Polarisation compensation in non-planar image-rotating OPO ring resonators.

Non-planar image-rotating OPO ring resonators necessitate polarisation compensation in contrast to their planar counterparts. This is essential for maintaining phase matching conditions for non-linear optical conversion in the resonator during each cavity round trip. In this study, we examine the polarisation compensation and its impact on the performance of two types of non-planar resonators: RISTRA with a 2 image rotation and FIRE with a fractional image rotation (2 fraction).

Effects of pump pulse energy and repetition rate on beam quality in a high-power mid-infrared ZnGeP OPO.

We report on changes of beam quality with rising pump pulse energy and repetition rate in a high-power mid-infrared ZnGeP (ZGP) OPO in a non-planar cavity. The ZGP OPO generates 25 W in 3 - 5 μm pumped by a 10 kHz Q-switched Ho:LLF MOPA system at 2 μm. The beam quality factor increases from nearly diffraction-limited at OPO threshold to a M = 1.

Mid-infrared ZGP OPO with divergence compensation and high beam quality.

Divergence compensation, optimization of the optical-to-optical efficiency, and high beam quality of signal and idler beams of a high-energy mid-infrared ZnGeP (ZGP) optical parametric oscillator (OPO) have been demonstrated by use of a Galilean telescope inside the nonplanar fractional-image-rotation enhancement (FIRE) ring resonator. With a small variation of the distance between the lenses of the telescope, the divergences of signal and idler beams could be adjusted. Up to 36 mJ of mid-infrared pulse energy in the 3-5 µm wavelength range is obtained with 92 mJ of pump energy on crystal.

Improvement of the beam quality of a high-pulse-energy mid-infrared fractional-image-rotation-enhancement ZnGeP optical parametric oscillator.

The beam quality of a high-energy mid-infrared ZnGeP (ZGP) optical parametric oscillator has been improved by use of a negative lens inside the nonplanar fractional-image-rotation enhancement (FIRE) resonator compensating for the thermal lensing and gain guiding effects. With an f=-0.9  m CaF lens, the beam quality is 1.