Photothermal CH vibrational overtone detection by two‐color laser absorption. (18th November 2018)

• Record Type: Journal Article
• Authors: Diaz, Marlon; Nyaupane, Parashu R.; Diaz, Ashley; Manzanares, Carlos E.; Polli, Dario; Marrocco, Michele; Zheltikov, Aleksei; Kiefer, Johannes
• Is Part Of: Journal of Raman spectroscopy. Volume 50:Number 9(2019)
• Page Start: 1339
• Page End: 1345
• Publication Date: 2018-11-18
• Subjects: Benzene -- CH overtone -- Naphthalene -- Nonlinear absorption -- Photothermal; Raman spectroscopy -- Periodicals; 535.846
• DOI: 10.1002/jrs.5510
• Languages: English
• ISSNs: 0377-0486

Abstract

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 CH 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 CH overtone bands in molecules and the sensitivity of the technique is emphasized to convey the potential use of CH overtone spectroscopy for imaging in thermal lens microscopy. Abstract : The thermal lens technique using two‐color laser excitation is applied to vibrational overtone spectroscopy of solutions of benzene and naphthalene in liquid n‐Hexane. The absorption process begins with the excitation laser ( hν 1 ) promoting the vibrational excitation ( υ = 0 → 6) of the CH bond (red line). A second laser ( hν 2 ) promotes the excited molecule to an electronic excited state (blue line). A probe laser detects the nonradiative relaxation inside the cell. Enhancement of the thermal lens signal is achieved.