Abstract
We report a wide nematic range and low absorption loss chlorinated liquid crystal mixture, designated as IR-M2, for mid-wave infrared applications. IR-M2 is quite transparent in the 3.8-5.0 μm window while keeping a high birefringence (Δn~0.194) in the infrared region and a modest dielectric anisotropy. For long-wave infrared applications, we propose another high Δn chlorinated cyanoterphenyl compound.
Highlights
In addition to amplitude modulation, liquid crystals (LCs) have found useful applications for phase modulation [2], such as spatial light modulators for laser beam steering [3], adaptive optics in the mid-wave infrared (MWIR 3~5μm) and long-wave infrared (LWIR 8~12μm) regions [4], as well as phase shifters in the microwave [5,6] and terahertz regions [7,8,9]
To steer a high power laser beam in the IR region, the absorption of LC must be minimized because the absorbed light is converted to thermal energy, which in turn heats up the LC material and causes spatial phase non-uniformity [12]
To shorten the response time, a polymer network liquid crystal can be considered and the response time can be improved by 100x, but the tradeoff is incresased operation voltage [18]
Summary
In addition to amplitude modulation (e.g., displays [1]), liquid crystals (LCs) have found useful applications for phase modulation [2], such as spatial light modulators for laser beam steering [3], adaptive optics in the mid-wave infrared (MWIR 3~5μm) and long-wave infrared (LWIR 8~12μm) regions [4], as well as phase shifters in the microwave [5,6] and terahertz regions [7,8,9]. Deuteration shifts the CH vibration bands to a longer wavelength by 2 , i.e. from 3.4μm to 4.8μm, which is still in the MWIR region [13]. In order to shift the vibration bands and overtones outside the region of interest, we consider the replacement of fluorine with a heavier atom, e.g. chlorine. Some chlorinated compounds we have reported previously [18] just show monotropic phases and relative high melting points (Tm) as the heavy atom substitution reduce the molecules’ flexibility. The mixture is highly transparent (transmittance >98%) in the MWIR region It shows a relatively high birefringence Δn~0.194 at λ = 4μm, and modest dielectric anisotropy (Δε = 6.89).
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