Pulsed Lamp Research Articles

Relative enhancement of near-UV emission from a pulsed low-pressure mercury discharge lamp, using a rare gas mixture

In this paper, we explain the physical reasons for the enhancement of near-UV and visible emissions from a low-pressure mercury–argon discharge under pulse drive conditions. The conditions of operation that maximize the enhancement of near-UV and visible radiation, including the effect of the buffer gas, are investigated. We show that for a pulsed discharge, electron–ion recombination followed by cascade radiative transitions is the process responsible for most of the 365 nm emission and that argon with a small admixture of krypton is the buffer gas composition that leads to maximum radiative emission due to near-resonant energy transfers to mercury high-lying levels.

Measurement of Stark parameters of HeII P\alpha, P\betaand P\gammaspectral lines

This work reports information on the pressure broadened profiles of the HeII P α , P β and P$_\gamma$ spectral lines measured in a pulsed discharge lamp. Information relative to the line shapes, full width at 1/2, 1/4 and 1/8 of the maximum intensity and the dip of the HeII 320.3 nm is provided. The electron density has been determined by two-wavelength interferometry and from the Stark width of the HeI 501.6 nm. and ranges during the HeII emission from 0.54 to $0.64 \times 10^{23}$ m -3 in the plasma. Temperature (1.7–2.4 eV) has been simultaneously determined from the Boltzmann-plot of HeI and from local thermodynamic equilibrium (LTE) assumptions. The final results have been compared with most of the previous existing data.

Optical characteristics of a repetitively pulsed low-pressure discharge in a krypton-freon-12 mixture

Results of a study of the plasma radiation of a repetitively pulsed discharge in a Kr/CF2 Cl2 mixture (P≤1.5 kPa) in the 130–300 nm spectral range are presented. Spatial, spectral, and temporal characteristics of the discharge are studied in a spherical anode-plane cathode system, in which the repetitively pulsed mode is established due to the evolving instability of the glow discharge. It is demonstrated that a discharge of this type can be used for the development of a repetitively pulsed low-pressure bactericidal lamp which emits in the band system of KrCl (222 nm) and Cl2 (257, 200 nm) in the 180–270 nm spectral range.

Transition probability measurement of several OII spectral lines

This work reports atomic transition probabilities of 33 spectrallines belonging to 3s-3p, 3p-3d and 3d-4f multiplets of OII, all of them measured in the 405-465 nm spectral regionin an emission experiment. Relative intensitymeasurements have been made on a pulsed discharge lamp and theabsolute Aki-values have been obtained taking the NISTdatabase as a reference in temperature diagnosis. Theresults of this work confirm the other recent available data measured byVeres and Wiese (Veres G and Wiese W L 1996 Phys. Rev. A 541999) with a different source and the calculations of Bell et al (Bell K L, Hibbert A, Stafford R P and McLaughlin B M 1994 Phys. Scr. 50 343) with a very satisfactory agreement (usuallywithin 10%).

Transitionprobability measurement in Ne II

This work reports 94 Ne II transition probabilities oflines in the spectral region 337-463 nm, all of them measured inan emission experiment. To the authors' knowledge, for 20 ofthe lines these are the first measurements. Relative intensitymeasurements have been made on a pulsed discharge lamp and theabsolute Aki-values have been obtained by using data takenfrom the bibliography as reference. Electron density, which rangesfrom 0.2 to 0.8×1023 m-3 in the plasma, has beensimultaneously determined by interferometry and fromHα-Stark broadening. The Ne II excitation temperature(25 000-44 000 K) has been determined from Boltzmann plots. Inaddition, Boltzmann plots with several O II lines measured fromthe same plasma allowed a complementary temperaturedetermination. Comparisons have been made with previousliterature values.

Measurement of several transition probabilities in singly-ionized krypton

This work reports a collection of 35 transition probabilities of lines in the spectral region 450{580 nm, all of them measured in an emission experiment. Relative intensity measurements have been made in a pulsed discharge lamp and the absolute Aki values have been obtained by using reference data taken from the literature. The electron density has been determined by two-wavelength interferometry and ranges from 0: 1t o 0:810 23 m 3 in the plasma. Temperature (14 000{24 000 K) has been simultaneously determined from three dierent methods, including the Boltzmann-plot of KrII lines and the KrII/KrI intensities ratios. The nal results have been compared with most of the previous existing data.

