Heterodyne pump-probe and four-wave mixing in semiconductor optical amplifiers using balanced lock-in detection

We demonstrate a new detection scheme for pump-probe and four-wave mixing h eterodyne experiments, using balanced detection and a dual-phase lock-in fo r spectral filtering. The technique allows the use of low repetition-rate l aser systems, as is demonstrated on an InGaAsP/InP bulk optical amplifier a t 1.53 mu m. Ultrafast pump-induced changes in the amplitude and phase of t he transmitted probe signal are simultaneously measured, going from small t o large signal changes and with no need of an absolute phase calibration, s howing the versatility and the sensitivity of this detection scheme. The re sults for small perturbations are consistent with previous pump-probe exper iments reported in literature. Time-resolved four-wave mixing in the absorp tion regime of the device is measured, and compared with numerical simulati ons, indicating a 100 fs dephasing time. (C) 1999 Elsevier Science B.V. All rights reserved.