A Deformable Low-Threshold Optical Limiter with Oligothiophene-Doped Liquid Crystals

Abstract

Optical limiting is a phenomenon widely recognized as the potential application for a protector of human eyes and optical sensors from irradiation with lasers. However, a high optical limiting threshold and low flexibility have restricted such applications. Here, we report that oligothiophene-doped liquid crystals (LCs) function as a low-threshold optical limiter with deformability. Irradiation of dye-doped LCs with a continuous wave (CW) laser beam brings about the formation of diffraction rings, and the number of rings changes depending on the incident light intensity due to their photoinduced molecular reorientation. Utilizing such reorientation enables reversible optical limiting without additional multilayered optical components. In particular, an electric field application to a LC-based optical limiter decreases their optical limiting threshold from 2100 to 25 mW/cm², and the threshold can be tuned by adjusting the applied voltage. Furthermore, the softness of LCs allows for the fabrication of the deformable optical limiter; optical limiting due to the molecular reorientation occurs even in largely bent states. The low-threshold and deformable optical limiter based on oligothiophene-doped LCs thus will enable one to develop the protector of eyes and optical sensors from glaring light-induced damage.

Keywords: bending; electric field assistance; flexible; liquid crystal; molecular reorientation; nonlinear optical effect; optical limiting.