Characterization and modeling of a noncollinearly phase-matched femtosecond optical parametric oscillator based on KTA and operating to beyond 4 /spl mu/m

We describe the design and operation of a critically phase-matched femtosecond optical parametric oscillator based on KTA. By employing a small pump-signal noncollinear angle, tuning of the idler to beyond 4 /spl mu/m is achieved using a Ti:sapphire pump laser. A Gaussian-beam model is described which can be used to identify the optimal noncollinear phase-matching geometry. Idler and signal pulses are characterized fully both temporally and spectrally and interferometric autocorrelation data at 3.5 /spl mu/m showing idler pulses of only eight optical cycles duration are presented.