Innovative Facet Passivation for High-Brightness Laser Diodes

The objective of this effort is to increase the power of low fill-factor (20%) laser diode (LD) bars from the present state-of-the-art (SOA) of 60-70 W/bar to operate reliably at 300W/bar. This dramatic 5X increase in the power/bar will be accomplished by increasing the power at which SOA LDs fail, namely, increasing the threshold for catastrophic optical damage (COD) of the LD mirrors by improving the passivation of the facets. The SOA facet passivation is the E2 passivation that was invented by IBM in the early 1990s. While E2 passivation is perfectly acceptable for SOA bars operating at 60-70 W, it is not capable of withstanding the 300 W/(20% fill-factor bar) desired for military high energy lasers (HELs). COD of the front facet (laser mirror) is the main failure mechanism that constrains scaling LD power by 10X over the SOA to 600 W per bar. COD is due to optical absorption at the facets as a result of dangling bonds resulting from the facet formation process (cleaving) or from contamination from the ambient.