Reaction pathways of water dimer following single ionization

Water dimer $\mathrm{(H_2O)_2}$ - a vital component of the earth's atmosphere - is an important prototypical hydrogen-bonded system. It provides direct insight into fundamental chemical and biochemical processes, e.g., proton transfer and ionic supramolecular dynamics occurring in astro- and atmospheric chemistry. Exploiting a purified molecular beam of water dimer and multi-mass ion imaging, we report the simultaneous detection of all generated ion products of $\mathrm{(H_2O)_2^+}$-fragmentation following single ionization. Detailed information about ion yields and reaction energetics of 13 ion-radical pathways, 6 of which are new, of $\mathrm{(H_2O)_2^+}$ are presented, including strong $\mathrm{{}^{18}O}$-isotope effects.Comment: 7 pages, 4 figures, (SI: 4 pages, 6 figures

Phonon-pump XUV-photoemission-probe in graphene: evidence for non-adiabatic heating of Dirac carriers by lattice deformation

We modulate the atomic structure of bilayer graphene by driving its lattice at resonance with the in-plane E1u lattice vibration at 6.3um. Using time- and angle-resolved photoemission spectroscopy (tr-ARPES) with extreme ultra-violet (XUV) pulses, we measure the response of the Dirac electrons near the K-point. We observe that lattice modulation causes anomalous carrier dynamics, with the Dirac electrons reaching lower peak temperatures and relaxing at faster rate compared to when the excitation is applied away from the phonon resonance or in monolayer samples. Frozen phonon calculations predict dramatic band structure changes when the E1u vibration is driven, which we use to explain the anomalous dynamics observed in the experiment.Comment: 16 pages, 8 figure

Generation of narrowband, high-intensity, carrier-envelope phase-stable pulses tunable between 4 and 18 THz

We demonstrate the generation of narrowband (<1 THz) high-energy (~2 uJ) carrier-envelope phase-stable pulses, tunable between 4 and 18 THz as achieved by difference-frequency mixing between chirped near-infrared pulses in organic DSTMS

Electron tunneling through barriers of adjustable width : Role of the image potential and the wetting behavior of Cs by He

Photocurrents from cesium, flowing through gaseous 3He or 4He and also through thin liquid helium films, are investigated as a function of the chemical potential of helium at T=1.33 K. At low pressures, the two isotopes behave similarly as the photocurrent is governed by scattering by the gas. At higher pressures, a film of 3He grows on the Cs and forms a tunnel barrier; but for 4He, the film is too thin to form a tunnel barrier below liquid-vapor coexistence. This is because 4He does not wet Cs at this temperature and the finite thickness needed to form a tunnel barrier is larger than the thickness of the thin-film state. 3He enables a continuously variable tunnel barrier thickness to be studied. We show that the image potential is important and confirm that an electron in liquid 3He has a potential energy of 1.0 eV. We find that the thickness d of a hlium film is given by for films thicker than approximately three monolayers

Generation of narrowband, high-intensity, carrier-envelope phase-stable pulses tunable between 4 and 18 THz

We demonstrate the generation of narrowband (<1 THz) high-energy (~2 uJ) carrier-envelope phase-stable pulses, tunable between 4 and 18 THz as achieved by difference-frequency mixing between chirped near-infrared pulses in organic DSTMS

Metallic Si(111)-(7x7)-reconstruction: A surface close to a Mott-Hubbard metal-insulator transition

