Simultaneous measurements of laser-induced fluorescence (LIF dip) and laser-enhanced ionization (LEI enhancement) in flame—investigation of physical properties

Axner, Ove; Norberg, M.; Rubinsztein‐Dunlop, Halina

doi:10.1016/0584-8547(89)80067-9

Cited by 22 publications

(3 citation statements)

References 32 publications

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“…As a result, the ion enhancement of TLEI/SLEI may become dependent upon the power of the first-step excitation laser, which is neglected in our model. 31,32 In addition, the Einstein spontaneous emission coefficient A32 , as reported in Ref. 44, bears an uncertainty of 25 to 50%.…”

Section: Resultsmentioning

confidence: 98%

Ion Enhancement Effect of Laser-Enhanced Ionization Induced by One-Step Excitation and Two-Step Excitation

Sü

Lin

1994

Appl Spectrosc

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The two-step laser-enhanced ionization (LEI) technique is believed to be more sensitive and selective in trace analysis than one-step LEI. As reported previously, for optimization of the two-step LEI configuration, factors involving laser intensity, transition probability of second-step excitation, collisional ionization rates, and transition linewidth should be taken into account. We have derived a simple theoretical model in relation to these parameters that is rough but suitable in practice for characterizing the ion yields enhanced by two-step LEI over one-step LEI. According to the model, each parameter affecting the ion enhancement has been systematically examined and compared to the theoretical evaluation. The findings of the relative ion enhancement as a function of each related parameter are consistent with the model prediction, except for the effect of transition linewidth, which is underestimated theoretically due to the difficulty of establishing the experimental conditions.

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Section: Resultsmentioning

confidence: 98%

Ion Enhancement Effect of Laser-Enhanced Ionization Induced by One-Step Excitation and Two-Step Excitation

Sü

Lin

1994

Appl Spectrosc

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“…The ion enhancement of two-step LEI (TLEI) over single-step LEI (SLEI) may be attributed to such factors as second-step transition probability, laser intensity, colli- sional ionization rate coef® cients, and transition linewidth, which is associated with the effective lifetime of the states involved in the transition. Equation 6, ignoring the possibility of atom depletion during the laser pulse, is equivalent to equation 36 given by Axner et al 29 The atom depletion effect may become negligible by an appropriate selection of the upper state h, so that the inverse of collisional ionization rate from this state is larger than the laser pulse duration. 15 Provided that the laser energy and wavelength for the second-step excitation are ® xed, the enhanced factor becomes constant.…”

Section: Theoretical Modelingmentioning

confidence: 99%

Spatially Resolved Temperature Determination of an Air/Acetylene Flame Using the Two-Step Laser-Enhanced Ionization Technique

Lin

1998

Appl Spectrosc

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We have demonstrated a two-step laser-enhanced ionization (LEI) technique to be potentially useful in measuring a spatially resolved temperature in an atmospheric air/acetylene flame. As a complement to the existing optical methods, LEI detection shares the advantages of extremely high sensitivity and the capability of achieving a high spatial resolution, confined to the dual-beam intersection area of 1 mm × 1 mm. A theoretical model was developed to precisely extract the temperature information from the obtained two-step LEI signal. The physical parameters required in the experiment include simply the relative values of the LEI signals, associated with the fine-structure doublets of a selected thermometric species, and their corresponding laser energies. The subsequent treatment is also convenient without the need to know the absolute energy of the incident laser beam and to accurately calibrate the detection system. Al and Ga were selected as the thermometric species. The resultant radial and axial temperature mappings are consistent with each other and are also comparable with those reported by other optical methods.

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“…(i) Under optimum conditions, it is possible to ionize a large fraction of all the atoms in the interaction region [30,31]. (ii) The electrical detection implies a high (close to 100%) signal collection efficiency.…”

Section: Detection Limits and Sensitivitiesmentioning

confidence: 99%

Analytical applications of laser-enhanced lonization spectrometry in flames and furnaces

1989

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This paper is concerned with a critical analysis of the analytical performance of laser-enhanced ionization (LEI) spectrometry in flames and furnaces as an ultra-sensitive trace-element technique. Updated tables of LEI detection limits, both in flames and furnaces, are given. Special attention is paid to interference phenomena which are unique to the LEI technique. Ways of reducing their influence on the analytical signals are proposed. Finally, advantages and disadvantages of LEI spectrometry as a tool for ultra-sensitive trace element analysis are discussed.Key words: laser-enhanced ionization (LEI), flame, furnace, trace element.Laser-enhanced ionization (LEI) spectrometry is a very powerful technique for detecting low concentrations of metal atoms in solutions I-1-23]. The major characteristics of the technique constitute of a high sensitivity and a rather high resistance to interferences. The general principle of the LEI technique is that an enhancement of the normal ionization processes (collisions) is obtained by optical excitation of the atoms under study by resonant laser light. The enhanced ionization rate is detected as a change in the current passing through a medium (atomic reservoir) exposed to a voltage by means of an electrode arrangement.When a sample is analyzed by LEI, the atomization can, in principle, be done in any of the conventional atomic reservoirs which previously have been developed for standard analytical techniques (absorption or emission techniques). However, LEI has so far most often been done in atmospheric pressure flames (primarily air/acetylene flames) and only recently LEI has been applied to graphite furnaces [8,16,17,[24][25][26].The atoms under study are excited from low lying, highly populated levels (primarily from the ground level) to high lying excited states by resonant laser light. Solution Boxcar Oscilloscope Fig. l. A typical experimental set-up for two-step LEI in flames. C = 10 nF and R = 50 k~This is almost exclusively done by using pulsed dye-laser systems for production of resonant laser light.Since the atomic reservoirs used for LEI are characterized by high temperatures in fairly dense media the collision rates between analyte atoms and buffer molecules are high. Hence, the atoms have certain probabilities of undergoing ionizing collisions. The probability of such collisional ionization is higher the less energy needed for ionization of the (excited) atoms. Therefore, the ionization probability increases the closer to the ionization limit the atoms are being excited [-27].The excitation of atoms in LEI spectrometry can be carried out in several ways. The most common excitation scheme is to excite the atoms from the ground state by absorption of one photon. By using ultra-violet light or by exciting the atoms in two consecutive steps a high ionization rate (efficiency) can be obtained. The two-step excitation is practically done by illuminating the atoms with light from two simultaneously pumped dye lasers, each tuned to a suitable transition wavelength in the...

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Simultaneous measurements of laser-induced fluorescence (LIF dip) and laser-enhanced ionization (LEI enhancement) in flame—investigation of physical properties

Cited by 22 publications

References 32 publications

Ion Enhancement Effect of Laser-Enhanced Ionization Induced by One-Step Excitation and Two-Step Excitation

Ion Enhancement Effect of Laser-Enhanced Ionization Induced by One-Step Excitation and Two-Step Excitation

Spatially Resolved Temperature Determination of an Air/Acetylene Flame Using the Two-Step Laser-Enhanced Ionization Technique

Analytical applications of laser-enhanced lonization spectrometry in flames and furnaces

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