Wavelength Independent “Babinet Compensator Optical Limiter” (BCOL)

Abstract

We present a new, wavelength-independent optical limiter based on the Babinet compensator principle. The initial polarization change of an incident optical wave passing through a nematic liquid crystal placed between two parallel polarizers is compensated with a second identical sample, with its director vector perpendicular to that of the first cell. If there is some small absorption in just one of the cells, there is a thermally induced index change that produces an irradiance-dependent retardance. The resulting polarization change causes a decrease in the transmittance by more than one order of magnitude as the input energy is increased. Experiments were performed using a frequency-doubled 7 ns pulsed Nd-YAG laser, at a 10 Hz repetition rate as a pump, and a cw He-Ne as a probe to monitor the pump laser generated limiting effect.