Efficient and stable holographic gratings stored in an environmentally friendly photopolymer

Abstract

Holographic gratings stored in one of the greenest photopolymers, called Biophotopol and patented by Holography and Optical Processing group at the University of Alicante, have been analyzed to achieve stable over time and efficient holograms. A curing process usually produces a diffraction efficiency (DE) decrement. However, when a curing process is not performed, the holographic gratings are not stable and DE will decrease over time due to the diffusion of molecular components inside the photopolymer. In this work, a DE increment has been demonstrated after a curing stage (performed with an incoherent and lowcost LED lamp). A detailed curing protocol to stabilize the holograms while maintaining high DE, has been carried out in unslanted transmission gratings of 1205 l/mm. The holographic transmission reflection setup allows the possibility to evaluate the transmitted and diffracted intensity beam relation, in real time, by using a He-Ne laser (633 nm), while the gratings were recording with an Argon laser (488 nm). It has been demonstrated more than a 30% DE increment after a curing process when a maximum DE in the recording stage had not been still achieved. However, in the singular case that a maximum DE in the recording stage has been already obtained, a curing stage process could produce overmodulation effects, and therefore, a DE decrement. In conclusion, a maximum DE is obtained in curing and stable hologram gratings (recording them with proper radiant exposures) over an environmentally compatible photopolymer.