Measurements of Induced Transmission and Absorption-of SF6 after Pumped by a CO2 Laser (Ⅱ)-Spatial Evolution of Vibrational Energy -

The spatial distribution and dissipation of vibrational energy in SF6 gas after multiphoton excitation was measured with the pump-probe technique by use of two tunable TE C02 lasers. The probe beam (0.5mm radius) monitored the induced transmission and absorption both inside and outside of the pumped region (0.6mm)，or the in-axis and off-axIs vibrational distribution. The vibrationally excited (hot) molecules are extended over the radial distance of 3mm out of the the pumped region at the delay time of 50μs after pumping. It was observed that the probed spectra and time behavior of the off-axis absorption was quite different from that of the in-axis. The vibrational temperature of the off-axis molecules seems much lower than that of the in-axis. Thus，it is considered that the surrounding molecules are sufficiently excited by the T-V collisional process due to the gas expansion out of the pumped region rapidly heated up by the V-T relaxation. The effects of gas pressure，additive gas (He，N2 )and pump intensity were also studied