Search results for "ULTRAVIOLET"
showing 10 items of 853 documents
Photoemission microscopy with microspot-XPS by use of undulator radiation and a high-throughput multilayer monochromator at BESSY
1999
We present a new experiment for photoelectron microspectroscopy by use of undulator radiation, which has been set up at the beamline U2 at the Berlin electron storage ring BESSY 1. This approach employs a non-imaging simulated hemispherical electron energy analyser attached to an imaging photoemission electron microscope (FOCUS IS-PEEM) with integrated microarea selector. The photoemission microscope exhibits a lateral resolution of 25 nm (with 4.9 eV UV-excitation), while the resolution with incident synchrotron radiation in the soft X-ray range is about 100-120 nm (mainly due to chromatic aberrations). Photoemission microscopy as well as photoelectron microspectroscopy of selected areas o…
NanoESCA: imaging UPS and XPS with high energy resolution
2005
Abstract A novel imaging electron spectrometer has been used for laterally resolved ultraviolet photoelectron spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS) in the soft X-ray range. The instrument is based on a high-resolution emission microscope optics using a cathode lens and an imaging dispersive analyser. The analyser is corrected for the leading aberration term ( α 2 -term) by means of two hemispherical analysers in antisymmetric configuration with an appropriate transfer lens. Small-area spectra as well as energy-filtered images have been taken in the soft X-ray range for a meteorite sample and in the range of the d-band of a Cu polycrystal. An energy resolution of 106 …
Temperature-dependent angular resolved UV-photoemission spectroscopy from CeNi2Ge2
2001
Abstract Pronounced temperature effects in angular resolved ultraviolet photoelectron spectroscopy from the (001) surface of the ternary heavy fermion compound CeNi 2 Ge 2 are presented. The measurements were performed on atomically clean and well-ordered thin films grown on a W(110) substrate. A strongly enhanced intensity at the Fermi edge ( ϵ F ) is observed at low-temperatures if the spectra are excited by means of HeI light ( hν =21.2 eV). In addition, the work function is dramatically increased with temperature, exhibiting an unusually high positive temperature coefficient of about 0.65 meV/K. The observed temperature dependency suggests a strong redistribution of the states near the …
Spectral heterogeneity of oxygen-deficient centers in Ge-doped silica
2004
Abstract We report an experimental investigation of the emission spectra of a 1000 mol ppm sol–gel Ge-doped silica by fine tuning the excitation energy in the ultraviolet (UV) range, around 5 eV , and in the vacuum-UV range, around 7.3 eV , at room temperature and at 10 K . The sample is characterized by a blue (centered at ∼3.2 eV ) and an UV (centered at ∼4.3 eV ) bands. We have found that the ratio between the area of the blue and the UV bands depends on the temperature and on the excitation energy in both the vacuum-UV and the UV range. At both temperatures the spectral features of the blue and the UV bands are weakly affected when the excitation is varied in the vacuum-UV. At variance,…
Bulk sensitive photo emission spectroscopy of compounds
2007
This work reports about bulk-sensitive, high energy photoelectron spectroscopy from the valence band of CoTiSb excited by photons from 1.2 to 5 keV energy. The high energy photoelectron spectra were taken at the KMC-1 high energy beamline of BESSY II employing the recently developed Phoibos 225 HV analyser. The measurements show a good agreement to calculations of the electronic structure using the LDA scheme. It is shown that the high energy spectra reveal the bulk electronic structure better compared to low energy XPS spectra.
A Preliminary Estimation of the Direct Ultraviolet Spectral Irradiance in Valencia (Spain): Comparison with Measured Values
2000
UVSPEC and SMARTS2 models have been used to estimate the UV spectral irradiance values in Valencia, Spain, and the results of these estimations have been compared with experimental measurements of direct irradiance at normal incidence obtained using an Optronic OL 754 in the 300-400 nm range. The relative RMSD and MBD parameters have been used to estimate the deviations of the modelled values with respect to the experimental values. The results indicate that the deviations are smaller when the SMARTS2 model is used with the appropriate aerosol coefficients.
Laser driven parametric amplification in the xuv and soft-x-ray spectral range
2011
We present the first experimental realization of a new x-ray laser scheme based on strong-field parametric amplification of high-order harmonic radiation. With a simple semi-classical model, we can identify the most important experimental parameters, the spectral range and the small signal gain in gases. Using a single amplifier stage a small signal gain of 8000 has been obtained in Argon for the spectral range of 40-50 eV, using 350 fs, 7 mJ pulses at 1.05 µm. In Helium, we observed a small signal gain of 280 around 300 eV using 6 fs, 1.5 mJ pulses at 800 nm.
Two-color ionization of hydrogen by short intense pulses
2010
Photoelectron energy spectra resulting by the interaction of hydrogen with two short pulses having carrier frequencies, respectively, in the range of the infrared and XUV regions have been calculated. The effects of the pulse duration and timing of the X-ray pulse on the photoelectron energy spectra are discussed. Analysis of the spectra obtained for very long pulses show that certain features may be explained in terms of quantum interferences in the time domain. It is found that, depending on the duration of the X-ray pulse, ripples in the energy spectra separated by the infrared photon energy may appear. Moreover, the temporal shape of the low frequency radiation field may be inferred by …
Tuning the high-order harmonic lines of a Nd:Glass laser for soft x-ray laser seeding
2010
Taking advantage of the non-adiabatic blue-shift of high-order harmonics generated by a fixed frequency Nd:Glass laser system, we are able to report more than 50 % coverage of the XUV spectral range between 18 nm and 35 nm. The generated harmonic lines are capable of seeding Ni-like Y, Zr and Mo soft x-ray lasers and others.
Luminescence of γ-radiation-induced defects in α-quartz
2004
Optical transitions associated with γ-radiation-induced defects in crystalline α-quartz were investigated by photoluminescence excited by both pulsed synchrotron radiation and steady-state light. After a 10 MGy γ-dose we observed two emissions at 4.9 eV (ultraviolet band) and 2.7 eV (blue band) excitable in the range of the induced absorption band at 7.6 eV. These two luminescence bands show a different temperature dependence: the ultraviolet band becomes bright below 80 K; the blue band increases below 180 K, but drops down below 80 K. Both emissions decay in a timescale of a few ns under pulsed excitation, however the blue band could also be observed in slow recombination processes and it…