Time average holographic interferometry with photoconductive electrooptic Bi(12)SiO(20) crystals

Fast photorefractive response in B(12)SiO(20) in the near infrared

The polarization self-modulation effect was applied for effective measurement of the characteristic response time of nominally pure Bi(12)SiO(20) (BSO) at wavelengths of 810 and 980 nm. Owing to oxygen deficiency in the crystal lattice, the BSO crystals showed unusual photorefractive sensitivity and remarkable operation speed in the near-infrared spectral region. A response time of 130 ms was measured at 810 nm, and a response time of 540 ms was measured at 980 nm, with incident intensities of 110 and 200mW/cm(2), respectively. To our knowledge, this is the first experimental evidence of a subsecond response in the infrared for a nonsemiconductor photorefractive material.

Real-time holographic interferometry with double two-wave mixing in photorefractive crystals

We present a real-time holographic interferometer for which two reference waves of different phases are created by two-wave mixing with a stationary signal wave in a photorefractive crystal. These waves are reconstructions of the stationary signal wave and interfere with the momentary (changing) signal wave in the manner of a holographic real-time interferometer. A fast change (phase or intensity) of the signal wave leads to different intensity changes in both interferograms that are jointly used for evaluation. With an electric dc field applied to the crystal, a high sensitivity for measuring phase changes (down to lambda/50, lambda = 633 nm) is found, and the sign of the phase change can be determined.

Noise filtering in the interference pattern by dynamic holographic recording in photorefractive Bi(12)TiO(20) crystals

The possibilities of stabilization of the interference pattern by filtration of a random-phase noise caused by vibrations, turbulence, and other local changes in the wave front in interferometric measurements are investigated. Dynamic holographic recording in photorefractive Bi(12)TiO(20) crystals is used. The parameters of the holographic recording are presented for determination of the dynamic range for filtering. Noise filtering takes place in real time and contributes to the enhancement of the contrast and the signal-to-noise ratio of the interference pattern. This results in a considerable increase in the sensitivity and the accuracy of the interferometric measurements.

Dynamic holographic interferometry by photorefractive crystals for quantitative deformation measurements

A holographic interferometer that uses two-wave mixing in a photorefractive (Bi12SiO20) crystal under an applied ac field is described. The interferometer uses a repetitive sequence of separate record and readout times to obtain quasi real-time holographic interferograms of vibrating objects. It is shown that a good signal-to-noise ratio of the interferometer is obtained by turning off the object illumination and the applied ac field during readout of the hologram. The good signal-to-noise ratio of the resulting holographic interferograms enables phase measurement, which allows for quantitative deformation analysis.

Phase-compensated holographic recording based on anisotropic photorefractive diffraction

We report a simple actively stabilized setup for holographic recording on sillenite photorefractive crystals that is based on the anisotropic diffraction properties of these materials. The method is much simpler than previously published ones, requires neither phase modulation nor synchronous phase-sensitive detection, and needs no external reference. We describe the successful operation of this stabilization procedure for a Bi(12)TiO(20) crystal in a practical holographic interferometry setup, using the 632.8-nm wavelength of a He-Ne laser.

Simultaneous acquisition of pi/2 phase-stepped interferograms with a photorefractive Bi(12)GeO(20) crystal: application to real-time double-pulse holography

We present a novel method for real-time analysis of vibrations in double-pulse laser holography. Two pi/2 phase-stepped interferograms are obtained simultaneously. An experimental demonstration gives a phase measurement with an accuracy of 4 degrees .

Photorefractive two-wave mixing in the presence of high-speed optical phase modulation

Equations that describe the steady-state dependence of the coherent-coupling properties of photorefractively induced refractive-index gratings on high-speed periodic biphase, sinusoidal, and triangular phase modulation impressed on one of the input optical beams are found and solved for both depleted and undepleted pump conditions. The period of the phase modulation wave form was kept short compared with the grating-formation time but did not cause significant spectral broadening. The results obtained were verified with data obtained from measurements of two-wave mixing in the photorefractive material, InP:Fe.

Noise and sensitivity characteristics of Bi(12)SiO(20) crystals for optimization of a real-time self-diffraction holographic interferometer

The optimization of a real-time holographic interferometer that uses photorefractive Bi(12)SiO(20) crystals as the recording media through anisotropic self-diffraction is considered with regard to the optical noise and sensitivity characteristics of two particular crystals. A simple theoretical treatment is given to describe the factors influencing the maximum area of an object that can be viewed interferometrically by using these crystals. Experimental values of the noise distribution and sensitivity of the crystals are presented and used to obtain a value for the maximum observable object area of the order of 1 m(2).

Holographic interferometry using anisotropic self-diffraction in Bi(12)SiO(20)

Anisotropic self-diffraction in photorefractive Bi(12)SiO(20) crystals is applied to the investigation of dynamic holographic recording through the diffusion process. Specific attention is paid to optimization of experimental parameters for real-time holographic interferometry. The resultant interferometer is applied to obtain both timeaverage and double-exposure interferograms of vibrating and displaced structures.

