New nonlinear crystal spans mid-IR region

Recognizing that nonlinear oxide-based crystals can only shift the output of 1.06 μm (neodymium-based) and 1.55 μm (erbium-based) solid-state lasers up to approximately 4 μm wavelengths, while chalcopyrite crystals suffer from low damage thresholds and are not suitable for high-average-power applications, researchers at BAE Systems (Nashua, NH) and the U.S. Air Force Research Laboratory (Wright-Patterson AFB, OH) have developed a new, robust nonlinear optical crystal that generates mid-IR output in the 2 to 9 μm range.

The high-optical-quality cadmium silicon phosphide (CdSiP2) crystals—measuring 19 mm in diameter and several centimeters in length—were grown using directional solidification in a modified high-temperature furnace. The unpolarized-absorption spectrum of the crystal shows transparency between 560 nm and 9.5 μm. This new crystal can be pumped with 1.06 or 1.55 μm solid-state lasers to generate output beyond 4 μm in a single optical-parametric-oscillator step; that is, 1.55 µm pumping provides continuous tunability from 1.7 to 9.5 µm, while 1.06 µm pumping produces a 6 µm output that could be useful for medical applications. Contact Peter Schunemann at [email protected].