Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA.
Anal Chem. 2010 Jul 1;82(13):5697-706. doi: 10.1021/ac1007128.
There is a need to develop mid-infrared (IR) spectrometers for applications in which the absorbance of only a few vibrational mode (optical) frequencies needs to be recorded; unfortunately, there are limited alternatives for the same. The key requirement is the development of a means to discretely access a small set of spectral positions from the wideband thermal sources commonly used for spectroscopy. We present here the theory, design, and practical realization of a new class of filters in the mid-infrared (IR) spectral regions based on using guided mode resonances (GMR) for narrowband optical reflection. A simple, periodic surface-relief configuration is chosen to enable both a spectral response and facile fabrication. A theoretical model based on rigorous coupled wave analysis is developed, incorporating anomalous dispersion of filter materials in the mid-IR spectral region. As a proof-of-principle demonstration, a set of four filters for a spectral region around the C-H stretching mode (2600-3000 cm(-1)) are fabricated and responses compared to theory. The reflectance spectra were well-predicted by the developed theory and results were found to be sensitive to the angle of incidence and dispersion characteristics of the material. In summary, the work reported here forms the basis for a rational design of filters that can prove useful for IR absorption spectroscopy.
需要开发中红外（IR）光谱仪，用于仅需记录少数振动模式（光学）频率的吸收的应用中；不幸的是，可供选择的方案非常有限。关键要求是开发一种方法，以便能够从常用于光谱学的宽带热光源中离散地访问少数几个光谱位置。我们在这里提出了一种基于导模共振（GMR）用于窄带光反射的新的中红外（IR）光谱区滤波器的理论、设计和实际实现。选择了一种简单的、周期性的表面浮雕结构，使其既能实现光谱响应又能便于制造。开发了一种基于严格耦合波分析的理论模型，将滤波器材料在中红外光谱区的异常色散纳入其中。作为原理验证演示，我们制造了一组用于 C-H 伸缩模式（2600-3000cm-1）附近光谱区的四个滤波器，并将其响应与理论进行了比较。所开发的理论很好地预测了反射率谱，并且结果发现对入射角和材料的色散特性敏感。总之，这里报道的工作为滤波器的合理设计奠定了基础，这对于红外吸收光谱学可能是有用的。
