Optical parametric oscillators : a comparison of new materials

Abstract

A study of new materials for optical parametric oscillators (OPOs) was carried out using an XeCI excimer laser as a pump source. The three non-linear optical materials studied were lithium borate (LBO), deuterated L-arginine phosphate (d-LAP) and β-barium borate (BBO). These optical parametric oscillators were characterised for oscillation thresholds, tuning ranges, linewidths and efficiencies. A novel device in LBO was demonstrated, using the non-critically phase matched type II geometry. The device displayed a low oscillation threshold, which was independent of pump beam area thus made it attractive for use with low energy pump sources. The device was also shown to have a narrow inherent linewidth, oscillating on only one or two axial modes. Other geometries in LBO were also explored. The type I critical geometry displayed a very large tuning range covering the near ultra-violet, the visible and the near infra-red spectral regions. The type IT yz geometry was also studied. An OPO in d-LAP was demonstrated for the first time. The device was tunable in the blue/green spectral region and also in the near infra-red. A low threshold was observed for large beam sizes. Optically induced damage caused by the ultra-violet pump was also encountered. A comparison of the thresholds, efficiencies and tuning ranges of the three materials, LBO, d-LAP and BBO, was made and the suitability of each material for use in a line-narrowed oscillator discussed. Although possessing the largest linewidth, BBO was found to be the best suited due to its low oscillation threshold and large tunability. A single axial mode BBO OPO was demonstrated that was tunable from 385 nm to 560 nm and from 2300 nm to 684 nm. The line-narrowed OPO was then used for linewidth control of other devices. Firstly, an injection seeded OPO was demonstrated and the device was characterised for threshold and linewidth. Secondly, the line-narrowed OPO was used to seed an optical parametric amplifier (OPA). Single pass gains of ~20 were observed from the OPA.