Diode Laser Lifetime

The long lifetime of laser diodes as compared to arc lamps is an important consideration for pumping solid-state lasers with these devices. We will distinguish between catastrophic failures and normal degradation during operation. Laser diodes, like all semiconductors, are very susceptible to damage by electrostatic discharges or high-voltage transients. Therefore handling of these components requires electric discharge control such as wearing wrist straps and grounded work surfaces. Also great care has to go into power supply and driver design to protect this very expensive pump source from transients, current surges, and high voltage. Operation at excessive currents will lead to catastrophic mirror facet damage. Also, insufficient cooling combined with high currents can melt the solder joints or vaporize the wire bonds within the diode structure.
Under proper operating conditions laser diodes degrade in a fairly predictable manner which results in a decrease in output over time. The higher the operating current and/or the operating temperature, the faster the degradation. The decrease in output over time can be caused by structural defects, which spread through the laser diode forming light absorbing clusters. Dark lines or spots in the output beam are a manifestation of this damage. The degradation of AlGaAs laser diodes, the most common pump source, is usually attributed to oxidation and migration of aluminum under high-power operation. Structural defects can also be caused by thermal stress due to different thermal expansion coefficients of semiconductor and heat sink material.
Facet damage due to the environment or high-radiation flux is another source of degradation, so is diffusion of solder into the semiconductor lattice over time caused by the high-current density. After-screening of the laser diodes during a burn-in period performed by the manufacturer has eliminated early failures due to production problems, and very long operational lifetimes can be achieved. Lifetimes of cw devices are typically on the order of 10⁴ hr. In most commercial systems requiring long life, diode arrays are typically operated at 75% of their rated output. Quasi-cw bars and stacked arrays achieve lifetimes of several billion shots.