title: Fast infrared chemical imaging with a quantum cascade laser.
abstract: Infrared (IR) spectroscopic imaging systems are a powerful tool for visualizing molecular microstructure of a sample without the need for dyes or stains. Table-top Fourier transform infrared (FT-IR) imaging spectrometers, the current established technology, can record broadband spectral data efficiently but requires scanning the entire spectrum with a low throughput source. The advent of high-intensity, broadly tunable quantum cascade lasers (QCL) has now accelerated IR imaging but results in a fundamentally different type of instrument and approach, namely, discrete frequency IR (DF-IR) spectral imaging. While the higher intensity of the source provides a higher signal per channel, the absence of spectral multiplexing also provides new opportunities and challenges. Here, we couple a rapidly tunable QCL with a high performance microscope equipped with a cooled focal plane array (FPA) detector. Our optical system is conceptualized to provide optimal performance based on recent theory and design rules for high-definition (HD) IR imaging. Multiple QCL units are multiplexed together to provide spectral coverage across the fingerprint region (776.9 to 1904.4 cm(-1)) in our DF-IR microscope capable of broad spectral coverage, wide-field detection, and diffraction-limited spectral imaging. We demonstrate that the spectral and spatial fidelity of this system is at least as good as the best FT-IR imaging systems. Our configuration provides a speedup for equivalent spectral signal-to-noise ratio (SNR) compared to the best spectral quality from a high-performance linear array system that has 10-fold larger pixels. Compared to the fastest available HD FT-IR imaging system, we demonstrate scanning of large tissue microarrays (TMA) in 3-orders of magnitude smaller time per essential spectral frequency. These advances offer new opportunities for high throughput IR chemical imaging, especially for the measurement of cells and tissues.
authors.affiliation: Department of Bioengineering, ‡Department of Mechanical Science and Engineering, and §Department of Electrical and Computer Engineering, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801, United States.
authors.forename: Kevin
authors.initials: K
authors.lastname: Yeh
authors.forename: Seth
authors.initials: S
authors.lastname: Kenkel
authors.forename: Jui-Nung
authors.initials: JN
authors.lastname: Liu
authors.forename: Rohit
authors.initials: R
authors.lastname: Bhargava
mesh_terms: D001940:Breast / Q000737:chemistry* / Q000473:pathology; D003952:Diagnostic Imaging; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000295:instrumentation* / Q000379:methods; D054023:Lasers, Semiconductor; D008853:Microscopy / Q000295:instrumentation* / Q000379:methods; D017550:Spectroscopy, Fourier Transform Infrared / Q000295:instrumentation* / Q000379:methods; D046888:Tissue Array Analysis / Q000379:methods*