Optical Refrigeration for Dramatically Improved Cryogenic Technology

ABSTRACT: The demonstration of 155 Kelvin refrigeration by optical cooling performed by the co-PIs of this proposal is a first step toward revolutionizing Air Force cryogenic systems. The stated focus of this STTR solicitation is"developing the concepts of a solid-state optical cryocooler that can approach 100 K with a cooling power exceeding 200 mW."To achieve this performance, a crucial proposed task will examine the scaling behavior of our ytterbium-doped yttrium lithium fluoride crystals (Yb:YLF) optical cryocooling crystals, establishing the optical and thermal design configurations necessary for the lowest achievable temperature and the highest cooling power. Another task will develop low mass and low jitter prototype designs based on two optical pumping configurations. At least one of these configurations can be scaled to a microscale design, offering significant spot cooling capability in a lightweight format. Thermal jitter and drift will be modeled by including optical monitoring and feedback control into the system design. Finally, a task addressing efficiency improvements through the incorporation of narrowband photovoltaic elements is included. Our initial modeling shows that this approach allows the total optoelectronic efficiency to approach the Carnot limit. BENEFIT: The development of lightweight, cryogen-free, and efficient cryocoolers will have significant benefits to both DoD and commercial customers. By eliminating weight and logistical requirements, the DoD will be able to expand the use of cryogenic systems down to the individual soldier, vastly increasing the market. Commercial use includes reducing the cost of high performance IR electro-optical systems, vastly expanding the market for high performance systems.