This PDF contains the communication section which includes "Measurement of in-plane displacement with twofold sensitivity using phase reversal technique".

Measurement of in-plane displacement with twofold sensitivity using phase reversal technique

photorefractive two-beam coupling and energy transfer in BaTiO3 are studied at multiple wavelengths using He-Cd, He-Ne, and diode lasers. The photorefractive signal beam gain is measured as a function of the pump beam intensity, beam ratio intensity, spatial frequency of the grating, and angle between the grating vector and c axis of the crystal. The exponential gain coefficient is calculated from signal beam gain, and its dependence on the same parameters is studied. The dependence of the signal beam gain and exponential gain coefficient on spatial frequency are also evaluated theoretically and found to be in good agreement with the experimental data. Also, the signal beam gain is studied as a function of wavelength, and a very high value is obtained at 441.6 nm. Figure-of-merit parameters such as the maximum change in the refractive index, the space charge field at saturation, the trap density of the charge carriers, and the photorefractive sensitivity of the crystal are calculated from the experimental data. since the absorption in BaTiO3 varies strongly with wavelength, its influence has been included in the calculations of the figure-of-merit parameters. The results are discussed in the light of the present understanding of photorefractive phenomena in crystals.

Parametric study of photorefractive beam coupling in BaTiO3 at multiple wavelengths

A collimated optical beam is required in several applications such as metrology, optical processing, free space propagation of information, and laser-based instrumentation. Prior to the advent of the laser, the size of the aperture at the focal point of a collimating lens determined the degree of collimation based purely on geometrical optics consideration. Because the laser beam can be focused to a tiny size, effectively making it a point source, the degree of collimation is governed by diffraction at the aperture of a collimating lens. A large number of procedures have been developed to collimate the beam. We examine the development of these techniques from the historical perspective.

Optical beam collimation procedures and collimation testing: a summary

This study concerns the automatic high precision beam collimation system using the Talbot interferometry. When the collima-tion beam is obtained placed point-source of light in focal position of the collimation lens, the defocus value is calculated f roma moire fringe width in the Talbot interferometry using only two grating. With the advance of collimation, the moire fringe ca nnotbe confirmed. Using the movement of moire fringe when one of grating shifts, the expanded moire fringe width is measured high-precisely from the phase difference of intensity change of two detecting points, using peak position of the cross-correlationcoefficient. With the result of the defocus value, the collimator lens is positioned by motor controller. Keywords : collimation, Talbot interferometry, moire fringe, phase difference, cross-correlation coefficient1. INTRODUCTION Because of high precision measurement to be realized for micro/nano-technology, some optical measurement systems have beenproposed and reported

Automatic collimation system by Talbot interferometry

A double exposed reflection hologram and interferometry will be used to analyze the structural integrity of a carabiner. The first exposure will depict the carabiner unstressed, and the second will illustrate the carabiner under stress. After this, the carabiner will be broken and then compared with a developed hologram. The breaking strength will be determined using this method. A double exposed hologram of a control block - which moves approximately one micrometer - will be used to find a relationship between the amount of displacement and the weight applied to the carabiner. A hologram will then be made using the weight needed to move the carabiner one-micrometer to verify the relationship. Once the theory is validated, another carabiner, of the same model with little use, will be used as a test piece. Another double exposed hologram will then be taken of the new carabiner. Next the carabiner will be cycled approximately 500,000 times with a two Kilo-Newton load for duration of one week. Then one more double exposed hologram will be made after the cycles are completed. Once the holograms are developed, the two will be compared thus showing any changes in structural integrity if any are present. If changes in structural integrity are observed, a guide to determine if the carabiner being tested should be retired will be recommended.

Strain/displacement of a carabiner via interferometry

A real-time visual approach for the calibration of phase step in image plane holography using BaTiO3 crystal as a recording medium is reported. In this method, the diffuse object is illuminated symmetrically with two collimated beams and a pump beam is added at the crystal plane. Each illuminating beam generates an individual interferogram at the observation plane when the object is subjected to load. A p phase shift to one of the illuminating beams results in the complete disappear- ance of the fringes due to phase reversal between the individual inter- ferograms, and at 2p phase change, the fringe pattern is restored. After calibration, a single-beam illumination configuration is used for phase measurement. We present the theory of the method and experimental results for a centrally loaded diaphragm rigidly clamped along the periph- ery. © 1998 Society of Photo-Optical Instrumentation Engineers. (S0091-3286(98)01611-0)

Phase step calibration and phase measurement in image plane holography using BaTiO3 crystal as a recording medium

A new type of collimation testing technique using a single wedge plate in conjunction with a dual-field grating has been described. Interference pattern produced by a wedge plate illuminated by the test beam is superposed on a grating to get moire fringes. By using two different types of dual-field gratings, two testing configurations are obtained. These dual-field moire patterns provide self-referencing and improved sensitivity in collimation testing. The principle of the proposed techniques and experimental results are presented.

J. S. Darlin

Papers

Phase step calibration and phase measurement in image plane holography using BaTiO3 crystal as a recording medium

Hybrid wedge plate-grating interferometer for collimation testing