Surface contouring by phase-shifting real-time holography using photorefractive sillenite crystals

This work proposes to obtain surface contouring by phase-shifting real-time holography using photorefractive sillenite crystals which provides the surface contouring from a change in phase of wavefront of the object illumination beam. The real-time holography using the photorefractive Bi₁₂SiO₂₀ crystal and the four-frame phase-shifting technique was used to obtain the phase map, this map was filtered by an anisotropic sin/cos filter and the unwrapping process used was the cellular-automata technique. We obtained experimental results of the surfaces of the large objects with real discontinuities, and these results agree with the dimensions of the object.     

Light-induced lens analysis in photorefractive crystals employing phase-shifting real-time holographic interferometry

The purpose of this work is to study the potentialities of phase-shifting real-time holographic interferometry for the analysis of light-induced lens in photorefractive and nonlinear optical materials. We show that this technique can be used for quantitative evaluation of the phase distribution of a wavefront changed by a light-induced lens and, consequently, the refractive index changes in these materials. The basic principle of this technique combines real-time holographic interferometry with phase-shifting technique for interferogram analysis. This method is demonstrated with in situ visualization, monitoring and analysis in real-time and uses a Bi₁₂SiO₂₀ crystal as the holographic medium and a Bi₁₂TiO₂₀ as the test sample.     

Fringe formation theory for real-time holographic interferometry using Bi12SiO20

A simple theory has been developed to explain the fringe formation in real-time holographic interferometry using BSO (bismuthsiliconoxide) crystal for interferometric applications. Detailed analysis has been given to choose the optimum size of the crystals.     

Wave optics analysis by phase-shifting real-time holographic interferometry

The purpose of this work is to study the potentialities in the phase-shifting real-time holographic interferometry using photorefractive crystals as the recording medium for wave-optics analysis in optical elements and non-linear optical materials. This technique was used for obtaining quantitative measurements from the phase distributions of the wave front of lens and lens systems along the propagation direction with in situ visualization, monitoring and analysis in real time.     

Real-time holographic interferometry using sillenite photorefractive crystals. Study and optimization of a transportable set-up for quantified phase measurements on large objects

We present the development of a holographic interferometer that uses a photorefractive crystal of the sillenite family as holographic recording medium. The aim of this work is to achieve a transportable and breadboard instrument, with a flexible design and which is user friendly for the quantified measurements of displacements on large scattering objects. The state of the art of the use of photorefractive crystals in holographic interferometry is presented. Based on the latter, a method that is the best suited to our mentioned objectives is chosen: the real-time interferometric technique associated with the crystal configuration exhibiting diffraction anisotropy. On this basis, we have studied and compared two imaging systems, we have experimentally determined the holographic figures of merit of three sillenite crystals samples, and, finally, we have shown the use of two measurement quantification methods. The result of these investigations is a certified and transportable holographic camera prototype containing all the necessary equipment for its operation, which can be easily adapted to various applications. Among these, we show its use in the detection of defects in composite structures, in the measurement of time-evolving deformations, and in the measurement of vibration modes. Received: 4 December 1998 / Revised version: 6 March 1999 / Published online: 12 April 1999     

Holographic solitons in centrosymmetric photorefractive crystals

The conditions necessary for obtaining holographic solitons in centrosymmetric photorefractive crystals are discussed. When both the intensity modulation of the two interacting waves and the angle between the vector of each beam and the longitudinal axis are small, centrosymmetric photorefractive crystals with a positive (or negative ) effective quadratic electro-optic coefficient are able to support bright (or dark) holographic solitons. The intensity width at half maximum of bright and dark solitons is inversely proportional to the external bias field. The holographic solitons can also exit in dissipative centrosymmetric photorefractive crystals when the applied external bias field is large enough.     

Monitoring of residual stresses in injection-molded plastics with holographic interferometry

Residual stresses are often trapped in injection-molded plastic parts due to the rapid cooling of the material in this manufacturing process. These stresses are a common source of failure in plastic components in automobiles, appliances and computers and are difficult to measure with conventional residual-stress experimental methods. Real-time holographic interferometry appears to be a viable technique to identify and monitor these stresses in plastic parts. In this investigation, holographic interferometry was used to monitor the relaxation of residual stresses in the plastic-molded actuator arm of a computer hard drive. In the first phase of this study, the relaxation of these residual stresses as a function of temperature was observed. In the second phase, the time to completely relax the residual stresses in the plastic part at an elevated temperature, the annealing temperature, was determined. In the third phase of this investigation, the rate of relaxation of these residual stresses as a function of time at various operating temperatures, was studied. Based on the results of this study, holographic interferometry appears to be a powerful research tool in the study of residual stresses in plastic parts. It also has the potential to be a practical tool for the inspection of manufactured plastic parts for the presence of residual stress.     

Diffusion studies in liquids by holographic interferometry

Liquid diffusion coefficients are very important basic data for research and many applications in chemical engineering and in other fields, such as biological systems, pollution control and separation of isotopes. Holographic interferometry technique with accuracy and promptness is one of the most widely used techniques for diffusivity studies. We report an interferometric technique to determine the diffusion coefficient of transparent liquid solutions. As the diffusion progresses with time the refractive indices at different planes in the cell are different, and the characteristic extreme points of the fringe patterns shift outward. The interference fringes was obtained and recorded on a PC using a CCD camera. By judging the interferogram with a computer procedure the concentrations at different planes can be obtained by the relation between concentration and refractive indices, furthermore, the diffusion coefficient can be obtained by calculation. The obtained diffusivity values matched very well with the existing experimental results.     

