Simple aspects of femtosecond stimulated Raman spectroscopy

Abstract

Femtosecond stimulated Raman spectroscopy (FSRS), using an overlapping pair of narrow band Raman pump and broadband probe pulses with heterodyne detection along the probe pulse direction, is a new nonlinear spectroscopic technique to record vibrational spectra of even highly fluorescent molecules and to study vibrational dynamics on excited electronic states of molecules, as in photoisomerization. FSRS is described by diagrammatic third-order perturbation theory with wave packet analysis. The phase matching condition gives rise to forty-eight terms for FSRS, but the resonant condition reduces it to just eight terms, which can be depicted by Feynman dual time-line diagrams, or closed time path loop diagrams, or the complementary four-wave mixing energy level diagrams. The eight terms fall into four sets-SRS(I), SRS(II), IRS(I), IRS(II)-where SRS stands for stimulated Raman scattering and IRS stands for inverse Raman scattering. The SRS(I) set can also account for spontaneous Raman scattering, but the remaining SRS(II), IRS(I) and IRS(II) terms are only present in stimulated scattering with the presence of a probe field. The SRS(I) set accounts for the Stokes Raman lines while the IRS(I) term accounts for the anti-Stokes lines, relative to the Raman pump frequency, in the FSRS spectrum. The remaining SRS(II) and IRS(II) terms give rise to broad baselines. Using a harmonic oscillator model, analytic results are obtained for the four-time correlation functions in the third-order polarizations. The issue of high time and high frequency resolution in time-resolved FSRS spectra is discussed. Calculations are made with the theory to compare with experimental results for: (a) resonance FSRS of fluorescent Rhodamine 6G and (b) 2D-FSRS from a coherent vibrational state that has been prepared by an impulsive, off-resonant pump pulse on CDCl 3 . The calculated results compared well with experimental results, and in the case of 2D-FSRS on CDCl 3 there is a dominant cascade effect contributing to the FSRS spectra.femtosecond stimulated Raman spectroscopy, temporal and spectral resolution, cascade effect

Resonant broadband stimulated Raman scattering in myoglobin

“…On the contrary, when the RP is tuned in resonance with an electronic transition, besides intensity enhancements, spectral features in SRRS possibly experience lineshape modifications due to the specific conditions in which the experiment is done (mismatch from the “full” resonant wavelength, shape of the absorption spectrum, Condon factors, vibronic coupling, or multimode effects) and to additional diagrams, representing different matter–fields interactions with no spontaneous analogues. Notably, although the specific dependence of the SRRS blue side lineshapes on the RP wavelength and absorption spectrum has been recently addressed, the nature of the spectral profiles in the red side of an SRRS spectrum is currently debated . In particular, the presence of peak shifts and dispersive shapes under specific electronic resonances has been advanced .…”

Femtosecond Stimulated Raman Spectroscopy

“…Since Lee's initial theoretical treatment of FSRS in 2004, a tremendous body of work has contributed to our understanding of its properties and limitations. Lee and co‐workers have described the theory of FSRS in great detail both based on a classical coupled‐wave and a quantum mechanical density matrix formalism. In addition, Agarwalla et al .…”

“…Terms from class (II) give rise to a broad background which becomes evident in the spectra as a non‐vanishing baseline. The individual contributions of these four terms to the total FSRS signal are shown in Figure B, calculated for rhodamine 6G, which has been extensively used as model compound for both experimental and theoretical studies of resonance FSRS.…”

From China to the world: Science China Chemistry celebrates the International Year of Chemistry

“…"Lichens are unique individuals which have been widely Heather F. Greer [16] Fengjiao Yu [16] Carol A. Fierke [18] Xiaomu Guan [18] Mina Han [27] Maria Luisa Cerón [30] Eleonora Echegaray [30] Bárbara Herrera [30] Soledad Gutiérrez-Oliva [30] Xiuting Li [31] Ada Yonath [34] Fang Liu [38] Figure 2 Photos of some female authors in the special issue on IYC 2011. used in traditional medicines," M. Iqbal Choudhary, Atta-ur-Rahman, and coworkers indicated [23]. They presented their findings of new antiglycation and enzyme inhibitors from the lichens species Parmotrema cooperi collected from Nepal at the altitude of 16001700 meters.…”

“…They presented a description of high time and high frequency resolution in time-resolved FSRS spectra. "Calculations were made with the theory to compare with experimental results for: (i) resonance FSRS of fluorescent Rhodamine 6G and (ii) 2D-FSRS from a coherent vibrational state that has been prepared by an impulsive, off-resonant pump pulse on CDCl 3 " [31].…”