Quartz Glass Laser Cools To Record Magnitude

A team of researchers from the Fraunhofer Institute for Applied Optics and Precision Engineering in Germany and the University of New Mexico in the U.S. have succeeded in cooling quartz glass by 67 kelvins from room temperature for the first time by laser cooling. The research results are reported in the latest issue of the journal Optics Express.
People usually associate lasers with the heating of materials, such as cutting, drilling, welding, and performing precision work on metal or stone objects. But in specific cases, materials can also be cooled by laser radiation, such as Doppler cooling of gases. However, laser radiation can also cool solids.
By means of so-called anti-Stokes fluorescence cooling, this cold-heat-contrary effect becomes possible. In this process, a special high-purity material is excited by laser radiation. Due to the energy difference between the laser light and the radiation emitted by the material (i.e. fluorescence), the laser draws energy from the material in the form of heat and the material is cooled.
For years, laser cooling of quartz glass was considered impossible. But in 2019, the team demonstrated for the first time that ytterbium (Yb)-doped quartz glass could be cooled by a laser. At the time, it could only be cooled by 0.7 Kelvin from room temperature. To go beyond the previous cooling limit, they optimized the preparation process of the doped material.
As a result, the team achieved a new record-breaking cooling: by radiating ytterbium-doped quartz rods through a laser with a power of 97 watts and a wavelength of 1,032 nanometers, the temperature was lowered by 67 Kelvin from room temperature.
This new advance could contribute to the future development of extremely stable lasers and low-noise amplifiers for precision measurements or quantum experiments. In addition, the optimized process could advance vibration-free cooling, which could be useful in materials analysis and medical diagnostics with the help of cryogenic microscopy and gamma energy spectroscopy.
The material also has potential uses in fibers. In the future, the new process could be used to develop high-performance fiber lasers that overcome the disadvantage of thermal instability.