Transverse patterns in degenerate optical parametric oscillators; specific reference to roll patterns

Summary form only given. The degenerate optical parametric oscillator (DOPO) is a device which is capable of producing complicated spatial emission profiles distinct from the usual axial Gaussian beam. This oscillator can be forced into emitting off axis, which due to the nature of the conversion results in two spatially dislocated beams. These beams interfere within the oscillator cavity, with the resulting pattern known by the name roll pattern. This oscillator system can be modelled using equations for the finite number of resonator modes excited near (but above) threshold. These modal equations are very good at providing an idea as to the region of stability for the roll pattern. Higher order patterns produced by the excitation of larger numbers of modes are also predicted by these equations. The experimental set-up consisted of a (type I phase matched) BBO crystal housed within a Fabry-Perot optical cavity. The dependence of roll pattern formation upon cavity detuning is presented along with the stability region for this pattern. In this way the use of modal equations is shown to be a useful tool for modelling OPOs, and similar related pattern forming systems.