Strong-field above-threshold photoemission from sharp metal tips

We present energy-resolved measurements of electron emission from sharp metal tips driven with low energy pulses from a few-cycle laser oscillator. We observe above-threshold photoemission with a photon order of up to 9. At a laser intensity of 2*10^11 W/cm^2 suppression of the lowest order peak occurs, indicating the onset of strong-field effects. We also observe peak shifting linearly with intensity with a slope of around -1.8eV / (10^12 W/cm^2). We attribute the magnitude of the laser field effects to field enhancement taking place at the tip's surface.Comment: 5 pages, 3 figure

Ultracold Bose gases in time-dependent 1D superlattices: response and quasimomentum structure

The response of ultracold atomic Bose gases in time-dependent optical lattices is discussed based on direct simulations of the time-evolution of the many-body state in the framework of the Bose-Hubbard model. We focus on small-amplitude modulations of the lattice potential as implemented in several recent experiment and study different observables in the region of the first resonance in the Mott-insulator phase. In addition to the energy transfer we investigate the quasimomentum structure of the system which is accessible via the matter-wave interference pattern after a prompt release. We identify characteristic correlations between the excitation frequency and the quasimomentum distribution and study their structure in the presence of a superlattice potential.Comment: 4 pages, 4 figure

Selective late steroid withdrawal after renal transplantation

Steroid withdrawal (SW) after paediatric renal transplantation (RTPL) is controversial. Selective late SW has been performed in our unit since 1995. The safety and effects of SW were analysed retrospectively in 47 patients undergoing RTPL between 1995 and 2004. Initial immunosuppression consisted of cyclosporine A, azathioprine or mycophenolate mofetil and steroids. Criteria for SW were: (1) stable renal function, (2) time interval after RTPL ≥ 1year, (3) no rejection or time interval after last rejection ≥ 1year and (4) good compliance. SW was performed in 30 patients at an age of 13.5years (range 4.5-18.5) and 2.2years (range 1-6.6) after RTPL. After SW, one patient experienced a steroid-sensitive rejection. Follow-up after SW (1.3year; range 0.25-7.5) showed maintained renal function: glomerular filtration rate at SW and currently was 82 (65-128) and 82 (42-115) ml/min per 1.73m2, respectively. The number of patients on antihypertensive treatment did not significantly change (at SW: n = 15; currently: n = 11). Height and body mass index (BMI) remained stable: Median standard deviation score (SDS) for height/BMI at SW and currently was −1.1/0.2 and −0.8/0.1, respectively. Selective late SW was safe regarding renal function and had no significant effect on blood pressure and growt

Electron rescattering at metal nanotips induced by ultrashort laser pulses

We report on the first investigation of plateau and cut-off structures in photoelectron spectra from nano-scale metal tips interacting with few-cycle near-infrared laser pulses. These hallmarks of electron rescattering, well-known from atom-laser interaction in the strong-field regime, appear at remarkably low laser intensities with nominal Keldysh parameters of the order of $\gtrsim 10$. Quantum and quasi-classical simulations reveal that a large field enhancement near the tip and the increased backscattering probability at a solid-state target play a key role. Plateau electrons are by an order of magnitude more abundant than in comparable atomic spectra, reflecting the high density of target atoms at the surface. The position of the cut-off serves as an in-situ probe for the locally enhanced electric field at the tip apex