Pump-probe Raman Spectroscopy Research Articles

Ultrafast Hot Phonon Dynamics in MgB_{2} Driven by Anisotropic Electron-Phonon Coupling.

The zone-center E_{2g} modes play a crucial role in MgB_{2}, controlling the scattering mechanisms in the normal state as well the superconducting pairing. Here, we demonstrate via first-principles quantum-field theory calculations that, due to the anisotropic electron-phonon interaction, a hot-phonon regime where the E_{2g} phonons can achieve significantly larger effective populations than other modes, is triggered in MgB_{2} by the interaction with an ultrashort laser pulse. Spectral signatures of this scenario in ultrafast pump-probe Raman spectroscopy are discussed in detail, revealing also a fundamental role of nonadiabatic processes in the optical features of the E_{2g} mode.

Time‐resolved pump–probe Raman spectroscopy with temporally incoherent light

AbstractA method for picosecond time‐resolved pump–probe Raman spectroscopy using temporally incoherent light (‘incoherent pump–probe Raman spectroscopy, or simply IPPR spectroscopy’) is proposed. The theoretical formulation of IPPR scattering based on Gaussian random statistics is described. It is predicted that the temporal resolution in IPPR experiment is not determined by the duration of pump and probe pulses, but by the cross‐correlation time between the pump and probe lights. The delay‐time dependence of the IPPR intensity is expected to show the same behaviour as that in conventional time‐resolved Raman spectroscopy which uses coherent ultra‐short light pulses, except for a constant background always existing in IPPR scattering. This method was examined experimentally for Raman scattering from electronically excited trans‐stilbene in n‐hexane solution. In accordance with the prediction, picosecond decay of the Raman band at 1565 cm−1 arising from the trans‐stilbene molecules in the S1, state is observed with the use of nanosecond pump and probe pulses with a cross‐correlation time of ca. 100 ps. No decay is observed for the Raman bands of the solvent. Effects of saturation arising from the frequency‐doubling, pumping and Raman processes on the IPPR signal are also discussed. The ratio of the delaytime dependent part to the background (contrast ratio) is predicted to decrease in the presence of saturation.

Cis-stilbene photochemistry: direct observation of product formation and relaxation through two-color UV pump-probe Raman spectroscopy

The formation of hot trans-stilbene by photoisomerization of cis-stilbene, and its subsequent vibrational cooling, have been monitored by picosecond two-color UV pump-probe anti-Stokes Raman spectroscopy. Pairs of pump (295 nm) and probe (278 nm) pulses at a 500 Hz repetition rate interrogate flowing samples of cis-stilbene in cyclohexane or methanol, and the anti-Stokes Raman scattering due mainly to the trans-stilbene product is detected. Hot ground-state trans-stilbene appears promptly within our 10 ps experimental time resolution, and the anti-Stokes intensity decays with a time constant of 39 ± 10 ps in cyclohexane and 17 ± 5 ps in methanol. The decay of the anti-Stokes intensity is accompanied by a shift of the C=C stretching vibrations by about 20 cm−1 to higher frequencies. The question of whether or not the initial vibrational distribution is statistical is addressed, but the present data do not allow firm conclusions to be drawn.

Incoherent time-resolved pump-probe Raman spectroscopy

A new experimental method for ultrafast time-resolved pump-probe Raman spectroscopy by use of temporally incoherent light is proposed. It is predicted that the temporal resolution of this pump-probe Raman experiment is not determined by the duration of pump and probe pulses but by the cross-correlation time between pump and probe lights. This idea is experimentally examined for Raman scattering from electronically excited trans-stilbene in n-hexane solution. In accordance with the prediction, the picosecond decay of the Raman band at 1560 cm -1 arising from the stilbene molecules in the S 1 state is observed by use of nanosecond pump and probe pulses, while no decay is observed for the Raman bands of the solvent