Optical Properties of Coherent Transients which are Stimulated by Picosecond Pulses at Three Frequencies

Abstract

The coherent transient effects such as optical nutation, free induction decay, photon echoes, pulses formed by probe pulses, Carr-Purcell echoes, phase conjugation, etc. can be expected to be generated by picosecond pulses. Some of these effects have been observed already [1]. Many of these nonlinear effects are due to coherent space phase as well as time-phase information which is stored in the off diagonal density matrix elements and become observable via the electric polarization. In a somewhat more subtle manner space phase information can be stored in the diagonal density matrix elements and lead to phenomena such as forward or backward phase conjugation, probe pulse effects, etc. Thus the decay of both the diagonal and off diagonal density matrix elements can be measured. This paper is primarily concerned with the optical properties of the waves which are generated by picosecond pulses at three frequencies, ω₁, ω₂, ω₃ between energy states a, b, c, d which are shown in Fig. 1. Three wave effects are considered since the sum frequency is an allowed electric dipole transition for gases, isotropic liquids, and cubic solids.