Electron beam generation from semiconductor photocathodes

Several measurements on a variety of semiconductor photocathodes were performed in order to determine their photoelectric quantum efficiency. Two different excimer lasers (XeCl and KrCl) and a pulsed Xe lamp were used as light sources for electron photoextraction from doped and undoped samples of cadmiun telluride, indium antimonide, and indium phosphide. Large current densities were obtained up to the limit of the Child–Langmuir law. This suggests the use of these materials for the production of intense electron sources, which could also be used for purity measurements of noble liquids.

An externally controlled, nanosecond-pulsed, Xe lamp using a high voltage semiconductor switch

We have constructed a nanosecond pulsed Xe lamp which is controllable by a small-sized, high-voltage semiconductor switch that is driven by a transistor-transistor-logic level external signal. The Xe lamp used here is commercially available and it is usually operated in a direct-current (dc) mode. The aim of the external control is to solve a discharge difficulty in a free-running Xe lamp that we have developed previously. The problem is that the free-running discharge Xe lamp suddenly switches in its operation mode from a pulsed spark-discharge mode to an undesirable, weak, dc arc-discharge mode. The pulse width of emitted light from the pulsed Xe lamp was 3.8 ns and the repetition frequency was 0.5–1 kHz with a peak power 100 W. In order to obtain an accurate timing signal required for a fluorescence-lifetime measurement system, a current probe circuit was added in the control circuit. Details of the lamp and the results of fundamental performance tests are shown.

Multi-step photoionization spectroscopy in uraniumbetween 5900 and 6060 Å using a pulsed hollow-cathodelamp

The observation of current in the afterglow of the discharge ina pulsed hollow-cathode lamp illuminated by tunable lasers,combined with optogalvanic techniques, provides a simple andreliable tool for multi-step photoionization spectroscopystudies. A three-photon photoionization spectroscopy study wasperformed in a uranium hollow-cathode lamp, using thiscombination of techniques. Single-, double- and triple-frequencyphotoionization paths were identified for uranium, in the rangebetween 5900 and 6060 Å.

Experimental transition probabilities in NII lines

This work reports an extensive collection of 108 transition probabilities of NII lines in the visible spec- tral region, all of them measured in an emission experi- ment. Relative intensity measurements have been made on a pulsed discharge lamp and the absolute Aki val- ues have been obtained by using the literature available data. Electron density and temperature range in this ex- periment from 0: 2t o 1: 11 0 23 m 3 and from 17000 to 29000 K respectively. The rst one has been simultane- ously determined from two-wavelength interferometry and from the Stark broadening of HeI 471.3 nm, the second from Boltzmann-plot of NII lines and from NII/NI in- tensities ratios. The results are compared with the recent available literature.

Time-resolved high-performance liquid chromatography fluorescence detector using a nanosecond pulsed light source for detecting lanthanide-chelated compounds

We have constructed a time-resolved fluorescence detection (TRFD) system for the analysis of amino compounds with high-performance liquid chromatography (HPLC) using lanthanide ion chelates. In order to carry out time-resolved measurements, we have employed a nanosecond pulsed xenon-arc lamp as an excitation light source. Amino compounds derivatized by isothiocyanobenzyl-EDTA (IEDTA) with the lanthanide chelate are mixed with an enhancer solution in a post-column manner and detected by TRFD. Taking advantage of a property of the long fluorescence lifetime of the lanthanide chelates, high selectivity against background fluorescence was achieved. In order to demonstrate the usefulness of TRFD, fundamental performance tests were carried out. Details of the system are also described.

Measurement of Stark broadening and shift of singly ionized Ar lines

A very extensive compilation of Stark widths and shifts for more than 125 Ar II visible spectral lines is presented in this work. These atomic parameters have been measured in a pulsed discharge lamp by using different mixtures of pure argon or argon and helium. The electron density, which typically ranges from 0.2 to has been determined interferometrically and, in the case of pure argon plasmas, also spectroscopically from -Stark broadening. The Ar II excitation temperature (15 000-31 000 K) has been determined by Boltzmann-plot techniques from the intensity of Ar II lines. A detailed description of all the relevant points in this kind of measurement is given. Comparisons with most of the data published about this topic for Ar II are also included.

Transition probability measurement in an Ar II plasma

This work reports a collection of 200 Ar II transition probabilities of lines in the spectral region 360 - 750 nm for 16 lifetime values, all of them measured in an emission experiment. Relative intensity measurements have been made on a pulsed discharge lamp and the absolute values have been obtained by using data taken from the literature. The electron density, which ranges from 0.2 to in the plasma, has been determined simultaneously by interferometry and from -Stark broadening. The Ar II excitation temperature (15 000 - 27 000 K) has been calculated by a new method which also provides transition probabilities and plasma composition. The high number of measurements has allowed us to properly discuss the plasma equilibrium model. Comparisons have been made with the most recent experimental and theoretical data collections.

