This research program will develop new concepts for producing infrared filters for sensors based on integrated circuit microstructure technology. These components will be used in infrared through millimeter wave applications for remote sensing instruments in astrophysics, planetary, and space science. Infrared filters play an integral role on every infrared sensor, ground-based or portable, airborne and/or space mission, yet are currently a weak link in the US infrared technology infrastructure. The group uses state-of-the-art modeling and fabrication to undertake the development. The plan is to develop and test filters for operation of all types of spectral sensors applied to a broad range of monitoring and detection systems from the visible to the THz region.
This interdisciplinary proposal is combines fundamentals of wave propagation with applications to 3-D periodic hybrid structures to produce a robust technology that serves a wide rating of sensor needs. The study will enable novel three-dimensional design of spectral filters, splitters and combiners and novel imaging devices. In addition this project will be incorporated into the interdisciplinary program of Optical Science and Engineering (OPSE) at NJIT through two new modules. The program is geared to seniors and first year graduates across the campus and combines design and laboratory work.
IIS 0514361: Sensors: Narrow Band, Broad Band and Low Pass Metal Mesh Filters for sensors in the IR to THz region and instant multiple wavelength detection of chemical agents H. Grebel (PI) and K. D. Moeller (C-PI) Electronic Imaging Center, The department of Electrical and Computer Engineering, NJIT, Newark, NJ 07102 Summary This project has developed a novel, integrated three-dimensional structured electromagnetic filter technology for ground-based and space missions, so important for the US infrastructure. Such new concept could be useful for millimeter (mm) and terahertz (THz) frequency bands, as well as for the infrared (IR) spectra. Specifically, our objective was to develop a unified filter concept for (a) chemical weapon detection and (b) environmental monitoring of narrow spectral fingerprints, distributed over a large spectral range. The metal mesh screens are shown in Fig 1. In general, detection of pollutants is made by assessing their specific absorption when irradiating the sample with a broadband (white light) source. The original spectrum of the source contains all spectral lines. Upon analysis of the transmitted data, the absorption lines specific to the pollutant are those lines missing from the original spectra. The assessment of the ‘missing lines’ is made with the help of a spectrometer. In Fig. 2, we schematically show the detection’s configuration. A detection problem is encountered whenever narrow spectral absorption lines, characteristic of a specific chemical agent, are distributed over a broad spectral range. As shown schematically in Fig. 3 for the simple example of water H2O and its isotope D2O, there are two spectral lines that are shared by the two species (18 and 25 cm-1) and several lines, which are unique to only deuterium oxide, or heavy water (D2O). From molecular point of view, while some of the bands seem to be shared by both species, a closer look reveals a slight shift in the position of the lines. Moreover, the spectroscopic origin of the ‘shared’ lines is different (for example, and as indicated by the table in Fig. 3, the lines at 18 cm-1 for heavy water and ordinary water originate from two different transitions). As noted above, a spectral absorption signature is monitored by scanning spectrometers of various types. The speed of the scan is determined by the required spectral resolution; obviously, high-resolution assessment necessitates a slower scan, thus compromising the efficiency of the detection process. Instead and as shown in Fig. 4, we proposed the use of pre-determined ‘finger-printing’ filters. On one hand, one could claim that these filters have a limited scope in comparison to the scanning properties of broad band spectrometers. On the other hand, such approach could become useful when assessing the damages inflicted by known chemicals: in that case, a pass/fail analysis is what needed to make an evacuation or treatment decision. The approach is general and may be implemented in the infrared (IR), Terahertz (THz) and sub-millimeter spectral regions. This fast-detection option increases the efficiency of radiation collection by alleviating constraints of optical alignment. In addition, the spectral width of the filter may be adapted to the requirement for the lines detected; this is in contrast to a fixed spectral resolution, set for all lines, by a typical spectrometer. Moreover, if we could combine the linear transmission or, reflection properties of these filters with a nonlinear detection techniques such as, Raman spectroscopy, we have in principle integrated two of the most powerful molecular detection methods onto a single platform. During the course of the project we were able to design, simulate, fabricate and test such narrow-band filters. The project involved several graduate students, undergraduate students and National Lab personnel (Dr. Ken Stuart, Navy Research Lab). Transmittance of three filters is provided in Fig. 5.
