金ナノ粒子をドープした高分子分散液晶のテラヘルツ複屈折異方性と緩和効果

Terahertz birefringence anisotropy and relaxation effects in polymer-dispersed liquid crystal doped with gold nanoparticles.

• Yun-Yun Ji
• Fei Fan
• Xin Zhang
• Jie-Rong Cheng
• Sheng-Jiang Chang

抄録

金ナノ粒子(Au NP)をドープした高分子分散液晶(PDLC)のテラヘルツ(THz)複屈折異方性をテラヘルツ時間領域偏光分光法を用いて調べた。金ナノ粒子をドープしたPDLCの屈折率の変化率は電圧の増加に伴って0.91%Vとなり、純粋なPDLCよりも小さくなった。このことから、Au NPをドープしたPDLCの電界に対する応答は、純粋なPDLCよりも一様であることが明らかになった。さらに、高周波交流電場下では、この電場に対してPDLCの異方性分極効果が消失すること、すなわち分極緩和現象が生じることを見いだした。しかし、Au NPをドープしたPDLCは、より高い周波数の交番電界に応答できることが示され、Au NP濃度0.2 wt%のPDLCの緩和周波数は、純粋なPDLCと比較して2倍以上、紫外線を照射しない前駆体混合物と比較して4倍以上改善された。本研究は、動作電界に対してより均一で高速な緩和応答を提供し、チューナブルなTHz液晶位相・分極デバイスの潜在的な応用に意義を持っている。

Terahertz (THz) birefringence anisotropy of the polymer-dispersed liquid crystal (PDLC) doped with gold nanoparticles (Au NPs) is investigated by using terahertz time domain polarization spectroscopy. Controlled by the electric field, the change rate of refractive index for PDLC doped with Au NPs is 0.91% V as the voltage increases, smaller than the pure PDLC, which indicates that the response of the PDLC doped with Au NPs to electric field is more uniform than that of pure PDLC. Therefore, the PDLC doped with Au NPs is more suitable for tunable phase shifters. Furthermore, we found that under the high-frequency alternating electric field, the anisotropic polarization effect of PDLC will disappear to this electric field, namely polarization relaxation phenomenon. However, the results show that the PDLC doped with Au NPs can respond to an electric field with higher alternating frequencies, and the relaxation frequency of PDLC with an Au NPs concentration of 0.2 wt% was improved over two times compared with the pure PDLC and four times higher than that of the precursor mixture without ultraviolet radiation. This work has the significance for the potential applications of tunable THz liquid crystal phase and polarization devices, providing a more uniform and faster relaxation response to the operating electric field.