Holographic interferometric microscope on the basis of a Bi(12)TiO(20) crystal

The applicability of cubic photorefractive crystals in which the recording can be fixed to holographic interferometric studies of microobjects is outlined. The possibility of observing the temporal behavior of the object by a method combining double exposure and real time interferometry is experimentally demonstrated.

Applications of Multiplexed real time permanent holographic recording in photorefractive BSO

Photochromic effects in crystals of photorefractive bismuth silicon oxide have been used for the recording of permanent holograms. The combination of this permanent recording with the usual photorefractive real time recording has revealed some novel techniques in information processing and interferometry. These are based on the possibilities of multiplexing two distinct holographic gratings having identical grating wave vectors within the same crystal volume. Techniques ranging from image synthesis and logic operations to holographic interferometry and all-optical switching are demonstrated.

Multiplexed permanent and real time holographic recording in photorefractive BSO

We report permanent hologram recording in crystals of photorefractive bismuth silicon oxide using reversible photochromic effects. At a recording wavelength of 488 nm, exposures of several minutes produce areas of faint discoloration in which the permanent hologram is stored. The normal photorefractive behavior is unaffected, however, permitting spatial multiplexing of both real time and permanent holograms. Experimental results and characteristics of this permanent recording in combination with the photorefractive process are presented.

Visualization of aerodynamic flow fields using photorefractive crystals

Interferometry based on double exposure Fourier transform holography in photorefractive crystals is applied for visualization of aerodynamic flow fields. The interferograms obtained are of similar quality as those produced using holographic film but with greatly simplified procedures. The results presented are obtained using a high-power cw argon laser and iron doped lithium niobate crystals. The angular characteristics of the Fourier transform data holograms are studied.

Detection of subsurface defects using phase conjugate waves and forced vibration

In four-wave mixing in BSO crystal, a periodic forced vibration is applied to both the object under test and the standard object to provide signal and reference waves, respectively. The system images subsurface defects of the test object by converting the difference of vibration between the test and the standard objects into image intensity. The principle and basic experimental results are given.

Two-dimensional, optical temporal bandpass filter using four-wave mixing in a BSO crystal: dynamic schlieren imaging system

In four-wave mixing in BSO crystal, the frequency of the reference wave is changed to construct a 2-D optical temporal bandpass filter with arbitrary center frequency. This filter achieves real-time precise observation of the spectral components of an oscillating object field, or it converts the frequency of the time-varying phase object field into intensity. In comparison with the traditional schlieren method imaging static states of the object, this novel method may be called the dynamic schlieren method. The principle and experimental results are given, showing the basic filtering characteristics and demonstrating two typical uses of the filter.

Amplified phase-conjugate beam reflection by four-wave mixing with photorefractive Bi(12)SiO(20) crystals

Phase-conjugate beam reflectivity in photorefractive Bi(12)SiO(20) (BSO) crystals is analyzed as a function of the following parameters involved in the four-wave mixing interaction: grating spatial frequency Lambda(-1), applied field E(0), and incident beam ratio beta. We report an amplified reflectivity (R = 2.7) for asymmetric pump-beam intensities and optimized fringe-displacement speed (moving-grating recording mode, E(0) = 10 kV cm(-1); Lambda(-1) approximately 45 mm(-1); beta > 10(4)). The conjugate-beam reflectivity is shown to depend closely on the same parameters as the exponential gain coefficient Gamma of the two-wave mixing configuration. Still higher reflectivities (R' = 35) are demonstrated by using a combination of two BSO crystals whose roles are, respectively, to generate and then to amplify the conjugate beam.

High-accuracy surface profile measuring system using a BSO phase conjugating mirror

A highly accurate real-time surface profile measuring system has been constructed by combining a Bi(12)SiO(20) (BSO) phase conjugating mirror (PCM) with a Twyman-Green interferometer. In this new interferometer the convex lens collects and focuses the scattering object waves in the BSO crystal, and the PCM reconstructs the object field through the same lens. The method of deriving surface profile is similar to conventional ones but differs in that it does not require exact phase modulation of the interferograms. This system features a quite high measurement accuracy free of aberrations of the lens and of hysteresis or aging of the piston actuator used to change the phase of the reference field. The principle and basic experimental results are presented.

Detector for an optical-fiber acoustic sensor using dynamic holographic interferometry

It is shown that the acoustically induced phase modulation of coherent light propagating within a multimode optical fiber may be linearly detected by an interferometer employing an unmodulated replica of the fiber beam as the reference. It is proposed that a dynamic hologram provide such a reference. This technique allows a performance comparable with that of a monomode interferometric sensor to be obtained, but with considerably relaxed alignment tolerances.

Speckle-free imaging in four-wave mixing experiments with Bi(12)SiO(20) crystals

We demonstrate that holographic speckle-free imaging is possible when a dynamic recording medium, such as a Bi(12)SiO(20) crystal, and a four-wave mixing configuration are used. The method is based on time integration in the conjugate-image plane of N coherent images having an independent speckle pattern. We apply this concept to a real-time optical processing operation. A speckle-free time-averaged interferogram of a vibrating structure is obtained.