Laser milestone Fraunhofer researchers cool quartz glass with laser by 67 Kelvin

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Laser light is often associated with heat. However, lasers can also cool materials. Now, a team from Jena and Albuquerque has managed to lower the low point.

A team of researchers from the Fraunhofer Institute for Applied Optics and Precision Engineering IOF and the University of New Mexico has for the first time succeeded in cooling quartz glass by 67 Kelvin through optical laser cooling. This paradoxical effect is made possible by so-called anti-Stokes fluorescence cooling. In this process, a special, highly pure material is excited by irradiation with laser light. Due to the energy difference between the excitation laser and the radiation emitted by the material, the fluorescence, energy in the form of heat is extracted from the material – thus, it is cooled. A research team consisting of scientists from the Fraunhofer Institute for Applied Optics and Precision Engineering (IOF) and the University of New Mexico has investigated and significantly advanced the laser cooling of doped quartz glass in their now published paper.

Record cooling achieved with improved excitation lasers

For many years, the laser cooling of quartz glass was considered impossible, as the researchers emphasize. However, already in 2019, experts from Jena and Albuquerque were the first to demonstrate cooling by laser in quartz glass doped with ytterbium. At that time, the cooling achieved was only 0.7 Kelvin below room temperature. To push the cooling even further, the special process for producing the doped material and its exact composition was optimized, as it is said. For the measurements conducted at the University of New Mexico, the excitation lasers used were also improved in close collaboration with the IOF researchers. This led to a record! Because during the irradiation of a similarly doped rod of quartz glass with an excitation laser with a power of 97 watts and a wavelength of 1,032 nanometers, a temperature reduction of 67 Kelvin below room temperature was demonstrated within two minutes.

The limit of what is possible is still set further out

With the current further development, novel, extremely stable lasers and low-noise amplifiers for precision metrology or quantum experiments could be developed in the future. Moreover, the optimized process could evolve vibration-free cooling, thus enabling new application potentials in material analysis and medical diagnostics through cryo-microscopy and gamma spectroscopy, according to the researchers. Particularly interesting is the now possible use of the material in fibers. Because based on the new process, high-performance fiber lasers could be developed in the future that operate without the limiting effects of thermal instability. The new method represents a significant advance in laser cooling and, according to theoretical considerations, does not yet mark the maximum possible temperature reduction achievable with laser light.