偶氮掺杂液晶中热致光学非线性的测量

偶氮掺杂液晶具有非常强的三阶光学非线性,其非线性机理包括光致热效应等多种物理机理。为了测量偶氮掺杂液晶三阶光学非线性,本文采用非线性干涉法,定量测量了波长632.8nm下,光强变化所引起的折射率改变。为了测量得到热效应对掺杂液晶非线性的贡献,我们提出了温度等效法,通过在暗室中加热掺杂液晶样品产生与光照时相同的温度变化,模拟出等效的热效应,从而将热效应从多种非线性机理中单独区分出来;通过测量此时的折射率改变,以及对应的温度和光强变化,得到了热效应导致的光学非线性。为了提高非线性干涉方法的灵敏度和消除环境震动带来的误差,本文采用了双路干涉的方法,使得测量精确性大为提高。测量结果表明:在波长632.8nm下,掺杂液晶三阶非线性系数n_2为0.268cm~2/W,其中热效应的贡献为0.091cm~2/W。

Measurement of optical nonlinearity originating from photo-induced thermal effect for azo-dye-doped liquid crystal

The azo-dye-doped liquid crystals (ADDLCs) have strong third-order optical nonlinearity, which arises from multiple nonlinear mechanisms, including photo-induced thermal effect and isomerization effect, etc. In this paper, in order to obtain the value of third-order optical nonlinearity in ADDLCs, we use a method of nonlinear interferometry to measure the change of refractive index at the wavelength 632.8 nm, deriving from intensity's change. A temperature equivalent method is proposed to quantitatively measure the contribution of thermal effect to the third-order optical nonlinearity, which simulates equivalent thermal effect through heating the ADDLC sample and producing the same temperature change as the irradiation light induces. Through this method, the thermal effect can be distinguished from multiple nonlinear effects. By measuring the change of refractive index and the corresponding temperature and intensity changes, we have obtained the value of third-order optical nonlinearity originating from thermal effect. Besides, a double-beam interferometry is used to improve the accuracy of measurement and eliminate the error from environmental shock, which increases the accuracy substantially. The measurement results show that, at the wavelength 632.8 nm, the third-order optical nonlinear coefficient n₂of DR1-doped LC is 0.268 cm²/W, to which the contribution of thermal effect is 0.091 cm²/W.