Abstract

The creation of a high coherence source of frequency converted laser radiation, for example as required in multi-coloured pulsed holography, requires the use of forward Raman amplification in the Dicke narrowed line of hydrogen at low pressures (3 - 4 atm). However, the conversion efficiency of Raman amplifiers is usually not sufficient even at high pressure. Indeed, in order to address this problem previous workers have used deliberately matched spatial profiles of the pump and seed Stokes beams at 17 atm [1] and superregenerative Raman amplification [2]. In this article we report the experimental observation of forward Raman amplification in the Dicke narrowed line at an H₂ pressure of 4 atm with an energy conversion efficiency of up to 68 %, a value close to the theoretical limit of 78 %. given by the Manley-Rowe relation. As such a Stokes pulse (λ_s - 674 nm) having an energy of ~ 0.7 J was achieved from only ~ 1 J of pump energy (λ_L = 526 nm).

© 1996 IEEE