Highly efficient broadband sum-frequency generation in the visible wavelength range.

We report on efficient broadband sum-frequency generation, converting a 140 THz near-infrared bandwidth to the visible regime with photon conversion efficiency greater than 90%. Using a 20-mm-long aperiodically adiabatively poled KTP crystal, the spectral range 660-990 nm was converted to 405-500 nm using a strong pump wave at 1030 nm. The photon conversion efficiency was confirmed to be 92±0.5% when pumped with an intensity of 0.94 GW/cm2. Our experimental results agreed very well with analytic predictions and numerical simulations.