Abstract

Time-resolved four-wave mixing (FWM) is a very powerful method to study the nature and dephasing of elementary excitations in condensed matter. In FWM experiments, two delayed ultrashort laser pulses with wave vectors k₁ and k₂ interfere in a sample to produce a diffracted signal (DS) in the direction k_s = 2k₂ – k₁ In the case of a homogeneously broadened system, the DS is emitted immediately after the second pulse ("tree-induction decay"), whereas in a strongly inhomogene ously^r broadened system the DS appears delayed by an amount equal to the time delay Δt = t₂ – t₁ between the input pulses ("photon echo").¹

© 1992 Optical Society of America