Researchers achieve record 8W output from mid-IR optical parametric oscillator

03 October 2024

Researchers achieve record 8W output from mid-IR optical parametric oscillator

CSP crystals outperform ZGP traditional materials in mid-IR wavelengths, pointing to new opportunities in sensing, defense and more

WASHINGTON - Researchers have demonstrated an unprecedented total output power of more than 8W from a high-power mid-infrared (mid-IR) cadmium silicon diphosphide (CSP) optical parametric oscillator (OPO) pumped at 2.06 μm. They also show that CSP crystals can outperform the commonly used zinc germanium phosphide (ZGP) for frequency down-conversion from 2 microns to the mid-IR band. This high-power mid-IR output could be useful for infrared spectroscopy, laser surgery, remote sensing and defense communications.

Marcin Piotrowski from French-German Research Institute in France of Saint Louis (ISL) leads this research that will be presented at Optica Laser Congress and Exhibition, held 20 - 24 October 2024 in Osaka, Japan.

"In the defense domain, laser power scaling in this spectral band is important for infrared countermeasures - protecting aircraft and other platforms from the growing threat of infrared-seeking missiles," said Piotrowski. "Efficient sources capable of delivering high power with good beam quality are critical, as the laser beam must travel long distances through the atmosphere."

CSP crystals are emerging as a promising alternative to ZGP for frequency conversion in OPOs. However, few studies have examined CSP for parametric conversion with pump wavelengths significantly longer than 1 micron.

In the new study, the researchers focused the pump laser to a 1-mm diameter spot inside an OPO resonator formed by two flat mirrors. The CSP sample was 9 mm long with a 4x4 mm² aperture. A ZGP sample of the same size was also used for comparison.

Although the conversion threshold for the two materials was notably different, CSP demonstrated a better conversion efficiency for high pump power. The absorption properties of ZGP cause thermal effects to become more significant. The researchers also found that CSP had a lower thermal load and less beam degradation while ZGP showed reduced beam quality at high powers due to higher residual absorption.

These initial experimental results suggest that CSP crystals may outperform the widely used ZGP for frequency down-conversion from 2 μm to the mid-IR range.

"We look forward to continuing our investigations on nonlinear crystals such as CSP for OPO emission in the mid-IR," said Piotrowski. "In particular, as the quality and maturity of the CSP material allows, we will combine it with the technologies actively investigated in our research group: monolithic non-planar cavities such as the FIRE cavity - particularly well suited for power scaling while maintaining good beam quality. In addition, compact and robust 2 µm fiber lasers are planned as future pump sources for these OPO cavities."

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