CAREER: Back-conversion suppressed optical parametric frequency conversion: Nonlinear evolution dynamics for overcoming longstanding device limitations

能够发射短脉冲光的激光器已经改变了工业和科学。它们被用于精密的汽车加工、识别癌细胞、进行眼科手术，以及跨越海洋传输声音和数据。它们被用来了解植物如何收获太阳能，DNA如何抵抗紫外线的照射，以及研究材料的组成和结构如何随着时间的推移而变化。它们被用来研究作为替代能源的光诱导核聚变，以及研究被加速到接近光速的粒子的行为。然而，只有少数颜色的光脉冲可以直接从激光获得足够的强度和简短的这些应用，这些颜色往往不适合手头的任务。为了改变激光的颜色，科学家们使用了所谓的“非线性光学”方法。通过这些方法，激光可以在频率上上下移动，并且通过将激光束组合在一个专门的光学设备（通常是晶体或光纤）中，光可以放大到激光无法获得的颜色。这些方法受到固有的“反向转换”行为的限制：在整个激光束的光转换完成之前，过程开始逆转。这使得非线性光学光转换方法效率低下，并限制了可以产生的频率范围。因此，光颜色的选择性是以可用于应用的光较少为代价的，这反过来限制了基础科学和工业应用的可执行性。该项目负责人的目标是通过研究抑制反向转换的非线性光学新方法来解决这些问题。将探索由晶体或光纤组成的设备，以证明这些光转换方法可以以前所未有的效率进行，并覆盖非常广泛的频率范围，从而使激光的新的科学和工业应用成为可能。首席研究员计划在他的职业生涯中，在计划的科学研究中使用这些方法，以研究人类视觉过程，量子信息处理的新平台，以及通过激光照射控制材料的电学，光学和磁性的新方法。首席研究员还将针对中学到大学水平的学生开发相关的教育资源，以提高对激光科学和技术的认识，并提高对工程研究过程的理解。为了避免非线性光频率转换器和放大器演化动力学中的反向转换的基本限制问题，从而展示具有超高转换效率和超宽带宽的光转换和放大器件，主要研究涉及异常传播动力学的非线性光频率转换的两个新颖且具有广泛应用潜力的概念。首先，我们将尝试一种新提出的抑制光参量放大中反向转换的方法，通过光参量放大和二次谐波产生两种混频过程同时进行相位匹配，以达到甚至超过量子缺陷水平的信号放大效率。要研究的实现将包括双折射和新的准相位匹配方法。其次，在抗谐振中空光纤中，通过绝热四波混频，尝试用近酉变换矩阵实现跨八度的近中红外光子下转换。这将通过对同时携带四束激光的微结构空心芯光纤施加压力梯度来实现。两种形式的非线性演化动力学将通过数值和实验方法进行研究，并将研究设备以证明其可行性。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Lasers that can emit brief pulses of light have transformed industry and science. They are used for precise automotive machining, to identify cancer cells and to perform eye surgery, and to carry voices and data across the ocean. They are used to understand how plants harvest solar energy, how DNA withstands irradiation from ultraviolet light, and to study how the composition and structure of materials changes over time. They are used to study light induced nuclear fusion as an alternative energy source and to study the behavior of particles that have been accelerated to near the speed of light. However, only a few colors of light pulses can be obtained directly from lasers with sufficient intensity and brevity for these applications, and these colors are often not appropriate for the task at hand. In order to change the color of laser light, scientists use so-called “nonlinear optical” methods. By these methods, laser light can be shifted up or down in frequency and light can be amplified at colors not available from lasers by combining laser beams in a specialized optical device, typically a crystal or optical fiber. These methods are limited by an inherent behavior known as “back-conversion”: before light conversion is completed across the entire laser beam, the process begins to reverse. This makes nonlinear optical light conversion methods inefficient and limits the range of frequencies that can be generated. As a result, selectivity in the color of light comes at the cost of having less light available for the application, which in turn limits both the fundamental science and industrial applications that can be performed. The Principal Investigator aims to solve these problems by investigating new nonlinear optical methods with suppressed back-conversion. Devices consisting of crystals or optical fibers will be explored in order to prove that these light conversion methods can be carried out with unprecedented efficiency and covering a very broad range of frequencies, thus enabling new scientific and industrial applications of laser light. The Principal Investigator plans to use these methods in planned scientific studies during his career to enable investigation of the human vision process, new platforms for quantum information processing, and new methods for controlling the electrical, optical, and magnetic properties of materials through irradiation with laser light. The Principal Investigator will also develop related educational resources aimed at middle school through college level students in order to increase awareness of laser science and technology and to improve understanding of the engineering research process.In order to avoid the fundamental limiting problem of back-conversion in the evolution dynamics of nonlinear optical frequency converters and amplifiers, and thus to demonstrate light conversion and amplification devices with ultrahigh conversion efficiency and ultrawide bandwidth, the Principal Investigator will investigate two novel and potentially widely applicable concepts for nonlinear optical frequency conversion involving unusual propagation dynamics. First, a newly proposed method for suppressing back-conversion in optical parametric amplification will be attempted through the simultaneous phase matching of two wave-mixing processes, optical parametric amplification and second harmonic generation, in order to achieve signal amplification efficiency at or even beyond the quantum defect level. Implementations to be investigated will include both birefringent- and novel quasi-phase-matching approaches. Second, octave-spanning near- to mid-infrared photon down-conversion with a near unitary transformation matrix will be attempted via adiabatic four-wave mixing in an anti-resonant hollow optical fiber. This will be carried out by applying a pressure gradient to a microstructured hollow-core fiber that carries four laser beams simultaneously. The two forms of nonlinear evolution dynamics will be investigated by numerical and experimental methods, and devices will be investigated to prove feasibility.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.