Analysis of the fabrication of diffractive optical elements in photopolymers

Recently the possibility to record phase diffractive optical elements (DOEs) onto photopolymers has been explored. Two of their properties when they are illuminated are useful to this goal: the relief surface changes and the refractive index modifications. The recording intensity distribution with a sinusoidal profile is the easiest profile to record in a holographic recording material, i.e. it can be obtained by the simple interference of two plane wave beams or alternatively using a spatial light modulator. This second method is more flexible and opens the possibility to record a wide range of diffractive elements such as binary, blazed gratings, diffractive lenses, etc. Sharp profiles may as well be recorded. In general they present a clear smoothing of the edges due to various reasons: the cut-off frequency (a low pass filtering) of the optical system, quality of the spatial light modulation, inhibition period, finite size of polymer chains, monomer diffusion, and non-linearities in the recording process. In this work we have analyzed the importance of some of these aspects of the photopolymer and the experimental set-up in order to record high quality DOEs. The photopolymer analyzed is based on polyvinylalcohol/acrylamide. To achieve this goal we have used a diffusion model to simulate the DOE's recording with different recording intensities distributions.