CAREER: Understanding and Controlling Nonlinear Frequency Conversion with Counter Propagating Light

非线性光学提供了一种独特的方法，通过一种称为频率转换的过程来创建可访问的、经济高效的激光光源。事实上，一些透明材料的自然反应是将强烈的激光从一种颜色或频率转换为另一种颜色或频率，从而实现了从绿色激光指示器到激光引燃聚变的各种应用。有效地将激光从一个频率转换到另一个频率需要对这种光-材料相互作用中的材料成分进行仔细的、有时甚至是复杂的设计。这些技术在很大范围的应用中都非常成功，但受到可为此目的设计的材料的限制。与光-材料相互作用中的工程材料不同，这项由该职业奖支持的研究探索了如何设计光。虽然这项研究的主要应用是开发新的光源，但光场工程也可以揭示光转换过程的基本物理，并为执行材料本身的测量提供极其精确的工具。这项研究将与一所研究密集型文科大学的教育相结合，方法是指导实验光学本科生，并通过跨学科的第一年研讨会课程制定提高科学素养的课程，并通过中级光学课程为学生提供早期参与光学在研究中的应用。非线性光学材料的色散是对二次谐波等非线性频率转换过程效率的主要挑战。最近发展了一种新的校正色散效应的方法，利用反向传播脉冲序列周期性地干涉谐波产生过程，实现了全光学版本的准相位匹配。虽然这项技术的实验证明只适用于高次谐波的产生，但该技术应该适用于更广泛的非线性过程。在这个项目中，将对当前的理论模型进行直接的实验测试，以产生二次谐波，从而更好地了解干扰所涉及的物理学。在此基础上，结合数值模型的发展，将利用超快反向传播脉冲的整形来优化相位匹配的效率。这些研究的结果不仅适用于低阶非线性光学过程，也适用于阿秒科学的主要来源--高次谐波。此外，超快反向传播脉冲的使用将被研究为一种高分辨率的、原位的复杂非线性材料的色散特性的探测器，这可能用于周期极化介质的表征或生物材料的成像。

Nonlinear optics provides a unique means for creating accessible and cost-effective laser sources, through a process called frequency conversion. The natural response of some transparent materials, in fact, is to convert intense laser light from one color, or frequency, to another, enabling applications ranging from green laser pointers to laser-ignited fusion. Efficient conversion of laser light from one frequency to another requires careful and sometimes complex engineering of the material component in this light-material interaction. These techniques have been very successful for a large range of applications, but are limited by what materials can be engineered for this purpose. Instead of engineering materials in the light-material interaction, the research supported by this CAREER award explores how we can engineer the light. While the main application of this research is the development of new light sources, engineering of light fields could also reveal fundamental physics of the light conversion process, as well as provide an extremely precise tool for performing measurements of the materials themselves. This research will be integrated with education at a research-intensive liberal arts college through mentoring of undergraduates in experimental optical science, as well as the development of curricula for improved scientific literacy through an interdisciplinary first-year seminar course, and providing students early engagement with applications of optics in research through an intermediate-level Optics course. The main challenge for the efficiency of nonlinear frequency conversion processes such as second harmonic generation is the chromatic dispersion of the nonlinear optical material. Recently, a novel method for correcting the dispersion effects has been developed, in which sequences of counterpropagating pulses are used to interfere periodically with the harmonic generation process, achieving an all-optical version of quasi-phase matching. While experimental demonstrations of this technique have been shown only for high-order harmonic generation, the technique should be applicable to a much wider range of nonlinear processes. In this project, direct experimental testing of current theoretical models will be performed for second harmonic generation, providing a better understanding of the physics involved in the interference. Building on this knowledge and in concert with development of numerical models, the efficiency of phase matching will be optimized using shaping of the ultrafast counterpropagating pulses. The results from these studies are applicable not only to low-order nonlinear optical processes, but also high harmonics, the major source for attosecond science. Additionally, the use of ultrafast counterpropagating pulses will be investigated as a high-resolution, in-situ probe of the dispersion properties of complex nonlinear materials, which may be used in the characterization of periodically-poled media or imaging of biological materials.