Nonlinear Midinfrared Photothermal Spectroscopy Using Zharov Splitting and Quantum Cascade Lasers

Alket Mertiri; Hatice Altug; Mi K Hong; Pankaj Mehta; Jerome Mertz; Lawrence D Ziegler; Shyamsunder Erramilli

doi:10.1021/ph500114h

Nonlinear Midinfrared Photothermal Spectroscopy Using Zharov Splitting and Quantum Cascade Lasers

ACS Photonics. 2014 Aug 20;1(8):696-702. doi: 10.1021/ph500114h. Epub 2014 Jul 18.

Authors

Alket Mertiri¹, Hatice Altug², Mi K Hong¹, Pankaj Mehta³, Jerome Mertz¹, Lawrence D Ziegler¹, Shyamsunder Erramilli⁴

Affiliations

¹ 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.
² 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.
³ 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.
⁴ 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.

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.

Keywords: Zharov splitting; infrared spectroscopy; liquid crystal; nonlinear spectroscopy; photothermal spectroscopy; pitchfork bifurcation; quantum cascade lasers.

Grants and funding

R21 EB013381/EB/NIBIB NIH HHS/United States