Li adsorption at extremely low coverages (10(-3) ML and below) on the metallic Si(111)-(7x7) surface has been studied by beta-NMR experiments (measurement of T-1-times). Instead of increasing linearly with the sample temperature, as expected for a metallic system, the relaxation rate alpha=1/T-1 is almost constant in between 50 K and 300 K sample temperature and rises considerably above. Comparison with T-1-times around 900 K (observed with Li-6-NMR) excludes adsorbate diffusion as the cause of the relaxation rate. Thus the almost temperature independent relaxation rate below 300 K points to an extremely localized and thus narrow band (width about 10 meV) which pins the Fermi energy. It is responsible for the metallicity of the (7x7)-reconstruction. Because of the steeply rising relaxation rate beyond 300 K this narrow band is located energetically within a gap (approximately 100-500 meV wide) in between a lower filled and an upper empty (Hubbard) band. Due to its extremely narrow width it can hardly be detected in photo electron experiments. In dynamical mean field theories based on Hubbard Hamiltonians this kind of density of states is typical for correlated electron systems close to a Mott-Hubbard metal-insulator transition

Comparative investigations on continuous wave operation of a-cut and b-cut Tm,Ho:YAlO3 lasers at room temperature

The Tm,Ho:YAlO3 laser performance for two crystal orientations pumped by a wavelength tunable Ti:Sapphire laser is presented in this paper. An experimental investigation comparing a- and b-oriented Tm,Ho:YAlO3 crystals laser performance is demonstrated and discussed. Single- and multi-wavelength operations of Tm,Ho:YAlO3 lasers have been investigated in detail. The maximum output powers of 890 mW at 2119 nm for a-oriented Tm,Ho:YAlO3 crystal and 946 mW at 2103 nm for b-oriented Tm,Ho:YAlO3 crystal have been obtained, respectively. The two crystals show very similar performance in terms of output power and conversion efficiency, only that the b-cut Tm,Ho:YAP crystal demonstrates more regimes of multi-wavelength operations

Effizienter kontinuierlicher und passiv modengekoppelter und Tm-gedopter kristalliner Silikatlaser

An efficient continuous wave and passively mode-locked thulium-doped oxyorthosilicate Tm:LuYSiO5 laser is demonstrated. A maximum slope efficiency of 56.3% is obtained at 2057.4 nm in continuous wave operation regime. With an InGaAs quantum well SESAM, self-starting passively mode-locked Tm:LuYSiO5 laser is realized in the 1929 nm to 2065 nm spectral region. A maximum average output power of 130.2 mW with a pulse duration of 33.1 ps and a repetition rate of about 100 MHz is generated at 1984.1 nm. Pulses as short as 24.2 ps with an average output power of 100 mW are obtained with silicon prisms where used to manage the intracavity dispersion. The shortest pulse duration of about 19.6 ps is obtained with an average output power of 64.5 mW at 1944.3 nm

Passively mode-locked Tm,Ho:YAG laser at 2 μm based on saturable absorption of intersubband transitions in quantum wells

We report the first demonstration of a solid state laser passively mode-locked through the saturable absorption of short-wavelength intersubband transitions in doped quantum wells: a continuous wave Ti:sapphire laser end-pumped Tm,Ho:YAG laser at the center wavelength of 2.091 μm utilizing intersubband transitions in narrow In0.53Ga0.47As/Al0.53As0.47Sb quantum wells. Stable passive mode-locking operation with maximum average output power of up to 160 mW for 2.9 W of the absorbed pump power could last for hours without external interruption and a mode-locked pulse with duration of 60 ps at repetition rate of 106.5 MHz was generated

Shot-by-shot 250 kHz 3D ion and MHz photoelectron imaging using Timepix3

We demonstrate the application of event-driven Timepix3-based detectors in combination with a double-sided velocity-map-imaging spectrometer to record the full 3D momentum of charged particles at the free-electron-laser facility FLASH. We measured the XUV induced fragmentation of $\text{N}_2$ using 250 kHz FLASH bursts with sub-pixel spatial resolution and up to 1.7 ns temporal resolution for photoelectrons. To further demonstrate the capabilities of this camera at even higher repetition rates we measured single-shot images of He($1s$) photoelectrons for bursts with a repetition rate of 1 MHz. Overall, with the Timepix3 camera we overcome limitations of standard-camera technology for advanced-imaging experiments with requirements on high event-rates and high spatio-temporal resolution