Gas-discharge lamps

For excitation in the visible range of the electromagnetic spectrum, lasers and gas discharge lamps, together with filters or monochromators, have been used. 

Nicollet Technologies www.nictec.com UV equipment, gas discharge lamps, ballasts... 

Scattering studies with metastable atoms are in many cases easier (and less expensive) than experiments with ground-state atoms, The discussion that follows is mainly concerned with helium, as most of the information is available for this atom. Figure 2 shows a skeletal setup of the experiment. A helium beam from a supersonic nozzle source is excited by electron impact to its two metastable states. The singlet state can be quenched by the 2g radiation from a helium-gas discharge lamp ... 

Gas-discharge lamps are used to optically pump the metastable helium atoms into a higher excited electronic state, which has a dipole-allowed transition to the ground state. Only He (2 S) can be pumped selectively, thereby producing pure He(23S) beams. For the heavier rare gases, both metastable states are equally pumped by gas-discharge lamps. The use of cutoff filters to selectively pump one state is not adequate because of the temperature dependence of the filter transmission and the low / numbers of the pumping transition. Metastable neon can be selectively pumped by a continuous wave (cw) dye laser,60 whereas Ar, Kr, and Xe have so far only been selectively pumped by pulsed dye lasers.61... 

The gas is also used to fill balloons, in gas discharge lamps, and as an additive in the breathing gases of astronauts and scuba divers. The rarer stable isotope of helium (3He) is produced by the decay of radioactive tritium, and is used in resonance imaging and in the attainment of very low temperatures, about 0.010 kelvin, via a process known as dilution refrigeration. see also Noble Gases Nuclear Fusion. 

The properties which we require from an ideal source in UPS is good monochromaticity, defined by a line width better than 100 meV, high intensity and continuous wavelength selectivity. Unfortunately only synchrotron radiation together with a suitable monochromator offers us all these features. The rare gas discharge lamps or, alternatively, monochromators with continuum or many-line sources have generally been used hitherto, but have certain disadvantages. 

Photoemission spectroscopy involves measurement of the energy distribution of electrons emitted from a solid under irradiation with mono-energetic photons. In-house experiments are usually performed with He gas discharge lamps which generate vacuum UV photons at 21.2 eV (He la radiation) or 40.8 eV (He Ila radiation ) or with Mg Ka (hv=1284.6 eV) or A1 Ka (hv=1486.6eV) soft X-ray sources. UV photoemission is restricted to the study of valence and conduction band states, but XPS allows in addition the study of core levels. Alternatively photoemission experiments may be performed at national synchrotron radiation facilities. With suitable choice of monochromators it is possible to cover the complete photon energy range from about 5 eV upward to in excess of 1000 eV. The surface sensitivity of photoemission derives from the relatively short inelastic mean free path of electrons in solids, which reaches a minimum of about 5A for electron energies of the order 50-100 eV. 

Tungsten-base materials are used for cathodes in power grit tubes, radio valves. X-ray tubes, as electrode material for gas-discharge lamps, electric arc welding, electron guns, electron microscopes, and plasma generators. The electron emission characteristic is also an important property for their use as electrical contact materials. Finally, tungsten is a... 

SOX-E Low Pressure Sodium Lamps, company brochure. Philips Lighting, The Netherlands (4/86). Metal Halide Gas-Discharge Lamps, company brochure. Philips Lighting, The Netherlands (4/86). 

In a photoelectric experiment monochromatic radiation, 1w, causes ionization of matter, and the properties of the ejected electrons are measured. Radiation is of three main types X-ray, U.V. (normally from an inert gas discharge lamp), and synchrotron radiation. The matter is usually in the solid or gaseous state, though some experiments have also been carried out on liquids and on matrix isolated species. Measurement of the kinetic energy, m v2, of the ionized electrons and use of the Einstein equation... 

Gas discharge lamps. They are manufactured for the determination of sodium, potassium, mercury, cadmium and thallium atoms. They emit specific mono or polychromatic radiation for these elements. 

The functioning principle of the gas discharge lamps can be explained based on Figure 2.55. A small amount of the element that is analyzable by this lamp is melted under pressure in the quartz chamber. The element emits light of a certain wavelength by a high frequency electrical stream. 

The gas discharge lamps have higher intensity of emitted light and can work for a longer time without being changed in comparison to cathode lamps. 

Xenon arc gas discharge lamps are recognized to approximate the spectrum of sunlight better than any other commercially available light sources. For this reason they are extensively used in commercial equipment for the indoor testing of polymers. Experiments with these instruments have been found to correlate well with outdoor tests. 

Conventional photoelectron spectroscopy uses a rare-gas discharge lamp to produce radiation at the wavelength of the He 2p <— Is atomic transition (hu = 21.218 eV). Synchrotron radiation is now widely used for PES because its photon energy is widely tunable yet monochromatic. The initial state, in the first PES experiments, has been the molecular ground state but now, by exploiting Resonance Enhanced Multi-Photon Ionization (REMPI) excitar tion/detection schemes (see Section 1.2.2.3), any excited state of the molecule can be used as the initial state for PES (for a review, see Pratt, 1995). 

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