INTERPLAY BETWEEN THE OPTICAL KERR-EFFECT AND STIMULATED LIGHT-SCATTERING IN BULK CARBON-DISULFIDE

Using a lens of focal distance 10 cm, we sent plane-polarized optical pulses of wavelength 532 nm and duration 30 ps into a transparent cell of length 1 cm, filled with carbon disulfide at standard pressure and temperature. If a pulse generates at the focus of the lens an input i ntensity of at least I-0 = 0.3 GW/cm(2), then stimulated light scatter ing takes place, and we observe a strong backward-propagating signal. By monitoring its spectrum and transverse spatial profile as a functio n of input intensity, we found quantitative information on the optical Kerr effect. At input intensities of I-0, 1.2I(0), and 1.8I(0), self- focusing leads to the formation of one, two, and four filaments, respe ctively. Each of these is subject to self-phase modulation and thus ge nerates in the backward spectrum a frequency band of a granular struct ure. The latter can be perfectly reproduced by evaluating the Fourier transform of a phase-modulated electric field on the basis of the meth od of stationary phase. This. allows us to calculate intensity and lif etime of a filament. If the input intensity exceeds the value of 1.8I( 0), fluctuations in refractive index destabilize the filamentation pro cess. Backward spectra no longer consist of separate bands, and their shape varies at random during each series of laser shots. For input in tensities higher than 3I(0) the combined action of stimulated scatteri ng and self-phase modulation causes the structure of spectra to become smooth. This explains why at an input intensity of 30I(0) one observe s for each laser shot a continuous backward spectrum, which possesses a large band that extends to relative wave numbers of approximately -2 00 cm(-1). (C) 1998 Optical Society of America.