  Ultra-stable, quasi-monochromatic laser light forms the basis for
high-precision interferometric measurements, e.g. for observing gravitational
waves and for time keeping with optical clocks. Optical frequency conversion
enables access to wavelengths at which optical materials have the lowest
absorption and the lowest mechanical loss. Here we report a 25 % reduction in
relative intensity noise (of technical origin) when converting 1064 nm to 2128
nm for powers far above parametric oscillation threshold. The new wavelength
has high potential for improving gravitational wave detection and other
ultra-high-precision experiments as well. Our results provide a better
understanding of the dynamics of nonlinear optical processes and have great
potential for the stabilisation of laser sources in optical sensing and
metrology.
