Development of Solid-state Optical Cooler Materials to Replace Conventional Cryocoolers Used for Cooling SWIR and LWIR Infrared Detectors and Focal-plane-arrays

Electro-optical infrared and long wavelength infrared detectors and sensors are increasingly important for the Chemical/Biological Defense community. Solid-state optical cooler materials are in demand for replacing mechanical closed cycle coolers used in current LWIR standoff sensors to achieve cryogenic temperatures. Recent advances in optical cooling of rare-earth doped materials are pointing towards a possible paradigm shift in vibration-less cooling systems. Optical cooling has been demonstrated experimentally in Yb3+-doped material operating at 1 micron and Tm3+-doped material at 2 microns, but their cooling efficiencies are very low. Higher cooling efficiencies can be achieved from materials operating at 3 microns. NP Photonics will investigate laser cooling materials at 3 microns and fabricate optical fiber coolers at this wavelength for higher efficiency. The proposed fiber cooler has seamless integration and is alignment-free, light-weight, and maintenance-free. In Phase I we fabricated Dy3+-doped glasses and studied their spectroscopic properties for laser cooling based on anti-Stokes fluorescence. We also completed theoretical modeling and simulation on Dy3+-doped fiber coolers and demonstrated the feasibility of optical cooling with Dy3+-doped material with reduced phonon energy. In Phase II we will develop an all-optical fiber cooling system based on our expertise in 3 micron fiber lasers and laser cooling.