Made to order

Pavel A Apanasevich, Anatolii A Afanas'ev, А. И. Урбанович

A theoretical analysis is made of the transformation of light waves by optically induced amplitude-phase gratings of different order in a saturable absorbing medium. Allowance is made for gratings appearing; due to the absorption saturation and inhomogeneous heating of the medium. It is shown that, under certain conditions, the higher-order gratings may play a considerable role in the diffraction process. The contributions made by multistage and direct mechanisms to the n-th order diffraction are calculated. Estimates are obtained of the conditions which must be satisfied by the intensity and duration of radiation pulses, as well as by the optical properties and thickness of the absorbing medium, for these contributions to be comparable.

Samuel A. Goudsmit, George L. Trigg

Pavel A Apanasevich, Anatolii A Afanas'ev, M. V. Korolkov

An investigation is made of a higher-order distributed feedback which appears in a medium characterized by nonharmonic modulation of the parameters due to different radiation diffraction processes. The averaging method is used to obtain reduced equations for the amplitudes of opposite waves and expressions for the gain (absorption coefficient) as well as for the coupling between the waves, subject to all the gratings induced in a medium. Competition between the contributions of various diffraction processes to distributed feedback of arbitrary order is studied. An analysis is made of the coupling coefficient of waves in a dye solution laser with a second-order distributed feedback due to gratings formed by the populations of levels participating in a resonance transition and also thermal gratings induced in the active medium because of saturation of spatially inhomogeneous pumping. A calculation is made of the parameters of the medium for which the competition between the various diffraction processes makes the greatest contribution to a higher-order distributed feedback

Sarah Tomlin

Iulia Georgescu

Toshiyuki Nishiyama, Yoshiki Watanabe

The momentum distribution of a charged Bose gas at high density has been figured out as the function of the reduced wave number k up to the terms of order 1/N in the 1/N-expansion method of our theory of the density-phase operator approach. In the low momentum limit, besides the well-known term which diverges as k-2, it has been shown that there appears another term which diverges as k-1 together with several regular terms. For higher wave numbers than k = 0.1 the computation has been made by following the Monte Carlo integration method. Remarks have been made on the condensate fraction and on the higher order terms of order 1/N2.