Multiple Backscattering Effects in Optical Coherence Tomography Images of Layered Turbid Media

We study the influence of multiple backscattering on optical coherence tomography (OCT) images or pulsed-sounding images of layered turbid media. A method for calculating the signal of various orders of backscattering is proposed. The retarding effects of OCT-signal dropping are analyzed. The contrast attenuation of an image of a layered medium due to multiple backscattering is examined. The blurring effect of an image of the back boundary of a scattering layer, caused by a delay of multiply scattered photons compared with single-scattered ones, is studied theoretically and experimentally using an OCT device.     

Backward influence of the interference signal from the sensors of physical quantities on the radiation intensity spectrum of a low-coherent source

We consider specific features of optical-circuit operation in the presence of radiation which is returned to the source after having passed an optical path exceeding the initial coherence length of the reference wave when, as was previously assumed, the delay modulation should not influence the oscillation mode. However, experiments with the Michelson and Sagnac fiber interferometers showed that intensity modulation of the interference signal and, therefore, intensity modulation of the source radiation related to the active-medium nonlinearity appear when the interfering waves with the phase-difference modulation return. The revealed effect leads to distortion of a signal at the interferometer output irrespectively of the delay time and can be removed by placing an optical isolator at the source output.     

Coherent noise compensation in Spectral-Domain optical coherence tomography

An efficient technique for the separation of and compensation for coherent noise in spectral optical coherence tomography with parallel spectrum detection is proposed and validated. The coherent noise is separated during one exposure by modulating the mutual delay of the signal and reference waves by a certain law. It is shown that the influence of internal motions in an object on the quality of the coherent noise separation can be reduced by the modulation frequency increasing. The technique has been numerically and experimentally validated with the help of an optical coherence tomography (OCT) setup with a radiation source operating at a wavelength of 1277 nm and a width of the recorded spectrum of about 100 nm.     

Influence of anisotropy and losses in beam splitters on the output characteristics of fiber ring interferometers

We consider the influence of phase characteristics of a beam splitter on the output signal of fiber ring interferometer (FRI). The relation between energy losses in the beam splitter and its phase characteristics is established. Allowing for these characteristics, we obtain expressions for the spurious signal at the FRI output, which differ from the known formulas, and consider methods for decreasing its value and drift. Institute of Applied Physics, Russian Academy of Sciences, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 40, No. 6, pp. 780–787, June, 1997.     

Polarization effects during the interaction of counterpropagating waves in isotropic resonant media

Using the method of nonlinear polarization spectroscopy in the oppositely propagating laser beams of different power at a wavelength of 3.39 μm, we study, both theoretically and experimentally, the mechanisms of the formation of dichroism and birefringence during the interaction of arbitrarily polarized fields of resonant radiation with gaseous methane under conditions of low pressure of the gas in the cell and saturation of the operating transition F ₂ ⁽²⁾ by the field of a strong wave. Spectral forms of the polarization resonances of the test-wave intensity at the output of the polarization spectrometer are studied experimentally. Based on the vector theory of light interaction with matter, we present an exhaustive theoretical interpretation of the experimental data on the dependence of the polarization state of a weak wave on the intensity of a linearly or circularly polarized high-power counterpropagating wave. A new technique of measuring the induced nonlinear anisotropy for test-field waves and the macroscopic parameters of the resonant gas is developed. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 50, No. 1, pp. 72–93, January 2007.