Molecular diffusion effects have been widely studied inside photopolymers for holographic applications. Recently some works have focused on low spatial frequencies to evaluate in real time the monomer diffusion effects. Assuming a Fermi-Dirac function-based profile, we have fitted the diffracted intensities, reflected and transmitted (up to the 8th order), to obtain the phase and surface profile of the recorded gratings. We have studied the influence of diffusion in polyvinyl-alcohol/acrylamide for the range of spatial frequencies between 2 lines/mm and 6 lines/mm. We have demonstrated the influence of the spatial frequency on the magnitude and sign of the material volume variations. We also studied in dark the evolution of the grating shape. We show that it is possible to achieve diffractive gratings with diffraction efficiency in the first order near 35% if the in dark evolution is taken into account. Furthermore we present a method to calculate the monomer diffusivity in photopolymers. The differential equation is deduced and solved, and experimental average value is obtained (D=1.1·10⁻⁸ cm²s⁻¹).

This letter describes an efficient algorithm to predict the RF gas breakdown power threshold in microwave devices with complex geometries. The two necessary calculations when investigating such a phenomenon have been performed: on the one hand, the computation of the electromagnetic fields inside the structure and, on the other hand, the determination of the breakdown onset itself. The electromagnetic fields are solved by means of modal techniques and coupled to the free electron continuity equation, which is solved by the Finite Element Method. Proceeding in this way, a very simple criterion to find out whether microwave corona breakdown will take place is derived. This numerical implementation of the developed algorithms has been tested with other theoretical approaches and with experimental measurements, showing very good agreement.

A numerical model for predicting the multipactor breakdown effect in wedge-shaped hollow waveguides is presented in this paper. The computation of electromagnetic fields is based on the boundary integral-resonant mode expansion method, which provides the modal chart of hollow waveguides with any arbitrary cross section. The advantage of using wedge-shaped waveguides with respect to conventional rectangular ones is the deviation of the resonant paths of the electrons toward regions with lower voltages, thus reducing the probability of multipactor threshold for certain input power. To validate this method, our results have been compared with simulations from previous theoretical studies. Once the simulation tool is validated, it is used to predict the multipactor threshold of wedge-shaped waveguides with different symmetric inclination angles of their horizontal plates. Finally, susceptibility curves as the ones already available for rectangular waveguides are presented. These charts are useful for designing innovative waveguide geometries with improved multipactor-free working power ranges.