Use of a diffraction-grating in a synchronously-pumped parametric oscillator for broad tuning around degeneracy

Puech, K., Lefort, L. and Hanna, D.C. (1999) Use of a diffraction-grating in a synchronously-pumped parametric oscillator for broad tuning around degeneracy. 14th National Quantum Electronics Conference QE14, Manchester, United Kingdom. 05 - 08 Sep 1999.

Abstract

Periodically poled lithium niobate (PPLN) has, in recent years, become a very useful and prominent material for use in optical parametric oscillators (OPO's) and other nonlinear optical devices. In synchronously pumped OPO's, the combination of high peak power from short pulse cw modelocked lasers and the large nonlinearity of PPLN, allows a very large parametric gain to be achieved. This, in turn, allows the use of convenient tuning elements, such as diffraction gratings, whose loss would be unacceptable for low gain cw devices. The strong frequency discrimination, of diffraction gratings, allows operation close to degeneracy, while still maintaining singly resonant operation (SRO). The attraction of operating around degeneracy is that due to the large parametric gain bandwidth, a broad tuning range can be conveniently achieved, without the need to change the temperature or the grating period of the PPLN. The standard approach for achieving singly resonant operation, by using resonator mirrors whose reflectivity discriminates against the idler wave, precludes reliable operation around degeneracy due to insufficient frequency discrimination. The diffraction grating in place of one of the mirrors overcomes this problem. In this paper we report on results obtained by equipping a PPLN OPO, pumped by a 4ps, 120MHz Nd:YLF laser at 1047nm, with a diffraction grating as one of its reflectors. A 20mm long PPLN crystal, with a grating period of 30.4 µm, held at a fixed temperature of 190 °C, was used to obtain a tuning range of 1900 - 2300nm, simply by tilting the diffraction grating. Fig. 1 shows this tuning behaviour. The good beam quality of the signal is confirmed by a measured M2 of 1.16. A measurement of the spectral width and pulse duration (via extra-cavity SHG auto-correlation) gives a time-bandwidth-product of 0.46.

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