We show that atoms from wide velocity interval can be concurrently involved in Doppler-free two-photon resonant far from frequency degenerate four-wave mixing with the aid of auxiliary electromagnetic field. This gives rise to substantial enhancement of the output radiation generated in optically thick medium. Numerical illustrations addressed to typical experimental conditions are given.PACS number(s): 42.50. Gy, 42.65.Dr, 42.65.Ky Strong optical resonances inherent to free atoms and molecules are negated by the fact that only small fraction of the species can be concurrently resonance coupled in warm bulk gases. This is because of Maxwell distribution of the Doppler shifts of their resonances. Doppler-free (DF) coupling is usually achievable under equal frequency counter-propagating weak waves in two-photon-resonant ladder schemes. Because of the phase matching requirements, such schematic can not be implemented for far from frequency degenerated four-wave mixing (FWM).Second, the conditions of intermediate one-photon quasi-resonance can be very seldom satisfied in this case. Third, DF coupling vanishes with the growth of not only frequency difference but with strengths of the coupled fields too due to ac-Stark effect. Forth, DF coupling can not be routinely achieved in Raman schemes, like considered in this paper, because of the inherent frequency difference. Fifth, DF absorption does not indicate readily achievable DF FWM polarization in general case. Moreover, it is not obvious that increased FWM polarization would result in enhanced output of generated radiation, because of accompanying increased absorption.This paper is aimed at demonstrating that the outlined limitations in optical physics can be removed by making use quantum coherence processes induced by an auxiliary intense control field. Considered effects lead to concurrent contribution of atoms from a wide velocity interval to the induced resonance and to eliminating it's Doppler broadening under moderate light intensities. We investigate two-photon-resonant Raman-type FWM, controlled by an
Abstract. New feasibity of coherent quantum control of four-wave mixing processes in a resonant Doppler-broadened medium are studied. We propose a technique which enables one to enhance the quantum efficiency of nonlinear optical conversion. At the same time, it allows one to decrease the required intensities of the fundamental beams compared to those necessary in the approach based on coherent population trapping. The major outcomes of the analysis are illustrated with numerical simulation addressed within a practical medium.
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