Hyperspectral chemical imaging (HCI) can provide the chemical composition and the ingredient distribution accurately and nondestructively. HCI in the near-infrared (NIR) range, 700–1400 nm, has been widely used for the quality inspection of pharmaceutical, chemical, petrochemical, and agricultural products. Electroluminescence imaging in the NIR range has been used to detect defects in solar cells such as cracks, grain boundaries, broken contacts and shuts, and photoluminescence imaging to check the quality of unprocessed wafers. Compared with IR imaging, NIR imaging allows for higher spatial resolution and deeper penetration into many materials, including glass and plastics. Of note, the 2D absorption map recorded in existing HCI is the integral of the 3D attenuation coefficient along the beam propagation direction. Because the depth information is lost, a specimen with a complicated internal structure cannot be examined with existing HCI and requires a separate inspection tool such as confocal microscopy. We are developing novel instruments for 4D NIR chemical imaging using snapshot optical tomography techniques.

Related publications:

• Sung Y. Snapshot holographic optical tomography. Phys Rev Appl. 2019; 11(1):014039.
• Sung Y. Spectroscopic microtomography in the visible wavelength range. Phys Rev Appl. 2018; 10(5):054041.

Funding sources: National Science Foundation (Chemical Measurement and Imaging Program, 1808331); Lynde and Harry Bradley Foundation.