Spectral purity transfer between optical wavelengths at the 10-18 level

Ultrastable lasers and optical frequency combs have been the enabling technologies for the tremendous progress made in precise optical spectroscopy over the last ten years(1,2). Recently, to improve the laser frequency stabilization beyond the thermal noise fundamental limit of traditional room-temperature high-finesse optical cavities(3), new solutions have been developed(4-7). These are complex and often wavelength-specific, so the capability to transfer their spectral purity to any optical wavelength is therefore highly desirable. Here, we present an optical frequency comb-based scheme that transfers 4.5 x 10(-16) fractional frequency stability from a 1,062 nm wavelength laser to a 1,542 nm laser. We demonstrate that this scheme does not hinder the transfer down to 4 x 10(-18) at 1 s, one order of magnitude below previously reported work with comparable systems(8-13). This exceeds, by more than one order of magnitude, the stability of any optical oscillator demonstrated to date(6), and satisfies the stability requirement for quantum projection noise-limited optical lattice clocks(14).