Search results for "SAP"
showing 10 items of 1142 documents
Efficient pulsed 946-nm laser emission from Nd:YAG pumped by a titanium-doped sapphire laser
2008
Efficient pulsed room-temperature laser emission at 946 nm is obtained from a Nd:YAG rod pumped by a Ti-doped sapphire laser in the free-running mode. Three bonded YAG rods of 3-mm diameter with different Nd concentrations and active lengths were tested. A maximum output energy of 83.5 mJ at 3 Hz was obtained with a slope efficiency of 32.3% in an end-pumping configuration.
Multilayer (Al,Ga)N Structures for Solar-Blind Detection
2004
We report on solar-blind metal-semiconductor-metal (MSM) detectors fabricated on stacks of (Al,Ga)N layers with different Al mole fraction. These structures were grown by molecular beam epitaxy on sapphire substrates to allow backside illumination and a low-temperature GaN buffer layer. They consist of a 0.3-0.4-/spl mu/m active layer grown on a thick (Al,Ga)N window layer (/spl ap/1 /spl mu/m) that is transparent at the wavelength of interest. Different Al contents were used in the window layer. We observed that, in general, samples with a high Al content were cracked, which is explained in terms of mechanical strain. MSM photodetectors fabricated on these samples showed large leakage curr…
Photoemission Electron Microscopy as a tool for the investigation of optical near fields
2005
Photoemission electron microscopy was used to image the electrons photoemitted from specially tailored Ag nanoparticles deposited on a Si substrate (with its native oxide SiO$_{x}$). Photoemission was induced by illumination with a Hg UV-lamp (photon energy cutoff $\hbar\omega_{UV}=5.0$ eV, wavelength $\lambda_{UV}=250$ nm) and with a Ti:Sapphire femtosecond laser ($\hbar\omega_{l}=3.1$ eV, $\lambda_{l}=400$ nm, pulse width below 200 fs), respectively. While homogeneous photoelectron emission from the metal is observed upon illumination at energies above the silver plasmon frequency, at lower photon energies the emission is localized at tips of the structure. This is interpreted as a signat…
Ultrafast laser-induced micro-explosion: material modification tool
2016
Femtosecond Bessel pulses with a needle-like intensity distribution were focused inside sapphire crystal to create voids and the shock-wave affected volume which is by more than two orders of magnitude larger as compared with that made by the Gaussian pulse.
Photoemission of spinpolarized electrons from strained GaAsP
1996
Strained layer GaAs.95P.05 photo cathodes are presented, which emit electron beams spinpolarized to a degree of P = 75% typically. Quantum yields around QE = 0.4% are observed routinely. The figure of merit P2 × QE = 2.3 × 10−3 is comparable to that of the best strained layer cathodes reported in literature. The optimum wavelength of irradiating light around 830 nm is in convenient reach of Ti:sapphire lasers or diode lasers respectively. The cathodes are produced using MOCVD-techniques. A GaAs.55P.45-GaAs.85P.15 superlattice structure prevents the migration of dislocations from the substrate and bottom layers to the strained overlayer. The surface is protected by an arsenic layer so that n…
Ion production from solid state laser ion sources.
2010
Laser ion sources based on resonant excitation and ionization of atoms are well-established tools for selective and efficient production of radioactive ion beams. Recent developments are focused on the use of the state-of-the-art all solid-state laser systems. To date, 35 elements of the periodic table are available from laser ion sources based on tunable Ti:sapphire lasers. Recent progress in this field regarding the establishment of suitable optical excitation schemes for Ti:sapphire lasers are reported.
On the potential of 914 nm pumping of Nd:YVO4 for laser operation at 1064 nm
2011
1064 nm-Nd :YVO4 lasers were pumped at 808 nm and 914 nm. The comparative study shows that 914 nm-pumping is adapted for cw operation whereas 808 nm-pumping provides higher population inversion interesting for Q-switched operation.
Characterization of a pulsed injection-locked Ti:sapphire laser and its application to high resolution resonance ionization spectroscopy of copper
2017
A high repetition rate pulsed Ti:sapphire laser injection-locked to a continuous wave seed source is presented. A spectral linewidth of 20 MHz at an average output power of 4W is demonstrated. An enhanced tuning range from 710-920 nm with a single broadband mirror set is realized by the inclusion of a single thin birefringent quartz plate for suppression of unseeded emission. The spectral properties have been analyzed using both a scanning Fabry-P´erot interferometer as well as crossed beam resonance ionization spectroscopy of the hyperfine levels of natural copper. Delayed ionization of the long-lived excited state is demonstrated for increased resolution. For the excited state hyperfine c…
Quality management in higher education: A comparative study of the United Kingdom, the Netherlands and Finland
2010
This chapter examines lecturers’ perceptions of the balance between quality assurance and quality enhancement in three case study higher education institutions in different European countries. Where quality initiatives emphasised assurance rather than enhancement, this was taken to indicate a significant limitation on a lecturer’s autonomy in the quality management process. In-depth interviews using a semi-structured schedule were conducted with 20 randomly selected academic staff in each of the three higher education institutions. The results from the interviews demonstrated a very wide range of views among the interviewees. However, generally, it was found that there was a high level of d…
Terbium Medical Radioisotope Production: Laser Resonance Ionization Scheme Development
2021
Terbium (Tb) is a promising element for the theranostic approach in nuclear medicine. The new CERN-MEDICIS facility aims for production of its medical radioisotopes to support related R&D projects in biomedicine. The use of laser resonance ionization is essential to provide radioisotopic yields of highest quantity and quality, specifically regarding purity. This paper presents the results of preparation and characterization of a suitable two-step laser resonance ionization process for Tb. By resonance excitation via an auto-ionizing level, the high ionization efficiency of 53% was achieved. To simulate realistic production conditions for Tb radioisotopes, the influence of a surplus of Gd at…