Abstract

We describe the results of experiments designed to study the spectral and temporal dynamics of stimulated rotational Raman scattering (SRRS) in air as a function of intensity, pulse shape, and pulse length.¹ Our experiments were performed using one arm of the Nova laser at Lawrence Livermore National Laboratory at a wavelength of 1053 nm. A collimated spatially uniform beam (11.5-cm diameter) was propagated over a 75-m air path to a diagnostic station. Data were obtained for nominally square and ramped temporal pulse shapes, 1 and 2 ns in length, with intensities ranging from 1.7 to 3.3 GW/cm². Time-resolved spectra were recorded using a 1-m spectrometer close-coupled to a film-backed streak camera. Experimental results indicate that the initial pulse shape is most influential in the evolution of SRRS. Differences of up to 50% in the temporal onset and intensity of SRRS for ramped and square pulses of equivalent average intensity have been observed. Numerical simulations of the laser and Stokes pulse evolution have been performed including pump depletion and multiple rotational transitions. These calculations are found to be in good agreement with experiment. Experimental results and additional modeling are discussed.

© 1988 Optical Society of America