Toward a highly stable master laser for the interrogation of SYRTE´s Sr and Hg optical lattice clocks

We report on the current developments at LNE-SYRTE to realize an ultra-stable laser based on spectral hole burning spectroscopy of rare-earth doped crystals at cryogenic temperature. Our goal is to realize a cw laser with a stability below 10^-16, suitable for quantum projection noise limited interrogation of optical lattice clocks after transfer to optical clocks wavelength via an optical frequency comb. Our laser system currently comprises two 1160nm lasers, one referenced to a pre-stabilization cavity and the second offset phase-locked to the first. After frequency doubling, we obtain spectral hole burning patterns in Eu³⁺:Y₂SiO₅ near 4K.