Crystaldiffract software7/6/2023 ![]() ![]() In a switched state, a director of the liquid crystal remote from the first and second inner surfaces (and optionally midway between the first and second inner surfaces) may be at an angle of at least 60 degrees, optionally at least 70 degrees, optionally at least 80 degrees and optionally at least 85 degrees to the first and second inner surfaces. In an unswitched state, a director of the liquid crystal remote from the first and second inner surfaces (and optionally midway between the first and second inner surfaces) may optionally be at an angle of no more than 20 degrees, optionally no more than 15 degrees, optionally no more than 10 degrees, optionally no more than 8 degrees, optionally no more than 5 degrees and optionally no more than 3 degrees to the first and second inner surfaces. In an unswitched state, a director of the liquid crystal adjacent the first and/or second inner surfaces may optionally be at an angle of no more than 20 degrees, optionally no more than 15 degrees, optionally no more than 10 degrees, optionally no more than 8 degrees, optionally no more than 5 degrees and optionally no more than 3 degrees to the first and second inner surfaces. The liquid crystal may comprise a cholesteric liquid crystal. The second state may be a switched state, i.e., with a voltage applied that switches the liquid crystal in the cell into the second state. ![]() The first state may be an unswitched state, i.e., with no or a low voltage applied to the first liquid crystal cell. ![]() In the other of the first and second state, the effective refractive index of the liquid crystal and the refractive index of the diffractive optical element do not match, and therefore the diffractive optical element diffracts incident light. Optionally, such differences may be calculated at a plurality of wavelengths from 450 nm to 700 nm. Such differences in refractive index may be calculated at a wavelength of 450 nm, and optionally at a wavelength 700 nm. Such differences in refractive index are to be calculated for a wavelength in the visible part of the electromagnetic spectrum (radiation with a wavelength of from 450 to 700 nm). In this context, the difference in the effective refractive index of the liquid crystal and the refractive index of the diffractive optical element may optionally be no more than 0.03, optionally no more than 0.02 and optionally no more than 0.01. In the first state or the second state, the difference in the effective refractive index of the liquid crystal and the refractive index of the diffractive optical element may be small or nil, i.e., the effective refractive index of the liquid crystal and the diffractive optical element may be approximately the same. In the first state, the difference in the effective refractive index of the liquid crystal and the refractive index of the diffractive optical element may be greater than, or lower than, in the second state. The first liquid crystal cell may be operable between a first, unswitched state and a second, switched state. ![]()
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