Continuous-wave optical parametric oscillators pumped by external cavity diode lasers

Abstract

In this thesis, high spatial, high spectral quality, ultra stable external cavity diode laser (ECDL) sources and continuous-wave optical parametric oscillators (cw OPOs) are designed, constructed and investigated. The ECDL device that was constructed had an output power of 80 mW, spectral linewidth less than 1 MHz, coarse tuning range of 18 nm, up to 6 GHz continuous mode-hop free tuning, and excellent amplitude and spectral stability, making it suitable to pump various cw OPO systems. The construction and characterisation of a new and simple electronic circuit is also reported that allowed the ECDL spectrum to be scanned continuously over 80 GHz. This thesis reports the novel direct pump of a doubly resonant (DRO) and a pump enhanced (PE-SRO) continuous wave optical parametric oscillators based on periodically-poled lithium niobate (PPLN) by an ECDL. The DRO device, based in a 19 mm PPLN crystal, showed a threshold of 15.5 mW and tuning outputs over 1.15-1.25 μm at the signal and 2.3-2.65 μm at the idler. Locked single mode pair operation was sustained for periods of more than 5 minutes. The PE-SRO was based on a 50 mm long crystal of PPLN with eight gratings equally spaced in period from A=21.0 to 22.4 μm. The device showed a threshold equal to 25- 30 mW. The tuning range at the signal was 1.06-1.19 μm, corresponding to a range of 2.58-3.44 μm at the idler while the pump source was fixed at 812.5 nm.. The ECDL pumped PE-SRO output was locked, using the Pound Drever technique, and showed mode-hop free operation for more than an hour.