Effects of gamma radiation on high-power infrared and visible laser diodes

The effects of gamma radiation on high-power semi-conductor laser diodes were measured. While operating, five commercial near-infrared (785 nm, 60 mW) and six visible laser diodes (670 nm, 30 mW) were exposed to approximately 10 kGy at a relatively high dose rate (5 kGy/h). The far-field output beam patterns were monitored during radiation and recovery, as well as the overall intensity (constant current mode) and the internal monitor photodiode current. The linear dimensions of the far-field beam patterns shrank in size by the end of radiation by 3%-20% for the IR lasers and 15%-20% for the visible. The ellipticity of the beams changed by -16% for the IR and +8% for the visible case. The intensity, as measured with an external camera, decreased during irradiation by a maximum of 2.7 dB for the visible laser and 2.5 dB for the infrared; however, the photodiode photocurrents changed by less than 1 dB. Both types of lasers recovered completely over several days. The near- and far-field patterns were examined both below and above threshold before and after radiation/recovery, with no evidence of defects or other gross changes.