Broadly tunable quantum cascade laser in cantilever-enhanced photoacoustic infrared spectroscopy of solids
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- Lehtinen, J. & Kuusela, T. Appl. Phys. B (2014) 115: 413. doi:10.1007/s00340-013-5617-9
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An external cavity quantum cascade laser (EC-QCL) is applied in the photoacoustic detection of solid samples. The EC-QCL used has a broad tuning range of 676 cm−1 (970–1,646 cm−1) in the mid-infrared region, which enables accurate broadband spectroscopy of large molecules. The high spectral power density of the EC-QCL is combined with an extremely sensitive optical cantilever microphone of the photoacoustic detector to achieve an ultimate sensitivity. The carbon black, polyethylene, and hair fiber samples were measured with the EC-QCL photoacoustic detection using electrical amplitude modulation to demonstrate the possibilities of the setup. The same measurements were repeated with a Fourier transform infrared (FTIR) spectrometer combined with a photoacoustic detector for a comparison. The EC-QCL photoacoustic setup yielded roughly a decade better signal-to-noise ratios than the FTIR setup with the same measurement time.