Coherent noise suppression at high-efficiency wavelength doubling for high-precision experiments

Increasing the laser wavelength in high-precision experiments such as gravitational wave detectors and optical atomic clocks holds great potential for a further increase in precision. The low-noise wavelength doubling of the existing ultra-stable light at 1064 nm allows access to the 2μm region, where new materials with low mechanical loss and low optical absorption are available. Here, we re-examine the theory of noise suppression at wavelength doubling by degenerate optical parametric oscillation (DOPO) pumped well above threshold and report an experimental validation. While we achieve highly efficient wavelength doubling of 0.3 W at 1064 nm, we also observe a 25% reduction in relative non-quantum intensity noise. Our results motivate the idea of shifting the laser wavelength of high-precision optical sensing and metrology to 2128 nm.