Direct measurement of facet temperature up to melting point and COD in high-power 980-nm semiconductor diode lasers

The authors describe a straightforward experimental technique for measuring the facet temperature of a semiconductor laser under high-power operation by analyzing the laser emission itself. By applying this technique to 1-mm-long 980-nm lasers with 6- and 9-μm-wide tapers, they measure a large increase in facet temperature under both continuous wave (CW) and pulsed operation. Under CW operation, the facet temperature increases from ∼25°C at low currents to over 140°C at 500 mA. From pulsed measurements they observe a sharper rise in facet temperature as a function of current (∼400°C at 500mA) when compared with the CW measurements. This difference is caused by self-heating which limits the output power and hence facet temperature under CW operation. Under pulsed operation the maximum measured facet temperature was in excess of 1000°C for a current of 1000 mA. Above this current, both lasers underwent catastrophic optical damage (COD). These results show a striking increase in facet temperature under high-power operation consistent with the facet melting at COD. This is made possible by measuring the laser under pulsed operation.