Monitoring of early catastrophic optical damage in laser diodes based on facet reflectivity measurement

We propose a convenient, inexpensive technique to monitor the fast early stage of catastrophic optical damage (COD) in 808-nm high-power laser diodes (LDs). Using an optical system based on the 1550-nm laser diode illuminant and photodiode, we measured the facet reflectivity, which gives information about the surface morphology of the output facet with a temporal resolution of 2 ns, allowing us to trace the rapid early COD process in a transient, real-time mode. The formation of the detected 4-μm-long COD damaged area, which caused a local uneven surface at the output facet and a rapid drop in facet reflectivity at 1550 nm from 28% to 2%, was completed within 20–30 ns, 10 ns shorter than that in the longer-wavelength devices.