Pulsed discharge lamps

Figure 3. Scheme of a fast-pulsed discharge lamp for TOF-PEPECO spectroscopy. After the condenser is charged to lOkV the HV control switch opens and the thyratron fires, driving a rapid rise of negative potential at the anode which caused spontaneous breakdown. Pulse lengths less than 5 ns at repetition rates of 10 kHz are possible. 

Radiative decomposition (glow discharge, photolytic, UV, pulsed discharge lamp). Photochemical decomposition [O]... 

Where vapour discharge lamp sources exist (for volatile elements such as Hg, Na, Cd, Ga, In, T1 and Zn) they can be used. Hollow-cathode lamps are insufficiently intense, unless operated in a pulsed mode. Microwave-excited electrodeless discharge lamps are very intense (typically 200-2000 times more intense than hollow-cathode lamps) and have been widely used. They are inexpensive and simple to make and operate. Stability has always been a problem with this type of source, although improvements can be made by operating the lamps in microwave cavities thermostated by warm air currents. A typical electrodeless discharge lamp is shown in Fig. 6.3. 

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... 

Disilene and its isomer silylsilylene were neither available by standard vacuum flash pyrolysis of precursors 59-63, nor by the more elaborate method of pulsed flash pyrolysis of 60-63, a pulsed discharge in mixtures of argon and mono- and disilane74 or by the matrix photolysis of educts 59-66 using various light sources (Hg lamps, excimer laser)69,70,72, the microwave discharge in disilane 66 or the cocondensation of silicon atoms with SiFLt. 

Pulsed hollow cathode or electrodeless discharge lamp... 

In the early stages of development of the technique the excitation was achieved by high energy discharge lamps which provided light pulses typically of a few microseconds duration... 

The schematic layout of a luminescence spectrometer for recording of fluorescence, phosphorescence and excitation spectra is shown in Fig. 20. As excitation source a mercury vapor discharge lamp or, as a continuous source, a pulsed xenon flashlamp is used. Excitation spectra are obtained by setting monochromator b2 at the maximum of the luminescence spectrum and varying by means of the monochromator bi the exciting wavenumber continuously over the whole absorption spectrum of the sample. The luminescence spectriun is corrected by diverting a portion of the incident light on a beamspHtter d to a quantiun counter... 

The second important limiting case concerns chaotic light as emitted from eonventional sources like gas discharge lamps, or thermal sources like thermal cavities or filament lamps, where special consideration must be given to classical, statistical aspects of the pulses and beams (Glauber, 1965,1970 Loudon, 1973). Formally, instead of the pure-state description based on Eqs. (54)-(57), we must then consider the incident light pulses or beam as an ensemble of photons in a mixed state represented by a statistical density operator p(fo) (Dicke and Wittke, 1961 Loudon, 1973). 

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