Optimisation of the performance of holographic beam-shaping diffractive diffusers through refinement of the recording process

Cara Jones, Technological University Dublin
Suzanne Martin, Technological University Dublin
Sanjay Keshri, Technological University Dublin
Dervil Cody, Technological University Dublin
Kevin Murphy, Technological University Dublin

Document Type Conference Paper

Event: SPIE Photonics Europe, 2020, Online Only


Optical diffusers have uses in laser applications and machine vision. Typical fabrication at a commercial level requires master production and the stamping/copying of individual elements at scale. This expensive, indirect process inhibits custom diffusers at reasonable cost. Previously the authors published a novel, direct, single beam method of recording customizable and controllable volume holographic diffusers by manipulating laser speckle and recording the pattern in photopolymer. This method allows for beam-shaping to produce diffusion patterns of various sizes and shapes. In this work, the direct method of recording controllable holographic diffusers is refined to improve diffuser performance (i.e., a decrease in zero order strength) for a simple diffuser. This is achieved through optimising the recording conditions (exposure energy, power and layer thickness) for a given photopolymer formulation. Significant improvement in the diffuser efficiency is observed through the optimisation process for a particular speckle size, resulting in a five-fold decrease in the remaining zero order. Kogelnik Coupled Wave Theory (KCWT) is explored as a first step towards developing an appropriate model for the behaviour of holographic elements recorded with interference patterns formed through stochastic processes, such as speckle patterns.