Abstract

The quantum nature of the source of stimulated Raman scattering and its effect on the output of Raman self-generators have been investigated in a number of studies.¹ Quantum theories of stimulated Raman scattering predict that its source is equivalent to spontaneous Raman scattering. We report on experimental investigations of spontaneous Raman scattering in the transient limit. In this regime the quantum theories predict that the spontaneous Stokes radiation produced in a single pass generator with Fresnel number 1 reproduces the amplitude and phase variations of the pump radiation, with the possible exception of a constant phase offset that can vary randomly from one laser pulse to the next. We have investigated the temporal behavior of spontaneously generated Stokes radiation from hydrogen using second harmonic 40-ps pulses from a mode-locked Nd:YAG laser. Our initial results indicate that the spontaneous Stokes pulse follows the pump pulse in its intensity profile, even though its duration is less than the material response time by a factor of 2.

© 1989 Optical Society of America