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It is well known that when two beams (object and reference) are incident on a recording material, high order diffraction may be observed during both the writing and reading of the hologram. These higher or non-Bragg orders contain the phase conjugate and the phase amplified versions of the object. In this talk, the utility of Bragg and non-Bragg orders during holographic construction and reconstruction using photorefractive materials and photothermoplastics is investigated with applications to object shape determination and deformation. Specifically, we discuss applications of non-Bragg orders in the 3d reconstruction of objects, and holographic interferometry using Bragg order to determine object attitude and deformation. The advantages of using non-Bragg orders (viz., phase conjugate and phase doubling) are also discussed.

In this paper we derive the underlying equations for real time holographic interferometry through selfdiffraction, and demonstrate experimentally on how to employ the different Bragg and non-Bragg diffraction orders to perform one shot determination of the phase deformation, or equivalently, the depth information of a deformed object. We also show that the various diffracted orders may be phase shifted with respect to each other with a constant phase shift which depends on the phase mismatch and the length of the recording material. This technique can therefore have an obvious advantage over traditional phase-shifting holography due to the elimination of the piezo-shifted mirror (inducing the different phase shifts) which limits the traditional technique to slow deformations.

Fiber Bragg gratings (FBGs) embedded in conventional fibers may serve as temperature sensors over a wide temperature range and withstand temperatures around 1200 K. A variety of linearly polarized (LP) modes for the wavelengths between 400 and 700 nm may be sustained in fibers with and without FBGs. The composition of the LP modes and their competition is instrumental for understanding physics of thermo-optics and thermal expansion effects in silica-based fibers. The first objective of this work was to model mathematically the competition between LP modes and modal distribution using the solutions of Bessel equations for the fibers with and without the gratings. Computer generated modes were constructed and the cut-off V-numbers (and Eigen values W and U ) were determined. Theoretical results then were compared with experimental observations of LP modes for two separate ranges of temperatures: 77– 300 K and 300-1200 K. To study the formation of LP modes over the first temperature range, liquid nitrogen was used to cool down the fiber and a thermocouple was used to monitor the temperature of the fiber. Real time recording of the modal structure was performed using digital imaging and data acquisition instrumentation. To study LP modes between 300– 1200 K, the fibers were inserted into a tube furnace with temperature control. The wavelength of the infrared radiation was reflected by a FBG and detected by an optical spectrum analyzer. Radiation at the visible wavelength propagated through the fibers, and transmitted visible light was collected, analyzed and recorded with a CCD camera to monitor distribution of the LP modes in the samples with and without the FBGs.

Dynamical sensing based on combination of classical optical effects and atomic force microscopy (AFM) presents challenge for analysis of the forces at the nanoscale and beyond. An interference effect between light reflected from an AFM cantilever and highly reflective silicon surface of the calibration grating was studied for relative humidity (RH) varied between 9 and 60%. Force-distance analysis indicates on separation of capillary, van der Waals, adhesion, and electrostatic forces. The measurements performed in contact AFM mode suggest that the period of interference pattern observed in displacement curves is a function of humidity and varies between 293 nm at RH = 9% and 335 nm at RH > 50% with standard deviation less than 8 nm. Clear change of the interference period suggests that other than hardwarerelated factors may be involved in the formation of the interference in force-distance curves.

We have developed the all-optical EO-modulator using a pulsed photogalvanic power supply driven by light illumination (coherent and incoherent). Generated by ferroelectric crystal with the photogalvanic effect (Fe-doped LiNbO 3 ), electrical pulses were used for driving a standard EO-modulator, based on transversal EO effect in Bi 12 SiO 20 (BSO) crystals. Both parallel and serial connections of photogalvanic crystal (LN), BSO and oscilloscope were tested. The depth of EO-modulation was very sensitive to the impedance of the connected cables, which implies the existence of transmission-line resonances. Secondly, a more compact version of EO self-modulation is realized with green (wavelength λ= 532 nm, P = 100mW) solid-state CW laser. In this case, reflection of the CW laser from the LN crystal was modulated in time. Pulsating optical reflection was correlated with the pulsating electrical signals. We report both modes of operation: (1) as pulsed high-voltage power supply, and (2) as compact-pulsed optical modulator. We have described these pulsations using model of photogalvanic effect and ferroelectric emission.

