偶氮苯聚合物全息光栅衍射效率和偏振特性研究

Study on Diffraction Efficiency and Polarization Characteristic of Azobenzene Polymer Holographic Grating

研究了不同偏振全息模式下基于交联偶氮苯聚合物薄膜的相位光栅的形成机理、衍射效率和偏振特性。利用琼斯矢量表征了正交线偏振(SP)和平行线偏振(SS)干涉模式下的偏振干涉场。基于SP和SS两种模式,制作了无明显表面起伏的纯折射率光栅和有表面起伏的浮雕光栅。偏光显微镜(POM)观测说明纯折射率光栅具有周期性的折射率分布;近场光学显微镜(SNOM)探测说明纯折射率光栅和浮雕光栅的表面起伏在5nm以下和85.23nm。实验表明,当探测光为水平偏振时,纯折射率光栅的衍射效率达到22.2%,浮雕光栅只能达到1.65%。纯折射率光栅的0、+1级衍射光分别为水平和竖直线偏振光,偏振度达到0.9969和0.9963;浮雕光栅的0、+1级衍射光均为水平线偏振光。

The forming mechanism, diffraction efficiency and polarization characteristic of phase gratings written in cross-linked azobenzene copotymer films under different holography modes were studied. Jones vector was utilized to express interference field, involving orthogonal linear polarization interference mode （SP） and parallel linear polarization interference mode （SS）. Based on SP and SS modes, pure refractive index grating （PRIG） without surface topology and surface relief grating （SRG） with unnegligible surface relief were fabricated respectively. Periodic refractive index distribution of PRIG induced under SP mode was observed in polarization optical microscope （POM）. Quantitative topographic measurement in near-field optical scanning microscope （SNOM） indicates that SRG has a surface relief at 85.23 nm, but PRIG less than 5 nm. When reconstructed light is set to horizontal polarization, diffraction efficiency of PRIG reaches 22.2 %, while SRG reaches only 1.65 %. The zero-and first-order diffraction beams of PRIG are horizontally and vertically polarized, with polarization degree at 0. 9969 and 0. 9963. Diffraction beams of SRG are both horizontally polarized.