Pico and Femtosecond Optical Pulses from Semiconductor Lasers

Dr. Nikolai Stelmakh



New demands on the stability of laser pulses, on the compactness and effectiveness of the optical pulsed sources, crucial to the multiple electro-optical applications and space telecommunications, bring a new interest to all-diode optical pulse sources based on single or array laser diodes. The main basic concepts and particularities of physical process in semiconductor laser that govern the different regimes of short pulse generation will be present as an introduction into the chirped mode-locked regime demonstrated for the first time in 1992. Special attention will be devoted to presentation of an unique semiconductor material obtained by heavy ion irradiation as a femtosecond saturable absorber. A huge capacity of carrier recombination of such material give a possibility to create an all optical gate with potential modulation frequencies over 1THz. These materials introduced in the cavity of semiconductor laser bring many surprising results: phase-amplitude coupling factor over 20, Q-switch with pulse duration less than round-trip of cavity, pulse repetition frequency higher than 500GHz, a typical pulse-width in mode-locking regime around of 1 picosecond. Nevertheless, the wide amplification spectra of laser diode (higher than 20nm) suggest the generation of pulses as short as 50 fs. During more then ten years, a large variety of ideas and cavity configurations were investigated to obtain this full spectra mode-locking. In 1992, crucial experiments were performed and 250 fs 25 W pulses were obtained directly from semiconductor laser. The conceptual development of Master equation for mode-locked laser diodes, key experiments leading to this results, recent achievements on array and matrix laser diode structures and today's perspectives will be discussed during the seminar.



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