Nonlinear Optics Group

Abstract A high-energy phase-conjugate mirror (PCM) I Nonlinear Isolator (NLI) basedon pressurized methane was tested to the 5 J level, using 200 ns, 300 MHz bandwidthpulses from a phase conjugated multiple Nd:glass amplifier. Performance was goodwhen a 50 cm focal length lens was employed. With a 25 cm lens, PCM performancewas good except when gas breakdown occurred. In the presence of gas breakdown,reflectivity and return beam quality dropped. NLI isolation was aided by breakdown.A model was developed that shows that if breakdown occurs for a short focal lengthlens, then increasing the focal length raises the breakdown threshold but does noteliminate the problem at all input energies. This is a consequence of the fact that asinput energy increases, the amount of energy leaking into the focal region increasesfaster than the breakdown threshold increase due to temporal broadening ofthe leakedpulse. High reflectivity (> 80%) single-cell tight-focus PCMs are feasible for use at the10 J level, but as an NLI appears limited compared to glass based Faraday rotators.