Properties of a CW pumped, doubly resonant, optical parametric oscillator

The spectral and temporal output of a CW pumped, doubly resonant parametric oscillator (DRO) are reported. The DRO consists of a Ba2- NaNb5O15crystal in a hemispherical cavity with mirrors coated for degenerate operation; the pump radiation is 5145Å from a continuous argon ion laser. Pump feedback is eliminated by the use of Faraday rotator, and cavity length changes are minimized by coupling together the components of the DRO. The output of the oscillator is analyzed with a 1.0 meter spectrometer (.5Å resolution) and a streak camera with an S-1 response and 20 nsec temporal resolution. The experimental results show that for pump powers just above threshold, the DRO operates on a single cluster of modes for the duration of one scan. Mode jumping occurs on most scans and large frequency sweeps can also be observed. At higher pump powers (2-3 times above threshold), another cluster of signal modes starts to oscillate, sometimes simultaneously with the first cluster. This second cluster occurs at the next coincidence of signal-idler pairs for which ωp- ωso- ωio= 0. For all of these pump powers, oscillation in higher transverse order modes is observed; these can be eliminated by use of an aperture within the DRO cavity. Sources of these frequency instabilities and their interpretation will be discussed.