Noncatastrophic degradation of GaAs lasers under CW operation

Three types of noncatastrophic degradation have been observed during CW life tests of GaAs injection lasers at 77°K. First, when operated submerged in liquid nitrogen, a comparatively rapid decrease occurs in the power output. This effect appears to be due to the liquid nitrogen environment and is reversible. This phenomenon has not been observed to start until the laser is energized, which suggests that it is due to fine polarizable particles in the liquid nitrogen which are attracted to the junction region. Second, some lasers have been operated on a cold finger in vacuum at current levels less than three or four times threshold for as long as 1000 hours with no significant change in output. The power outputs under such conditions were
\sim\frac{1}{3}
watt. When the current was increased byeond three or four times threshold, however, the light output decreased
\sim\frac{1}{2}
in several hours, and this degradation was irreversible. Third, a cyclic variation in output occurs when a cold trap is not used; apparently this variation is due to an oil film being slowly deposited on the laser mirrors. This effect is not observed when precautions are taken to prevent the growth of the oil film.