Frequency stabilization to 6 x 10(-16) via spectral-hole burning
We demonstrate two-stage laser stabilization based on a combination of Fabry-Perot and spectral-hole burning techniques. The laser is first pre-stabilized by the Fabry-Perot cavity to a fractional-frequency stability of sigma(y)(tau) < 1 x 10(-13). A pattern of multiple spectral holes written in the absorption spectrum of Eu3+:Y2SiO5 serves to further stabilize the laser to sigma(y)(tau)