. The optimization of electrical and optical characteristics of liquid crystal, photoconductor, dielectric mirror and blocking layers resulted in fabrication of samples of OA LC SLM that allowed writing diffraction gratings with the phase amplitude up to 2π and variable profile of grating fringes.
The paper discusses several approaches to record of so-called 'blazed' dynamic holograms (thin dynamic holograms with asymmetric fringe profile) in optically addressed spatial light modulators (OA SLMs). Such holograms have much higher (up to 100% in comparison with standard 30-40%) diffraction efficiency to the working order of diffraction, than the traditional dynamic holograms, recorded in OA SLMs, and can be thus used for holographic correction of distortions in laser systems of various kind.
It was found out, that in optically addressed liquid crystal spatial light modulator with the nematic liquid crystal and photoconductor, comprised by p-i-n diode on the base of amorphous hydrogenated silicon, it is possible to record the dynamic diffraction gratings with diffraction efficiency over 50%. The gratings were recorded with the use of S- effect. Possible reasons of the discovered effect are considered in the paper.
In recent experiments of M. Gruneisen et al., the possibility was shown to record the so-called 'blazed' dynamic holograms in optically addressed liquid crystal spatial light modulator (OA LC SLMs). In such holograms the phase retardation distribution across the holographic fringe has a saw-like shape (asymmetrical triangle). Such holograms can provide a very high (in a limit - nearly 100%) diffraction efficiency. In previous experiments such 'blazed' holograms were recorded with the use of digital computer methods. We propose a novel, analogous an completely optical approach to the record of such holograms. One can record a saw-like profile of phase retardation in an OA SLM, placed into the nonlinear interferometer. In such interferometer the probe wave reads out the phase retardation in SLM, interferes with reference wave, and the phase retardation in the said SLM is controlled by their interference pattern. The results of the direct numerical simulation of the system show that by this method can be formed the saw-like grating, providing nearly 100% diffraction efficiency. Presented is the analysis of the system dynamics and stability.
The theoretical and experimental study of eye-safe single- mode beam SRS amplification in the barium nitrate crystal at 1.32 micrometers Nd:YAG laser pump field with wide angular spectrum was performed. It was ascertained that most effective method for improving of Stokes beam divergence lies in inclining of the pump beam.
We discuss the system of laser energy delivery to a remote object using joint action of high-sensitive phase conjugation mirror and of dynamic hologram in optically addressed liquid crystal spatial light modulators. This scheme (the scheme of "frozen" phase conjugation) makes it possible to use the advantages of phase conjugation application in laser systems, whose radiation can be hardly subjected to standard methods of phase conjugation.
The reflective type optically addressed spatial light modulators (OASLMs) with an amorphous hydrogenated carbon (a- C:H) light-blocking layer (LBL) sandwiched between an intrinsic hydrogenated silicon carbide (a-Si:C:H) photoconductor and broad-band and narrow-band dielectric mirrors have been developed. FLC was used as a light modulating medium. The DHF effect in an FLC with tilt angle (Theta) equals 39 degrees and SS (Clark-Lagerwall) effect with angle 22,5 degree(s) were employed. The study showed that a flexible design of the OASLMs are possible. As a result of optimal design of the reflective type OASLMs with the dielectric mirrors of two types, the following performance characteristics have been obtained. Diffraction efficiency (DE) was about 30%, net diffraction efficiency (NE) was about 20% (spatial frequency equal 30 lp/mm and frame refreshment rate equal 200 Hz). This net diffraction efficiency practically does not depend on the direction of the reading- out light polarization for the OASLMs operating on the DHF mode.
Paper presents the results of experimental demonstration of dynamic holographic correction in mid-IR, using optically addressed liquid crystal spatial light modulators and method of two-wavelength holography, when the hologram is recorded at one wavelength and reconstructed at some shifted wavelength. On such a basis one can realize the dynamic interferometer, providing the arbitrary scaling of the wave front distortions and thus to record the dynamic hologram on the differential wavelength, which can be used for dynamic holographic correction of distortions in mid-IR. Method feasibility was confirmed in experiment.
We discuss application of dynamic holography in optically addressed liquid crystal spatial light modulators to correction for thermo- optical distortions in high average power solid-state pulse- repetitive picosecond lasers. Possible scheme of multipass laser and possible schematics of dynamic hologram-corrector record, including the novel technique of blazed dynamic holograms are discussed.
