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Rotational coherence imaging and control for CN molecules through time-frequency resolved coherent anti-Stokes Raman scattering
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View: Figures


Image of FIG. 1.
FIG. 1.

The three lowest potential energy surfaces V(R) of the CN molecule. The 2Σ states are located closely on top of each other yielding a high contrast Franck–Condon selection for a v = v transition. Furthermore, the femtosecond laser pulse bandwidths are smaller than the vibrational level separation of ∼2000 wavenumbers yielding a state selective excitation scheme for the CARS setup.

Image of FIG. 2.
FIG. 2.

Schematic representation of the creation of the third-order polarization by the three time-delayed laser pulses pump, dump, and probe. Left panel shows the (ro-)vibronic transition path injf alternating between the X2Σ and B2Σ electronic states. Right panel shows the rotational connection diagram for the six possible routes from the initial level N i  (v = 0). P and R represent the two allowed rotational branches while plus and minus signs denote a change in the rotational quantum number N for each of the four transitions.

Image of FIG. 3.
FIG. 3.

The time-gated images as obtained by the use of Eq. (15) for two gate widths (a) 500 fs and (b) 3 ps, where thermal distributions correspond to the 30 K case. The wavenumber scale relative to the anti-Stokes origin at 27922 cm−1 separates the R branch emission (positive side) from the P branch (negative). The upper interferogram shows a signal oscillation pattern between the R and P branches (at the zero wavenumber shift) and carries information about the rotational wave packet in the time domain. Panel (b) case approaches the spectrally resolved limit leaving only the next-neighbor polarization beating visible. Panel (c) shows the shift-zero cut S(0, t g ) of the panel (a) signal, and panel (d) shows the FFT power spectrum of the panel (c) trace resolving the interference as separable quantum and intermolecular beats.

Image of FIG. 4.
FIG. 4.

The time-integrated frequency-resolved CARS interferogram for the 10 K ensemble of wave packets as obtained by the use of Eq. (16). The contour level increment corresponds to 4% of the intensity maximum. Labeling corresponds to the most intense P and R branch traces. The dashed and dotted lines denote intervals for a global intensity minimum and a maximum, respectively, which relates to a dimmer switch function of the pulse delay.

Image of FIG. 5.
FIG. 5.

2D spectrograms for the CARS signal for two values of the control parameter τ32: 890 fs (a,b) and 495 fs (c,d). Images show the light switching functionality between the branches. The interferogram bandwidths are set by the gate durations 500 fs (a,c) and 3 ps (b,d) which demonstrates the temporal versus spectral resolving power.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Rotational coherence imaging and control for CN molecules through time-frequency resolved coherent anti-Stokes Raman scattering