OP: Compressive Nonlinear Optical Microscopy for Dynamic Chemical Imaging of Surfaces

在化学系化学测量与成像项目的支持下，休斯顿大学的巴尔代利教授和莱斯大学的凯利教授正在开发一种新型显微镜，这种显微镜能够比普通显微镜更快地看到表面上的分子，而且灵敏度更高。有了相机，可以拍摄显示颜色的照片，以帮助识别物体；例如，草是绿色的，天空是蓝色的。然而，要观察分子，需要更多关于分子吸收的“颜色”的具体信息。对许多分子来说，这种吸收发生在光的红外光区。为了观察这些红外颜色，传统的相机不是很好，所以没有相机就可以获得图像的方法是必要的。巴尔代利教授和凯利教授正在开发一种新型显微镜，用于观察表面分子的表面图像。这种新型显微镜的结果对所有对与生物材料、能源和环境主题相关的表面感兴趣的研究人员都很有用。例如，它可以用来研究细胞膜上脂质分子的分布，脂质分子控制蛋白质进出细胞，从而调节细胞生长和信号传导。它还可以用来观察薄膜上的化学掺杂物，这些化学掺杂物可以加速燃料电池中的氧还原反应，这是高效能量转换的重要一步。该研究项目也为学习和体验多学科合作研究提供了宝贵的机会——这是当前科学和工程教育的重点。课题和研究项目有许多组成部分，以鼓励本科生和高中生参与研究，包括仪器制作，数据分析和解释，以及研究报告。后一点是一个重要的方面，因为它在年轻的学生和科学家中建立了很大的信心。巴尔代利教授和凯利教授正在开发一种新的最先进的表面光谱成像显微镜，用于研究许多基础和技术重要系统中存在的模式和化学异质性的分子、空间和时间演变。这种新的CS-SFG（压缩感知和频率产生振动光谱）成像技术利用了一个数字镜像装置（DMD）。DMD是DLP投影机和平面显示器的核心。它是一个二维的镜子阵列，将SFG图像反射到探测器上。利用计算机控制和随机模式发生器，信号强度的变化取决于哪些镜子反射到探测器上。每种图案都是随机选择的50%的镜子在每次测量中被打开。经过多次这样的测量，基于信号和已知的镜像模式重建图像。CS允许有效的图像采集，其中只需要总信息的百分之几就可以忠实地重建表面特征。建立了宽频带和窄频带两种配置，评估了对图像重建的影响。此外，检测系统采用外差检测从单层信号中提取相位信息。这种新功能允许替代成像方案和方向分析。压缩算法和定量分析的影响最终有助于解释表面上的非均质单层薄膜。CS-SFG显微镜将是对现有方法的重大改进，现有方法要么使用毫米级的探针区域，要么获得完整的高光谱数据立方体，但在样品吞吐量方面花费相当大。一旦证明了这一点，Baldelli教授和Kelly教授将使用这台显微镜来研究在光版印刷控制条件下形成的化学模式（如脂质结构域）的分子水平静态和动态细节，并通过Langmuir-Blodgett技术将薄膜转移到固体基片上。该研究项目为研究生和当地高中生提供化学、物理、工程和计算机科学等跨学科的培训。

With support from the Chemical Measurement and Imaging Program in the Division of Chemistry, Professor Baldelli at the University of Houston and Professor Kelly at Rice University are developing a new type of microscope that is able to see molecules on surfaces faster and with higher sensitivity than regular microscopes. With cameras, pictures can be taken that show colors to help identify objects; for example, grass is green and sky is blue. However, to look at molecules, more specific information is needed about the "colors" that molecules absorb. For many molecules, this absorption occurs in the infrared region of light. To look at these infrared colors, traditional cameras are not very good so methods that can obtain pictures without cameras are necessary. Professor Baldelli and Professor Kelly are developing a new type of microscope to figure out the surface image of surface molecules. The results of this new microscope are useful to all researchers interested in surfaces related to biomaterials, energy, and environmental topics. For example, it can be used to study the distribution of lipid molecules on cell membranes that controls proteins moving in and out of cells, which in turn regulate cell growth and signaling. It can also be used to look at chemical dopants on a thin film that accelerate the oxygen reduction reaction in fuel cells, an important step in efficient energy conversion. The research project also presents a valuable opportunity to learn and experience collaborative multidisciplinary research -- a current emphasis of science and engineering education. The topics and research project have many components to encourage undergraduate and high school students into the research, including instrument building, data analysis and interpretation, and research presentations. This later point is an important aspect since it builds much confidence in the younger students and scientist.Professors Baldelli and Kelly are developing a new state-of-the-art surface spectroscopic imaging microscope to study the molecular, spatial, and temporal evolution of patterns and chemical heterogeneity present in many fundamental and technologically important systems. This new CS-SFG (compressive sensing-sum frequency generation vibrational spectroscopy) imaging technique utilizes a digital mirror device (DMD). The DMD is the heart of the DLP projector and flat screen displays. It is a 2-D array of mirrors that reflects the SFG image onto a detector. Using computer control and a random pattern generator, the signal intensity changes depending on which mirrors are reflecting toward the detector. Each pattern results from 50% of the randomly chosen mirrors being turned on for each measurement. After many such measurements, the image is reconstructed based on the signal and the known mirror pattern. CS allows for efficient image acquisition where only a few percent of the total information is necessary to faithfully reconstruct the surface features. Two configurations broad-band and narrow-band IR are set up to evaluate the effect on the image reconstruction. In addition the detection system incorporates heterodyne detection to extract phase information forth monolayer signal. This new capability allows for alternate imaging schemes and orientation analysis. The effect of compression algorithms and quantitative analysis ultimately aid in the interpretation of heterogeneous monolayer films on surfaces. The CS-SFG microscope will be a significant improvement over current approaches that either use probe areas on the order of a millimeter or acquire the full hyperspectral data cube but at considerable expense in sample throughput. Once demonstrated, Professors Baldelli and Kelly are to employ this microscope to investigate the molecular-level static and dynamic details of chemical patterns (such as lipid domains) formed under the control condition of lithography and the transfer of films to solid substrates via the Langmuir-Blodgett technique. The research project provides both graduate students and local high school students with highly interdisciplinary training in chemistry, physics, engineering, and computer science.