Generation of coherent picosecond pulses using modelocked semiconductor lasers

Double-heterojunction semiconductor diode lasers operating in an external cavity can be actively and passively mode-locked to generate continuous trains of picosecond pulses of about 1-W peak power. These lasers, which are also frequency-tunable, provide convenient and inexpensive sources of coherent ultrashort laser pulses for time-domain spectroscopy of semiconductor and molecular materials. Further developments in laser diode fabrication techniques should make it possible to extend the spectral range from the visible to the near-infrared (up to 4μ). Intracavity time-domain spectroscopy with increased sensitivity is also possible, particularly in the case of studies of semiconductor carrier dynamics. Other applications include investigation of coherent pulse propagation, two-photon spectroscopy, and development of laser oscillators exhibiting testability, phase conjugation, and other types of nonlinear behavior.