@article{ISI:000327007800024,
  title = {Indirect absorption spectroscopy using quantum cascade lasers: mid-infrared refractometry and photothermal spectroscopy},
  journal = {OPTICS EXPRESS},
  abstract = {We record vibrational spectra with two indirect schemes that depend on the real part of the index of refraction: mid-infrared refractometry and photothermal spectroscopy. In the former, a quantum cascade laser (QCL) spot is imaged to determine the angles of total internal reflection, which yields the absorption line via a beam profile analysis. In the photothermal measurements, a tunable QCL excites vibrational resonances of a molecular monolayer, which heats the surrounding medium and changes its refractive index. This is observed with a probe laser in the visible. Sub-monolayer sensitivities are demonstrated. (C) 2013 Optical Society of America},
  volume = {21},
  number = {22},
  pages = {25643-25654},
  year = {2013},
  slug = {isi-000327007800024},
  author = {Pfeifer, Marcel and Ruf, Alexander and Fischer, Peer}
}