Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Ultrafast Molecular Dynamics High Harmonic Generation (HHG) Attosecond transient absorpt ion spectroscopy around the bromine M-edge reveals mult iple dynamics initiated by a st rong few-cycle (3.5 fs) NIR pul se in methyl bromide. In the n eutral, C-Br bond vibration (1 ), with a period of 40 fs, is visi ble. The coupled dynamics (3) of the signals converging to 5s a1 (65.2 eV) and Br P3/2 (64.3 eV) is instead signature of a fr agmentation pathway throug h multiple conical intersectio ns. In the ion, a spin-orbit wa vepacket in the ground state ( 2), with a period of 13 fs, is re solved. Attosecond Electronic Dynamics in Molecules http://www.jaslab.ca/atto2_e.html (a)pulse Slow ion The electric field from a femtosecond NIR laser 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 oddorder harmonic of the original NIR. We utilize attosecond pulses in conjunction with noncollinear NIR pulses to generate four wave mixing (FWM) emission signals. Attosecond FWM allows for highly selective, backgroundfree measurements of coherent superpositions of electronic states. The delay dependent FWM emission signal generated in argon reveals NIR-induced coupling with states within the bandwidth of the NIR pulses. We will extend this technique in order to study dynamic ultrafast processes such as autoionization, Auger decay, dissociation, and curve crossings in the time domain. Kristina, Maurizio, Yuki Femtosecond X-ray Spectroscopy of Photochemical Reactions Attosecond spectroscopy at the carbon K-edge 2A State (2p/1p*) Sample interaction The ultrafast light-activated ring-opening reaction of 1,3cyclohexadiene is investigated using femtosecond soft x-ray spectroscopy near the carbon k-edge (~284 eV) on a tabletop apparatus. 2A State (2p/1p*) Soft x-ray spectrometer The evolution of the valence electronic structure during this ubiquitous reaction is directly revealed and the x-ray spectroscopic signatures of the elusive intermediate states are characterized. Ultrafast Solid State Dynamics Ultrafast Charge Carrier Dynamics by XUV Transient Absorption The initial excited state of aFe2O3 is given by a ligand-tometal charge transfer. Relaxation happens through electron-phonon coupling leading to polaron formation. High-harmonic generation Recombination with pump pulse (IR to visible) 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 attosecondprobe experiments. Andrew R., Peter Attosecond Solid State XUV Transient Absorption Marieke, Chris Attosecond Transient Reflectivity in XUV Broadband attosecond XUV pulses are utilized to probe electron dynamics in semiconductors such as Ge and GaAs. 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. Transient reflectivity gives experimental access to the complex-valued index of refraction n or to the dielectric function e = e0 n2 / m02. Attosecond transient absorption simultaneously tracks electron and hole dynamics in germanium thin films Hung-Tzu, Michael Lucas, Scott, Ilana, Angela Ultrafast Charge Carrier Dynamics at Semiconductor Interfaces 1.4 fs oscillations during photoexcitation as a consequence of a laser-induced polarization of the bands. Broadening of hole feature over 10 fs indicates collective electron response time. Peter, Chris, Andrew R., Marieke Single Molecule Spectroscopy Fluorescence Spectroscopy of Semiconductor Nanostructures In this experiment we investigate the ultrafast charge carrier dynamics at three different interfaces, i.e. semiconductor-gas phase, semiconductor-metal, and semiconductor-semiconductor, by monitoring the full suite of steps from charge excitation to charge separation and subsequent charge recombination. Here is presented an experiment in which the charge carrier dynamics at the n-TiO2/p-Si(100) interface is investigated. E Atto-Atto Endstation (collaboration project with UCF) 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, Aditi, Kirsten, Marina, Chris X. We study the charge carrier dynamics in semiconductor materials after excitation by visible light. Transient XUV absorption spectroscopy has advantages of element/chemical valence specificity and low femtosecond temporal resolution, which is suitable to study ultrafast electron migration processes in semiconductor heterostructures. Erika, Ashley, Hugo New Attosecond Projects 1s→2p/1p* Science (2017) Attosecond Four-Wave Mixing Spectroscopy 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 confocal fluorescence microscopy and time-correlated single photon counting. These techniques are being used to study emerging, all-inorganic perovskite materials. Single CsPbBr3 perovskite nanowires exhibit low-threshold and wavelengthtunable lasing, which persists over one billion excitation cycles, even in ambient atmosphere, demonstrating unprecedented stability in perovskite nanowires. E 2 μm Charge carrier dynamics at the n-TiO2/p-Si(100) interface Brett, Bethany Charge carrier trapping leading to fluorescence intermittency or blinking is being studied in CsPbBr3 nanocubes and nanoplates. Natalie