Vladimir P. Ryabukho

Longitudinal pure spatial coherence of a light field with wide frequency and angular spectra

We have observed the longitudinal pure spatial coherence of a light field in an interference experiment when the length of the temporal coherence is significantly smaller than the length of the longitudinal spatial coherence of the light field. We introduce into consideration new spatial and temporal scales of a light field: the length of the coherent (free) run and the coherent time (the time of life) of a wave train.

Interferometric system with resolution better than coherence length for determination of geometrical thickness and refractive index of a layer object

The idea of a new low coherence interferometric system with axial resolution better than coherence length providing simultaneous measurement of the geometrical thickness and refractive index of transparent layers by sharp focusing of light on the measured object is considered. The presented interferometric system consists of two parts -- the so-called Wave Front Matching Interferometer (WFMI) and a low coherence Michelson interferometer (LCMI) as a light source for the first. The WFMI provides high separation of interference signal peaks from demarcations in layer object at high numerical aperture focusing of light on the object. The tandem optical scheme of these interferometers allows to make this system very compact and mobile.

Influence of longitudinal spatial coherence on the signal of a scanning interferometer

The physical conditions for observing the longitudinal spatial coherence of light of an extended thermal source in interference experiments are defined. For experimental verification of these conditions a Michelson interferometer with a longitudinal scanning mirror was used. The influence of the longitudinal spatial coherence of thermal light on a fringe envelope is demonstrated experimentally.

Numerically focused full-field swept-source optical coherence microscopy with low spatial coherence illumination

We propose a 3D imaging technique based on the combination of full-field swept-source optical coherence microscopy (FF-SSOCM) with low spatial coherence illumination and a special numerical processing that allows for numerically focused coherent-noise-free imaging without mechanical scanning in longitudinal or transversal directions. We show, both theoretically and experimentally, that the blurring effects arising in FF-SSOCM due to defocus can be corrected by appropriate numerical processing even when low spatial coherence illumination is used. A FF-SSOCM system was built for testing the performance of this technique. Coherent-noise-free imaging of a sample with longitudinal extent exceeding the optical depth of field is demonstrated without displacement of the sample or any optical element.

The effects of longitudinal spatial coherence of light in interference experiments

The physical conditions needed to observe the effects of longitudinal spatial coherence of emission of an extended thermal source are considered. Results of experiments on observation of interference pulses of longitudinal spatial coherence, performed using a scanning longitudinal shearing Michelson interferometer, are presented. Distinctions between the effects of temporal and longitudinal spatial coherence of light are established. It is shown that the presence of a noncompensated optical layer in one of the arms of the interferometer makes the interference pulses of the temporal and spatial coherence of light shift relative to each other (“recession”).

Longitudinal purely spatial coherence of a light field

The effects of longitudinal purely spatial coherence of light and the results of observation of these effects in an interference experiment are considered under the condition that the length of temporal coherence lc is considerably smaller than the length of longitudinal spatial coherence ρ‖ of the field. It is shown that, for lc ≪ ρ‖, the longitudinal purely spatial coherence of the light field in fact governs the coherence of the wave train in the process of its propagation. The length and the time of coherent (“free”) path of the wave train are considered as new spatial and temporal scales of a partially coherent light field.

Coherence effects of thick objects imaging in interference microscopy

In this paper we present a model of interference microscope image formation, which allows for analysis on unified basis of imaging different types of samples with different interference microscope modalities. The applicability of the proposed model to analysis of the coherence effects, arising in confocal and full-field interference microscopes, when imaging in depth of a layered sample, is shown. The effect of sample transversal structure on the coherence signal is also analyzed, showing that in this case the interference microscope can not be characterized by a single effective aperture and both illuminating and imaging apertures are important.

Numerical correction of coherence gate in full-field swept-source interference microscopy

A big problem in low-coherence interference microscopy is the degradation of the coherence signal caused by shift of the angular and temporal spectrum gates. It limits the depth of field in confocal optical coherence microscopy and degrades images of sample inner structure in most interference microscopy techniques. To overcome this problem we propose numerical correction of the coherence gate in application to full-field swept-source interference microscopy. The proposed technique allows three-dimensional sample imaging without mechanical movement of the microscope components and is also capable of determining separately the geometrical thickness and the refractive index of the sample layers, when the sample contains a transversal pattern. The applicability of the proposed technique is verified with numerical simulation.

Interference of speckle fields in the diffraction zone of a focused spatially modulated laser beam by a random phase screen

The processes of formation of average-intensity interference fringes upon diffraction by a random-phase object of a laser beam having interference fringes and focused on the surface of the object are considered. The dependences of the fringe contrast on the parameters of scattering inhomogeneities of the object and the parameters of the focused laser beam are established in analytical form for various diffraction regimes. Practical possibilities of a method of probing of scattering objects in problems of measuring the parameters of inhomogeneities and problems of interference-pattern formation in optical systems with scattering media are discussed.

Interference of laser speckle fields

The theoretical principles of noncorrelated and correlated (identical) speckle fields interference with due account of spatial photoreceiver resolution is considered. The physical analogies between identical speckle fields interference and that of partially coherent radiation of extended thermal light sources are followed.