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Particle Image Velocimetry
Published in Rajpal S. Sirohi, Speckle Metrology, 2020
To operate this correlator to the advantage of PIV we should have a recording material for the holographic filter that allows a high-frequency throughput of writing and reading while the PIV record is scanned through the different interrogation areas. Recording media of choice are photorefractive materials [66] that exhibit nonlinear properties at milliwatt light power levels. Typical representatives of this family are ferroelectric lithium niobate (LiNbO3) or bismuth silicon oxide (Bi12SiO20; BSO). When a photorefractive material is illuminated, photoexcited carriers migrate from bright regions to dark regions. This charge separation produces a space-charge field that gives rise to a refractive index modulation due to the electro-optic effect. The incident light field is thus stored by an appropriate phase pattern in the material. Dopants like Fe2+ are often responsible for the charge generation. In the dark regions electrons are caught by Fe3+ traps. LiNbO3 has a crystallographic axis of preferential electric polarization that induces photovoltaic drift of the electrons. In BSO a drift may be induced by an external electric field. Some recently investigated photorefractive semiconductor materials have the advantage of high sensitivity [67]. Readout, of course, causes a gradual erasure of the stored pattern if no special fixation is carried out.
Adaptive Optics and Phase Conjugate Reflectors
Published in Chunlei Guo, Subhash Chandra Singh, Handbook of Laser Technology and Applications, 2021
Michael J. Damzen, Carl Paterson
The photorefractive effect is a change in the refractive index due to the optical transfer of charge in the medium leading to change in refractive index. The effect was first observed in lithium niobate (LiNbO3) and was a detrimental effect due to its change in the propagation properties of the light. The basic mechanism is due to the photoexcitation of electrons (or holes) from donor (or acceptor) sites to the conduction (or valence) band, where they are free to migrate by drift or diffusion before recombining into an empty trap site. The dominant rate of charge photoexcitation is in the bright intensity regions with preferential trapping in dark regions. Hence, with an intensity interference pattern, the charge is redistributed to dark fringes. The imbalance of charge leads to a space-charge electric field ESC that modulates the refractive index ∆n through the electro-optic (Pockels) effect ∆n = 1/2n3reffESC, where n is the refractive index and reff is the effective electro-optic coefficient. Hence, good choices of photorefractive media exhibit high photoconductivity and have high electro-optic coefficient; examples include barium titanate (BaTiO3), bismuth silicon oxide (BSO) and lithium niobate (LiNbO3). Later, interest has been centred on photorefractive polymer materials where the composite polymer material can be engineered to have particular donor and trapping species, but they tend to require high externally applied electric fields and have high absorption.
Detectors and Recording Materials
Published in Rajpal S. Sirohi, Optical Methods of Measurement, 2018
Lithium niobate crystals—particularly Fe-doped—have been used for holographic interferometry and data storage. The recording is fixed by temperature. The disadvantage of lithium niobate is that it is rather slow. Higher sensitivity is obtained with photoconductive electro-optic crystals such as bismuth silicon oxide (BSO) and bismuth germanium oxide (BGO) by the application of an external electric field. These crystals are available in the form of thin slices several centimeters in diameter. Barium titanate crystal is used in holographic interferometry and speckle photography because of its very slow response. Recordings can be made over a very wide spectral range.
Mechanical and microstructural properties of silt roadbed filling improved with cement, red mud and desulfurization gypsum
Published in European Journal of Environmental and Civil Engineering, 2023
Sai Zhang, Jianwen Ding, Zhenyuan Lai, Qinying Guo, Xing Wan
The XRD patterns, which represent the mineral components of the materials, are presented in the Figure 3. The major compositions of the AS are quartz-SiO2 and calcite-CaCO3; The major compositions of the OPC are dicalcium silicate-C2S, tricalcium silicate-C3S, tetracalcium aluminoferrite-C4AF and tricalcium aluminate-C3A. The gypsum-CaSO4·2H2O is nearly the only mineral composition in terms of DG. Furthermore, the major compositions of the RM are aluminum hydroxide-Al(OH)3, bismuth silicon oxide-Bi2SiO5, ferric oxide-Fe2O3 and calcite-CaCO3, respectively. Table 2 shows the chemical composition of the raw materials determined by XRF. It can be seen that the SiO2 occupies over 60% of AS, the primary chemical compositions of the OPC are SiO2 and CaO with a CaO-to-SiO2 of 1.99:1; Fe2O and Al2O3 are the major composition of the RM; CaO and SO3 occupy over 95% of DG, which nearly identical to those of natural gypsum, further confirms the major mineral composition of DG is CaSO4·2H2O.
W-shaped, dark and grey solitary waves in the nonlinear Schrödinger equation competing dual power-law nonlinear terms and potentials modulated in time and space
Published in Journal of Modern Optics, 2019
Mati Youssoufa, Ousmanou Dafounansou, Alidou Mohamadou
The sign of and can be positive or negative indicating that the interactions are attractive or repulsive respectively. Indeed this model can also be used to describe the saturation of the nonlinear refractive index. The NLSE with dual power-law nonlinearity is a consistent model to describe the spatial soliton dynamics in photovoltaic-photorefractive materials such as Lithium Niobate (LiNbO) and Bismuth Silicon Oxide (BiSiO). The case n=1 corresponds to the parabolic-law nonlinearity. This nonlinearity is involved in nonlinear media such as the p-toluene sulfonate crystals. In addition, the parabolic-law describes the nonlinear interaction between the high-frequency Langmuir waves and the ion acoustic waves in a region of reduced plasma density and the nonlinear interaction between Langmuir waves and electrons (25,17).