Publications de Majed Chergui | EPFL Graph Search

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We compare UV transient grating (TG) experiments of aqueous tryptophan with transient absorption (TA) and fluorescence up-conversion measurements. The TG and TA signals show a bi-exponential rise with sub-ps and ps time constants, which are consistent with ...

Disentangling electronic and thermal effects in photoexcited perovskite materials is crucial for photovoltaic and optoelectronic applications but remains a challenge due to their intertwined nature in both the time and energy domains. In this study, we emp ...

Lifetime studies of the NO A2S+ (v = 0) Rydberg fluorescence in rare gas matrixes are reported. The fluorescence stems from two types of sites, red and main. The red site fluorescence shows a lifetime lengthening of 25% in Kr matrixes and 100% in Xe matrixes. The main site fluorescence exhibits dramatic lengthenings by orders of magnitude increasing with the host at. polarizability. These results also stress the role of the microscopic structure of the solvent around the mol. on the Rydberg lifetimes. [on S

A review. The crucial steps of cellular photoperception are characterized and followed in real time by laser spectroscopy down to a few tens of femtoseconds. The photoactive proteins studied here are involved in major natural processes such as vision (bact ...

Femtosecond photoluminescence (PL) up-conversion studies in polychromatic mode and laser-power-dependence studies of the PL were carried out on colloidal solutions of CdSe quantum dots with diameters ranging from 2.4 to 4 nm. The main features of the spect ...

A tuneable repetition rate extreme ultraviolet source (Harmonium) for time resolved photoelectron spectroscopy of liquids is presented. High harmonic generation produces 30-110 eV photons, with fluxes ranging from similar to 2 x 10(11) photons/s at 36 eV t ...

Excited-state dynamics and electronic structures of Al and Ga corrole complexes were studied as a function of the number of beta-pyrrole iodine substituents. Using spectrally broad-band femtosecond-resolved fluorescence upconversion, we determined the kine ...

The medium response of solid hydrogens to an impulsive perturbation has been studied using Rydberg excitation of an NO impurity. This leads to formation of an "electronic" bubble which corresponds to a cage radius increment of about 25%. The process has been followed in real-time using femtosecond pump-probe spectroscopy. Bubble dynamics is characterized by a one-way expansion of the cage with no recurrencies of the cage boundaries in both solid H2 and D2. The data is interpreted in terms of a dominant en

We have developed a simple and accurate method for calibrating the amplitude of vibration of quartz tuning fork sensors commonly used in at. force- and near field optical-microscopy. Unlike interferometric methods, which require a complex optical setup, th ...

The intensity distributions in the overtones of resonance Raman spectra for I2 in liq. CCl4 and Xe are presented for several excitation energies in the bound part of the B 3P0u+ state. In liq. CCl4, the decrease in intensity with v" is monotonous and for all excitation energies similar to that of a free wave packet in the gas phase. A dephasing time shorter than the round trip time of 300 fs and a dephasing process which occurs beyond 3 z is inferred, in accordance with predissocn. to the a or a' states ea

Time-resolved x-ray absorption fine structure (XAFS) spectroscopy with picosecond temporal resolution is a new method to observe electronic and geometric structures of short-lived reaction intermediates. It combines an intense femtosecond laser source synchronized to the x-ray pulses delivered into the microXAS beamline of the Swiss Light Source (SLS). We present key experiments on charge transfer reactions as well as spin-crossover processes in coordination chemistry compounds next to solvation dynamics st

We report on the observation of the solvation shell rearrangement after abstraction of the electron from aq. I- in a laser pump/X-ray probe expt. by recording the X-ray absorption L1- and L3-edge spectra, 50 ps after laser excitation. The L1-edge spectra c ...

In nodal-line semimetals, linearly dispersing states form Dirac loops in the reciprocal space with a high degree of electron-hole symmetry and a reduced density of states near the Fermi level. The result is reduced electronic screening and enhanced correla ...

