Nonlinear optical coherence tomography

光学相干断层扫描（OCT）显微镜可以产生微米级的三维图像，在活体组织中的深度为几毫米。 尽管OCT在眼科领域取得了重大进展，但它仍存在一些困难，包括对比度低。 我们建议建立一个新的仪器，它将利用光学相干断层扫描的微米级分辨率的能力与非线性时间选通的光子选择性，以提高成像对比度，减少数据采集时间。 亚皮秒光学时间选通，通过非线性晶体中的和频混合，在检测发生之前拒绝来自选通时间窗口之外的光（及其相关噪声）。 这将在接近高散射介质和较长穿透深度时显著提高成像质量。 也将避免在OCT的当前傅立叶域实现中引起鬼像和噪声的混叠。 时间选通过程也是有益的，因为样品探测可以用1300 nm左右的波长进行，这对于样品穿透是最佳的，而光电检测是用可见光进行的，允许使用高性能硅基检测器技术。 与标准傅里叶域OCT系统相比，时间选通减少了所需检测器元件的数量，从而显著减少了采集和处理时间。 该研究计划广泛利用了我们现有的超快基础设施，我们在光脉冲表征方面的经验，以及我们与其他OCT研究人员，工业工程师和潜在最终用户的合作。 这只是将超快光学材料处理技术与改进的成像模式结合起来用于临床应用的总体愿景的第一步。 两名目前的研究生需要立即为他们的研究计划的设备。 估计另外七名女王大学的学生（本科生和研究生）和至少两名访问研究人员将在未来三年内接受关于这一设备的实际培训。

The optical coherence tomography (OCT) microscope can produce micron-scale three-dimensional images to depths of several mm in living tissue.  Though it has made major inroads in ophthalmology, OCT suffers from several difficiencies including low contrast.  We propose to build a new instrument which will exploit the micron-scale resolution capabilities of OCT with the photon selectivity of nonlinear time-gating to improve imaging contrast and decrease data acquisition time.  Subpicosecond optical time gating, by sum-frequency mixing in a nonlinear crystal, rejects light (and its associated noise) from outside the gated time window before detection occurs.  This will yield significant improvements in imaging quality close to highly scattering media and at longer penetration depths.  Aliasing which causes ghost images and noise in current Fourier-domain implementations of OCT will also be avoided.  The time gating process is also beneficial since sample probing can be done with wavelengths around 1300nm which are optimal for sample penetration, while photodetection is done with visible light allowing the use of high performance silicon-based detector technology.  Time gating decreases the number of detector elements required thus dramatically reducing aquisition and processing time compared to standard Fourier-domain OCT systems.     This research program makes extensive use of our preexisting ultrafast infrastructure, our experience with optical pulse characterization, and our collaborations with other OCT researchers, industrial engineers and potential end users.  It is only the first step within an overall vision to integrate ultrafast optical material processing techniques with improved imaging modalities for clinical applications.  Two current graduate students require the equipment immediately for their research program.  An estimated seven additional Queen's students  (undergraduate and graduate) and at least two visiting researchers will have hands-on training on this equipment over the next three years.