  Liquid-crystal devices (LCDs) offer a potential route toward adaptive optical
components for use in the < 2 THz band of the electromagnetic spectrum. We
demonstrate LCDs using a commercially available material (E7), with unbiased
birefringence values of 0.14-0.18 in the 0.3-4 THz band. We exploit the linear
dichroism of the material to modulate the emission from a 3.4-THz quantum
cascade laser by up to 40%, dependent upon both the liquid-crystal layer
thickness and the bias voltage applied.