The reflective type optically addressed spatial light modulators (OASLMs) with an amorphous hydrogenated carbon (a-C:H) light-blocking layer sandwiched between an intrinsic hydrogenated silicon carbide (A-Si:C:H) photoconductor and broad-band and narrow-band dielectric mirrors have been developed. FLC was used as a light modulating medium. The DHF effect in an FLC with tilt angle (Theta) equals 39 degree(s) and SS (Clark-Lagerwall) effect with angle 22.5 degree(s) were employed. The study showed that a flexible design of the OASLMs are possible. As a result of optimal design of the reflective type OASLMs with the dielectric mirrors of two types, the following performance characteristics have been obtained. Diffraction efficiency was about 30%, net diffraction efficiency (NE) was about 20% (spatial frequency equal 30 lp/mm and frame refreshment rate equal 200 Hz). Sensitivity was in the interval from 50 to 100 (mu) W/cm2, depending on the mirror type. NE equals 12.5% for spatial frequency 100 lp/mm. The results of our work show promise for the development of novel FLC OASLMs with a significant decrease in the loss of light, operating in reflective mode. This net diffraction efficiency practically does not depend on the direction of the reading-out light polarization for the OASLMs operating on the DHF mode.
Large numerical aperture telescope with nonlinear optical correction for distortions, designed for the remote self- luminous object imaging, was realized in experiment and investigated. Dynamic hologram, recorded in optically addressed liquid crystal spatial high modulator, was used as the corrector. Nearly diffraction limited performance of the system was demonstrated.
The results are reported of theoretical and experimental studies of the dependence of diffraction efficiency of hologram-corrector upon an orientation of a diffraction grating vector and of the polarization of the reading-out radiation with respect to the normal to the smectic layers. The gratings recorded using DHF-effect and Clark-Lagerwall effect were studied. The conditions were determined when the dependence of diffraction efficiency vs. radiation polarization is weak. It was found out that in the hologram- corrector, using the polymer photoconductor, the diffraction efficiency is significantly dependent of the vector of grating orientation, while for the hologram-correctors using a-Si:C:H photoconductor this dependence is practically absent.
Two-wavelength holography, when the hologram is recorded at one wavelength and reconstructed at some shifted wavelength, is an efficient tool for many applications. Optically addressed liquid crystal spatial light modulators are very convenient for recording thin dynamic holograms and, in particular, for the purposes of the dynamic two-wavelength holography. On such a basis one can realize the dynamic interferometer, providing the arbitrary scaling of the wave front distortions. Such an interferometer can be of use for solution of some of the tasks of the adaptive optics, namely, for simplification of the procedure of measuring of the robust wavefront distortions, for recording of the dynamic holographic correctors, working in spectral ranges, where the direct holographic record is impossible, in particular, in mid-IR range of spectrum, and for extension of the range of distortions, which can be corrected by means of the phase valve, mounted in the negative optical feedback loop. We report the experimental realization of such an interferometer.
Large numerical aperture telescope with nonlinear optical correction for distortions, designed for the remote self- luminous object imaging, was realized in experiment and investigated. Dynamic hologram, recorded in optically addressed liquid crystal spatial light modulator, was used as the corrector. Nearly diffraction limited performance of the system was demonstrated.
Two-wavelength holography, when the hologram is recorded at one wavelength and reconstructed at some shifted wavelength, is an efficient tool for many applications. Optically addressed liquid crystal spatial light modulators are very convenient for recording thin dynamic holograms and, in particular, for the purposes of the dynamic two-wavelength holography. On such a basis one can realize the dynamic interferometer, providing the arbitrary scaling of the wave front distortions. Such an interferometer can be of use for solution of some of the tasks of the adaptive optics, namely, for simplification of the procedure of measuring of the robust wavefront distortions, for recording of the dynamic holographic correctors, working in spectral ranges, where the direct holographic record is impossible, in particular, in mid-IR range of spectrum, and for extension of the range of distortions, which can be corrected by means of the phase valve, mounted in the negative optical feedback loop. We report the experimental realization of such an interferometer.
Given are the results of experimental study on the quasi real time holographic correction for the lens distortions in the passive observational telescope in the visible range of spectrum, using the liquid crystal optically addressed spatial light modulator.
Proposed is the novel method of dynamic nonlinear-optical correction for distortions in wide spectral band. The method is based on combining of the negative feedback correction and dynamic holography correction in the system, using optically addressed phase modulators. State-of-the-art of key technologies is evaluated.
Large numerical aperture telescope with nonlinear optical correction for distortions, designed for the remote self- luminous object imaging, was realized in experiment and investigated. Dynamic hologram, recorded in optically addressed liquid crystal spatial light modulator, was used as the corrector. Nearly diffraction limited performance of the system was demonstrated.
