面向双光子泵浦上转换激射有机晶体研究

Two-photon punped lasing is currently of considerable interest for frequency upconversion lasers, as the gain medium can be pumped at red or near-infrared wavelengths, for which laser need no rigorous phasic matching compared to conventional inorganic double-frequency cryctals. The frequency up-conversion is considered as new principle to achieve tunable laser, as lasing wavelength can be tuned in range of tens of nanometers for one material. So far, internationally relative researches are limited in that, two-photon pumped lasing has been achieved with dye solutions, conjugated polymers and dye-doped solids as gain media. On account of their high purity and their rigorously defined structure, high-quality single crystals are more advantageous than polymer films and solutions. Crystal materials possess higher thermo-stability compared with amorphous materials, which are in thermodynamically metastable phases and tend to transit to a more stable phase at low temperature (glass transition temperature, Tg). Unlike solution-processed thin films, single crystals do not display grain boundary defects that may serve as carrier traps. Furthermore, a single crystal is excellent in optical properties, typically the low light propagation loss due to less light scattering and naturally formed crystal facet cavities with molecular-scale flatness. We propose here single crystals should be applied as laser medium. In the project, the functional crystals with large two-photon absorption cross-section and high fluorescent quantum yields will be designed and synthesised, the excited state of molecules and relaxation kinetics will be studied in both monodisperse system and crystal by using various spectral methods to clarify a key problem, modulation of the molecular aggregation to absorption and emission properties, and simple, stable and highly efficient two-photon pumped laser with frequency up-conversion from crystals will be achieved. The project will provide a scientific and technical base for extensive application of two-photon pumped laser device from organic crystals.

以有机分子双光子吸收效应为基础的频率上转换，和传统的非线性无机晶体倍频等激光频率转换方法相比不需要苛刻的相位匹配条件；同一材料的激光波长可在几十个纳米的范围内调谐，因而有望成为实现可调谐激光输出的新机制。但到目前为止，国际上相关的研究还局限于将具有大双光子吸收截面的有机分子分散于溶液或聚合物母体中作为激光介质，材料的均匀性、重复性和热效应等问题难以解决。本项目拟在研究组前期工作的基础上，提出采用有机单晶作为激光介质的新思路，以合成的晶体具有较大的双光子吸收截面和较高的荧光量子产率为目标，通过选择几类典型材料体系、改变取代基团、调控堆积模式研究分子结构、晶体的分子堆积结构对晶态材料的吸收和发射性质的调控，澄清单晶中不同的分子聚集态对吸收和发射特性的调制这一关键科学问题，实现简单、稳定、高效的双光子泵浦的有机晶体频率上转换激光输出。

以有机分子双光子吸收效应为基础的频率上转换，和传统的非线性无机晶体倍频等激光频率转换方法相比不需要苛刻的相位匹配条件；同一材料的激光波长可在几十个纳米的范围内调谐，因而有望成为实现可调谐激光输出的新机制。项目执行情况如下研究：利用具有良好发光性质的BP1T和BP2T材料利用气相沉积方法制备薄片状有机晶体，然后结合反应离子刻蚀方法制备微盘状有机晶体微结构，进一步证明该光子晶体的激射性质；开展了9,10-二苯乙烯基蒽(DSA)衍生物晶体和氰基取代苯乙烯齐聚物等有机晶体中的双光子荧光和放大自发辐射性质，比较了单光子放大自发辐射和双光子放大自发辐射的特点；利用有机材料的熔融特性制备有机固体激光器件，并对有机固体激光器的性质进行研究；提出利用激光加工有机晶体微纳结构，研究了纳秒激光器双光束干涉技术在有机晶体表面刻蚀加工光栅结构及上转换激射性质。