An intense, broadband emission spectrum, thyratron-gated nanosecond light source using a commercially available Xe short-arc lamp

We have developed a thyratron-gated, high-intensity nanosecond pulsed lamp using a commercially available Xe short-arc lamp. A dc voltage higher than 10 kV is applied to the electrode gap through a high-value resistor. A spark discharge in the electrode gap is generated by the trigger of the thyratron. Intense light pulses as large as 80 W (peak value) of 14–16 ns duration full width at half-maximum was obtained repetitively from the Xe lamps. This lamp produced broadband emission spectrum (220–600 nm) according to discharge of Xe gas. Because discharge voltage of the pulsed lamp is much higher than that of a conventional dc lamp, a high electron-temperature pulsed plasma is produced, resulting in enhancement of the UV component of the emitted light. The rich UV light from this lamp can be utilized as an excitation light source in time-resolved spectroscopy.

Quantum efficiency and ageing studies for bulk and porous CsI photocathodes in a MWPC

The quantum efficiency of CsI photocathodes operating in a proportional gas chamber is measured in the wavelength range 185–220 nm. The tests are carried out with methane gas at atmospheric pressure using a pulsed UV lamp. Two different techniques are used to produce the photocathodes. The CsI is either evaporated under high vacuum or under low pressure of argon. The quantum efficiency of the photocathodes produced by the first technique is measured to be 9% at 190 nm while it is enhanced by a factor of 1.3 and 2 at 190 nm and 200 nm respectively for the photocathodes prepared with the second method. No significative drop of the quantum efficiency is observed over a total period of one month.

Roll-over effect in graphite furnace atomic absorption spectrometry with a gold pulsed hollow-cathode lamp

The presence of stray light in graphite furnace atomic absorption spectrometry causes errors in background correction at high analyte concentrations. The stray light level originates in the hollow-cathode lamp, but can be modified in the atomizer. Some differences were noted for both wall and platform atomization. Other factors, such as the presence of matrix components (copper) or chemical modifiers (vanadium), also affect the sensitivity for gold and consequently have an effect on the roll-over phenomenon. Experimental results show that the stray radiation depends on the wavelength region used for the determination of gold.

Temperature-dependent kinetics of the quenching of O( 1S) by chlorofluoromethanes

The kinetics of the quenching of metastable O( 1S) atoms by a number of chlorofluoromethanes has been studied by a pulsed VUV resonance lamp for the generation of the metastable species and by the forbidden transition at 557 nm for their detection. The rate constants of all investigated quenchers are temperature indpendent in the range from 215 to 445 K. The constants vary greatly from 3.5×10 −10 to 2.2×10 −17 cm 3 s −1 and depend considerably on the number of Cl atoms of the methanes.

Electrode behaviour of pulsed high-pressure sodium lamps

Pulsed high-pressure sodium discharge lamps were investigated by the voltage noise method. The abrupt disappearance of the high-frequency noise of the burning voltage indicated a transition from the vapour arc mode to the thermionic arc mode 100-500 pulses after igniting the lamp. The mass loss of electrode material during one start-up was estimated to be in the same order of magnitude as in the case of a conventional inductive ballast. Under the given conditions, the electrodes worked in a pure thermionic mode when the lamp had reached its final state, providing a sufficient lamp lifetime.

Monitor and control systems for the SLD Cherenkov ring-imaging detector

To help ensure the stable long-term operation of a Cherenkov ring-imaging detector at high efficiency, a comprehensive monitor and control system is being developed. This system will continuously monitor and maintain the correct operating temperatures, and will provide an on-line monitor of the pressures, flows, mixing and purity of the various fluids. In addition, the velocities and trajectories of Cherenkov photoelectrons drifting within the imaging chambers will be measured using a pulsed UV lamp and a fiber-optic light injection system.

Microwave discharge-pumped excimer lamp.

New high-efficiency ultraviolet and vacuum ultraviolet excimer lamps pumped by microwavedischarge are reviewed. KrF (B→X) and ArF (B→X) fluorescences of a 9-ms pulse durationwith a 100-Hz operation frequency and of 6-μs pulse duration with a 100-kHz operation fre-quency were observed. The spectral widths were around 3nm as narrow as those of excimerlasers. The highest intrinsic efficiency of 12.5% was obtained with a high average KrF power of 43W. Theoretical analysis of a pulsed KrF excimer lamp is also described.