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.
Citation: Physical Review Letters
Pub Type: Journals
Hole burning spectroscopy, Metrological applications, optical frequency synthesizers for precision spectroscopy