Ultrafast Solid State Dynamics

Ultrafast Molecular Dynamics

Single Molecule Spectroscopy

(a) Slow ion

High Harmonic Generation (HHG)

The electric field from a femtosecond NIR laser pulse tunnel ionizes an electron away from the nucleus of an atom. Half an optical cycle later when the electric field of the laser reverses direction, the electron is accelerated back towards the nucleus, coherently emitting an XUV photon, with energy that is an odd-order harmonic of the original NIR.

http://www.jaslab.ca/atto2_e.html

New Attosecond Projects

Natalie

We investigate charge carrier dynamics in semiconductor nanostructures at the single molecule limit. Transfer,trapping and recombination of charges can be studied in individual molecules using a combination of confocalfluorescence microscopy and time-correlated single photon counting. These techniques are being used to studyemerging, all-inorganic perovskite materials.

Fluorescence Spectroscopy of Semiconductor Nanostructures

2 μm

Single CsPbBr3 perovskite nanowiresexhibit low-threshold and wavelength-tunable lasing, which persists over onebillion excitation cycles, even inambient atmosphere, demonstratingunprecedented stability in perovskitenanowires.

Charge carrier trapping leading tofluorescence intermittency or blinkingis being studied in CsPbBr3 nanocubesand nanoplates.

EE

In this experiment we investigate the ultrafast charge carrierdynamics at three different interfaces, i.e. semiconductor-gasphase, semiconductor-metal, and semiconductor-semiconductor,by monitoring the full suite of steps from charge excitation tocharge separation and subsequent charge recombination. Here ispresented an experiment in which the charge carrier dynamics atthe n-TiO2/p-Si(100) interface is investigated.

Charge carrier dynamics at the n-TiO2/p-Si(100) interface

Brett, Bethany

Ultrafast Charge Carrier Dynamics at Semiconductor Interfaces

Attosecond Transient Reflectivity in XUVAttosecond Solid State XUV Transient Absorption

Broadband attosecondXUV pulses are utilized to probe electron dynamics in semiconductors such as Ge and GaAs.

Attosecond transient absorption simultaneously tracks electron and hole dynamics in germanium thin films

Hung-Tzu, Michael Peter, Chris, Andrew R., Marieke

2A State

(2p/1p*)

Femtosecond X-ray Spectroscopy of Photochemical Reactions

The evolution of the valence electronic structure during thisubiquitous reaction is directly revealed and the x-ray spectroscopicsignatures of the elusive intermediate states are characterized.

The ultrafast light-activatedring-opening reaction of 1,3-cyclohexadiene is investigatedusing femtosecond soft x-rayspectroscopy near the carbonk-edge (~284 eV) on a table-top apparatus.

2A State

(2p/1p*)

1s→2p/1p*

Andrew, Aditi, Kirsten, Marina, Chris X.Science (2017)

Erika, Ashley, Hugo

We utilize attosecond pulses inconjunction with noncollinearNIR pulses to generate fourwave mixing (FWM) emissionsignals. Attosecond FWM allowsfor highly selective, background-free measurements of coherentsuperpositions of electronicstates. The delay dependentFWM emission signal generatedin argon reveals NIR-inducedcoupling with states within thebandwidth of the NIR pulses. Wewill extend this technique inorder to study dynamic ultrafastprocesses such as auto-ionization, Auger decay,dissociation, and curvecrossings in the time domain.

Ultrafast Charge Carrier Dynamics by XUV Transient Absorption

Lucas, Scott, Ilana, Angela

We study the charge carrier dynamics in semiconductor materials after excitation by visiblelight. Transient XUV absorption spectroscopy has advantages of element/chemical valencespecificity and low femtosecond temporal resolution, which is suitable to study ultrafastelectron migration processes in semiconductor heterostructures.

The initial excited state of a-Fe2O3 is given by a ligand-to-metal charge transfer. Relaxation happens through electron-phonon coupling leading to polaron formation.

The valley dependent carrier relaxation dynamics of Si are observed. The different relaxation processes known to occur in semiconductors can be followed with unprecedented detail, further demonstrating the promise of transient XUV absorption.

Atto-Atto Endstation(collaboration project with UCF)

A high power attosecond pulse source is developed in collaboration with Chang group at University of Central Florida, which will enable the first true attosecond-pump attosecond-probe experiments.

Attosecond transient absorption spectroscopy around thebromine M-edge reveals multiple dynamics initiated by a strong few-cycle (3.5 fs) NIR pulse in methyl bromide. In the neutral, C-Br bond vibration (1), with a period of 40 fs, is visible. The coupled dynamics (3)of the signals converging to 5sa1 (65.2 eV) and Br P3/2 (64.3eV) is instead signature of a fragmentation pathway through multiple conical intersections. In the ion, a spin-orbit wavepacket in the ground state (2), with a period of 13 fs, is resolved.

Kristina, Maurizio, Yuki

Attosecond Electronic Dynamics in Molecules

Attosecond Four-Wave Mixing Spectroscopy

Transient reflectivity gives experimental access to the complex-valuedindex of refraction n or to the dielectric function e = e0 n2 / m0

2.

1.4 fs oscillations during photoexcitation as a consequence of alaser-induced polarization of the bands.Broadening of hole feature over 10 fs indicates collective electronresponse time.

Attosecond spectroscopyat the carbon K-edge

High-harmonic generation

Recombination with pump pulse (IR to visible)

Sample interaction

Soft x-ray spectrometer

A new beamline is developed which will enable the first experiments in the soft x-ray region with attosecond resolution: This enables access to carbon-containing gases and materials through element-specific probing of the dynamics at the carbon K-edge by exciting 1s electrons of carbon into the valence states.Proposed experiments include electron dynamics in small carbon containing molecules as well as graphene and silicon carbide.

Andrew R., Peter Marieke, Chris