ABSTRACT
Transient light-induced absorption in LiNbO3 is observed in the blue-green spectral range after pulsed illumination with 532 nm. Its buildup and decay in Fe-doped LiNbO3 is satisfactorily described by a sum of two stretched exponential functions. For undoped LiNbO3, however, only one stretched exponential decay is observed. These experimental results are explained by the formation of both small Nb(Li)4+ electron polarons and O- hole polarons. The mechanism is discussed on the basis of a proposed band scheme.
ABSTRACT
A new phenomenon associated with a nonlinear interaction of optically excited space charge waves has been discovered in photorefractive crystals of the sillenite family. This interaction provides a spatial rectification of the electric field of the space charge waves and leads to a temporally oscillating, but spatially homogeneous electric field of the order of 50-60 V/cm which is detected by a probe beam via the electro-optic effect. Taking into account that the displacement current plays an important role, we demonstrate a very good agreement between the experimental data and the suggested theoretical model.
ABSTRACT
Illumination of oxidized iron-doped BaTiO(3) crystals with visible or ultraviolet light yields absorption changes of as much as 1300 m(-1) that are stable at room temperature. These photochromic effects cannot be erased by light, but heating the crystal to a moderate temperature (100 degrees C) can switch it back to its initial state. These effects, in particular the optical irreversibility, might be of interest, e.g., for optical control of charge-transport properties and for persistent data storage.
ABSTRACT
Holograms have been recorded in congruent LiTaO(3):Fe with continuous-wave laser light by use of a two-step process. Blue gating light (lambda=488 nm) sensitizes the crystals for holographic recording with red light (lambda=660 nm) of a diode laser. Refractive-index changes of as much as 1.0x10(-5) are achieved for intensities of the red light of 1 W/cm(2) . The saturation values are proportional to the intensity of the writing light. Nondestructive readout with red light is possible, and the holograms remain erasable for blue light.
ABSTRACT
We present an experimental study of thermally induced self-focusing effects and interactions of incoherent light beams in strontium barium niobate waveguides. Depending on the input power, a single parallel beam is strongly focused inside the sample up to diameters of several micrometers. For higher input power we observe the splitting of the beam in a sequence of several spots. We demonstrate that these thermally induced refractive-index patterns can be used to focus and deflect an incoherent guided probe beam in the waveguide with time constants below 1 ms.
ABSTRACT
We present a narrow-bandwidth interference filter in an optical monomode LiNbO>(3):Ti:Fe channel waveguide operating in the infrared wavelength region around lambda = 1.55 microm . The filter consists of a thermally fixed refractive-index Bragg grating recorded with visible green light by use of a holographic technique. In a first approach we measure a reflectivity for the infrared light of 60% and a linewidth (FWHM) of 0.11 nm.
ABSTRACT
A theoretical analysis is presented that describes wave-mixing processes in thin holographic gratings for phase-modulated beams. Experiments with photorefractive Bi(12)TiO(20) crystals in which the signals for Bragg diffraction and for the first non-Bragg diffraction order were measured support the analysis.
ABSTRACT
Recording of holographic gratings in z-cut LiNbO(3) waveguides with extraordinarily (TM) polarized light is demonstrated. In this geometry, photovoltaic currents perpendicular to the guiding layer and the grating vector set up space-charge fields. The mechanism has no equivalent in bulk material.
ABSTRACT
Four scattering lines are observed on a screen behind a BaTiO(3) sample pumped by two ordinary copropagating waves. If in addition counterpropagating pump waves meeting the same phase-matching condition are introduced, mirrorless oscillation occurs.
ABSTRACT
Photorefractive properties of a cerium-doped strontium barium niobate single crystal (Sr(0.61)Ba(0.39)Nb(2)O(6)) are investigated with Q-switched light pulses (wavelength 532 nm). Pyroelectric fields are the dominant charge driving force and significantly enhance light-induced refractive-index changes.
ABSTRACT
We report on the generation of an efficient phase-conjugate wave by anisotropic four-wave mixing in planar iron-doped y-cut LiNbO(3) waveguides. The pump waves are orthogonally polarized with respect to the signal and phase-conjugate waves. Reflectivities of the phase-conjugate signal of as much as 65% are reached in the waveguide. Experimental results are compared with numerical solutions of the corresponding system of coupled-wave equations.