Lez #55+56 Time-Domain Impulsive Vibrational Spectroscopy

 We discussed the Impulsive Vibrational Scattering technique, in which a pair of temporally separated pulses is used to map vibrational excitations in the time domain. The experimental setup follows a pump-probe scheme, where an ultrashort broadband pump pulse generates vibrational coherences via two interactions with spectral components shifted by one vibrational quantum. The coherences modulate the optical properties of the medium, which are then monitored by a delayed probe. We derived the analytical expressions using the diagrammatic formalism, assuming impulsive beams. On classroom some lecture notes.

Lez #53+54 Dephasing

 We discussed from a microscopic point of view how out-of-diagonal elements of the density matrix are damped due to the interaction with the environment. As a reference, you can use chapter 5 of the “Principles of Nonlinear Optical  Spectroscopy: A Practical Approach” by P. Hamm

Lez #51+52 Esercitazione 2

 Seconda parte della risoluzione del secondo esonero 2022. Risposta HL1 in condizioni di risonanza e fuori risonanza. Risposta di HL2. Interpretazione fisica dei risultati e confronto con la risposta RRS1.

Lez #49+50 Esercitazione 1

Prima parte della risoluzione del secondo esonero 2022. Diagrammi di Hot Luminescence (HL1 e HL2). Calcolo esplicito di HL1.

Lez #47+48 RRS under different pulse temporal profile

We derived an expression for the RRS signal as a function of arbitrary spectral profiles of the Raman pump and probe pulses. This formula was then used to numerically evaluate the Raman gain under different experimental conditions, specifically varying the pump pulse temporal profile and its relative delay with respect to the probe.

Lez #45+46 FSRS II Principles and applications (Vibrational cooling, internal conversion and conical intersections)

 We then discussed the case of MPT studied by FSRS, where an ultrafast motion outside the Franck Condon region is observed, followed by vibrational cooling and singlet to triplet internal conversion. This example illustrates the synergy among transient absorption, FSRS and DFT calculations.   

Lez #43+44 FSRS I Principles and applications (Heme proteins)

 We introduced the Femtosecond Stimulated Raman Scattering (FSRS) experimental scheme, where SRS is exploited to track the evolution of a system upon the photoexcitation of an Actinic pump pulse, preceding the Raman and Stokes pair. The experimental layout has been introduced and the temporal/spectral resolutions of FSRS have been compared with the time-resolved spontaneous Raman counterpart. Then we started to discuss the paradigmatic case of Myoglobin, where FSRS has been exploited to: i) interpret transient absorption experiments to discriminate between two possible contrasting scenarios related to the existence of transient electronic states vs vibrational cooling. ii) determine how the absorbed photon energy, initially stored in delocalized low frequency heme modes, is very efficiently funneled into specific high frequency modes prior to slow dissipation through the protein 

Lez #41+42 IRS signal, resonance effect in the blue-side SRS response

We investigated the IRS1 response under various resonance conditions, demonstrating that the resulting lineshapes - positive, negative, or dispersive- depend on the Raman pump wavelength relative to the sample absorption and the probed vibrational mode.

An expression for the IRS Raman gain was first derived for arbitrary spectral profiles of the Raman pump and probe pulses. The response was then analytically evaluated in the case of a monochromatic pump and an impulsive probe.

Lez #39+40 SRS signals

  Still on chi3 processes. We evaluated the SRS (RRS1 diagram) response in resonant and non resonant case, for monochromatic Raman pump and probe beams.