Backward fluorescence from dense cesium vapor induced by Ti:Sa femtosecond laser

Ticijana Ban, Damir Aumiler and Goran Pichler
Institute of Physics, Zagreb, Croatia

At very high cesium densities almost no light can be transmitted. However, backward fluorescence excited by the laser entering the vapor can be readily collected and spectrally analyzed. In the past c.w. and nanosecond lasers have been used for such observations. We were interested in the excitation of the backward fluorescence by a Ti:Sa femtosecond laser oscillator. The tuning range was 700-850 nm and the temperature of an all-sapphire cell was in the 400-600 oC range.
The spectrum was resolved between 280 and 1100 nm with numerous well known spectral features. However, a few new satellite bands especially in the infrared region revealed that two potential curves of 0g- symmetry made two avoided crossings. This interpretation of satellite bands in the near infrared spectral region has interesting connection with cesium ultracold molecule formation [1].
The rest of the visible spectrum consisted of numerous atomic emission lines and a few of molecular origin. We were also interested to compare obtained backward LIF with high pressure pulsed Cs lamp spectrum [2], which may serve in further development of cesium discharge lamp.
However, when the excitation wavelength approached 750 nm, we observed entirely different spectrum with irregular oscillations. Since this wavelength also correlates with the maximum cone angle (see next poster), we believe that it might be the consequence of self-phase modulation effect.