Solid-state laser cooling in Yb:CaF₂ and Yb:SrF₂ by anti-Stokes fluorescence

Area of Science:

• Solid-state laser physics
• Laser cooling technologies
• Materials science for optical applications

Background:

• Laser cooling offers a promising method for temperature reduction in various optical systems.
• Ytterbium-doped fluoride crystals are potential candidates for laser cooling due to their optical properties.
• Previous research has not demonstrated solid-state laser cooling in these specific ytterbium-doped crystals.

Purpose of the Study:

• To demonstrate and characterize solid-state laser cooling in ytterbium-doped calcium fluoride (CaF2) and strontium fluoride (SrF2) crystals.
• To investigate the cooling efficiency and potential low-temperature limits of these materials.
• To establish a foundation for the development of new laser cooling sources.

Main Methods:

• Crystal growth using the Czochralski method in a fluorine-rich atmosphere to ensure high purity and prevent unwanted ion formation.
• Anti-Stokes fluorescence measurements to detect and quantify laser cooling effects.
• Laser-induced thermal modulation spectroscopy (LITMoS) to precisely measure temperature-dependent spectroscopic properties.
• Photothermal spectroscopy to analyze material properties relevant to cooling.

Main Results:

• Successful demonstration of solid-state laser cooling in ytterbium-doped CaF2 and SrF2 crystals.
• Measured cooling efficiencies exceeding 3% for both crystal types at room temperature.
• Model calculations predict achievable temperatures as low as 150 K when excited around 1030 nm.
• Spectroscopic data confirmed the suitability of the crystals for laser cooling applications.

Conclusions:

• Ytterbium-doped CaF2 and SrF2 crystals are effective materials for solid-state laser cooling via anti-Stokes fluorescence.
• The demonstrated cooling efficiencies and potential low temperatures highlight their promise for advanced cooling technologies.
• This work opens new avenues for developing compact and efficient laser cooling systems based on fluoride crystals.