Absolute and relative stability of an optical frequency reference based on spectral hole burning in Eu3+:Y2SiO5
David R. Leibrandt, M Thorpe, Chin-Wen Chou, Tara M. Fortier, Scott A. Diddams, Till P. Rosenband
We present four frequency comparison measurements designed to investigate the performance of an optical frequency reference based on spectral hole burning in Eu$3+:Y2SiO5. The first frequency comparison, between a single unperturbed spectral hole and a hydrogen maser, demonstrates a fractional frequency drift rate of 5 × 10-18/s. Optical frequency comparisons between a pattern of spectral holes, a Fabry-P\'erot cavity, and an Al+ optical clock show a short term stability of 1 × 10-15√τ that averages down to 2.5+1.1-0.5 × 10-16 at τ = 540~s. Finally, spectral hole patterns in two different Eu3+:Y2SiO5 crystals located in the same cryostat are compared yielding a short term stability of 7 × 10-16 √τ that averages down to 3.4+3.2-0.8 × 10-17 at τ = 410~s.