System designers and end users of diode pumped solid state lasers often require knowledge of the operability limits of
QCW laser diode pump sources and their predicted reliability performance as a function of operating conditions.
Accelerated ageing at elevated temperatures, duty cycles and/or currents allows extended lifetime testing of diode stacks
to be executed on compressed timescales with high confidence.
We present a novel, time-efficient technique for the determination of accelerated lifetime test conditions using
degradation rate data, rather than the traditionally used failures against time data.
To assess the effect of thermally accelerated ageing, 4 groups of 4 stacks each were operated for 60 million pulses at
different temperature stress levels by varying the pulse repetition rate from 100Hz to 250Hz. The measured power
degradation rates fitted to an Arrhenius type model, result in activation energy of 0.47- 0.74eV, apparently indicating
two thermally activated degradation modes with different activation energies.
Similarly, for current accelerated ageing, another 4 groups of 4 stacks were tested at operation currents from 120A to
150A. The optical power degradation rates due to current stress follow a power law behavior with a current acceleration
factor of 1.7.
The obtained acceleration parameters allowed considerable reduction of the lifetime test duration, which would have
otherwise taken an unacceptably long time under nominal operating conditions.
The successful results of the accelerated lifetime have been a major milestone enabling qualification of SCD stacks as
pump sources for the laser altimeter in ESA Bepi-Colombo space mission.
The presented reliability analysis allows life test qualification programs to be accelerated for generic QCW stacks and
their lifetime to be predicted in various operating environments.