Abstract
We study singly-resonant optical parametric oscillators with chirped quasi-phasematching gratings as the gain medium, for which adiabatic optical parametric amplification has the potential to enhance conversion efficiency. This configuration, however, has a modulation instability which must be suppressed in order to yield narrowband output signal pulses. We show that high conversion efficiency can be achieved by using either a narrowband seed or a high-finesse intracavity etalon.
Highlights
Chirped quasi-phasematching (QPM) gratings have received attention for many optical frequency conversion schemes including difference frequency generation (DFG), optical parametric amplification (OPA), sum frequency generation (SFG), and related applications [1,2,3,4,5,6,7,8,9,10]. Their main role so far has been to broaden the phasematching bandwidth compared to conventional periodic QPM gratings, without the need to use short crystals with reduced conversion efficiency. This broadening can be understood through a simple spatial frequency argument: due to dispersion, there is a mapping between phasematched frequency and grating k-vector; in chirped QPM gratings, the grating k-vector is swept smoothly over the range of interest, thereby broadening the spatial Fourier spectrum of the grating and the phasematching bandwidth [1, 5,6,7]
The OPO efficiency enhancements made possible by chirped QPM gratings are likely to be most advantageous when using a pulsed pump, since high efficiencies are already possible for CW-pumped OPOs by appropriate near-confocal resonator design [12]
The OPO configuration where Eq (8) can apply most directly is for nanosecond pump pulses, for which dynamical effects including group velocity mismatch and dispersion (GVM and group velocity dispersion (GVD)) can, in the ideal limit, be neglected
Summary
Chirped (aperiodic) quasi-phasematching (QPM) gratings have received attention for many optical frequency conversion schemes including difference frequency generation (DFG), optical parametric amplification (OPA), sum frequency generation (SFG), and related applications [1,2,3,4,5,6,7,8,9,10] Their main role so far has been to broaden the phasematching bandwidth compared to conventional periodic QPM gratings, without the need to use short crystals with reduced conversion efficiency. The use of chirped QPM gratings offers a way of removing the above limitations on conversion efficiency of pulsed beams (in both the spatial and temporal domains) without the need for small beam areas, short pulse durations, or beam shaping One example where this efficiency enhancement could be useful is in nanosecond optical parametric oscillators (OPOs). We show that chirped QPM OPOs are even more susceptible to modulationally instabilities, discuss the suppression of the MI with additional intracavity elements, and numerically simulate the dynamics of chirped QPM ns-pumped OPOs
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