Enhancement of the measurement sensitivity in multiple-exposure holographic interferometry

Specific features of reconstruction of enhanced-sensitivity interferograms in the optical processing of a multiple-exposure hologram recorded under linear conditions are considered. To enhance the measurement sensitivity when visualizing the changes in the state of an object under study that take place during the time between exposures, it is proposed that the holographic structures corresponding to these exposures on a new carrier be rewritten and the double-exposure hologram thus obtained under nonlinear conditions be recorded. The proposed technique of enhancement of the measurement sensitivity was experimentally tested when visualizing a change of the temperature field in a flat glass plate.     

Multiple-exposure holographic interferometry with rotation of a recording medium for investigation of fast processes

Some specific features of recording holograms with rotation of a recording medium between exposures are considered. It is shown that the rotation of the recording medium makes it possible to exclude completely the effect of aberrations of the recording/rerecording system in the formation of interference patterns characterizing the phase change by an object under study during the time interval between the instants at which the corresponding holograms are recorded.     

Enhancement of measurement sensitivity in determination of changes in the shape of a wavefront by holographic lateral-shearing interferometry

A method for increasing measurement sensitivity in the visualization of dynamics of changes in wavefront shape with the use of holographic lateral-shearing interferometry is considered. At the first stage of this method, a photograph of a reference shear interferogram obtained with tuning to closely spaced fringes is recorded under linear conditions. After chemical treatment, the photograph of the reference shear interferogram is installed in exactly its initial position. At the second stage, a series of photographs of lateral-shear interferograms of the wavefront under study is recorded under nonlinear conditions using the photograph of the reference interferogram. The photographs of the lateral-shear interferograms are optically processed by two coherent beams with selection of the highest diffraction orders, which makes it possible to visualize the dynamic component of the wavefront deformation with an increase in the measurement sensitivity (the static component is excluded in this case). The effect of the degree of nonlinearity of photograph recording on the range in which the measurement sensitivity can be controlled during the optical processing of a pair of matched photographs or one double-exposure photograph of interferograms recorded at different values of a lateral shift is analyzed.     

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.     

Formation of lateral-shear holographic interferograms in diffusely scattered fields

An analysis in the Fresnel approximation is given of the formation conditions of lateral-shear holographic interferograms in bands of infinite width characterizing the wave aberrations of a microscope optical system over the field in the case of coherent diffuse illumination of a ground-glass screen.Tomsk State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 71–76, July, 1995.     

Double-exposure variable shear holographic interferometry with controlled sensitivity

A method of simultaneous recording of double-exposure holograms with different lateral shears is proposed. This method makes it possible to reconstruct a series of interference patterns representing the phase shift caused by the object under study with different sensitivities. Aberration-free interference patterns in fringes of infinite and finite width with different visualization sensitivities for melting zones of a flat polyme-thylmethacrylate sample are presented.     

Two improved methods of surface-displacement measurements by holographic interferometry

This paper describes two new methods for measuring surface-displacements. The first method is an improvement of Ennos' scheme in that multiple object beams are used instead of multiple hologram plates. This arrangement enables the three fringe patterns required for calculating displacement components to be viewed from the same direction, i.e., normal view. Thus the necessity of laborious fringe reprojection is eliminated. The second method involves making three holograms, one situated on each of the three coordinate axes assigned to the surface. Each hologram picks up one component of displacement. Hence no separation of displacement components is required. An experimental demonstration is presented which utilizes the first technique and checks with theoretical predictions.     

Extension of the controlled sensitivity range in holographic interferometry with a lateral shear

The possibility of controlling the measurement sensitivity in shearing interferometry with a small lateral shear is considered. A method based on recording several holographic interferograms with different magnitudes of lateral shear and with different carrier frequencies of holographic fringes during a single exposure is proposed. The measurement sensitivity of the interference patterns is controlled at the stage of optical processing of the combined holographic interferograms with lateral shear, when the interferograms are illuminated by two coherent light beams and the filtering of the corresponding diffraction orders is performed. The results of the experimental testing of the proposed method by using it for the visualization of the melting zones of planar polymethylmethacrylate samples under heat treatment are presented.     

Resonant holographic interferometry for species concentration measurements with saturated anomalous dispersion

A double-exposure resonant holographic interferometry measurement technique for full-field, instantaneous species is presented. This technique utilizes tuned pulsed dye lasers, separate reference beams, and a corrective holographic optical element. The resulting interferogram fringes represent the species number density of interest with variations in the bulk refractive index due to the temperature field automatically subtracted. Expressions for relating resonant absorption with fringe shift are disclosed. The relations suggest that RHI is well suited for optically dense media and long path lengths, where absorption measurements can be difficult. A saturation related modification of the dispersion near a broadened resonant transition is described. The depopulation of the ground state due to saturation by the probe beam causes an asymmetric modification of the resonant refractive index, which when convolved over the probing beam does not affect the measured fringe shift as measured by RHI. Resonant interferometry is demonstrated as an accurate and quantitative measure of the concentration of sodium vapor in a low pressure cell. Furthermore, as a combustion diagnostic, RHI is demonstrated on a minor combustion species, OH, in a nonpremixed slot burner. PACS 33.70-w; 42.40.Kw; 82.33.Vx     

Reference fringes in holographic interferometry

This paper describes the application of reference fringes in double exposure holography of transient phase objects. This includes selection of fringe patterns and fringe number densities suitable for the quantitative analysis of the hologram. Methods of realizing different reference fringe patterns are presented. As the focus of the interference fringes depends on the optical arrangement, different systems are discussed.     

