Programmable frequency reference for subkilohertz laser stabilization by use of persistent spectral hole burning

We report what is believed to be the first demonstration of laser frequency stabilization directly to persistent spectral holes in a solid-state material. The frequency reference material was deuterated ${\mathrm{CaF}}_2:{\mathrm{Tm}}^{3+}$ prepared with 25-MHz-wide persistent spectral holes on the ${}^{3}H_6^{ }\to {}^{3}H_4^{ }$ transition at 798 nm. The beat frequency between two lasers that were independently locked to persistent spectral holes in separate crystal samples showed typical root Allan variances of $780\pm 120 \mathrm{Hz}$ for 20–50-ms integration times.