Narrow-linewidth, widely tunable intracavity optical parametric oscillators for mid-infrared spectroscopy

This thesis describes work carried out on the design, construction and characterisation of two intracavity optical parametric oscillators based on Nd:YVO₄ pump lasers and using PPLN as the nonlinear material. Both systems generated narrow linewidth, tunable mid-infrared radiation in the 3-5 µm wavelength range. Two approaches were taken to achieve single frequency operation. The first system was based on a standing-wave cavity design and included a high finesse etalon to suppress spatially hole burnt modes, as well as two solid etalons for control and tuning of the signal field. ~90 mW of stable narrow linewidth idler output and ~16 GHz of mode-hop tuning were achieved. The second system made use of a ring cavity design, thus naturally avoiding multi-mode operation. It also included an etalon in the signal cavity for tuning. Here ~120 mW of single frequency idler was produced with a mode-hop tuning range of ~100 GHz. Both systems also included a second nonlinear crystal, phase matched for second harmonic generation of the pump field. This very effectively alleviated the long- standing problem of erratic and long-lived bursts of high frequency relaxation oscillations, which have previously stopped systems of this kind from being developed into viable sources for laser spectroscopy.