GaSe晶体的双光子吸收对太赫兹输出的影响

Two-photon Absorption Attenuated THz Generation in GaSe

根据光整流效应,利用超快激光脉冲泵浦GaSe晶体实现了0.2-2.5 THz的宽带太赫兹辐射输出。禁带中的电子在两个800 nm光子的作用下激发到导带中形成自由载流子,进而吸收所产生的太赫兹辐射,最终导致太赫兹的输出随泵浦功率的增加而趋于饱和。为了研究双光子吸收对太赫兹输出的影响,测量了800nm处的GaSe晶体的双光子吸收系数,结果为0.165 cm/GW。通过对太赫兹输出实验数据的拟合,得到GaSe晶体中自由载流子对太赫兹输出的吸收截面为1×10^-15cm^2。本文的研究结果可用于优化GaSe晶体在强激光泵浦下的太赫兹转换效率。

The broadband THz generation from 0 . 2 to 2 . 5 THz was measured as a function of pump intensity in a single pure gallium selenide crystal based on the optical rectification of ultrafast laser pulses. Two-photon absorption at 800 nm can generate free charge carriers which can absorb the generated THz radiation, and finally attenuate THz output. The result indicates that the pump inten-sity dependence of ouput THz radiation changes from square to sub-linear relationship and the satu-ration of output THz radiation appears at high pump intensity. To study the impact of two photon ab-sorption on THz generation, the two photon absorption coefficient of GaSe at 800 nm is measured to be 0. 165 cm/GW, which is determined by the measured nonlinear transmission. The THz output fitting result taking account of the free charge carrier absorption cross section of 1 × 10^ -15 cm^2 is con-sistent with the experiment data very well. This estimation result can be used to optimize the conversion efficient of THz generation in GaSe crystal under intense laser pump.