The Optics Laboratory
Group of Hans Hallen, Physics Department, North Carolina State University

Gradient-Field-Raman Spectroscopy (GFR)

Raman spectroscopy enables the study of vibrations in molecules and solids through the interaction of light with the vibrations. In normal Raman spectroscopy, the coupling between the light and the molecule is brought about by a change in polarizability (charge separation along a bond when it is placed in an electric field) as the molecule vibrates along that bond. We derived GFR to describe lines observed in a nano-Raman spectroscopy apparatus that could not be explained by the usual Raman excitation modes. The coupling between the light and molecule in GFR is moderated by a strong electric field gradient that shifts the potential energy of the atoms as they move during the vibration. The field gradient is due to the light itself, and exists nearby and perpendicular to a metal surface. [1] [2] [3] [4] [5] [6]

  Semi-classical Derivation

 Quantum Derivation

 NSOM-Raman Measurements

 Nano-bowtie Raman Measurements

 Surface Enhanced Raman Spectroscopy (SERS) Possible Observations.

  • [1] H. D. Hallen, "Nano-Raman Spectroscopy: Surface Plasmon Emission, Field Gradients, and Fundamentally Near Field Propagation Effects," NanoBiotechnology 3, 197-202, 2007 [online], -- An invited paper. [local preprint]
  • [2] E.J. Ayars, H.D. Hallen and C.L. Jahncke, "Electric field gradient effects in Raman spectroscopy," Phys. Rev. Lett. 85, 4180 - 3, 2000 [online]. [local preprint]
  • [3] C. L. Jahncke, E. J. Ayars and H. D. Hallen, "Raman selection rules in the presence of an electric field gradient," Microscopy and Microanalysis 8, 1518-1519, 2002 [online]. [local preprint]
  • [4]C.L. Jahncke , E.J. Ayars and H.D. Hallen, "Gradient-Field Raman: Selection Rules in the Near Field," in Proc. of the 7th International Conference on Near-field Optics, NFO-7, Rochester, NY, pp. 142, August, 2002. [local preprint]
  • [5]E. J. Ayars , M. A. Paesler and H. D. Hallen, "Near-field Raman spectroscopy: electric field gradient effects," in Proceedings of IUMAS 2000, The 2000 Meeting of the International Union of Microbeam Analysis Societies, Kailua-Kona, Hawaii 165:1, pp. 115, July, 2000 [online], -- An invited paper. [local preprint]
  • [6] Ling Li, Shuang Fang Lim, Alexander A. Puretzky, Robert Riehn and H.D. Hallen, "Near-field enhanced ultraviolet resonance Raman spectroscopy using aluminum bow-tie nano-antenna," Applied Physics Letters 101, 2012 [online]. [local preprint]
  •  More info is in the papers.

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