A compact, robust and efficient nanosecond pulsed optical parametric oscillator (OPO) generating radiation in the mid-
IR spectral range is reported. The OPO is based on periodically poled material for the efficient non-linear processes of
up-converting 1064 nm radiation to 1538 and 3450 nm respectively. Pulsed emission exceeding 130 mW average power
at the idler (3450 nm) with a total conversion efficiency of 30%, including both signal and idler, has been reached. The
maximum pulse energy of the idler is 11 μJ, pulse duration around 4 ns and peak power close to 3 kW. The results are
achieved for an optical pump power of 1.4 W at the entrance of the OPO and an electrical pump power of 14 W. The
total size of the OPO device is only 125x70x45 mm<sup>3</sup> (LxWxH) including the pump laser at 1064 nm. The idler output
radiation is narrowed by spectral filtering to < 1.5nm and temperature tuneable over > 50 nm. The OPO has a robust
design and withstands shocks up to 60g at 8 ms and the storage temperature is -20 °C to + 60 °C.
The compact size and low power consumption make this OPO device suitable for many kinds of molecular spectroscopy
applications in the areas of environmental monitoring and pollution control as well as in combustion physics and process
control. Integration of the OPO source into compact equipment for Photo Acoustic Spectroscopy (PAS) allowing fast
and highly sensitive detection of methane and ethanol at ppb-levels is also described.