In this work thermal and temporal changes of the light scattering by lithium niobate crystals have been investigated
under steady illumination by argon ion laser beam (λ = 514.5 nm) in the temperature range of 20-800°C and have
been observed the anomalies on the temperature curves of elastic light scattering intensity near of 100, 200 and
350°C for the nominally pure crystals and near 100 and 200°C for iron doped one if laser beam was directed along
the c-axis of crystal. Oscillations of light scattering intensity have been discovered on the screen in far field at room
temperature. The period of oscillations dependence on the kind of impurities, concentration and power of
illumination. Laser beam in this case was directed perpendicular to c-axis of crystal. Pulsations were spreading along
the c-axis. The threshold of power is about of 100 mW.
It was observed the split of the laser beam by nonlinear barium sodium niobate crystals at excitation of samples of He-
Ne laser (630.0 nm). The results are compared with earlier obtained focusing argon ion laser beam by this crystal and
connected to studies of x-ray crystallography with emphasis upon behavior of microdomain structure.
It were performed light scattering measurements of barium sodium niobate crystals from 20 to 800°C and connected these results to studies of x-ray and transmission electron microscop with emphasis upon behavior of nanodomain structure (S. Mori et al. and J. M. Kiat et al.). Using of the 90°- elastic light scattering investigation and far field observation it were clarified the relation between behavior anomalies of light scattering and evolution of the microdomain structures of BSN. It is correlation between temperature transformations of microdomains and anomalies on the temperatures curves of the elastic light scattering intensity at about 200, 240 and 300°C. The phase transition near 500°C could be explained by appearance of a new incommensurate phase. It is the consistent with the structural investigation Pan Xiao-qing et al. by means transmission electron microscopy method.
The study of light scattering by the barium sodium niobate crystals has been performed in range of 20-800°C at the excitation of the crystal by argon (514,5 nm) and helium neon (λ=630.0nm) lasers. At heating from room temperature near 500°C the laser observed increasing far field spot dimension for λ=514.5 nm. It was observed also on heating, that the elastic light scattering intensity increases near the ferroelectric phase transition (Tc=550°C) for λ=632.8 nm in contrast with decrease for λ=514.5 nm. It have related our measurements to results of x-ray and electron microscope investigations by works.3,4
The optical properties and nonlinear response of photorefractive crystals of quartz and barium sodium niobate (BSN) are investigated in the temperature range of 20 - 700 degree(s)C. The specl-structure of the laser beam in quartz crystal was observed in the narrow range of temperature at (alpha) -(beta) phase transition. The elastic light scattering intensity of the quartz sharp increases at phase transition and drops after. The specl-structure in BSN crystal appears in the wide range of the temperature, from room temperature to the temperature of ferroelectric phase transition, Tc equals 560 degree(s)C. The elastic light scattering in the BSN crystal rapidly decreases at the temperature Curie. The change of intensity of the elastic light scattering corresponds to the visually observed change in the laser beam trace in the crystals. The anomalies of scattering light probably reflect the structural changes associated with the formation of incommensurate phase in these crystals.
In this work we studied the optical spectra of dysprosium and ytterbium doped double chloride MePb2Cl5:RE3+ (Me equals K, Rb), and double fluoride LiYF4:RE3+ (RE3+ equals Dy, Yb) crystals. RE3+ doped double chloride and double fluoride crystals have been grown, by using Bridgeman technique. Optical spectra were studied, intensity parameters are determined using Judd-Ofelt method and radiative probabilities and branching ratio were calculated. Yb3+ -Dy3+ energy transfer processes in KPb2Cl5:Dy3+,Yb3+ and LiYF4:Dy3+,Yb3+ were considered.
A variety of streak/framing/synchroscan image tubes are now under design and manufacturing in the Department of Photoelectronics, General Physics Institute. Among them are: a series of the well-known PV001 image tubes introduced into wide practice since 1978, a set of more advanced PIF001 tubes originally designed in 1979, specially developed femtosecond streak tubes of BSV-type, which were initially proposed in 1987, and finally a number of PF-type tubes placed in service last year. The whole set of these image tubes may cover the spectral range from 115 nm up to 1.55 micrometers , providing maximum sensitivity of 0.5 (mu) A/W at 1.55 micrometers (S1/IR) and up to 3 mA/W at 900 nm (S25/ER). Various input photocathode windows may be used: fiber-optics or borosilicate substrates which blue transparency starts at 350 nm. UV-glass windows (> 200 nm), MgF2 input window (> 115 nm). All tubes with photocathode- accelerating mesh geometry have photocathode area of 6 mm in diameter, while the tubes in non-mesh configuration (PV and PF0 have a rectangular photocathode area of not less than 4 mm by 18 mm. The described tubes may be supplied with any type of phosphor screen (red, orange, blue, green) deposited onto fiber-optics faceplate.
The dependence of the speckle field was investigated in Ba2NaNb5O15 crystals in laser beam on the orientation of the crystals, temperature and direction of growth. In the crystal with 90 degree orientation the speckle structure of the beam disappears at about 300 degrees Celsius; in the crystal with 0 degree orientation the point scattering centers disappear near the Curie point.
Addition fringes are obtained in real time from Electronic Speckle Pattern Interferometry (ESPI) using a twin-pulsed laser, when two pulses are fired during a single frame of a CCD camera. However, the fringe patterns have poor visibility, because optical noise is reinforced. Automatic phase extraction from addition fringes has not previously been achieved: low-pass filtering to suppress random speckle noise also eliminates the fringes due to their low visibility. Two procedures to calculate phase from ESPI addition fringes are presented in this paper. This has enabled phase to be extracted from ESPI addition fringes for the first time.
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