Tunable-laser-induced grating dip for measuring sub-picosecond relaxation

F. Keilmann

Anthony E.. Siegman

This letter analyzes a suggested technique for studying excited atomic or molecular states on a picosecond to subpicosecond time scale by using tunable laser beams, without requiring ultrafast laser pulses or optical detectors. In the proposed technique the frequency transform of the impulse response of an excited state is determined by measuring the diffraction of a cw probe laser beam from a moving excited-state grating induced by two intersecting tunable excitation beams, as the frequency difference between the two cw excitation beams is varied.

Anthony E.. Siegman, Dirk J. Kuizenga, Donald W. Phillion

V. M. Kenkre

Yasuaki Masumoto

Picosecond relaxation processes of excitons, including dephasing processes, are systematically studied in CuCl, CdSe and GaAs/AlAs MQW (multi-quantum well structures) by observing time-resolved induced absorption, luminescence and non-degenerate four-wave mixing. By studying the transient induced absorption from the exciton (polariton) state to the excitonic molecule state, time-resolved energy distribution of excitons in CuCl is determined (Fig.1).1) Another technique, i.e. time-resolved luminescence measurement, is applied to excitons in CdSe and GaAs/AlAs MQW (Figs.2 and 3).2,3) By analyzing the above-mentioned experiments the distribution of excitons in the two-dimensional energy-time coordinates is successfully determined. Thus, energy relaxation processes of excitons are clearly visualized. Prior to energy relaxation, coherently generated excitons are considered to be dephased. Phase relaxation of excitons in CuCl is directly measured for the first time in the picosecond time domain by means of time-resolved non-degenerate four-wave mixing (Fig.4).4) These new techniques will be demonstrated and the dephasing as well as energy relaxation mechanism of excitons and excitonic polaritons will be discussed. In the above experiments characteristics of a picosecond tunable optical parametric oscillator pumped by a mode-locked Nd3+:YAG laser as well as a picosecond tunable dye laser synchronously pumped by a mode-locked ion laser are complementarily utilized.

Anne Débarre, J. Keller, J.-L. Le Gouët +1 more