Abstract
Wavelength tuning and stability characteristics of a singly resonant continuous-wave optical parametric oscillator (cw OPO) in the proximity of signal-idler degeneracy have been studied. The OPO is made singly resonant by using a Bragg grating as a spectral filter in the OPO cavity. The signal-idler frequency difference can be tuned from 0.5 to 7 THz, which makes the OPO suitable for cw THz generation by optical heterodyning. The operation of the OPO within this singly-resonant regime is characterized by a strong self-stabilization effect. A gradual transition to an unstable, doubly-resonant regime is observed for a signal-idler detuning smaller than ~0.5 THz.
Highlights
Optical parametric oscillators (OPOs) operated at or near degeneracy, i.e. so that the signal and idler frequencies are nearly equal to each other and half of the pump frequency, have some interesting properties that can be advantageous in various applications
Such insensitivity of the OPO to variations of the pump frequency is an intriguing observation, since the standard cold-cavity model predicts that the singly resonant OPO (SRO) should jump from one cavity mode to another whenever the detuning between the resonating cavity mode and the center of the parametric gain exceeds ± 1/2 free spectral range (FSR) of the cavity [4,22]
We have presented a detailed experimental study of the tuning and stability characteristics of a singly resonant continuous-wave optical parametric oscillator (cw OPO) close to degeneracy
Summary
Optical parametric oscillators (OPOs) operated at or near degeneracy, i.e. so that the signal (νs) and idler (νi) frequencies are nearly equal to each other and half of the pump frequency (νp), have some interesting properties that can be advantageous in various applications. The parametric gain bandwidth of a near-degenerate OPO is typically large, which is useful for generation of short mid-infrared pulses and mid-infrared supercontinua [1] Another interesting application is the generation of a pair of coherent beams (signal and idler), whose frequency difference is in the THz region. A major complication in obtaining stable near-degenerate operation of a bulk OPO is that the OPO becomes doubly resonant This is due to the difficulty of getting mirrors that are highly reflective for only one of the two wavelengths, signal or idler, while transmitting the other. Additional benefits of the grating-stabilized OPO are that the signal-idler frequency difference can be tuned over several THz, and that the stable output power of the SRO is typically an order of magnitude higher than that of the DRO. We discuss the transition from singly to doubly resonant regime when the frequency detuning from degeneracy becomes comparable to the reflection bandwidth of the Bragg grating
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