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Proceedings Paper

Electrically switchable optical vortex generated by a computer-generated hologram recorded in polymer-dispersed liquid crystals
Author(s): Y. J. Liu; X. W. Sun
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Paper Abstract

Photopolymerization offers a single-step and rapid formation of different kinds of structures in polymer-dispersed liquid crystals (PDLCs) for various applications. Here we investigate the fabrication of a computer-generated hologram in PDLCs to generate an electrically switchable optical vortex. First, a computer-generated hologram was numerically designed and then transferred to a transparency as a photomask. The photomask has an effective area of 1 × 1 cm2 with a resolution of 25 μm and a pattern containing almost parallel lines with a fork-like bifurcation at the vortex core. Then the photomask was clipped onto a cell filled with PDLC materials, and subjected to a collimated Ar+ laser (514.5 nm) beam. The intensity impinged on the photomask was about 12 mW/cm2. The optimal exposure time was 2 min in our experiment judged from the fading of the photoinitiator (rose bengal) color. Due to the photopolymerization induced phase separation between polymer and liquid crystal, an index modulation was formed between the polymer-rich and liquid crystal-rich regions. The structures inside the cell were examined under an optical microscope. A good optical vortex beam with high fidelity was reconstructed using a collimated He-Ne laser beam (543 nm). The diffraction efficiency was estimated to be about 13 - 17%. With a suitable voltage applied, the reconstructed optical vortex beam can be switched due to the index change between the polymer and liquid crystal. The experimental results show promising applications of PDLC materials in optical trapping.

Paper Details

Date Published: 29 January 2008
PDF: 8 pages
Proc. SPIE 6911, Emerging Liquid Crystal Technologies III, 69110M (29 January 2008); doi: 10.1117/12.760327
Show Author Affiliations
Y. J. Liu, European Lab. for Non-Linear Spectroscopy (Italy)
Nanyang Technological Univ. (Singapore)
X. W. Sun, Nanyang Technological Univ. (Singapore)

Published in SPIE Proceedings Vol. 6911:
Emerging Liquid Crystal Technologies III
Liang-Chy Chien, Editor(s)

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