Illumination Speckle Research Articles

High-speed reflectance confocal microscopy using speckle modulation.

We developed a spectrally-encoded, line reflectance confocal microscope (RCM) that uses a rotating diffuser to rapidly modulate the illumination speckle pattern. The speckle modulation approach reduced speckle noise while imaging with a spatially coherent light source needed for high imaging speed and cellular resolution. The speckle-modulation RCM device achieved lateral and axial resolutions of 1.1 µm and 2.8 µm, respectively. With an imaging speed of 107 frames/sec, three-dimensional RCM imaging over 300-µm depth was completed within less than 1 second. RCM images of human fingers, forearms, and oral mucosa clearly visualized the characteristic cellular features without any noticeable speckle noise.

ADMM algorithm for Computational ghost imaging using Hadamard derivative pattern

Aiming at the problems of long reconstruction time, high sampling rate and poor imaging effect caused by traditional illumination speckle in ghost imaging reconstruction, this paper proposes to use ordered orthogonal Hadamard derived speckle as the illumination speckle series of ghost imaging to reduce the measurement times and improve the quality of reconstructed images. In addition, the alternate direction multiplier method is introduced into the image reconstruction algorithm to further improve the imaging performance of ghost imaging. Finally, the method used in this paper is evaluated objectively, and the evaluation results show that the combination of Hadamard derived speckle and alternating direction multiplication has better imaging effect, and can obtain high-quality reconstructed images under low sampling conditions. It is expected that this method can be applied to target detection and recognition, improve detection and recognition ability, and help users get more useful information.

Surface roughness effects in dual beam illumination speckle interferometers: Theoretical study

Abstract Analyzed in this paper is the influence of surface roughness of the object on the quality of data or fringes obtained in dual beam illumination speckle interferometers. The theoretical analysis is based on the electromagnetic scattering of light from rough surfaces by observing the modulation of the speckles in the dual beam illumination speckle interferometric setup. It is shown that when object surface roughness is greater than the wavelength of light the quality of the signal is dependent on the angle of illumination of the beam and also on the observation direction. Both in-plane and out-of-plane sensitive dual beam illumination interferometers are investigated in this paper. We show that in one specific arrangement the modulation of the speckles is dependent on the surface roughness of the object being investigated.

Large in-plane displacement measurement in dual-beam speckle interferometry using temporal phase measurement

Measurement of in-plane displacements of a diffuse object by observing the temporal fluctuation of the speckle pattern in a dual-beam illumination speckle interferometer is illustrated. To conceive the temporal changes the object is displaced in its plane continuously. A high-speed camera is used to acquire a number of frames of the image of the object motion sequentially. Through Fourier transformation and inverse Fourier transformation of the frames stacked together, the total phase is determined. Finally, the magnitude of the in-plane displacement of the object motion is extracted. The range of displacement that can be measured using this novel method lies between few microns and over 100 μm on the upper end. Theory together with experimental results are presented in this paper.

Large in-plane displacement measurement in dual-beam speckle interferometry using temporal phase measurement

Abstract Measurement of in-plane displacements of a diffuse object by observing the temporal fluctuation of the speckle pattern in a dual-beam illumination speckle interferometer is illustrated. To conceive the temporal changes the object is displaced in its plane continuously. A high-speed camera is used to acquire a number of frames of the image of the object motion sequentially. Through Fourier transformation and inverse Fourier transformation of the frames stacked together, the total phase is determined. Finally, the magnitude of the in-plane displacement of the object motion is extracted. The range of displacement that can be measured using this novel method lies between few microns and over 100 μm on the upper end. Theory together with experimental results are presented in this paper.

Shape measurement by use of temporal Fourier transformation in dual-beam illumination speckle interferometry

We outline a novel method for determining the shape of an object by use of temporal Fourier-transform analysis in dual-beam illumination speckle interferometry. The object whose shape is to be determined is rotated about an axis, and a number of frames of the image of the object motion are acquired. Temporal in-plane displacement that is due to the object rotation is related to the shape of the object and is retrieved from this large set of data by Fourier transformation. With this method one can determine the absolute height of the object with variable resolution, thereby allowing shapes of objects with large and small slopes to be determined. The theory of the method along with experimental results is presented.

Whole-field strain measurement in a pin-loaded plate by electronic speckle pattern interferometry and the finite element method

The strain field in an epoxy plate loaded in tension through a steel pin is determined using electronic speckle pattern interferometry (ESPI) and the finite element method (FEM). In a dual-beam illumination speckle interferometer, the in-plane component of the displacement at the plate's surface is accurately measured using a four-step phase-shifting algorithm. Digital image processing algorithms have been developed for noise reduction and strain calculation directly in the computer from the phase map with a strain gage length of about 0.4 mm. A whole-field strain map is obtained, as well as distributions of strain concentration factor, in critical regions near the hole of the plate. FEM is used to perform a nonlinear contact analysis accounting for friction effects at the pin/hole interface. The agreement between experimental results and numerical predictions is good. In terms of speed, accuracy and ease of use, dual-beam ESPI appears to be a superior method of whole-field strain analysis.