Anomalous sub-kelvin thermal frequency shifts of ultra narrow-linewidth solid state emitters

TL;DR

This study explores the temperature-dependent frequency shifts of narrow spectral holes in doped crystals below 1 K, revealing a regime near 290 mK with minimal frequency variation, promising for ultra-stable laser applications.

Contribution

It identifies a specific temperature near 290 mK where the spectral hole frequency is highly stable against temperature fluctuations, advancing laser frequency stabilization techniques.

Findings

Zero first-order temperature-dependent frequency shift near 290 mK

Potential for laser fractional frequency instability as low as 6×10^{-22} at 1 s

Deviation from expected two-phonon Raman scattering behavior

Abstract

We investigate the frequency response of narrow spectral holes in a doped crystal structure as a function of temperature below 1 K. We identify a particular regime in which this response significantly deviates from the expected two-phonon Raman scattering theory. Namely, near 290 mK, we observed a behaviour exhibiting a temperature-dependent frequency shift of zero, to first-order. This is of particular interest for applications which require high frequency-stability, such as laser frequency stabilization, as by operating the scheme at this specific point would result in the spectral hole frequency being highly immune to temperature fluctuations, providing the potential for a laser fractional frequency instability as low as $\mathrm{\sim6\times10^{-22}}$ at 1 s.