Numerical approach to non-equilibrium carrier relaxation in picosecond and subpicosecond physics

We present a numerical resolution of the time-dependent Boltzmann equation which describes the electron relaxation kinetics in direct gap semiconductors under subpicosecond optical excitation. The calculation is specialized to GaAs. We investigate, around the Mott density, the conditions of internal thermalization and energy relaxation of electrons, which depend strongly on the plasma concentration.     

Generation of picosecond and subpicosecond light pulses with saturable absorbers

Single light pulses, generated by a mode-locked Nd-glass laser, were shortened with saturable absorbers of low initial transmissionT ₀. The pulse duration was reduced from 8 to 2.6 ps after a single pass through a dye cell ofT ₀=10^–7. Light pulses as short as 0.5 ps were observed after five transits through an absorberamplifier system. Detailed calculations of the stationary and the transient situation (with respect to the dye relaxation time) are presented to demonstrate optimum conditions for the pulse shortening.     

Comment on "Temporally resolved electro-optic effect"

We comment on the recent Letter by S. P. Jamison et al. [Opt. Lett.31, 1753 (2006)] where the analysis of a chirped probe pulse that is electro-optically modulated by a terahertz pulse reportedly results in a new expression for the electric field. While in principle the derived expressions for the total field after the crystal are correct, in their treatment the authors implicitly assumed that the derived total field is identical to the measured field, without regard to the residual birefringence of a typical electro-optic crystal or a crossed analyzer. Based on this analysis neglecting birefringence, they report that earlier expressions of the temporal field are incorrect. Here we show, on the contrary, that for chirped single-shot terahertz measurement schemes that include residual birefringence, the temporally resolved electro-optic effect is described correctly by the commonly used expression in the literature. We verify this result with our experimental data.     

爱因斯坦光电方程与光电效应实验外推法

讨论了爱因斯坦光电方程,指出现今在光电效应实验中普遍使用的爱因斯坦光电方程只是在T＝0K时才成立。对室温下光电流的J－U曲线的分析表明,除T＝0K情况外,光电子无明确的最大动能,也无明确的截止电压概念,改进了光电效应实验外推法,指出“截止电压”的确定必须在靠近零的同一光电流数值下进行,结果表明只有在以准爱因斯坦光电方程取代原有的爱因斯坦光电方程的情况下,光电效应外推法中内在的矛盾才可以消除。