Observation of continuous downshift of fs-pulse spectrum due to impulsive Raman scattering in SF/sub 6

• Published in: Technical Digest. Summaries of Papers Presented at the Conference on Lasers and Electro-Optics. Conference Edition. 1998 Technical Digest Series, Vol.6 (IEEE Cat. No.98CH36178) p. 491
• Main Authors: Korn, G., Nazarkin, A., Duhr, O.
• Format: Conference Proceeding
• Language: English
• Published: IEEE 1998
• Subjects: Frequency; Gas lasers; Hollow waveguides; Kerr effect; Optical pulses; Pulse measurements; Pulse shaping methods; Raman scattering; Shape measurement; Spectroscopy
• ISBN: 1557523390
• DOI: 10.1109/CLEO.1998.676536

Summary form only given. We report the first results of experimental and theoretical studies of intense fs-pulse propagation in a Raman-active medium with pulse durations /spl tau//sub p/<T/sub v/, e.g., when the process of impulsive excitation of molecular vibrational-rotational motion is involved in the pulse dynamics. We have found that the evolution of pulse spectrum in a gas of SF/sub 6/ molecules differs significantly from that in atomic gases, where fast electronic Kerr effect is dominant and, on the other hand, bears no resemblance to the traditional version of Raman scattering. Competing with pulse spectral broadening, we have observed a well-pronounced shift in the pulse central frequency toward lower frequencies that increased nearly proportionally to the gas pressure. In addition, a progressing asymmetry in the shape of the pulse spectrum was observed. With an increase in gas pressure, a noticeable suppression of the high-frequency wing of the spectrum occurred. We consider these features to be strong evidence for the impulsive excitation mechanism and characteristic of stimulated Raman scattering with extremely short pulses. We explain the observed dynamics on the basis of a model that accounts for the processes of Kerr-type self-action due to the contribution of distant electronic levels and stimulated Raman scattering in the ground electronic state.