Holographic polymer dispersed liquid crystal reflection gratings formed by visible light initiated thiol-ene photopolymerization

Visible laser light of wavelengths 442, 488 and 532 nm was used to write holographic reflection gratings with notches into the infra-red spectral region in polymer dispersed liquid crystals (H-PDLC). The gratings were formed by the spatially periodic phase separation of nematic liquid crystal during thiol-ene photopolymerization. An organic titanocene based complex, Rhodamine 6G (Rh6G) and Pyrromethene 597 (Pym) dyes in combination with benzoyl peroxide, were used as initiators. Using visible laser light and a single prism, electrically switchable reflection gratings with notches in the blue, green, yellow, red, and near infra-red (NIR) spectral regions were fabricated using angle tuning. The photophysics of the initiator dyes was studied by absorption and fluorescence spectroscopy. Morphology studies by TEM showed a periodic distribution of discrete nematic droplets of nearly spherical shape. The development of visible photoinitiator systems broadens the range of fabrication wavelengths of dynamic reflection filters using inexpensive visible lasers.