Experimental observation of coherent optical oscillations in picosecond semiconductor lasers under strong-field conditions

Extremely-high-frequency (1.1 THz) coherent oscillations of the optical field emitted by a semiconductor laser were observed for the first time. The optical spectrum had a doublet structure with a 2.6 nm separation. The oscillation frequency depended on the pumping conditions and was not equal to the reciprocal of the round-trip time of the laser cavity. The power density of the laser radiation was estimated to be in the range of 10⁹ W cm^-2.