基于非线性界面切伦科夫型谐波的波前探测方法及特性研究

Although nonlinear optical frequency conversion can effectively extend the sensing range of the sensor, the application of nonlinear optics in wavefront sensing is quite limited due to the obvious harmonics wavefront distortion induced by tiny phase mismatch during optical frequency conversion process. Here we propose a nonlinear optical wavefront sensing method based on Cherenkov type harmonic generation from nonlinear interface of nonlinear medium. According to Cherenkov type phase matching condition, this method can achieve broadband harmonics generation, during which process the wavefronts of harmonics and fundamental waves are connected through simple relationship so that we can easily reconstruct the fundamental wavefront from that of the harmonic. By properly changing the dispersion characteristics of fundamental and harmonic waves, we can also enlarge or shrink the beam size, which enables another advantage -- the adjustment of sensing resolution. We are aiming to establish a new wavefront sensing method through nonlinear optical process, grasp the main factors influencing the detection precision, and understand the key scientific problems. Meanwhile, we will try to demonstrate its validity in ultrashort laser pulse wavefront sensing and extend its applications in material nonlinear interface testing, digging its application potential in laser technologies and material researches.

非线性光学频率转换能够有效拓展波前探测中传感器的测量范围，但由于严格的位相匹配条件限制，微小的基频波前扰动都会引起谐波波前巨大的差异，因此非线性光学频率转换在波前探测领域的应用有限，公开文献中鲜有报道。本项目提出一种基于非线性界面切伦科夫型谐波的波前探测方法，利用切伦科夫型谐波的位相匹配特性，既能够实现宽带的谐波产生，又能利用谐波与基频波前简单关联的特性实现基频波前重构，还能通过改变色散关系实现无透镜系统下的扩束和缩束，改变波前测量的分辨率，因而具有传统探测方法不具备的诸多优点。本项目旨在建立一种新的非线性光学波前探测方法，深入把握影响探测精度的主要因素，理解其中的关键科学问题，并验证该方法在超短脉冲波前测量和材料内部非线性界面检测方面的效果，发掘其在激光技术和材料研究中的应用潜力。

提出一种利用材料非线性界面的切伦科夫型谐波实现基频光波前传感的新方法，该方法可以实现宽带谐波产生，进而实现对飞秒激光脉冲频率分辨的波前探测。通过本课题的理论研究和实验验证，明确了基频光波前分布是影响切伦科夫型谐波波前分布的主要因素。和频与多次谐波波前取决于入射基频光波前与非线性界面的面型，扩束与缩束仅影响谐波波前的空间比例。实现了对飞秒激光脉冲频率分辨的波前测量，证明在有限的谱宽内，不同频率分量的波前差异对脉冲压缩的影响很小。实验验证了切伦科夫型谐波对非线性界面测量的效果，结果表明，材料非线性界面产生的非线性切伦科夫谐波携带了界面的面型信息，并反映到谐波的波前分布上，可以用于非线性界面面型的探测。此外，还研究了利用晶体内表面产生高效紫外激光，并发明了一种新的波前探测方法，并在大型激光装置上得到应用。