Wide bandwidth frequency doubler with high conversion efficiency

Abstract

There has been a great deal of interest in extending the frequency range of currently available ultrashort pulse lasers by second harmonic generation. In this case, the frequency doubler must provide high conversion efficiency across the entire bandwidth of the ultrashort optical pulse. Traditional methods of frequency doubling have limited conversion efficiency over large bandwidths as a result of group velocity mismatch and limitations in input acceptance angle. Intracavity frequency doubling1 and spatial dispersion of the fundamental pulse prior to imaging onto the nonlinear crystal2 are two demonstrated approaches to this problem. We have designed a large bandwidth frequency doubler that provides simultaneous phase-matching over greater than 100 nm bandwidth. Higher conversion efficiencies are possible with this design than with previous spatially dispersive doublers, since the fundamental can be focused more tightly into the doubling crystal while preserving optimum phase-matching angles across the bandwidth of the fundamental of the laser pulse. Unlike other designs, this large bandwidth doubler can be designed with either net positive or negative group velocity dispersion.