SU-8光栅结构中的液晶激光特性

设计制作了SU-8光栅结构的染料掺杂手性向列相液晶激光器件,在器件正面和侧面均实现了随机激光辐射。将激光染料PM597、手性剂S-811、向列性液晶TEB30A按一定比例均匀混合,注入反平行摩擦处理的液晶盒中,器件的下基板通过光掩模法刻蚀出周期为15μm的光栅。利用532 nm的Nd∶YAG固体脉冲激光器作为泵浦源,器件的侧面既在580~590 nm范围内出现了多个离散分立的随机激光辐射峰,FWHM约0.19 nm,又在579~585 nm范围内出现独立的两个激光辐射峰,FWHM约0.19 nm;在器件正面获得了584~590 nm范围的随机激光辐射谱,FWHM约0.17 nm。加热器件至61℃,液晶相变为各向同性态,器件侧面仍出现了波长约590.60 nm、FWHM约0.24 nm的激光辐射峰。分析得出,液晶盒中引入SU-8光栅结构后,光子同时在液晶分子间多重散射和SU-8光栅中布拉格反射获得反馈放大,两种机制相辅相成。器件侧面出现的独立激光辐射峰主要由SU-8光栅布拉格反射提供反馈放大形成,而器件侧面和正面的随机激光辐射峰主要由液晶分子间多重散射提供反馈放大形成。

Features of Liquid Crystal Laser in SU-8 Grating Structure

The dye-doped chiral nematic liquid crystal(DDCLC)laser with the SU-8 grating structure is designed and fabricated.Random laser emission is realized on both front and side of the device.After an SU-8 grating with a period of 15μm is produced on the bottom glass substrate of an anti-parallel rubbing treatment cell by the lithography technique,uniformly mixed laser dye PM597,chiral compound S-811 and nematic liquid crystal(LC)TEB30A are infused into the cell.When the cell is pumped by a 532 nm Nd∶YAG pulsed solid-state laser,a series of discrete random lasers with a full width at half maximum(FWHM)of 0.19 nm and a range of 580-590 nm,and two independent lasers with an FWHM of 0.19 nm and a range of 579-585 nm are excited at the side of the cell.In addition,a random lasing emission with an FWHM of 0.17 nm and a range of 584-592 nm is generated on the front of the cell.If the cell is heated to 61℃in which the LC phase changes into an isotropic state,the laser emission with a wavelength of about 590.60 nm and FWHM of about 0.24 nm is still observed on the sideof the device.The experimental results show that after the SU-8 grating structure is introduced into the liquid crystal cell,photons can obtain feedback amplification not only through multiple scattering between liquid crystal molecules but also via Bragg reflection in the SU-8 grating.These two mechanisms can complement each other.The independent laser emissions on the side of the cell are mainly produced by Bragg reflection of the SU-8 grating.Whereas,the random lasers on the side and front of the cell are formed through multiple scattering between liquid crystal molecules.