<title>Angular selectivity of holographic polymer-dispersed liquid crystal materials with near-IR sensitivity</title>

Abstract

Holographic polymer dispersed liquid crystal (H-PDLC) material was recently sensitized that is sensitive in the near infrared (800 nm to 855 nm). The compound was based on mixture of an acrylate monomer and liquid crystals (e.g., E7 and MBBA were investigated). In the present work, the angular sensitivity of gratings, recorded in these H-PDLC films, was investigated for various wavelengths. The holographic recording was realized by a diode laser (834 nm), which produced 1000 lines/mm spatial frequency of intensity grating. Significant broadening in the angular selectivity for p-polarization was observed for the formulation based on E7. The half-height width (HHW) of the angular selectivity was approximately 7 degrees (for 850 nm) and 10 degrees (for 670 nm). However, for s-polarization, the same sample has an HHW of about 2 degrees for both. We believe that this behavior is the indicator of a spatial modulation in the shape of the liquid crystals (LC) micro droplets. Droplet's shape should change spatially from elliptical to spherical correlated with (but not necessarily the same) spatial frequency of the light grating. For MBBA based samples, there is almost no polarization dependence and the HHW of the angular selectivity is about 2 degrees. Thus, the shape of the micro droplets is strongly influenced by the chemical composition of the compound used. It has been demonstrated that angular selectivity for H-PDLC compound is strongly polarization dependent. This indicates that the forms and sizes of micro droplets could be strongly modulated along the gradient of light interference patterns.