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Delineation of the TRSTHG setup. Transient phonon dynamics can be retrieved by temporally delaying the two incident near-IR fundamental pulses and detecting the UV signals generated in between them. To reduce scattering interference and improve THG signal strength, we measure TH+1 that is farther away from the beam being chopped (FP1). The weak CTH+1 signal that arises from cascaded four-wave mixing is circled near the FP2 beam.
Transient TRSTHG signal of polycrystalline CaF2 up to 3.4 ps. The black dashed line shows the exponential fit of the non-oscillatory component. The inset exhibits the low-frequency modes of CaF2 from FFT (with Blackman window function) of the TH+1 intensity temporal oscillatory component (blue), in comparison with the standard Raman spectrum (red).
Morlet wavelet-transformed time-frequency contour plot of the TH+1 quantum beats in CaF2 up to 3.2 ps. Bottom panel manifests different dephasing dynamics for the underlying CP modes, which is indicative of varied structural origins for these low-frequency vibrational peaks. The vertical axis is presented as the normalized intensity of the three modes.
(a) Laser irradiation power dependence of the quantum beats in BK7 glass. The inset shows stronger coherent oscillations with the increase of FP2 power. (b) FFT spectrum of crystallized BK7 glass with the irradiation fs pulse energy of FP2 at 35 μJ (red), in comparison with the standard Raman spectrum of BK7 glass (blue) and danburite crystal (black).
Morlet wavelet-transformed time-frequency contour plot of the TH+1 temporal oscillations in BK7 glass at different FP2 pulse energy of (a) 10 μJ, (b) 15 μJ, (c) 20 μJ, (d) 25 μJ, (e) 30 μJ, and (f) 35 μJ. The dashed lines evince a continuous redshift of the ∼150 cm−1 mode with increasing FP2 power, while the colorbars show that the wavelet-transform contour height increases in accord with stronger temporal oscillations of the THG signal. (g) The FP2-power dependent frequency shifts of two CP modes in crystallized BK7 glass.
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