Fast Ferroelectric Spatial Light Modulators for Adaptive Optics Applications

摘要

Ferroelectric liquid crystals (FLCs) possessing the DHF (deformed helix ferroelectric) effect were developed with pitch of helix of the order of 0.2 micrometers and spontaneous polarization of the order of 150nC/cm2 at room temperature. The tilt angle is variable in range 31-42 degrees. The response time T is variable in range 0.5-5ms, depending on mixture. The refractive indicies of all developed materials were measured. The electrically and optically addressed spatial light modulators (OASLM) were fabricated utilizing the developed mixtures. Phase modulation was measured for double DHF modulator composed from two crossed DHF layers. The phase modulation depth was calculated for different cases of DHF materials. The strong nonlinear increase of the phase shift was found in dependence on voltage in accordance with calculations. The maximum phase shift agreed with the calculations and was equal 0.75 Lambda for cell thicknesses 16 micrometers without remarkable dependence on light polarization. Developed OASLM's based on DHF materials with large tilt angle 40 were investigated for real-time holography applications and showed very high figures of merit of basic parameters: diffraction efficiency, spatial resolution and operation rate. The new chemical structure of the DHF liquid crystal molecules was proposed for phase modulation only. Molecules should have banana shape and possess the perfluorinated fragment apart from chiral and dipole fragments. Proposed substances can have ferroelectric as well as antiferroelectric helical smectic packing. Low viscous nematic liquid crystals with high optical anisotropy above 0.25 were tested for phase modulation. Cell with thickness about 3.5 microns provided the phase modulation one wavelength in reflecting mode at frequency upto 60Hz. The operation rate for two-frequency nematic liquid crystal was measured up to 250Hz for phase modulation depth half of wavelength in t.