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Photothermal CH vibrational overtone detection by two‐color laser absorption
Author(s) -
Diaz Marlon,
Nyaupane Parashu R.,
Diaz Ashley,
Manzanares Carlos E.
Publication year - 2019
Publication title -
journal of raman spectroscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.748
H-Index - 110
eISSN - 1097-4555
pISSN - 0377-0486
DOI - 10.1002/jrs.5510
Subject(s) - laser , overtone , absorption spectroscopy , optics , dye laser , absorption (acoustics) , chemistry , materials science , laser pumping , photothermal therapy , analytical chemistry (journal) , spectral line , physics , chromatography , astronomy
Abstract In this experiment, the thermal lens technique is used with a modified arrangement of three lasers to induce a two‐color absorption. Two‐pump lasers, a variable wavelength orange dye laser (588–617 nm), a single line blue laser (488 nm), and a single line probe yellow laser (568 nm) are employed. A comparison is made between the magnitude of the thermal lens signal obtained with a one pump laser versus two pump lasers. The absorbing molecules are benzene and naphthalene in liquid n‐Hexane. The CH vibrational overtone spectra are obtained at room temperature for several concentrations. The molecules are excited to a high vibrational state ( Δυ = 6) with the first laser and to an electronic level with a second laser (two‐color absorption). Using two pump lasers, the limit of detection of the molecule is several orders of magnitude more sensitive than using one pump laser. A nonlinear behavior of the integrated signal versus concentration is shown for the two‐color laser process. Linear behavior is shown for the one pump laser experiment. A model of signal amplification for a nonlinear absorption is presented to explain the results. The separation and identification of CH overtone bands in molecules and the sensitivity of the technique is emphasized to convey the potential use of CH overtone spectroscopy for imaging in thermal lens microscopy.