what determines the lifetime of a laser module?

Typical lifetime of laser diode modules are 25,000 to 50,000 hours.  If the laser diode temperature continues to rise exceeding the maximum operating temperature, the diode can be catastrophically damaged or the long term performance may degrade significantly.  If the laser diode's operating temperature is reduced by about 10 degrees, the lifetime will statistically double.

  Laser module lifetimes can be extended significantly by maintaining the case temperature at the low end of the operating temperature range.  Heat sinks are recommended and must be used if the laser is operating constantly.  Operating the laser modules at the low end of the recommended voltage range will also help to extend the lifetime of the laser.