The dynamics of electron bubble formation upon excitation of the A(3ss) Rydberg orbital of NO in solid Ne was studied by femtosecond pump-probe spectroscopy. The authors observe an ultrafast expansion of the bubble, followed by a vibrational recurrence in .apprx.1.4 ps. The overall dynamics is slower than in the heavier Ar solid. Mol. dynamics simulations show that this results from the collective motion of several shells around the excited impurity, as a result of the nature of the excited NOA-Ne and the N

The (sub)-ps relaxation processes in PbSe quantum dots of different sizes were measured by near-IR luminescence upconversion. The early-time spectra are characterized by emission from several low-lying excited states. The direct measurement of the Huang-Rh ...

The authors present a new technique to record single x-ray pulses in time-resolved x-ray absorption spectra spectroscopy (XAS) expts. at low frequencies around 1 kHz compared to the multibunch repetition rate at synchrotron radiation storage rings of several hundred MHz. This scheme of electronic gating of the multibunch train is applied to record high-quality EXAFS spectra. Further measurements show that this scheme permits the authors to record high-quality x-ray absorption spectra with a noise level

We present a theoretical analysis for the K- and L-2/3-edge static and picosecond X-ray absorption spectra of Fe(bpy)(3). Simulations of the pre-edge region at the Fe K-edge using time-dependent density functional theory demonstrate the importance of ...

Measurements of the ultrafast broadband UV fluorescence of N-acetyltryptophanamide (NATA) provide detailed information on its relaxation patterns in three different solvents: methanol (MeOH), water and acetonitrile (ACN). Several processes leading to excit ...

The H fragment produced in the photodissocn. of water (H2O -> H + OH) is lighter than the lattice atoms and a local heating occurs over long time scales and large spatial regions. Therefore, use of a continuum model for the lattice is justified. The local heating is promoted by a decreasing heat cond. with increasing temp. Solns. of a nonlinear heat cond. equation show that the heat release inside the cage leads to a temp. increase in its nearest surroundings up to the m.p. in argon. Melting enables the lig

We developed a fast multichannel detection system for pump-probe spectroscopy, capable of detecting single shot super-continuum spectra at the repetition rate (10-50 kHz) of an amplified femtosecond laser system. By tandem pumping the amplifier with three ...

Majed Chergui

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Ultraviolet transient absorption, transient grating and photon echo studies of aqueous tryptophan

Disentangling Thermal from Electronic Contributions in the Spectral Response of Photoexcited Perovskite Materials

Lifetime lengthenings of molecular Rydberg states in condensed matter

Cellular photoperception and photoactive proteins

Spectral and dynamical characterization of multiexcitons in colloidal CdSe semiconductor quantum dots

Harmonium: A pulse preserving source of monochromatic extreme ultraviolet (30–110 eV) radiation for ultrafast photoelectron spectroscopy of liquids

Photophysical Heavy-Atom Effect in Iodinated Metallocorroles: Spin-Orbit Coupling and Density of States

Photoinduced dynamics in solid hydrogens

A simple and accurate method for calibrating the oscillation amplitude of tuning-fork based AFM sensors

Femtosecond dynamics of I2(B 3Π0u+) in liquids from resonance Raman spectra

Ultrafast x-ray spectroscopy for structural dynamics studies in chemistry and biology

Observation of the Solvent Shell Reorganization around Photoexcited Atomic Solutes by Picosecond X-ray Absorption Spectroscopy

Light-Induced Renormalization of the Dirac Quasiparticles in the Nodal-Line Semimetal ZrSiSe

Ultrafast expansion and vibrational coherences of electronic 'Bubbles' in solid neon

Subpicosecond near-infrared fluorescence upconversion study of relaxation processes in PbSe quantum dots

Towards structural dynamics research with ultrashort pulse lasers and synchrotron radiation

The role of Hartree-Fock exchange in the simulation of X-ray absorption spectra: A study of photoexcited [Fe(bpy)(3)](2+)

The Role of Site-Specific Hydrogen Bonding Interactions in the Solvation Dynamics of N-Acetyltryptophanamide

Photodissociation of water in rare gas matrixes: cage effect and local heating of the lattice

Femtosecond pump/supercontinuum-probe setup with 20 kHz repetition rate