Selection of Voltage and Spectral Range in Liquid Crystal Gating
Liquid crystal device (LCD) used as spatial gating apparatus has a lot of new using at low light detecting, imaging spectrum and so on. Since LCD's lattice characteristic, it can come true point gating, local field gating and whole surface gating. It can carry out point-by-point control and feedback of imaging cooperating with CCD detector. Some characteristics of we used LCD, LCX023CMT (SONY), have been detected in order to use conveniently, those include spectra transmittance and which’s changing with gating voltage. The results show that when incident wavelength more than 650nm, this LCD couldn't be used as spatial gating because of polaroid's extinction ratio becoming worse; LCD can modulate the incident light from 400 to 650nm, and the modulates of wavelength range, extent and linearity were related to the modulate voltage clearly. The results indicate that LCD modulates the incident light better and better at voltage more than 2.5V for 550nm; the action modulated become linear with voltage approximately; the modulate extent goes to saturation at voltage more than 5V, and the spectral range modulated is steady in 400-650nm. At voltage more than 5V, transmittance of spectrum is a horizontal beeline almost with incident wavelength range from 400 to 650nm. This indicates that transmittance of spectrum in this range is same, and liquid crystal has none selectivity in colored light. As a result, there is no chromatism between transmitted and incident light. However, because that there is lower transmittance, the reflected light can be used which can ensure not only effective using ratio of light, but also the consistency between reflected and incident light.
Yuan Ming Huang
H. C. Liu et al., "Selection of Voltage and Spectral Range in Liquid Crystal Gating", Key Engineering Materials, Vols. 428-429, pp. 406-410, 2010