Limits to the power scalability of high-gain optical parametric amplifiers

We investigate the power scaling of optical parametric amplifiers in the high-gain regime. With Gaussian or similarly shaped pump beams, the generated beams tend to become narrower than the pump beam, and back-conversion distorts the intense central part of the beams before the peripheral parts of the pump beam are efficiently converted. Good beam quality and high conversion efficiency can nevertheless be combined when diffraction is strong enough to keep the diameter of the generated beams comparable to that of the pump beam. In practice, this requires narrow pump beams and consequently limits the peak power. Recent experiments have already exceeded this limit. As a solution, we find that a two-stage optical parametric amplifier can combine good beam quality and efficiency for much wider beams than a single-stage optical parametric amplifier. (C) 2004 Optical Society of America