Refined beam expansion method for unstable resonator modes

A refined and simplified version of the beam expansion method for computing the modes of unstable resonators is presented here.The principle of the beam expansion method is to express the field pattern on a basis of Hermite-Gaussian functions. Propagating each individual component around the resonator enables a transfer matrix to be constructed from which the eigenvalues and eigenvectors of the modes can be determined.Whereas the earlier proof-of-principle approach performed well for low Fresnel numbers, the refined technique gives good results for the challenging test case of magnification M=1.9 and equivalent Fresnel number Neq=49.4. The performance enhancement has been achieved by incorporating a number of adjustments that improve the accuracy of the calculation

Improving both transverse mode discrimination and diffraction losses in a plano-concave cavity

International audienceThe paper considers the interest in using two apertures rather than one in a plano-concave cavity for improving the discrimination between TEM00 and TEM10 modes while keeping the diffraction losses unchanged or even decreasing them. Such an investigation involves stochastic methods like simulated annealing that can be used if and only if the resonant field computation time is low. Fortunately, a quad–double arithmetic recurrence formula allows to compute round-trip operators faster than any adaptative numerical integrator with the same accuracy

Alternative model for computing intensity patterns through apertured ABCD systems

International audienceWe propose an alternative model based on mode conversion for computing axial and transverse intensity field distributions of apertured systems. We then develop a new method for the integration of oscillating functions that derive from the model. The integration technique we developed is efficient, very fast and would be useful in many other fields of physics