O. I. Matveev

Novel uses of lasers in atomic spectroscopy. Plenary Lecture

This paper reviews several novel uses of lasers in atomic spectroscopy. A tutorial discussion is given of the basic processes involving the interaction of laser radiation with atoms and the measurement approaches. Laser microprobes, especially laser induced breakdown spectroscopy and laser ablation-inductively coupled plasma-optical emission or mass spectrometry are reviewed thoroughly with respect to principles, instrumentation and applications. Laser excited atomic fluorescence and atomic absorption spectrometry with diode lasers are considered primarily with respect to recent publications. Laser-enhanced ionization, resonance ionization and resonance ionization imaging are also thoroughly reviewed with respect to recent publications. Diagnostical measurements of plasmas and atom reservoirs are discussed. The principles of six laser based atomic absorption methods are given and the methods are compared with respect to detection limits. Finally, future uses of lasers in atomic spectroscopy and a comparison of the characteristics of various atomic methods for trace elements are given.

Resonance ionization image detectors: basic characteristics and potential applications.

A type of spectrally selective imaging optical detector that is based on resonance ionization in an atomic vapor is proposed. It has the potential for improved spatial, spectral, and temporal resolutions compared with those of available techniques. Figures of merit are calculated and compared with those of existing techniques. Several potential applications such as the imaging of moving objects, ultrasonic fields, high-energy particle detection, and optical communications are discussed.

Experimental studies of charge transfer reactions between argon and the third row metals calcium through copper in the inductively coupled plasma

Abstract The effect of charge transfer reactions on analyte excitation and ionization in the inductively coupled plasma was studied by two independent techniques. In one technique, pulsed lasers were used to either deplete the ground state of neutral analyte atoms or enhance the population of selected states of the singly charged ion. In both cases the perturbed species were collision partners with argon in potential charge transfer reactions. The effects of charge transfer collisions could be detected in the form of changes in emission from product species. In the second technique, a simple correlation method was used to detect the link via charge transfer of neutral atom ground states and highly excited ionic levels. In the presence of charge transfer collisions, the populations of such linked levels show strong positive correlations. The two techniques were used to study the effects of charge transfer reactions on the third row elements Ca–Cu. With the exception of Cr and Mn, all of the elements studied showed positive evidence of excitation and ionization by charge transfer collision with argon.

A cesium resonance fluorescence imaging monochromator

Abstract A cesium-based resonance fluorescence imaging monochromator (RFIM) is described. The spectral bandwidth of the detector was shown to be 0.4 GHz, the line width of one component of the hyperfine structure. The RFIM features sharp attenuation as close as 0.5 GHz from the center of a hyperfine component. The two-step excitation scheme gave a linear dependence on photon signal from the first ground state transition (852.12 nm), which was the wavelength detected in the RFIM. The spatial resolution of the detector was approximately 200 μm .

Narrow-band resonance-ionization and fluorescence imaging in a mercury-vapor cell.

Characteristics of a novel type of ultranarrow-band image detector have been experimentally studied. The principle of this new imaging approach is to detect a resonance-ionization and (or) fluorescence-imaging signal formed on a thin planar cell filled with atomic vapor. A planar vapor cell with a thickness of 1.6 mm was used for imaging 253.7-nm radiation by Hg atoms. One- and two-dimensional images were produced and detected with ionization and fluorescence-signal acquisition. The feasibility of atomic-vapor image detectors with a spectral resolution of several megahertz is discussed.

Sealed-cell mercury resonance ionization imaging detector

A sealed, compact mercury atomic-absorption resonance ionization imaging detector has been developed and evaluated. The sensitivity of the detector as well as its ability to form two-dimensional images has been demonstrated. Images of faint light (1000 photons) have been recorded by image summation. It is shown that one can obtain high-quality images with a spatial resolution of at least 130 mum by detecting the ionic component of the imaging signal. Distortion, more noise, and poorer spatial resolution were observed when the electron component of the signal was detected. We studied the influence of voltage on the cell electrodes to find the conditions for optimum signal-to-noise ratio.

Single photo-electron and photon detection in a mercury resonance ionization photon detector (RID)

Abstract Avalanche detection of a laser enhanced ionization (LEI) signal has been studied in a resonance ionization detector (RID) cell containing mercury vapor at room temperature. An avalanche multiplication factor of more than 8000 was achieved. The limit of detection of Hg resonance radiation ( λ = 253.7 nm) was at the level of 0.5 quantum during the lifetime of the excited 6 3 P 1 0 state. Detection of radiation from a conventional CW Hg discharge lamp source with a signal to noise ratio of more than 10 4 has been achieved.

A low pressure mercury vapor resonance ionization image detector

Narrow-band spectrally selective image detection based upon the resonance ionization of mercury atoms in a low pressure cell is described. Image dimensions and intensities were measured versus the wavelength of ionizing laser radiation and the dependence upon the voltage applied to electrodes was studied. The position sensitive image of the electron beam, created by two-step resonance photoionization of mercury, was studied when the detected laser beam was scanned spatially. A distorting influence of space charge due to positive mercury ions on the electron beam image was observed. Means of eliminating these distortions are discussed.

The determination of lead in whole blood by laser enhanced ionization using a combination of electrothermal vaporizer and flame

Abstract A system for electrothermal vaporization — laser enhanced ionization spectrometry (ETV-LEIS), developed in this laboratory, was used for the determination of lead concentrations in whole blood. Blood standards from the Centers for Disease Control (CDC) and the National Institute of Standards and Technology (NIST) were diluted 21:1 with ultrapure water and analyzed. Good agreement was found between the CDC and NIST standards. A linear analytical curve was obtained with a detection limit (3σ) of 8.9 × 10 −3 μ g dl −1 (890 fg absolute) for lead in whole blood. This compares favorably with other current methods for blood-lead determinations including isotope dilution inductively coupled mass spectrometry (ID-ICP-MS) and graphite furnace atomic absorption spectrometry (GFAAS).

Analytical and spectroscopic characterization of double-resonance laser-induced fluorescence of gold atoms in a graphite furnace and in a flame

Two excimer laser-pumped dye lasers were utilized to excite gold atoms in a graphite furnace to a high level whose energy is about 1.5 eV lower than the ionization potential of the atom. Collisional coupling populates several levels close to that reached by the second laser step, from which fluorescence is observed longitudinally with a pierced, plane mirror and detected with a solar blind photomultiplier. The lasers are tuned to 267.595 and 406.508 nm, respectively, while the fluorescence is measured around 200 nm. Several other excitation–detection schemes are possible and are discussed. The best detection limit obtained, for a signal-to-noise ratio of 3, was 3 fg as absolute amount in the furnace, or 0.15 pg ml–1, since a sampling volume of 20 µl was used. A system in which the vapour produced in the furnace is swept into a small flame and the resulting fluorescence observed with the solar blind photomultiplier was also tested and found to be flame background noise limited, with a detection limit of 8 pg (0.4 ng ml–1). The technique was developed in order to determine trace levels of gold in size-segregated, atmospheric particulate samples.