Linewidth measurements of tunable diode lasers using heterodyne and etalon techniques

Measurements of the linewidths of Pb-salt diode lasers operating in the 8- and 9-microm region are reported. The linewidths of the 9-microm lasers were determined by conventional heterodyne techniques, while for the 8-microm lasers a new technique based on a Fabry-Perot etalon was used. The new technique avoids the complexity and limited wavelength range of the heterodyne measurements and can be used for any tunable laser. The linewidths observed varied from 0.6- to >500-MHz FWHM. The linewidth was found to vary dramatically from device to device, to depend strongly on junction temperature and injection current, and to be correlated with vibrations caused by operation of a closed-cycle refrigerator.