Lez #51+52 Principles of advanced microscopies I. RIKES.

 We described the basics of RIKES: a vibrationally resonant combination of pump and stokes can induce optical anisotropy which generates an electric field along a direction orthogonal to the incoming stokes, via a four wave mixing process. This effect can be homodyne detected, or via balanced detection, to measure separately the real and imaginary parts of the non linear susceptibility.

Lez #49+50 Principles of advanced microscopies I. Coherent Vibrational imaging.

We introduced the basic principles of linear and non linear imaging, with or without vibrational sensitivity. We then discussed the basics of CARS imaging, the nor resonant background issues and how to resolve them.

Lez #47+48 FSRS II: molecular photoexcitations and transient states: the example of Tiophene

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 #45+46 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 and a few slides discussed.

Lez #43+44 IRS signal. RRS under different pulse temporal profile

 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's absorption and the probed vibrational mode.

Then, 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 #41+42 DephasingII SRS blue side

 Final considerations on dephasing. Homogeneous and inhomogeneous limits (fast and slow modulation regimes) and motional narrowing. Spectral line shapes: Lorentzian, Gaussian, and Voigt. Derivation of the SRS response in the blu side (IRS diagram) for a monochromatic pump and a generic Stokes beam

Lez #39+40 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