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Abstract

In this work, a photopolymer formulation is presented that demonstrates significant improvements in layer hardness and temperature stability, while retaining the excellent holographic recording characteristics and ease of preparation associated with acrylamide (AA)/polyvinyl alcohol (PVA)-based photopolymers. This is achieved through the use of N-phenyl glycine as an electron donor and, for the first time, D-Sorbitol, a naturally occurring sugar-alcohol, as a plasticizer. The plasticizing effect of D-Sorbitol is demonstrated through the minimal loss of diffraction efficiency (η) observed upon UV bleaching (fixing) of 500 lines/mm gratings, which is evidence for effective mass transport during holographic recording. This solves a key challenge for holographic optical elements: balancing the need for the permeability that ensures diffusion during holographic recording, with the need for a permanent refractive index modulation in a hard, robust layer/coating. Gratings made in previous photopolymer formulations using NPG demonstrated improved hardness but were partially erased during the UV bleaching step. Plasticizers such as TEA and glycerol helped, but also caused a severe reduction in hardness. Here, we report holographic gratings made with 21 wt. % D-Sorbitol that demonstrates stability after prolonged exposure to a temperature of 95 °C and has a permanent RIM of 0.002. An increased indentation hardness was also observed in samples with D-Sorbitol compared to the TEA or glycerol, at the optimum concentration of 21 wt. % D-Sorbitol layers were measured to have more than three times higher hardness than the samples with glycerol or TEA. A similar trend was observed for the elastic modulus (E), which was found to be approximately 4 GPa for layers with 21 wt. % D-Sorbitol; one order of magnitude higher than the elastic modulus of samples prepared with glycerol or TEA.

Publication Date

2026-03-01

Publication Title

Optical Materials Express

Volume

16

Issue

3

First Page

628

Last Page

645

Deposit Date

2026-05-11

Funding

This work was funded by Taighde Éireann - Research Ireland under grant number 20/FFP-P/8851. The authors would like to acknowledge IEO colleagues for helpful discussions and the Physical to Life Sciences Hub and CREST Centre for equipment and technical support. Open access funding provided by Irish Research eLibrary.

Creative Commons License

Creative Commons Attribution 4.0 International License
This work is licensed under a Creative Commons Attribution 4.0 International License.

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