Nonlinear optical (NLO) materials play a crucial role in high-energy laser applications by enabling efficient frequency conversion. One of the most widely used NLO materials is ZnGeP2 (ZGP) due to its excellent transparency and phase-matching properties in the mid-infrared (2-8 microns) range. However, ZGP has its limitations, including its incompatibility with 1- and 1.5-micron laser pumping and its limited usefulness in generating output in the 8-12 micron atmospheric window due to severe multi-phonon absorption.
To address these limitations, researchers have been working to develop new NLO materials with improved properties. One such material is CdSiP2 (CSP), a bulk birefringent chalcopyrite analog of ZGP. CSP offers several advantages over existing materials, including its larger band gap, higher birefringence, and dramatically higher nonlinear coefficient and thermal conductivity. CSP is also compatible with 1- and 1.5-micron laser pumping and offers lower absorption losses than ZGP, making it a promising alternative for power-scaling 2-micron-based devices.
Another promising class of NLO materials is quasi-phase matched (QPM) semiconductors, including OP-GaAs and OP-GaP. QPM materials are grown by all-epitaxial processing, which involves producing GaAs (GaP) with an inverted orientation with respect to the substrate, photo-lithographically patterning the desired grating structure, and re-growing the material by hydride vapor phase epitaxy (HVPE) at rates up to 200 (need to remove brand name). This process allows for precise control of the grating period and orientation, resulting in efficient frequency conversion and tailoring of the spectral response to specific applications.
In summary, the development of new and improved NLO materials is critical for advancing high-energy laser applications. Materials such as CSP and QPM semiconductors offer promising alternatives to traditional NLO materials like ZGP, with improved properties and compatibility with a wider range of laser pumping wavelengths. Continued research and development in this area will undoubtedly lead to further advances in NLO technology and its applications.