Laser-speckles show displacement accompanied by structure change when diffuse objects generating them undergo displacement and/or deformation. This behaviour is theoretically investigated by calculating the cross-correlation functions of speckle intensities before and after the deformation. The dependences of speckle displacement on geometries of object illumination and speckle observation as well as on deformation parameters are clarified. The relations derived are interpreted physically by introducing the shift in diffraction rays due to displacement and deformation of a grating. Distributions of speckle displacement are calculated numerically and shown graphically.

Speckle Displacement and Decorrelation in the Diffraction and Image Fields for Small Object Deformation

The statistical properties of dynamic speckles produced by a moving diffuse object were reviewed by providing the space–time correlation function and the power spectrum of speckle-intensity fluctuation for five combined cases of both the optical configuration and the illumination light. In the optical configuration, three kinds of geometry (free-space, single-lens, and double-lens) were taken, and three kinds of illumination light (a Gaussian beam, a plane-wave beam, and a Gaussian Schell-model beam) were used. Consequently, it was shown that the cross-correlation function and the power spectrum are both Gaussian under some assumptions. From the dynamic properties, two types of speckle motion, boiling and translation, were also evaluated for various conditions of object motion, optical configuration, and illumination light.

Statistical properties of dynamic speckles

In connection with the parameters of the optical configuration used to produce speckles and under illumination of a Gaussian beam over a moving diffuse object, this paper discusses the statistical properties of dynamic speckles produced in the diffraction and image fields by the diffuse object moving in a plane with constant velocity. Especially, the space-time correlation function of the dynamic speckle intensity is examined in detail. Two typical speckle motions of translation and boiling are interpreted for various optical configurations in the diffraction and image fields. As one of the interesting applications of dynamic speckles to metrology, various methods for velocity measurements of the diffuse object are introduced.

Dynamic Laser Speckles and their Application to Velocity Measurements of the Diffuse Object

Dynamic laser speckles and their application to velocity measurements of the diffuse object

Quasi real-time digital version of single-exposure speckle photography for full-field monitoring of velocity or flow fields

The dynamic behaviour of laser speckle caused by uniform in-plane motion of a diffuse object has been studied by deriving the cross-correlation functions of the complex disturbance and the intensit...

Theory and applications of dynamic laser speckles due to in-plane object motion

Holographic interferometry is applied to obtain the contour lines of deformation of a plate by pure bending. According to the theory of elasticity they are hyperbolas and from the angle between their asymptotes Poisson's ratio of the plate material is determined. By the real time method an accuracy of 1% is attained in the case of steel plates. The dependence of the value on the plate shape is also examined.

https://iopscience.iop.org/article/10.1143/JJAP.8.768/pdf

Application of Holographic Interferometry to the Measurement of Poisson's Ratio

The dynamic behaviours of laser speckles caused by a uniform in-plane movement of a diffuse object are investigated by deriving the general formulas of the intensity cross-correlation function in both the diffraction and image fields of the object. The formulas obtained suggest the new methods of pattern correlation and MTF measurement. Validity and applicability of these methods are verified experimentally.

https://iopscience.iop.org/article/10.7567/JJAPS.14S1.301/pdf

Dynamics of speckles produced by a moving object and its applications

Velocity measurement using structural change of speckle

A new method of velocity measurement using dynamic properties of speckles produced at the gaussian image plane of a moving diffuse object is discussed theoretically and experimentally. The relation between the principles of this method and a laser Doppler velocimeter is made clear. It is shown that these two methods utilize different kinds of light intensity fluctuations and have complementary conditions for effective measurement. Experimental verification and application of the present method for the visualization of velocity distribution are also given.

Ichirou Yamaguchi

Papers

Theory and applications of dynamic laser speckles due to in-plane object motion

Application of Holographic Interferometry to the Measurement of Poisson's Ratio

Dynamics of speckles produced by a moving object and its applications

Velocity measurement using structural change of speckle

Velocity Measurement of Diffuse Objects by Using Speckle Dynamics