A research team from the Fraunhofer Institute for Applied Optics and Precision Engineering in Germany and the University of New Mexico in the United States has achieved a remarkable feat: cooling quartz glass by 67 Kelvin using laser cooling for the first time. This research achievement is reported in the latest issue of the Optics Express journal.
Traditionally, lasers are associated with heating materials, such as cutting, drilling, and welding for precise machining on metal or stone objects. However, under specific conditions, materials can also be cooled using laser radiation, such as Doppler cooling of gases. Surprisingly, laser radiation can also induce cooling in solids.
This counterintuitive effect is made possible through a process called anti-Stokes fluorescence cooling. In this process, a special, high-purity material is excited by laser radiation. Due to the energy difference between the laser and the radiation emitted by the material (i.e., fluorescence), the laser absorbs energy from the material in the form of heat, thereby cooling the material.
For years, laser cooling of quartz glass has been deemed impossible. However, in 2019, the research team demonstrated for the first time that ytterbium-doped quartz glass could be laser-cooled. At that time, they could only cool it by 0.7 Kelvin from room temperature. To surpass the previous cooling limit, they optimized the fabrication process of the doped material.
As a result, the research team achieved a new record-breaking cooling: using laser radiation with a power of 97 watts and a wavelength of 1032 nanometers to cool ytterbium-doped quartz rods, lowering the temperature by 67 Kelvin from room temperature.
This breakthrough paves the way for the future development of extremely stable lasers and low-noise amplifiers for precision measurements or quantum experiments. Furthermore, optimizing the process could also advance vibration-free cooling, aiding in material analysis and medical diagnostics with low-temperature microscopy and gamma spectroscopy.
This material also holds potential applications in fibers. In the future, the new process could be utilized to develop high-performance fiber lasers, overcoming the drawbacks of thermal instability.
The researchers note that while the new process represents a significant advancement in laser cooling, the cooling record they've achieved does not necessarily represent the maximum potential of solid-state laser cooling.
