Coherent tunable laser sources in the longwave infrared (LWIR) spectral region
are in high demand for military applications. Most lasers cannot produce outputs far into
the infrared region, and therefore a conversion process is needed to achieve desired
wavelengths. Quasi-phase matching is a technique that spatially modulates the nonlinear
properties of a given material, periodically reversing the induced nonlinear polarization to
ensure positive energy flow from the pump source to the converted fields, subject to
conservation of energy and momentum. Through the use of optical parametric oscillation
(OPO), and nonlinear quasi-phase matched orientation-patterned gallium arsenide
(OPGaAs), producing LWIR wavelengths is possible. The OPGaAs OPO was pumped
with a Q-switched 2.054μm Tm,Ho:YLF laser. As a precursor to the LWIR OPGaAs
OPO, different resonator geometries were explored with a midwave (MWIR) OPGaAs
OPO utilizing both SRO and DRO mirror sets. While thresholds increased with cavity
length, the slope efficiencies remained relatively similar with the respective mirror set.
The LWIR OPGaAs OPO explored the performance using two separate cavity
configurations, an SRO and an asymmetric cavity; and five different OPGaAs samples
representing three different grating periods. The highest slope efficiency in the SRO
LWIR cavity was found to be ~29%, with threshold values of ranging from ~45-90μJ.
The slope efficiencies for the asymmetric cavity range from ~4-16% while experiencing
higher thresholds of ~150-220μJ, lower overall output power, and increased cavity
instability. At higher pump energies, rollover was observed in both cavity
configurations. SNLO was used to model the OPO output in the hopes that it might
provide some insight into this behavior. The theoretical performance plot fit the acquired
data decently but failed to predict the behavior at the higher energies. Spectroscopic data
were collected for both OPO signal and idler output, presenting good agreement with
theoretical tuning curves.