New Milestone In Laser Cooling: Research Team Achieves Record Cooling Of Quartz Glass By 67 Kelvin

A team of researchers from the Fraunhofer Institute for Applied Optics and Precision Engineering IOF and the University of New Mexico have succeeded for the first time in cooling quartz glass by 67 Kelvin using optical laser cooling. The scientists from Jena and Albuquerque have now published the results in the specialist journal Optics Express.

Cutting, drilling, welding – we usually associate laser light with heating materials, for example in order to precisely process objects made of metal or rock. However, under certain circumstances it is also possible to cool materials by irradiating them with laser light - an effect that is known for Doppler cooling of gases. But cooling through laser irradiation can also occur in solids.

This paradoxical effect is made possible by the 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energy difference between the excitation laser and the radiation emitted by the material, the fluorescence, energy is withdrawn from the material in the form of heat - it is cooled.

In their recently published paper, a research team consisting of scientists from Fraunhofer IOF and the University of New Mexico has investigated and significantly further developed the laser cooling of doped quartz glass.

Researchers are once again overcoming the previous cooling limit of quartz glass
For many years, laser cooling of quartz glass was considered impossible. However, in 2019, researchers from Jena and Albuquerque were able to demonstrate laser cooling in ytterbium-doped quartz glass for the first time . At that time, however, the cooling achieved was only 0.7 Kelvin below room temperature. In order to overcome this previous cooling limit, the special process for producing the doped material and its exact composition were optimized. For the measurements carried out at the University of New Mexico, the excitation lasers used were also improved in close collaboration with researchers at Fraunhofer IOF.

The scientists have now achieved a new record cooling: By irradiating a ytterbium-doped rod made of quartz glass with an excitation laser with an output of 97 watts and a wavelength of 1032 nanometers, the researchers were able to reduce the temperature by 67 Kelvin within two minutes Detect room temperature.

Fiber-like material opens up new potential applications
The current further development will enable the development of new, extremely stable lasers and low-noise amplifiers for precision measurement technology or quantum experiments. The optimized process can also further develop vibration-free cooling and thus enable new application potential in material analysis and medical diagnostics using cryo-microscopy and gamma spectroscopy.

What is particularly interesting is the possible use of the material in fibers. Based on the new process, high-performance fiber lasers could be developed in the future that do not have the limiting effects of thermal instability.

The new process represents a significant advance in laser cooling and, according to the experts' theoretical considerations, does not yet represent the greatest possible reduction in temperature using laser light.