title: Nonlinear Midinfrared Photothermal Spectroscopy Using Zharov Splitting and Quantum Cascade Lasers.
abstract: We report on the mid-infrared nonlinear photothermal spectrum of the neat liquid crystal 4-octyl-4'-cyanobiphenyl (8CB) using a tunable Quantum Cascade Laser (QCL). The nonequilibrium steady state characterized by the nonlinear photothermal infrared response undergoes a supercritical bifurcation. The bifurcation, observed in heterodyne two-color pump-probe detection, leads to ultrasharp nonlinear infrared spectra similar to those reported in the visible region. A systematic study of the peak splitting as a function of absorbed infrared power shows the bifurcation has a critical exponent of 0.5. The observation of an apparently universal critical exponent in a nonequilibrium state is explained using an analytical model analogous of mean field theory. Apart from the intrinsic interest for nonequilibrium studies, nonlinear photothermal methods lead to a dramatic narrowing of spectral lines, giving rise to a potential new contrast mechanism for the rapidly emerging new field of mid-infrared microspectroscopy using QCLs.
authors.affiliation: Division of Materials Science and Engineering, Photonics Center, Department of Electrical and Computer Engineering, Department of Physics, Department of Biomedical Engineering, and Department of Chemistry, Boston University , Boston, Massachusetts 02215, United States ; Division of Materials Science and Engineering, Photonics Center, Department of Electrical and Computer Engineering, Department of Physics, Department of Biomedical Engineering, and Department of Chemistry, Boston University , Boston, Massachusetts 02215, United States.
authors.forename: Alket
authors.initials: A
authors.lastname: Mertiri
authors.affiliation: Division of Materials Science and Engineering, Photonics Center, Department of Electrical and Computer Engineering, Department of Physics, Department of Biomedical Engineering, and Department of Chemistry, Boston University , Boston, Massachusetts 02215, United States ; Division of Materials Science and Engineering, Photonics Center, Department of Electrical and Computer Engineering, Department of Physics, Department of Biomedical Engineering, and Department of Chemistry, Boston University , Boston, Massachusetts 02215, United States ; Department of BioEngineering, Ecole Polytechnique Federale De Lausanne , Lausanne, CH-1015, Switzerland.
authors.forename: Hatice
authors.initials: H
authors.lastname: Altug
authors.affiliation: Division of Materials Science and Engineering, Photonics Center, Department of Electrical and Computer Engineering, Department of Physics, Department of Biomedical Engineering, and Department of Chemistry, Boston University , Boston, Massachusetts 02215, United States ; Division of Materials Science and Engineering, Photonics Center, Department of Electrical and Computer Engineering, Department of Physics, Department of Biomedical Engineering, and Department of Chemistry, Boston University , Boston, Massachusetts 02215, United States.
authors.forename: Mi K
authors.initials: MK
authors.lastname: Hong
authors.affiliation: Division of Materials Science and Engineering, Photonics Center, Department of Electrical and Computer Engineering, Department of Physics, Department of Biomedical Engineering, and Department of Chemistry, Boston University , Boston, Massachusetts 02215, United States.
authors.forename: Pankaj
authors.initials: P
authors.lastname: Mehta
authors.affiliation: Division of Materials Science and Engineering, Photonics Center, Department of Electrical and Computer Engineering, Department of Physics, Department of Biomedical Engineering, and Department of Chemistry, Boston University , Boston, Massachusetts 02215, United States ; Division of Materials Science and Engineering, Photonics Center, Department of Electrical and Computer Engineering, Department of Physics, Department of Biomedical Engineering, and Department of Chemistry, Boston University , Boston, Massachusetts 02215, United States.
authors.forename: Jerome
authors.initials: J
authors.lastname: Mertz
authors.affiliation: Division of Materials Science and Engineering, Photonics Center, Department of Electrical and Computer Engineering, Department of Physics, Department of Biomedical Engineering, and Department of Chemistry, Boston University , Boston, Massachusetts 02215, United States ; Division of Materials Science and Engineering, Photonics Center, Department of Electrical and Computer Engineering, Department of Physics, Department of Biomedical Engineering, and Department of Chemistry, Boston University , Boston, Massachusetts 02215, United States.
authors.forename: Lawrence D
authors.initials: LD
authors.lastname: Ziegler
authors.affiliation: Division of Materials Science and Engineering, Photonics Center, Department of Electrical and Computer Engineering, Department of Physics, Department of Biomedical Engineering, and Department of Chemistry, Boston University , Boston, Massachusetts 02215, United States ; Division of Materials Science and Engineering, Photonics Center, Department of Electrical and Computer Engineering, Department of Physics, Department of Biomedical Engineering, and Department of Chemistry, Boston University , Boston, Massachusetts 02215, United States ; Division of Materials Science and Engineering, Photonics Center, Department of Electrical and Computer Engineering, Department of Physics, Department of Biomedical Engineering, and Department of Chemistry, Boston University , Boston, Massachusetts 02215, United States.
authors.forename: Shyamsunder
authors.initials: S
authors.lastname: Erramilli
keywords: Zharov splitting; infrared spectroscopy; liquid crystal; nonlinear spectroscopy; photothermal spectroscopy; pitchfork bifurcation; quantum cascade lasers