title: In dark analysis of PVA/AA materials at very low spatial frequencies: phase modulation evolution and diffusion estimation.
abstract: 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 x 10(-8) cm(2)s(-1)).
authors.affiliation: Dept. Física Enginyeria de Sistemes i Teoria del Senyal, Universitat d'Alacant, Spain, Apartat 99 E-03080 Alacant. Sergi.Gallego@ua.es
authors.forename: Sergi
authors.initials: S
authors.lastname: Gallego
authors.forename: Andrés
authors.initials: A
authors.lastname: Márquez
authors.forename: Stephan
authors.initials: S
authors.lastname: Marini
authors.forename: Elena
authors.initials: E
authors.lastname: Fernández
authors.forename: Manuel
authors.initials: M
authors.lastname: Ortuño
authors.forename: Inmaculada
authors.initials: I
authors.lastname: Pascual
mesh_terms: D020106:Acrylamide / Q000737:chemistry* / Q000528:radiation effects; D003198:Computer Simulation; D008027:Light; D008422:Materials Testing; D008956:Models, Chemical; D009391:Nephelometry and Turbidimetry / Q000379:methods*; D011142:Polyvinyl Alcohol / Q000737:chemistry* / Q000528:radiation effects; D012031:Refractometry / Q000379:methods*; D012542:Scattering, Radiation
chemical_list: D020106:Acrylamide; D011142:Polyvinyl Alcohol