新型多环芳烃分子中双光子诱导单重态吸收的调控机制及其超快宽带光限幅研究

The research of mechanism in optical limiting and the developing of advanced optical limiting materials are vital to the application of laser protection. The restricts in present research have limited the application of optical limiting in several typical wavelengths with long pulse widths. With the rapid developing and popularizing of tunable ultrafast laser sources, corresponding optical limiting materials are required. Recently, broadband (UV-Vis) reverse saturable absorption along with the response under multiple laser pulses (fs ~ ns) were achieved in a series of PAHs (polycyclic aromatic hydrocarbon) molecules via two-photon induced singlet state absorption. Following this idea, optical limiting in these PAHs would be further studied in this project. The mechanism of two-photon induced singlet-state absorption is investigated via transient optical nonlinearity experiments, aiming to find an effective method to modulate the transient absorption in PAHs. Furthermore, DFT (density functional theory) calculation is employed to systematically research the structure-property relationship. Base on the results, optical limiting combining high linear transmittance, broadband response and multiple pulses adaptation would be achieved. This project would greatly promote the research of broadband ultrafast optical limiting in PAHs materials and lead a way to the applications in laser protection and other photoelectron areas.

光限幅机制的研究、光限幅材料的开发对激光防护应用有着非常重要的意义。目前绝大多数光限幅材料只能应对典型波长的长脉冲激光，光限幅性能单一，对外部光源选择性强，严重落后于可调谐、超快光源日益普及下的激光防护需求。最近，申请人在一组多环芳烃类分子中基于双光子诱导的单重态吸收，获得了覆盖可见光-近红外区域的宽带非线性吸收，并兼顾了飞秒至纳秒间的多种脉冲响应。据此思路，本项目拟在多环芳烃类分子体系中，通过瞬态光学非线性研究，深入探索调控双光子诱导单重态吸收的超快光物理机制；同时结合密度泛函计算，系统性地分析其结构-性质关系。依此进行优化设计，在单一光限幅材料中兼顾高线性透过、宽带与多种脉冲响应。该项目的研究预计将极大丰富有机材料超快宽带光限幅的研究，为推进多环芳烃类材料在激光防护及其他光电子领域的应用提供科学指导。

随着超短脉冲激光技术在各个领域的广泛应用及其潜在的武器化前景，针对超快激光作用时间短、峰值功率高、易形成超连续白光等特点开发防护技术和材料具有重要意义。传统的光限幅材料由于响应速度慢、限幅光谱窄，针对超短脉冲激光的防护能力弱，无法满足需求。本项目结合理论与实验，以多环芳烃为代表的有机共轭分子为基础，在超快光学非线性的产生和增强机制，基于单线态的超快宽带非线性吸收，多种吸收机制共同作用下的超快宽带光限幅等方面取得以下研究成果：.（1）新型查尔酮分子中饱和-反饱吸收转换机制和非线性折射。通过不同的末端取代改变分子的空间结构，研究了同分异构体中平面π共轭体系和分子内电荷转移对超快光学非线性的作用。分析了共振激发下饱和-反饱和的转换机制及其对非线性吸收的影响。.（2）新型芴酮基分子的宽带非线性吸收与瞬态折射。以芴酮为中心构建π共轭体系并形成两端至中心的分子内电荷转移。通过瞬态吸收光谱和飞秒Z扫描实验区分了不同波长激发下，激发态吸收、双光子吸收、双光子诱导激发态吸收的产生和作用机制。.（3）扭转并苯与氮杂平面π共轭体系中的超快宽带光限幅性能。通过单、双光子吸收诱导单线态上的宽带激发态吸收，多种吸收机制共同作用实现了高线性透过率，宽光谱，超快响应的光限幅能力。.我们相信上述的研究与成果对理解共轭有机分子中的超快光物理过程，发展针对超短脉冲激光的光限幅材料具有重要的参考价值