We have suggested a mathematical model of bio-optical nonlinearities for the suspensions of motile microorganisms (MO). Modeling of photophobic and photokinetic types of the photoresponse of MO suspensions allow us to predict effects of aggregation and 'hole burning' in the spatial distribution of MO concentration. Theoretical description of nonlinear diffraction may help with the diagnosis of the vitality of MO culture and for characterization of photomovement.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Recent measurements revealing new aspects of the nature and physics of space-charge waves in photorefractive Bi12SiO20 crystals are presented. A Bessel-function family of space-charge wave resonances are shown to exist for excitation by a frequency modulated running interference pattern. It is also demonstrated that space-charge waves may continue into regions of the crystal not subjected to the driving light field. Subharmonic space-charge gratings are shown to have an internal structure that for running waves moves with a group velocity opposite the driving optical interference pattern, which is moving with the phase velocity of the space-charge field and the associated refractive-index grating. We also describe how the subharmonics evolve dynamically from a speckle-like pattern towards a regular wave structure. Finally, self-excitation of spontaneous scattered beams ins described, and it is demonstrated that space-charge waves with a long decay time and a high Q-factor are associated with this phenomenon.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Using anomalous large diffusion we report a recording of reflection type gratings in a PVK-based photorefractive polymer without any external electric field. Diffraction efficiency of the gratings was measured to be 7%. An efficient modulation of beams during two-beam coupling up to 12% was demonstrated by using phase mutilation technique. This practical scheme can be used in dynamic vibration measurements.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We provide a direct experimental observation of space charge waves in photorefractive crystals with point group 23 based on their penetration into an area with uniform light illumination. Those are the results of excitation of eigen modes of space charge filed excited by moving light fringes. We have found experimental conditions when the quality factor of the space charge waves attempts dramatical increase with respect to what current theory predicts. This leads to self- excitation of the waves and results in self-oscillation of light. The competition between space charge waves and fundamental grating results in appearance of K/2, K/4 components in the fundamental grating and to spontaneously occurring beams called subharmonics. The subharmonic beams are generated in a pattern of domains that evolve dramatically as they move through the crystal. The domains are result of non- homogeneity of the space charge waves and separated by narrow boundary regions, where the phase of subharmonics changes by pi. We experimentally prove the domains move with the group velocity of running space charge waves.

The physical mechanisms of the light interaction with different materials are discussed. The modulation of refractive index and conductivity gives a physical basis for the different applications: Information Storage, Image Processing, Material Characterization and Control. A concept of the dual-use devices is formulated, based on the simultaneous use of the light-induced modulation of the optical and electrical material parameters. The latest results in the high-contrast dynamic holography are presented with emphasis on nonlinear interaction of the optical and space-charge waves.

We report the effect of Asymmetry of Bragg reflective band of Cholesteric Liquid CRystal caused by the excited doping molecules of 4-phenilchalkon. Two possible reasons giving the explanation of the effect are nonuniform concentration of khalkon molecules in the bulk and absorption of the molecules on the inner surfaces of the cells. The influence of nonuniform variations of pitch step and the refractive index modulation on the shape of Bragg band are studied numerically. It has been shown that the variations of pitch step are probably the reason of asymmetry of the Bragg band. The used model is based on solving the equations of the Theory of Dynamical Reflection for the wave propagates along the cholesteric director axis.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Coherent beam coupling in photorefractive crystals leads to an energy transfer. An analytical expression of the c.w. gain can be calculated from the charge transport equations for a crystal under illumination. The experimental results of gain versus grating wavenumber is fitted with this expression and lead to a determination of the material parameters. Such an analysis has been performed on semi insulatin GaAs and InP. For this last crystal this study reveals the important role of the excited state of Fe (5T,).