Controle de fase em experimentos de mistura de duas ondas com cristais fotorrefrativos

AUTOR(ES)
DATA DE PUBLICAÇÃO

1996

RESUMO

A new approach for the independent, direct measurement of the amplitude and phase between two interfering beams is reported. The technique is based on phase modulation and synchronous detection by using a novel harmonics processor and a two-phase lock-in amplifier. The two lock-in output signals can be used in a negative feedback loop to control the phase between the interfering beams at any chosen value and, simultaneously, to monitor the amplitude of the optical interference term. This nondestructive technique exhibits excellent sensitivity and permits phase measurements to within 1º. Applications in two-wave mixing experiments with photorefractive crystals were performed. We detected the hologram bending caused by self-diffraction effects in a LiNbO3:Fe crystal. It was shown that the bending of the hologram phase planes can be avoided, or at least strongly reduced, by controlling the phase between the interfering transmitted and diffracted beams behind the crystals, leading to higher diffraction efficiencies and lower light scattering. This technique was also applied to a Bi12TiO20 crystal to produce phase controlled running holograms. We showed that the phase control between the transmitted and difracted beams can be regarded as a hologram speed control. In this way, one can record noise-free holograms with controllable speed, diffraction efficiency, hologram phase shift and other associated characteristics

ASSUNTO(S)

sistemas de controle por realimentação holografia otica não-linear materiais fotorrefrativos interferometria otica

ACESSO AO ARTIGO

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