Electronically-tuned optical filters utilizing nematic liquid crystals

Cooperative phenomena in nematic liquid crystals under electric fields have been the subject of numerous studies conducted in our laboratories over the past several years. A systematic study of the relationship between molecular structure and the electrical properties of nematic liquid crystals has recently led to the discovery that cooperative alignment of certain nematic "host" compounds by external electric fields can be used to orient "guest" pleochroic dye molecules molecules whose absorption spectrum is a function of their molecular orientation with respect to the polarization of the incident light). The purpose of the present work was the development of electronically-tuned filters based on this effect. Thus, it was possible to produce electronically tuned, monochromic, optical filters with a variety of colors by suitable choice of pleochroic dye. Electronic color switching was achieved using fields of the order of 10 KV/cm (dc through audio) at powers of 1 milliwatt/cm²with a variety of dye structures. A detailed study of the response and relaxation time of the effect was also conducted. Rise times of 1 to 5 msec and relaxation times of 30 to 200 msec were obtained.