Discrete frequency infrared microspectroscopy and imaging with a tunable quantum cascade laser

Matthew R. Kole, Rohith K. Reddy, Matthew V. Schulmerich, Matthew K. Gelber, Rohit Bhargava

Research output: Contribution to journalArticlepeer-review


Fourier-transform infrared (FT-IR) imaging is a well-established modality but requires the acquisition of a spectrum over a large bandwidth, even in cases where only a few spectral features may be of interest. Discrete frequency infrared (DF-IR) methods are now emerging in which a small number of measurements may provide all the analytical information needed. The DF-IR approach is enabled by the development of new sources integrating frequency selection, in particular of tunable, narrow-bandwidth sources with enough power at each wavelength to successfully make absorption measurements. Here, we describe a DF-IR imaging microscope that uses an external cavity quantum cascade laser (QCL) as a source. We present two configurations, one with an uncooled bolometer as a detector and another with a liquid nitrogen cooled mercury cadmium telluride (MCT) detector and compare their performance to a commercial FT-IR imaging instrument. We examine the consequences of the coherent properties of the beam with respect to imaging and compare these observations to simulations. Additionally, we demonstrate that the use of a tunable laser source represents a distinct advantage over broadband sources when using a small aperture (narrower than the wavelength of light) to perform high-quality point mapping. The two advances highlight the potential application areas for these emerging sources in IR microscopy and imaging.

Original languageEnglish (US)
Pages (from-to)10366-10372
Number of pages7
JournalAnalytical Chemistry
Issue number23
StatePublished - Dec 4 2012

ASJC Scopus subject areas

  • Analytical Chemistry


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