Population mechanisms of the green Er3+:LiYF4 laser

In computer simulations the mechanisms that lead to room-temperature continuous-wave green upconversion lasing in Er3+:LiYF4 are investigated. The rate-equation system considers the full erbium level scheme up to 2H9/2, ground-state depletion, excited-state absorption on the pump and laser wavelengths, three interionic processes, stimulated emission, and the crystal and resonator data of the experiments. Experimental results performed at the University of Hamburg, Germany, are reproduced in the simulation. The influence of different parameters as pump wavelength, absorption cross sections, interionic parameters, dopant concentration, and temperature is investigated. An avalanche effect which exploits the strong cross relaxation from the upper laser level and the upconversion from 4I13/2 leads to an efficient population of the upper laser level. At higher dopant concentrations the cross relaxation becomes detrimental to stimulated emission due to the depletion of the upper laser level. This concentration dependence can be considered as a general behavior of rare-earth-doped avalanche lasers

Excited-state absorption in ZBLAN:Er3+: implications for a diode-pumped 3-µm fiber laser

Effective excited-state absorption (ESA) cross-sections are measured in ZBLAN:Er3+ at 780-840 nm. Pump losses by ESA are present over the whole absorption band. Diode pumping at 979 nm seems more favorable for high-power 3-µm fiber lasers

Human pharmacokinetics and CSF penetration of clavulanic acid

Clavulanic acid, a product of Streptomyces clavuligerus with β-lactam structure, is a potent inhibitor of several β-lactamases. To study its pharmacokinetic and CSF penetration in patients without meningeal inflammation, a single oral dose of 250 mg of clavulanic acid was given to 21 patients. One patient was studied in a multiple dose schedule. Fifteen of these 21 patients had a diagnostic lumbar puncture and 3 neurosurgical patients had a continuous CSF drainage. Serum and urine concentrations of clavulanic acid were available from 22 patients. The mean peak serum concentration was 4·3 mg/l and individual peak serum concentrations ranged from 0·1-9·5 mg/i between 40 and 60 mm after ingestion of clavulanic acid. Urinary recovery between 300 and 400 mm ranged from 0·8-54·3% of the administered dose. The mean absorption half life was 0·26 h and the mean elimination half life was 0·9 h. Considerable degradation of clavulanic acid occurred in vitro at 37°C. In pooled human serum, phosphate buffer pH 7 and 5, an hourly loss of activity of about 10, 7 and 10% respectively, was observe

Investigations on the slope efficiency of a pulsed 2.8-µm Er3+:LiYF4 laser

A slope efficiency of 40% from an Er3+:LiYF4 laser is demonstrated under pulsed Ti:sapphire pumping at 973 nm. With reduction of the pump-pulse duration a significant decrease of the slope efficiency and an increase of the threshold is observed in the experiment and confirmed with high accuracy in a computer simulation. This behavior is due to interionic upconversion from the lower laser level, which leads to energy recycling into the upper laser level. The upconversion rate is negative at threshold but increases strongly with rising pump pulse energy, thus enhancing the slope efficiency. The conditions are derived that are necessary for achieving the high slope efficiency of the energy-recycling regime

Thermo-optically driven adaptive mirror for laser applications

An adaptive mirror is investigated that is based on the deformation of the reflective surface due to thermal expansion of an underlying material that can be locally heated with an external light source. The mirror is made from a glass plate coated with a 1-mm-thick layer of a material with a large thermal expansion coefficient that was finally sputter coated with a thin gold film. The adaptive mirror is thermo-optically heated with an incandescent lamp. To generate the desired temperature pattern an aperture mask is used. The deformation of the adaptive mirror is measured with a Michelson interferometer. It is shown that the spatial resolution and amplitude of the deformation are sufficient for the application as an adaptive mirror. As a possible application the suitability of this mirror type as part of a laser resonator to generate a super-Gaussian mode is discusse