Ultrafast selective excitation of surface-enhanced Raman scattering from a single molecule by shaping pump and Stokes pulses

Abstract

Surface-enhanced Raman scattering (SERS) has attracted much attention as an important technique for studying and monitoring the behavior of molecules. Coherent control by shaping femtosecond pulses is an efficient method for controlling molecular vibration state, rotation state, ionization state, and other molecule dynamics. In this paper, we propose a theoretical scheme of selective excitation of SERS from a single porphycene molecule with two Raman peaks at 327[Formula: see text]cm[Formula: see text] and 367[Formula: see text]cm[Formula: see text] placed in the gap between silver dimer nanospheres. Based on the theory of quantum coherent control, selective excitation of the peak at 327[Formula: see text]cm[Formula: see text] and depression of another at 367[Formula: see text]cm[Formula: see text] are demonstrated by properly shaping femtosecond laser pulses with central frequency of 12500[Formula: see text]cm[Formula: see text] and a full width at half maximum (FWHM) of 300[Formula: see text]cm[Formula: see text]. Ultrafast dynamics of the response of dimer nanospheres to the shaped pump and Stokes pulses are simulated by finite difference time domain (FDTD) method followed by Fourier transform. The enhanced and selected single molecule SERS is realized simultaneously. The SERS probability is enhanced by more than six orders in magnitude compared with the case in air environment, and the FWHMs of the enhanced and the depressed Raman peaks are both larger than 17[Formula: see text]cm[Formula: see text] despite the narrow gap of only 40[Formula: see text]cm[Formula: see text] between the two Raman peaks.