Instrument Development: 4-D Near-Infrared Chemical Imaging Using Snapshot Tomography

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With support from the Chemical Measurement and Imaging Program in the Division of Chemistry, Professor Sung at University of Wisconsin-Milwaukee (UWM) develops new instruments for 4-dimensional (4D) chemical imaging in the near-infrared (NIR) range. NIR hyperspectral imaging has been widely used for nondestructive quality inspection; however, existing methods cannot examine a specimen with a complicated internal structure or detect the chemical impurities buried deep inside a 3-D volume because the depth information is lost in the recorded 2-D projection images. Traditional approaches to 3-D tomographic imaging require a scanning mechanism, which significantly increases the data acquisition time and the complexity of an instrument. Professor Sung and his group is developing instruments using a technique called snapshot tomography, which can acquire the 3-D tomogram in a single snapshot. By incorporating various wavelength-scan strategies, the new instruments can acquire the 4-D hyperspectral data at a high speed and good spatial resolution. The instruments, once developed, could potentially impact many industries by allowing nondestructive quality inspection of pharmaceutical, chemical, petrochemical, or agricultural products. Applications such as improving human health by detecting counterfeit medicines or being used in failure analysis of 3-D integrated-circuit chips in solar cells or micro-electro-mechanical system (MEMS) devices are envisioned. Professor Sung strives to provide training opportunities to undergraduate researchers and K-12 students, the future generation of scientists and engineers. He also works on incorporating cutting-edge science into course materials and is actively engaged in many on-campus programs to recruit more women and minority students into his group.Professor Sung is developing a 4D NIR absorption and refractive index imaging where a wavelength-scanning light source is combined with a snapshot tomography technique that is enabled by a micro-lens array and digital holography. A common-path design is incorporated to further increase the robustness to environmental vibrations and a spatial light modulator to actively compensate for the chromatic aberration. For 4-D NIR emission imaging, a tunable bandpass filter or Fourier transform spectroscopy is combined with another snapshot tomography technique for luminescence light. The theoretical frameworks to be developed is believed to extend the application of diffraction tomography to more general classes of absorbing specimens and increase the accuracy of emission tomography by including the wave nature and the partial coherence of light in the image formation and reconstruction models.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.