SBIR-STTR Award

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.

Keywords:
Cryocooling, Optical Refrigeration, Laser Cooling Of Solids, Rare-Earth Doped Crystals, Thermal Link, Opsl, Thermal Management, Fiber Lasers

Optical refrigeration is currently the only demonstrated all-solid-state cryocooling technology. Optical cryocoolers are devices that use laser light to cool small crystal or glass cooling elements. The cooling element absorbs the laser light and reradiates it at higher energy, an example of anti-Stokes fluorescence. The difference between the energy of the outgoing and incoming light comes from the thermal energy of the cooling element, which in turn becomes colder. In Phase I of this STTR program, the collaboration of ThermoDynamic Films LLC (TDF) and the University of New Mexico (UNM) has cooled an optical-refrigerator cooling element comprised of an ytterbium-doped yttrium lithium fluoride crystal from room temperature to 123 K with about 2% efficiency. This is the world record in optical refrigeration and an important step toward revolutionizing cryogenic systems for sensor applications. This Phase II proposal addresses the improvement and integration of the key components of an optical cryocooler to enable the transition of this scientific breakthrough into DoD sensor applications. The TDF/UNM collaboration will improve the performance of optical refrigerators by making them more efficient, less massive and more reliable for space-born applications.

Benefit:
Rugged, compact, quiet cryogenic refrigerators are essential for a wide range of emerging space-borne and ground-based defense and non-proliferation applications. Optical refrigerators have the potential to meet both national security and commercial needs. In particular, cryogenic optical refrigerators are well suited to cooling space-borne radiation detectors and infrared imagers in small satellites where low weight and a lack of vibrations are especially important. For example, optical cryocoolers could cool infrared detectors for the Department of Defense’s Space-Based Infrared System. After the successful completion of this Phase II project, TDF, together with a strategic partner, will be prepared to build and market optical cryocoolers for space-based missions and for ground-based applications such as medical devices and handheld thermal imagers.

Keywords:
Optical Cooling, Optical Refrigeration, Cryocooling, Solid-State Cooling, Lasers, Anti-Stokes Luminescence, Space-Borne, Infrared Sensor Cooling.