Adiabatic frequency conversion of ultrafast pulses

A new method for efficient, broadband sum and difference frequency generation of ultrafast pulses is demon- strated. The principles of the method follow from an anal- ogy between frequency conversion and coherent optical ex- citation of a two-level system. For conversion of ultra- fast pulses, the concepts of adiabatic conversion are devel- oped further in order to account for dispersion and group velocity mismatch. The scheme was implemented using aperiodically poled nonlinear crystals and a single step nonlinear mixing process, leading to conversion of near- IR (∼790 nm) ultrafast pulses into the blue (∼450 nm) and mid-IR (∼3.15 µm) spectral regions. Conversion band- widths up to 15 THz FWHM and efficiencies up to 50% are reported.