title: Thermal lensing effect of CS2 studied with femtosecond laser pulses.
abstract: By chopping 820 nm 18 femtosecond (fs)-laser pulses, continuously generated by a self-mode locked Ti:Al2O3 laser at 82 MHz, into trains with both train-width and train-to-train separation considerably longer than the thermal diffusivity time constant τth of CS2, we conducted Z-scan measurements on it at various times relative to the leading pulse of each train (T's). As a result, we observed negative nonlinear refraction strengthening with T within τth and gradually stabilizing with T exceeding τth. We quantitatively explain the experimental results in terms of the thermal lensing effect. In particular, we attribute the heat generation to non-radiative relaxation of libration excited by individual 18 fs-pulses via stimulated Raman scattering. In contrast to the commonly held view of multi-photon excitation, we propose and verify a new heat-generating mechanism for the thermal lensing effect in CS2.
authors.affiliation: Department of Physics, National Chung Cheng University, Min-Hsiung, Chia-Yi 621, Taiwan, Republic of China. twei@ccu.edu.tw.
authors.forename: Yi-Ci
authors.initials: YC
authors.lastname: Li
authors.forename: Yu-Ting
authors.initials: YT
authors.lastname: Kuo
authors.forename: Po-Yuan
authors.initials: PY
authors.lastname: Huang
authors.forename: Sidney S
authors.initials: SS
authors.lastname: Yang
authors.forename: Cheng-I
authors.initials: CI
authors.lastname: Lee
authors.forename: Tai-Huei
authors.initials: TH
authors.lastname: Wei