The paper describes the decade history and the recent advances in the field of the telescopes, where the nonlinear-optical effects are used for the correction for image distortions, caused by the defects and deformations of the primary mirror and of some other elements. Described are the schemes, based on phase conjugation use, which can work with the coherent radiation (beam direction, laser collimators and imaging with coherent illumination) and the schemes, based on the use of the dynamic holography, applicable to the remote objects (astronomy, Earth observation) in the incoherent radiation with the wide spectrum.
Large numerical aperture telescope with nonlinear optical correction for distortions, designed for the remote self- luminous object imaging, was realized in experimental and investigated. Dynamic hologram, recorded in optically addressed liquid crystal spatial light modulator, was used as the corrector. Nearly diffraction limited performance of the system was demonstrated.
Proposed is the novel method of dynamic nonlinear-optical correction for distortions in wide spectral band. The method is based on combining of the negative optical feedback correction and dynamic holography correction in the system, using optically addressed phase modulators. State-of-the-art of key technologies is evaluated.
Given are the results of experimental study on the quasi real time holographic correction for the lens distortions in the passive observational telescope in the visible range of spectrum, using the liquid crystal optically addressed spatial light modulator.
Given are the results of experimental study on the quasi real time holographic correction for the lens distortions in the passive observational telescope in the visible range of spectrum, using the liquid crystal optically addressed spatial light modulator.
Proposed is the novel method of dynamic nonlinear-optical correction for distortions in wide spectral band. The method is based on combining of the negative optical feedback correction and dynamic holography correction in the system, using optically addressed phase modulators. State-of-the-art of key technologies is evaluated.
Large numerical aperture telescope with nonlinear optical correction for distortions, designed for the remote self- luminous object imaging, was realized in experiment and investigated. Dynamic hologram, recorded in optically addressed liquid crystal spatial light modulator, was used as the corrector. Nearly diffraction limited performance of the system was demonstrated.
Proposed is the novel method of dynamic nonlinear-optical correction for distortions in wide spectral band. The method is based on combining of the negative optical feedback correction and dynamic holography correction in the system, using optically addressed phase modulators. State-of-the-art of key technologies is evaluated.
Given are the results of experimental study on the quasi real time holographic correction for the lens distortions in the passive observational telescope in the visible range of spectrum, using the liquid crystal optically addressed spatial light modulator.
The basic characteristics of the optically addressed spatial light modulators are presented based on ferroelectric liquid crystal (FLC) as a light modulating media and amorphous hydrogenated silicon carbide a-SiC:H and dye-doped polyimide films as photoconducting layers. The parameters of the constituent parts are described, among them: photoconductivity of photosensitive layers, data about newly developed light blocking layers, characteristics of the FLC materials, utilizing the deformed helix ferroelectric effect. The dynamics of the response in hundreds Hz region, the diffraction efficiency of 20% at spatial resolution better than 501 p/mm, and sensitivity in range of microWatt/cm2 are obtained.
Large numerical aperture telescope with nonlinear optical correction for distortions, designed for the remote self- luminous object imaging, was realized in experiment and investigated. Dynamic hologram, recorded in optically addressed liquid crystal spatial light modulator, was used as the corrector. Nearly diffraction limited performance of the system was demonstrated.
Given are the results of experimental study on the quasi real time holographic correction for the lens distortions in the passive observational telescope in the visible range of spectrum, using the liquid crystal optically addressed spatial light modulator.
Large numerical aperture telescope with nonlinear optical correction for distortions, designed for the remote self- luminous object imaging, was realized in experiment and investigated. Dynamic hologram, recorded in optically addressed liquid crystal spatial light modulator, was used as the corrector. Nearly diffraction limited performance of the system was demonstrated.
GIven are the results of experimental study on the quasi real time holographic correction for the lens distortions in the passive observational telescope in the visible range of spectrum, using the liquid crystal optically addressed spatial light modulator.
Large numerical aperture telescope with nonlinear optical correction for distortions, designed for the remote self- luminous object imaging, was realized in experiment and investigate. Dynamic hologram, recorded in optically addressed liquid crystal spatial light modulator, was used as the corrector. Nearly diffraction limited performance of the system was demonstrated.
Arkady Onokhov, Vladimir Berenberg, Aleksander Chaika, Nataliya Ivanova, Mikhail Isaev, Nikolai Feoktistov, Leonid Beresnev, Wolfgang Dultz, Wolfgang Haase
The subjects of the study were spatial light modulators (SLM), comprised by polymer photoconductor (PC) or a-Si1-x:Cx:H photoconductor, and ferroelectric liquid crystal. The polymer PC provides the highest available diffraction efficiency (DE) among all layers when the spatial frequency of the hologram exceeds approximately 100 lp/mm. At the same time the parameters of the a-Si1-x:Cx:H PC layer can be varied across the wide range and thus the proper tradeoff between the spatial resolution and reversibly can be chosen.
