Researchers from the University of New Mexico have just achieved the lowest temperature recorded in a solid via the use of optical cooling.
The team, led by Mansoor Sheik-Bahae, used lasers to cool a special type of crystal all the way down to 91 Kelvin (-182°C, -296°F), a cooling mechanism that doesn’t require complex machinery.
"Right now, anything that cools other parts of a system has moving parts. Most of the time, there's liquid running through it that adds vibrations which can impact the precision or resolution of the device," explained Aram Gragossian, a research assistant who worked on the discovery, in a statement. "But, when you have optical refrigeration, you can go to low temperatures without any vibrations and without any moving parts, making it convenient for a lot of applications."
Cooling a solid is much more difficult than cooling, say, air (where the lowest temperature achieved is less than one-billionth of a Kelvin) because it's more difficult to take energy out of a solid.
This refrigeration system, technically called a solid-state cryocooler, was made of synthetic crystals with Ytterbium ions embedded in them. Lasers are shined on the ions, and they then emit light at different wavelengths, taking energy from their surroundings to do so. This breakthrough is the product of more than 20 years of research, which has improved the purity of the crystals and the precision of the cooling lasers.
"We are really on the cutting edge when it comes to solid-state laser cooling," said Sheik-Bahae. "While achieving major milestones in the fundamental science aspect of this field, in parallel, we are making rapid advances in implementing this technology for real-world applications.”
This breakthrough, published in Scientific Reports, could help with a variety of technologies that can benefit from being constantly cooled. In medicine, for example, sensitive infrared cameras are used to scan a patient’s skin to find evidence of skin cancer. Cooling without the vibration would make the device more precise in spotting unhealthy cells.
The solid-state cryocoolers could also help in creating more precise lasers, prompting a significant jump in precision measurements, from clocks to tiny distances.
The team will continue to improve on this technology, though. After all, in thermodynamics, absolute zero is the limit.