On the coherent vibrational phase in polarization sensitive resonance CARS spectroscopy of copper tetraphenylporphyrin

Abstract

Polarization sensitive multiplex spectroscopy of resonance coherent anti-Stokes Raman scattering (CARS) of copper(II)-tetraphenylporphyrin in solution (CH2Cl2) is reported. The measurements were performed in the Q band range of the porphyrin electronic absorption. Four polarized CARS spectra were resolved in 1300–1650 cm−1 Raman range and were simultaneously fitted with a single set of vibrational parameters (band positions, bandwidths, amplitudes, depolarization ratios, and phases). The obtained coherent vibrational phases of A1g, A2g, and B1g skeletal modes of the porphyrin macrocycle appeared to correlate strongly with the mode vibrational symmetry. The origin of such correlation is analyzed within a model of the third-order nonlinear electric susceptibility χ(3). The proposed model is based on multidimensional displaced harmonic oscillator in the Herzberg–Teller expansion of Raman polarizability. The coherent vibrational phases of modes of different symmetry classes are directly affected by the symmetry dependent vibronic couplings between the pairs of Qx, Qy and Bx, By electronic transitions of the porphyrin. The phase contrast between the modes of various symmetries is most pronounced near the Q00 resonance.

Single-shot detection of bacterial endospores via coherent Raman spectroscopy

“…Here, we use a recently introduced time-frequency adaptation of CARS that brings together the concepts of frequency-resolved (18)(19)(20)(21)(22) and time-resolved (23-25) CARS measurements. The scheme combines broadband Raman excitation by a pair of ultrashort laser pulses and a time-delayed narrowband probing of the resultant coherent molecular vibrations (Fig.…”

Polarization‐sensitive CARS spectroscopy on free‐base porphyrins: coproporphyrin I tetramethyl ester

“…Like the depolarization ratio, the coherent phase also represents an appropriate parameter for symmetry-based interpretations; this has been demonstrated, for example, in several previous studies on metallo porphyrins 13,15 and free-base porphyrins. 19,20 From the values listed in Table 3, the meaning of a correlation between the parameter  R and the mode symmetry becomes especially clear by comparing the values determined for 19 b 1g with the values for 11 a g , 2 a g , and 10 a g .…”

“…The six spectra measured with the analyzer polarization planes that are indicated as lines (a)-(f) in Fig. 2(B) were then fitted simultaneously according to the following expression, which describes the dispersion of the CARS signal intensity I CARS : 13,29 …”

“…21 -23 Owing to the interference of coherent signals, the quantitative evaluation of spectra is, however, more demanding for coherent Raman spectroscopy as compared to spontaneous Raman spectroscopy. In this context, the combination of a polarization-sensitive (PS) measurement scheme 24 -28 with an appropriate theoretical model, 11,13,29 which describes the wavenumber dependant dispersion of the third-order nonlinear susceptibility 3 , has been proven as an effective way to quantitatively determine a complete set of Raman band parameters from coherent spectra.…”

Contrast in coherent Raman scattering microscopy

“…Nearly a decade and a half after the first collinear CARS microscopy a tremendous number of additional techniques have been introduced. The effects of adjusting every property of the input fields have been well studied: a small sample includes polarization [30][31][32][33][34][35][36][37]; temporal overlap [38][39][40][41][42]; focusing geometry [10,[43][44][45]; phase modulation [13,[46][47][48]; spectral phase [49][50][51][52]; and frequency modulation [53,54].…”