Given are the results of experimental study on the quasi real time holographic correction for the lens distortions in the passive observational telescope in the visible range of spectrum, using the liquid crystal optically addressed spatial light modulator.
Given are the results of experimental study on the quasi real time holographic correction for the lens distortions in the passive observational telescope in the visible range of spectrum, using the liquid crystal optically addressed spatial light modulator.
A repetitively pumped ruby laser including long (16 m) intracavity optical delay line is described emitting microsecond pulses. A prototype model of laser lithotriptor was made using this laser, and histological and clinical studies were made.
The modes of laser cavity with deflectors which perform the fast misalignment in two orthogonal planes are investigated. The possibility of beams formation with rotating around the cavity axis energy center of intensity distribution at mirror and beam direction is shown. The peculiarities of temporal and spatial structure of ultrashort modelocked pulses are analyzed.
Physical mechanisms of ms laser lithotripsy in the visible range are discussed. Theoretical model for the case of stones which can be represented as a high-scattering low-absorption medium containing high-absorptive organic micropores is developed. The evolution of the state for such individual pore under the influence of laser radiation is described. Governing equations are derived and it was shown that there exists avalanche-like process of pore absorption increase due to the process of pyrocarbon generation. This generation is caused by the thermochemical dissociation of pore organic matter. Such effect leads to the increasing of laser pulse energy absorption and pressure front formation. This front may account for destruction of significant layer of the stone surface. Plasma can not flush under the conditions typical for described process. It starts to play a significant role only after primary stone destruction produced by proposed mechanism. Sharp increasing of stone absorption and modification of the destructed layer state may be considered as a good boost for the later effective plasma generation.
For the last two years we have applied continuous dual-wavelength Nd:YAG 20 - 60 W power laser to various urologic operations. Transmission of laser irradiation via a flexible quartz fiber permitted operating at any depth of the wound. High-intensity irradiation of 1.06 mkm wavelength was effective in making thin incisions into a variety of tissues, including skin, subcutaneous fat, aponeurosis, muscles, urinary bladder wall, prostate gland, renal pelvis, renal capsule and parenchyma, and urethra. The incisions were especially effective if the contact method was used. Operational access was accomplished in 3 - 5 minutes. At the same time, hemostasis occurred in small diameter vessels. More reliable hemostasis could be achieved by means of 1.32 mkm wavelength. With the present laser device, we carried out 57 different urologic operations in our clinic. Examples of such operations include prostatectomy, pyelolithotomy, ureterolithotomy, nephrectomy, resection of renal cysts, condylomata acuminata of the urogenital organs, and papilloma of the urethra and bladder. The results suggest that a combination of these two wavelengths may prove most effective. Advantages of this approach include a decreased blood loss and decreased surgical time, asepsis, good short- and long-term results, and no complications.
Theoretical model of microsecond shockwave laser lithotripsy is developed. The destroying stone is considered to be a medium with low absorption and high scattering which contains high-absorptive organic inclusions. Laser radiation penetrates deep into such type of media and bulk destruction processes may occur in its significant volume. The distribution of energy fluence in stone volume was found in diffusion approximation. The evolution of state for each individual inclusion was studied. It was shown that the organic matter thermochemical decomposition plays an important role here. Such process leads to gas and high-absorption pyrocarbon generation. It produces sharp increasing of pore volume, cracks formation, and results shockwave generation. These processes change the state of illuminated stone layer-- lead to the formation of highly absorptive loose composition. Such layer change-- predestruction--produces conditions for the later effective transformation of laser energy. Some important dependencies for such processes were found both in simplified analytical form and numerically. Computer simulation for described model of microsecond laser lithotripsy was done with the parameters typical for ruby microsecond laser. Obtained results give the basis for the estimation of lithotripsy efficiency.
Open surgeiy for the removal of renal and ureteric calculi has been rendered almost obsolete in the last ten years. The development ofthe extracorporeal and the intiOCOTpOTeaI lithotripters has permitted many patients to have their stones treated without operation. Several kinds ofalternative disintegration methods such as electrohydraulic lithotripsy, ultrasound lithotiipsy, stone disintegration by laser irradiation, electric drill disintegration, microexplosion lithotripsy and extracorporeal shock wave lithotripsy have contributed to this advancement.
Analysis of possible ways for organic minerals destruction by laser-induced shockwave is presented. Physical mechanisms describing lithotripsy with microsecond laser pulses are discussed. Theoretical considerations show that the most probable fragmentation mechanisms are connected with the existence of absorptive inclusions in the stone volume. We have shown that surface plasma flash may be considered as attendant phenomenon which does not necessarily play an important fragmentation role under our conditions of observation.
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