Efficient femtosecond optical parametric oscillators based on aperiodically poled nonlinear crystals

We discuss the use of aperiodically poled nonlinear crystals to improve conversion efficiency in a synchronously pumped ultrafast optical parametric oscillator. We show theoretically that with these crystals the conversion efficiency can be considerably higher than that obtained when a periodically poled crystal with the same length is used. Moreover, we show that pump threshold can be simultaneously improved by use of longer crystals.