Spatially Resolved Analysis of Bragg Selectivity

Abstract

This paper targets an inherent control of optical shrinkage in photosensitive polymers, contributing by means of spatially resolved analysis of volume holographic phase gratings. Point by point scanning of the local material response to the Gaussian intensity distribution of the recording beams is accomplished. Derived information on the local grating period and grating slant is evaluated by mapping of optical shrinkage in the lateral plane as well as through the depth of the layer. The influence of recording intensity, exposure duration and the material viscosity on the Bragg selectivity is investigated.

Dimensional changes in slanted diffraction gratings recorded in photopolymers

“…This year it has been published an interesting work that report a complete analysis of the problem combining the Bragg's angle detuning and Bragg's wavelength detuning, using the Kogelnik's wave coupled theory, KCW, and the rigorous analysis, RCW, proposed by Moharam et al [19]. Nowadays new alternative techniques have been proposed in order to measure the shrinkage in photopolymers [20][21][22][23] and the influence of different parameters on the changes observed in the spatial period [24]. These alternative methods to the holographic Bragg-angle detuning measurements provide information of the material shrinkage in real time.…”

“…As we commented before, one of the most studied photopolymers is the one based on polyvinyl alcohol acrylamide (PVA/AA) [19][20][21]24]. Along this work, we have analysed three different types of photopolymers, firstly PVA/AA and secondly one of the greenest photopolymers whose patent belongs to the Alicante University called Biophotopol [26] and on the last place a holographic-dispersed liquid crystal photopolymer (H-PDLC) [27].…”

Volume Holography: Novel Materials, Methods and Applications

“…The lateral scan reveals the material response, resulting in overmodulation ( ν > π __ 2 ) in case of E > 330 mJ/cm 2 . The results from spatially resolved investigations of the grating constant reveal the influence of the recording intensity and exposure duration on the Bragg selectivity [30]. The advantage of lateral scanning consists in the exploitation of the Gaussian intensity distribution of the recording beams.…”

“…This applies to material parameters, such as composition or viscosity, to grating parameters such as grating constant or geometry as well as to recording parameters, such as exposure duration or recording intensity [30].…”

“…Local values of thickness d, refractive index contrast Δn, as well as grating period Λ and the grating slant Φ can be obtained. The lateral scan method is keeping track of the hologram shape, which is determined by the material response to the Gaussian intensity distribution of the recording beams [30].…”