Storage optimization of transmission volume holograms in hydrogel matrix

Abstract

Emerging applications such as holographic sensing [1] require the storage of time-stable volume holographic gratings while the material is immersed in a liquid medium. For this purpose, hydrogels can be used as matrices for the introduction of the necessary components for the hologram formation. Hydrogels are 3D polymer networks capable of undergoing reversible volume changes due to their high swelling capacity. Their liquid permeable structure allows the diffusion of molecules inside their matrix. Unslanted transmission volume phase holographic gratings (TVPHG) with a period of 0.830 μm have been stored in hydrogels based on acrylamide (AAm) and N,N’-methylenebis(acrylamide) (MBA). For this, solutions containing monomer (AAm), crosslinker (MBA) and photoinitiator system (triethanolamine (TEA) and yellowish eosin (YE)) in DMSO:H2O were deposited onto the hydrogel matrices and then exposed with a laser of wavelength 532 nm. TVPHG need to be washed to eliminate the components that do not react during the recording process. With the main objective of optimizing this washing with PBST (phosphate-buffered saline with Tween 20), high-performance liquid chromatography (HPLC) and UV-visible measurements have been employed to analyze the composition of the washing solutions. The recorded holograms were reconstructed using a laser of wavelength 633 nm immediately after the recording process and after each washing stage to obtain the diffraction efficiency (ratio between the intensities of diffracted and incident beams).