Open AccessIndirect absorption spectroscopy using quantum cascade lasers: mid-infrared refractometry and photothermal spectroscopy
Author(s) -
Marcel Pfeifer,
A. Ruf,
Peer Fischer
Publication year - 2013
Publication title -
optics express
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.394
H-Index - 271
ISSN - 1094-4087
DOI - 10.1364/oe.21.025643
Subject(s) - photothermal spectroscopy , refractometry , optics , spectroscopy , materials science , refractive index , quantum cascade laser , photothermal therapy , infrared spectroscopy , laser , absorption (acoustics) , absorption spectroscopy , infrared , total internal reflection , optoelectronics , chemistry , physics , organic chemistry , quantum mechanics
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.