Real-time analysis of 3-D axisymmetric refractive index field by photorefractive holographic interferometry

A real-time test method for determining the refractive index distributions of 3-D axisymmetric temperature field around a flame with the use of a photorefractive holographic interferometer is proposed. Some techniques in data processing for improving the quality of resultant interferogram are developed. Experimental results, which show the effectiveness of this method and agree with theoretical expectations, are also given.     

One-dimensional modulational instability of broad optical beams in biased centrosymmetric photorefractive crystals

We study the one-dimensional modulational instability of broad optical beams in biased centrosymmetric photorefractive crystals under steady-state conditions. The one-dimensional modulational instability growth rates are obtained by globally and locally treating the space-charge field, which depend on the external bias field and the ratio of the intensity of optical beam to that of the dark irradiance. Our analysis indicates that the modulational instability growth rate in local effects can be determined from that in nonlocal effects.     

Nanoscale deformation measurement by using the hybrid method of gray-level and holographic interferometry

This study extends the use of holographic interferometry to measure the nanoscale out-of-plane displacement with high surface resolution. It is noted that if the deformation is less than half of the optical wavelength, it is hard to find an obvious fringe pattern. Under such a situation, in general, the phase shift method is used. However, it needs to take more than 3 images for phase shifting and phase reconstruction In this paper, a more simple hybrid method of gray-level and holographic interferometry is used to extract fringe skeletons, in which it just needs to take one or two images for the normal deformation measurement directly, even if there exists no obvious fringe pattern. The displacement field with high surface resolution can also be obtained. The proposed method yielded a theoretical precision of 0.15 nm for out-of-plane displacement with a monochromatic CCD camera of 10-bit gray scale (1024 gray scales) sensitivity and microscale surface resolution for millimeter scale object with 640×480 pixels image resolution by an He–Ne LASER (632.8 nm wavelength) light source. The gray-level method is proposed to calculate the non-obvious interferometry fringe by traditional holographic interferometry hologram, and the result showed that this method works for this purpose.     

Adaptive filter for unwrapping noisy phase image in phase-stepping interferometry

An adaptive filter for preprocessing wrapped phase image with high noise content has been developed. The window size of this median filter is adjustable according to its location in the noisy phase image. This size-adjustable median filter has not only high noise-rejection ability, but also both good phase-jump identification and image-detail preservation properties. Phase unwrapping can then be done to recover the real phase image without the hampering influence of noise, especially the noise near the phase jumps. Both numerical simulation and experimental results used to examine the effectiveness of this adaptive filter are presented.     

Time-average holographic interferometry with a sinusoidally modulated laser diode

Laser diodes have the features of a single-mode operation and a frequency tunability. Holographic interferometry is described for investigating the vibrating amplitude and phase with a frequency-modulated laser diode. Sinusoidal wavelength change by varying laser injection current produces the sinusoidal phase modulation of relative phase difference between the reference and vibrating object paths. Holograms are made by time-average exposure of three-type recording modes with a laser diode. The phase of vibrating object is extracted from the measurements of Bessel-type fringe irradiances in three kinds of time-average holographic reconstruction. Experimental results of phase and amplitude for a vibrating cantilever object are shown.     

用全息干涉法测量杨氏模量

通过对悬臂梁受力前后双曝光全息图进行再现，测量出干涉条纹序数与相对应的位置坐标，再利用最小二乘法求杨氏模量．     

Generalized linear prediction method in phase-shifting interferometry in the presence of noise

The effectiveness of phase-shifting interferometry (PSI) techniques employing piezoelectric device PZT in the estimation of phase depends largely on the accuracy with which the phase shifts are imparted to the device and the noise influencing the measurement. Several effective algorithms have been proposed to compute the phase shifts imparted to the device and subsequently obtain the phase using least-squares estimation technique. In this paper, we propose a generalized approach, which accurately estimates the phase shifts in the presence of noise. The method is based on the idea of linear prediction and explores the fact that sampling more data frames yields a reliable phase step estimate in a least-squares sense. We also compare our method with a commonly used generalized phase-shifting method based on histogram analysis and show that our proposed approach is highly effective. We also present simulation and experimental validations of our proposed method.     

Fast image-processing technique in phase-shifting holographic interferometry

A fast image-processing method in phase shifting holographic interferometry is proposed, in which the complicated phase calculation is completed with a logic circuit and look-up table. An electronic circuit was designed for the purpose. With these techniques, the processing time can be greatly reduced.     

Real-time non-destructive testing of phase objects using four-wave mixing with photorefractive BGO crystals

Real-time non-destructive testing of phase and transparent objects using degenerate four-wave mixing with photorefractive BGO crystals is described. Some quantitative results of thickness variations of phase objects such as a thin optical wedge and a thin BGO crystal are also given.     

Estimation of trap concentration in photorefractive crystals by a technique of adaptive holographic interferometry

12 GeO₂₀, Bi₁₂SiO₂₀, Bi₁₂TiO₂₀). Received: 17 June 1998/Revised version: 3 August 1998