Phase-shifting real-time holography with photorefractive crystals

Abstract

ABSTRACT The phase-shifting interferometry techniques is a well-known technique which has been used with great success in optical profilers, micro-displacements, micro-deformations and others applications in Non-Destructive Test in basic research, engineering and biotechnology areas. This work presents our Advances in Phase-Shifting Real-Time Holography using Photorefractive Sillenite. And we have obtained quantitative results in many applications in measurements of micro-rotation, micro-displacements, deformation, surface contouring and whole lens wave-optics. The real-time holography process is doing using the photorefractive Bi 12 SiO 20 crystal recording me dium, where the phase-shifting 4-frames method for obtained the phase map, this wa s filtered by sin/cos filter and was applied the unwrapping process. The experimental results agree with the expected one in these applications and with promises potentialities of this method for studies with in situ visualization, monitoring and analysis. 1. INTRODUCTION The Holographic Interferometry T echniques [1] comprise a powerful optical me thod for surfaces analysis, in the field of Non-Destructive Testing. It is represented in the following methods: Real-Time Holographic Interferometry (RTHI); Double-Exposure Holographic Interferometry (2EHI); and Time-Average Holographic Interferometry (TAHI). These techniques present advantages over the conventional techniques: they do not present any contact with the surfaces, providing them an absolute reliability, presenting besides a high accuracy; and also it allows to do qualitative analysis through visual inspection. The photorefractive sillenite crystals come presenting an attractive recording medium for RTHI. The light-induced effects that characterize these crystals are the photorefractive effect [2][3], consisting of the refractive index modulation through photo-induction and linear electro-optic effect (Pockels Effect); thermo-optic effect of refractive index modulation through the temperature gradiente in crystal surface[3]; and photochromic effect, of absortion coefficient modulation for high light intensities [3]. The use of these crystals in photorefractive holographic recording present advantages as in situ self-proceeding of recording medium, indefinide reusability, or else, it does not present fatigue, and the processes are dynamic and reversible. These properties qualify the sillenite crystals for use in the real-time holographic interferometry. Many works of Holographic Interferometry using photorefractives crystals have been studied through out the last decades. The most prominent works of J. P. Huignard et al [3], A. A. Kamishilin and M. P. Petrov [4]. The spatial phase measurements technique with phase-shift was described by Creath [5] as th e Phase-Shifting Technique. Many captured interferograms have had their intensities changed due to the phase-shift, provided by piezoelectric linear micro-displacements (PZT). If the phase shift is co ntinuous in time , it will be named Ph ase-Shifting Technique, and else, the phase shift is discrete it will be named Phase-Stepping Technique. Along the years, many works on unwrapping techniques have been published. In 1994 Judge et al [6]. Although these exist many techniques, their use depends on the particular conditions prevailing in each case. Other diverse groups became working in the development of instruments for biomedical and technological applications, as the G. von Bally et al [7], and works of M.P. Georges and Ph. C. Lemaire [8]. Too, the phase-shifting interferometry is a well-known technique which has been used with great success in optical profilers, this is very important, because noncontacting and whole-field measurements of surface shape with high resolution is requered in variuos fields in biotechnology and engineering. The shape determination of surfaces can be done by means of holographic interferometry[9]. The basic principle of holographic contouring use the generation of a contouring fringes pattern, by means of the interference of two holographic reconstructed images[10]. This work developed an optimized holographic interferometer that uses the photorefractive Bi