Laser cooling in Yb:KY₃F₁₀: a comparison with Yb:YLF

Area of Science:

• Solid-state physics
• Laser cooling technology
• Materials science

Background:

• Laser cooling via anti-Stokes fluorescence enables all-solid-state optical cryocoolers.
• Yb³⁺-doped fluoride crystals are promising laser cooling media.

Purpose of the Study:

• To grow and characterize novel Yb³⁺-doped KY₃F₁₀ (Yb:KYF) crystals for laser cooling.
• To compare the cooling performance of Yb:KYF with Yb³⁺-doped LiYF₄ (Yb:YLF) crystals.
• To evaluate the potential of Yb:KYF for achieving cryogenic temperatures.

Main Methods:

• Growth of Yb:KYF and Yb:YLF crystals.
• Measurement of temperature-dependent absorption and emission cross sections.
• Measurement of fluorescence lifetime.
• Calculation of material figure-of-merit for laser cooling.
• Observation of laser cooling in Yb:KYF.

Main Results:

• Yb:KYF exhibits a higher figure-of-merit than Yb:YLF below 200 K.
• The unique excitation transition in Yb:KYF is advantageous for cryogenic cooling.
• First observation of laser cooling in Yb:KYF achieved.
• Background absorption coefficient of ~10^-4 cm^-1 for Yb:KYF is among the lowest reported.
• Model calculations predict cooling down to ~100 K is possible.

Conclusions:

• Yb:KYF is a promising material for advanced laser cooling applications, potentially reaching sub-boiling point of liquid nitrogen temperatures.
• Further optimization of crystal growth and material purity can enhance Yb:KYF cooling performance.
• Yb:KYF demonstrates significant potential for all-solid-state optical cryocoolers.