Dmitry V. Lyakin

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.

What type of coherence of the optical field is observed in the Michelson interferometer

The types and corresponding coherence functions of the optical field are considered depending on the frequency and angular spectra of the field. The main concepts of the theory of coherence effects in the interference experiment with the amplitude splitting of the initial field are discussed. It is shown that, in strict correspondence with the theory of coherence of the random wave fields, the Michelson interferometer reveals manifestations of the transverse and longitudinal spatial (rather than temporal, as it is commonly adopted) coherence of the optical field; the purely temporal coherence of the optical field is revealed only under special conditions of the interference experiment. Beyond these conditions, either spatial or spatiotemporal coherence is revealed.

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.

Method for distant diagnostics of layered media inner structure

The method of autocorrelation low coherence interferometry is proposed for diagnostics of layered media inner structure. The possible applications of this method in technology and biomedicine are presented. In this method the low coherence optical field is reflected from the objects structure and then analyzed using the Michelson interferometer. Since the object is outside of the Michelson interferometer the axial position of the object is not important and thus the object can move during the measurements. The theoretical background of this autocorrelation method for a media with discrete and continuous optical structure modification is presented.

Manifestation of longitudinal spatial coherence of light in the interference experiments

The phenomenon of longitudinal spatial coherence of light and conditions of manifestation of this type of coherence in the interference experiments with Michelson interferometer are discussed. Manifestation of longitudinal spatial coherence of light of an extended thermal source at large (in comparison with length of longitudinal spatial coherence) and short lengths oftemporal coherence oflight has been experimentally shown.

Laser wave front matching interferometer for thickness measurements

The so-called Laser Wave Front Matching Interferometer (LWFMI) is developed for thickness measurements of transparent films and layers with high spatial resolution. This interferometer is constructed under scheme of Michelson interferometer with focusing microobjectives in the interferometer arms (Linnik scheme) and wide integrating detector aperture in common exit branch. The peaks are observed in the envelope of interference LWFMI signal as function of object displacement relatively to the focal point of an interferometer focusing objective when the probing beam is focused on the front and rear surfaces of a layer. The distance between the interference peaks is proportional to the geometrical thickness of a layer and can be measured by the technique of interference fringe counting, if the refractive index of layer medium is known. The results of geometrical thickness measurements of some objects by this interferometer for high numerical aperture of probing focused beam are discussed.

Tissue structure and blood microcirculation monitoring by speckle interferometry and full-field correlometry

In this paper a few speckle techniques is discussed from the point of view of their application for medical diagnosis in dermatology and ophthalmology using monitoring of tissue structure and blood microcirculation. The basic principles of proposed techniques and corresponding hard and software descriptions are presented. Results of model (tissue phantoms), in vitro and in vivo measurements for the human eye tissues and skin are discussed.

Correlation technique for exploration of local features of emission spectrum of laser and superluminescence diodes

It is well known that the spectral properties of the light source relate explicitly to the correlation properties of the source field. Thus it is possible to have an action on the correlation function of the source affecting on emission spectrum. It is shown in this paper that correlation analysis of the light source field allows to perform control of the spectral properties of the source. Availability of Michelson interferometer for investigation of the thin structure of emission spectrum of superluminescent diodes (SLD) and appreciation of the use of its in low coherence interference schemes are discussed in this work.