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In our research on a cholesteric liquid crystal (CLC) material with a negative dielectric constant, we have discovered the conditions for controlling the helical pitch of the CLC. This pitch control can be actively exercised through the electrothermal effect by altering the voltage intensity at a frequency higher than a critical value. By changing the pitch of the parallel CLC cell, which has a thickness of 25um, the wavelength of the laser line can be tuned over a 130.81 nm (from 550.41 nm to 681.22nm) spectral range depending on the applied low AC voltage of 5.4 Vrms or less at 3 MHz. However, due to the free spectral range of the parallel cavity structure of the CLC cells, the laser wavelength was tuned discontinuously. This particular CLC cell is constructed with ITO electrode substrates having a finite resistance of 10 Ω/□ and is filled with general CLC mixtures consisting of a nematic liquid crystal with negative dielectric anisotropy, a chiral molecule with supersaturated concentration (45 wt%), and two laser dyes of DCM and LDS698. The dynamic behavior of CLC molecules was studied as a function of the applied electric field intensity and frequency.
