Thorium-doped strontium fluoride crystal: a unique candidate for a solid nuclear optical clock material.

Area of Science:

• Materials Science
• Atomic Physics
• Optical Engineering

Background:

• Solid-state nuclear optical clocks require stable, miniaturized, and spaceborne-compatible materials.
• Existing thorium-doped crystals face challenges with doping efficiency, uniformity, and radiation-induced degradation.
• Thorium-doped vacuum ultraviolet transparent crystals are crucial for advanced clock applications.

Purpose of the Study:

• To introduce Th:SrF2 as a novel material for solid-state nuclear clock applications.
• To evaluate the doping characteristics, optical properties, and radiation resistance of Th:SrF2.
• To address the limitations of current materials used in nuclear clock development.

Main Methods:

• Crystal growth and characterization of Th:SrF2.
• Measurement of optical transmittance at vacuum ultraviolet wavelengths.
• Assessment of doping concentration and uniformity using segregation coefficient analysis.
• Irradiation testing under alpha radiation to evaluate color center formation.

Main Results:

• Th:SrF2 exhibits a segregation coefficient close to 1, enabling highly efficient and uniform thorium doping.
• Achieved high transmittance (~69% at 149 nm) with extremely high doping concentration (>6x10^20 cm^-3).
• Demonstrated resistance to coloration under strong alpha radiation, preserving transmission in the nuclear transition band.

Conclusions:

• Th:SrF2 is a promising new material for solid-state nuclear optical clocks.
• Its superior doping and radiation stability overcome limitations of existing crystal hosts.
• This discovery significantly advances the development of next-generation nuclear clock technology.