100 mW of coherent blue light with a wavelength of 405 nm was generated utilising a BiB3O6 (BiBO) nonlinear
crystal to frequency double a Ti:Sapphire laser. Phase match curves as well as sensitivity to angular misalignment
was calculated. The BiBO crystal was found to be excellent for this application. Temperature dependance was
uncritical for this crystal, while power stability was good. The pump-to-blue optical conversion efficiency was
approximately 2%. Unfortunately catastrophic coating damage was observed.
We have developed an educational optics learning tool, which allows students to work in parallel with a real hardware system and a matching, realistic looking, virtual model. We have implemented the idea as an educational laser-kit, and we describe the educational ideas behind it and our experience with its use for motivating and inspiring grade school teachers, educate high school students and train college students. The present system is a relatively advanced laser system consisting of a unique combination of a 2-D breadboard with magnetic mounts carrying the optical components and a corresponding, realistic 2-D display, layout and analysis software.
We discuss phenomena of the optical photons and charged particle channeling in the periodic structures. While particle (as protons) channeling is widely used for the characterization of defects in crystals, channeling of photons is less known. We have demonstrated feasibility of optical channeling method for copying of phase radial grating on the chalcogenide semiconductor glass film and photo-thermoplastic films (PTPF). Chalcogenide glassy semiconductors (CGS) as a medium for recording of optical information have some advantages such as the possibility of achieving a higher resolution power, stability, and a high photosensitivity. We report about recording of the radial phase grating in the doped As-S-Se (CGS). Radial grating was recorded by making copy from the master phase grating placed in the near-field zone and exposure to the CW green (λ=532 nm) low power (P=100 mW) solid-state laser or incoherent UV source. The exposure time has been varied from 15 to 30 min. The recording process could be explained by optical channeling. This phenomenon gives us an opportunity to create phase radial grating using coherent and incoherent illumination.
Fluctuations in the field of a 2nd order nonlinear multi-mode parametric downcoverter exhibit nonclassical correlations in the transverse plane. We present results of measurements of the classical pattern for a degenerate, multi-mode parametric optical parametric oscillator (OPO) operating above threshold. We also present results of autocorrelation measurements of intensity fluctuations in the transverse plane both in the near field and in the far field with the OPO operating both below and above threshold -- a method we believe will ultimately enable us to display the nonclassical correlations of the OPO output.
We discuss manifestation of the channeling effect in the visualization of hexagonal patterns in KNbO3 and phase gratings in LiNbO3. We have shown that visualization of the domain patterns, discovered earlier in the subharmonic beam in the photorefractive BSO crystal, may be explained by the channeling effect. A wave-packet description allows us to explain backward movement of domains due to the specific dispersion law for the space-charge waves. An analogy is discussed with domain formation in the charge-density-waves, known in quasi-1D conductors. Non-linear phase shift of the couple's waves may lead to discomensuration.
We study the cross-talk between the competing holographic gratings in photorefractive cubic crystal Bi12SiO20. The cross-talk technique applies to measure a reduction factor which distinctly appears at low spatial frequency free electron distribution in diffusion regime under conditions so that direct observation of photorefractive gratings can not be performed. We suggest a hypothesis for the reduction factor of the carriers distribution with respect to light modulation is a long-distance photoelectron migration related to a high initial kinetic energy of the free carriers.
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.
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.
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.
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.
Three ways of implementing the 2-dimensional autocorrelation function (ACF) used for the extraction of displacement information in particle image velocimetry (PIV) records have been compared. The three methods are: (1) Numerical computation by means of two consecutive FFT algorithms directly from the digitized image, (2) a hybrid method by which an optical Fourier transform first forms the spatial power spectrum of the image, after which the ACF is computed by a numerical FFT (this method is usually known as the Young's fringe method) and (2) an all-optical correlator. These three methods are compared in terms of resolution and 'quality of data', a term covering signal-to-noise and detectability considerations. In spite of the fact that three methods in principle carry out the same underlying mathematical operation the resulting ACFs may look very different. However, as it turns out, the differences may be explained by artifacts characteristic of the practical implementations, and when these differences are taken into account, the three methods are seen to perform quite similarly.
The properties of a self-pumped photorefractive phase conjugator as an amplifier of amplitude modulated signal beams are investigated. In principle the crystal acts as a self-adjusting beam combiner which allows homodyne detection of the weaksignalbeam superimposed on a stronger reference beam. In our experiments the mixing takes placevia a four wave interaction process in the crystal. In this paperwe investigate the salient characteristics ofthe self-pumped phase conjugate amplifier and explain details of the beam interaction inside the ciystal.
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