Operation of a coherent ensemble of five diode lasers in an external cavity

A theoretical analysis of the coherent external cavity semiconductor laser ensemble is presented. The theoretical analysis lends insight to the limits of stability of the coherent ensemble for different spatial filter designs and indicates differences in operating behavior expected for different current drives to the gain elements. The theoretical analysis obtained from considerations of both spectral control and stability predicts an experimental observation that spatial filter duty cycles of 30-40% optimize system behavior. The measurements demonstrate the effects on both the intensity and spectrum of the laser output that results from changing the DC and pulse drive currents to the elements in the array. With current pulses applied to only two of the elements, single-spectral-mode pulse output is possible with a linewidth of less than 7.5 MHz. Approximately 100% modulation depth pulses in a single spectral mode are reported, with measured linewidths of ~9 MHz compared to the 7.5 MHz instrument resolution