SINGLE-FREQUENCY INASSB LASERS EMITTING AT 3.4-MU-M

Single frequency InAsSb lasers operating from 77 to 110 K in CW mode h ave been tested for their suitability for trace gas analysis. The thre shold current I-th was as low as 25 mA at 78 K with a characteristic t emperature T-0 of 25 K. Selected lasers show single-frequency operatio n over a large range of currents and temperatures with a side mode sup pression ratio of 25 dB. The FWHM of the far-field pattern was 30 and 50 degrees in lateral and transverse directions, respectively. The bea m elliptical factor was 1.7. The maximum CW optical power was up to 1. 2 mW per facet to single frequency at 80 K. The lasers allowed tuning by the injection current without mode hopping of about 1.2 cm(-1) with a tuning rate of 0.032 cm(-1) mA(-1). The average temperature tuning was 1.3 cm(-1) K-1. Relative intensity noise in normal operation was a s low as 4 x 10(-16) at 1 Hz. Therefore, a theoretical detection limit in terms of optical density of 2 x 10(-8) has been estimated for meas urements by tunable diode laser spectroscopy at 3.4 mu m.