Efficient operation of an all-solid-state synchronously-pumped lithium triborate optical parametric oscillator

Abstract

The achievement of broad tuning ranges in cw pumped lasers has generally called for the use of multiwatt pump sources, with the Argon laser being particularly widely used. The average pump power requirements for a synchronously-pumped optical parametric oscillator (OPO) can be much lower, with average pump powers in the region of a few tens of milliwatts being sufficient to allow very extensive tuning ranges. This brings the pump power requirements within the range of laser-diode-pumped mode-locked lasers, with the attractive prospect of future tunable lasers being much more compact, cheaper and more reliable than their Argon-pumped forebears. A particularly promising OPO system is based on the nonlinear crystal lithium triborate (LBO), pumped by the second harmonic of an additive-pulse mode-locked laser-diode-pumped neodymium laser. The additive-pulse mode-locking scheme enables much shorter (and hence higher peak-power) pulses to be produced than for active mode-locking. LBO is eminently suitable for this scheme in that it allows temperature-tuned non-critical phase-matching, and hence tight focusing and high intensity to be maintained over a very broad range of signal and idler wavelengths. Results reported for such a system, using an anti-reflection (AR) coated LBO crystal, demonstrated tuning over the range 0.81 to 1.48µm. A limitation of that system was posed by the reflection losses of the AR coatings, which increased rapidly towards the limits of the tuning range. Hence we report much improved results, with wider tuning range and higher efficiency using a Brewster-angled LBO crystal.

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