Collaborative Proposal: Ultrabroadband Supercontinuum Studies

在过去的两年中，光学领域最激动人心的事件可能是微结构光纤的发展。与传统光纤相比，这种光纤的色散特性可定制的程度要大得多。因此，它可以用于将商业上可用的低能量超短脉冲转换为带宽为500太赫兹的超宽带连续光。这种光在电信、固态光谱学、化学反应的相干控制和超高空间分辨率光学相干层析成像中具有许多深远的应用。它已经彻底改变了光学计量领域。不幸的是，处理超宽带光的技术仍处于起步阶段。在这个阶段，除了功率谱之外，不可能测量其特性。脉冲整形和压缩技术在窄带应用中取得了成功，但不适用于这种超宽带辐射。即使是像准直和传播超宽带光这样简单的任务也不可能实现。例如，超宽带透镜不存在，反射镜也因为这种光的衍射角超过60度而失效。此外，人们对这种光产生的过程充其量也知之甚少。因此，我们建议1)进行广泛的建模以了解连续光的潜在机制和特性，2)开发其表征的实验技术，以及3)设计操纵和压缩该光的新技术。我们将采用两种不同的方法来产生超宽带光。其中一个将使用标准的fs Ti：蓝宝石激光器和微结构光纤产生光谱从400nm到1.6 um的连续光。第二种方法同样很有前途，但尚未被探索，它将使用由IMRA美国公司开发的放大光纤激光器，在传统的红外通信光纤中产生超宽带连续体：从800纳米到2.5微米。这种超宽带光非常复杂，具有超过1000的时间带宽积（TBP），而已经完全表征的最复杂的超短脉冲的TBP为~10。后一种测量方法使用了频率分辨光门控（FROG），它将FROG技术推向了极限。因此，我们建议开发一个更宽带版本的FROG，用于测量超宽带连续体，其额外复杂性超过两个数量级。这必然涉及到一些创新，例如，为了获得更大的带宽，对非线性晶体进行角度抖动。

Probably the most exciting event in optics in the past two years has been the development of microstructure optical fiber. The dispersion properties of this fiber can be tailored to a far greater extent than conventional optical fibers. As a result, it can be used to transform commercially available, low-energy ultrashort pulses into ultrabroadband continuum light with a bandwidth of 500 THz. This light has numerous far-reaching applications in telecommunications, solid-state spectroscopy, coherent control of chemical reactions, and ultrahigh-spatial-resolution optical coherence tomography. It has already completely revolutionized the field of optical metrology.Unfortunately, techniques for working with ultrabroadband light remain in their infancy. At this stage, it is not possible to measure its properties other than the power spectrum. Pulse shaping and compression techniques, which are successful in narrowband applications, are not applicable to this type of ultrabroadband radiation. Even simple tasks such as collimating and propagating ultrabroadband light are not yet possible. For example, ultrabroadband lenses do not exist, and mirrors also fail because the diffraction angle of this light is over 60s. Furthermore, the process by which this light is created is at best poorly understood.As a result, we propose to 1) perform extensive modeling to understand the underlying mechanisms and the properties of the continuum light, 2) develop experimental techniques for its characterization, and 3) devise new techniques for manipulating and compressing this light. We will take two distinct approaches to ultrabroadband-light generation. One will utilize a standard fs Ti:Sapphire laser and microstructure optical fiber to produce continuum light with spectrum from 400 nm to 1.6 um. The second approach, which is equally promising -but as yet unexplored- will use amplified fiber lasers developed by IMRA America to generate ultra-broadband continuum in conventional telecommunications fiber in the IR: from 800 nm to 2.5 um.This ultrabroadband light is extremely complex, having a time-bandwidth product (TBP) in excess of 1000, whereas the most complex ultrashort pulse that has been completely characterized had a TBP of ~10. This latter measurement used frequency-resolved optical gating (FROG), and it pushed the FROG technique to its limits. As a result, we propose to develop a much broader-band version of FROG for measuring ultrabroadband continuum with more than two orders of magnitude of additional complexity. It will necessarily involve several innovations, including, for example, angle-dithering the nonlinear crystal for much greater bandwidth.