Deformation measurements of specularly reflecting objects using holographic interferometry with diffuse illumination

It is demonstrated that, by using diffuse object illumination, deformation measurements with holographic interferometry can be performed on a specularly reflecting object without the use of any additional coating of the object surface. An analytical expression for the secondary fringe formation is found, and the system is demonstrated only to be sensitive to deformations along the surface normal. A method for carrying out topographic measurements on specularly reflecting surfaces is suggested. The fringe visibility is studied for a rigid rotation of the object by using matrix methods. It is found that maximum fringe visibility is obtained if the recording camera is focused on the surface of the object.     

Fringe interpolation by two-reference-beam holographic interferometry: Reducing sensitivity to hologram misalignment

Accurate fringe interpolation in holographic interferometry requires two-reference-beam holographic recording. Using two reference sources close together, the sensitivity to (angular) misalignement of the hologram is drastically reduced (10° instead of 0.01°). Overlapping of the cross-reconstructions can be tolerated, unless extreme precision and spatial resolution are demanded. Experimental results obtained by video processing of such holograms show an accuracy of better than $\text{1}\text{100}$ of a fringe. The optical setup becomes nearly as compact and simple as in classical holographic interferometry.     

双波长全息干涉计量分析

本文分析和讨论了双波长全息干涉计量的单次曝光法和双曝光法。这两种方法都提供了用可见光得到相当于不可见的长波干涉的结果,其测量灵敏度和测量精度可以通过选择合适的工作波长而能得到调整。     

The determination of electron density profiles from refraction measurements obtained using holographic interferometry

The angles a fourth-harmonic holographic interferometer probing beam is refracted upon passing through a neodymium laser-produced plasma have been measured by varying the focus during reconstruction of the hologram. A method (not requiring the numerical inversion of an integral equation) for using such refraction measurements to give the plasma electron density profile is shown to produce a profile in agreement with that obtained from the phase information on the reconstructed in-focus interferogram.     

Femtosecond holographic interferometry for studies of semiconductor ablation using vanadium dioxide film

A recording medium based on the phenomenon of phase transition from semiconductor to metal is applied to holography in the femtosecond time domain. The results of holographic interferometry studies of semiconductor ablation are presented.     

Spatial filtering of holographic lateral-shear interferograms for control of negative-lens aberrations. II

The conditions for lateral-shear interferogram formation in diffusively scattered fields are analyzed taking into account hologram aberrations for the case of transverse displacement of a mat screen and a negative lens before second photoplate exposure. It is shown that the error of control of wave aberrations of the negative lens results at the hologram reproduction stage when the diffusive field is subject to an off-axis spatial filtering. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 58–62, October, 2005.     

Measuring the displacement vector by holographic interferometry

Triple exposure holographic interferometry provides knowledge of the displacement vector. Between the first two exposures the object is displaced by a calibrated amount, and before the last exposure it is translated by an unknown amount.     

Improvement of the sensitivity of measurements in the formation of holographic interferograms of wedge plates

We consider the method for improving the sensitivity of measurements in the formation of aberration-free interference images of wedge plates, which do not require a priori knowledge of the position of the wedge edge. It is shown that the sensitivity in the measurement of the wedge angle in real time interferometry is doubled in the case of recording on the reference hologram of the wedge plate followed by its reconstruction by the object light wave that has passed through the wedge plate rotated through 180° relative to the normal. It turns out that recording of a pair of holograms of the wedge plate, one of which is the image of the wedge plate turned through 180° relative to the normal to the plate, makes it possible to increase the sensitivity of measurements by more than an order of magnitude by eliminating the systematic components of measuring errors due to complete compensation of aberrations. The results of experimental testing of the method are considered.     

Methods for achieving high measurement sensitivity in holographic interferometry by rewriting holograms using incoherent light

Methods for increasing the measurement sensitivity in the rewriting of holograms by one beam of incoherent light are proposed. To achieve high measurement sensitivity it is suggested that an additional transmitting diffraction grating be used in optical rewrite systems. The linear and nonlinear forms of hologram rewriting are examined. The methods make it possible to lift the restrictions on the number of hologram rewrite cycles and to achieve maximum measurement sensitivity. The results of an experimental check are presented for the visualization of weak convection air flows near a heated body. Zh. Tekh. Fiz. 69, 70–75 (December 1999)     

全息干涉计量中干涉计量场的统计特性

本文运用统计学方法推导了全息干涉计量中散斑计量场的统计特性.证明了:干涉计量场的复振幅为复圆高斯随机变量;干扰计量场强度的概率密度服从负指数分布;散斑干涉计量场的系综平均值代表变形信息.