ABSTRACT
The avalanche amplification of the laser-enhanced ionization signal of Cs atoms in a flame has been studied. Ionization of Cs atoms, enhanced by two-step excitation, was detected in hydrogen and propane flames. By employing the effect of avalanche amplification of electrons, high signal-to-noise ratio (approximately 10(4)) was obtained for a 100 ppt Cs solution. The extrapolated limit of detection was 30 fg/mL (ppq).
Subject(s)
Cesium/analysis , Flame Ionization/methods , Lasers , Flame Ionization/instrumentation , Microchemistry/instrumentation , Microchemistry/methodsABSTRACT
A cesium-based resonance fluorescence monochromator with a spectral resolution of 200 MHz and a tunable response over the D(2) absorption line of cesium (380 MHz) is described. The narrow spectral response is achieved through excitation of a monokinetic population of the 6(2)P(3/2)( degrees ) state by arrangement of the excitation lasers in either a copropagating or a counterpropagating orientation. The narrow spectral response of the detector allows for excitation of specific hyperfine components involved in the 6(2)P(3/2)( degrees ) (F=3-5) to 6(2)D(5/2) (F=2-6) transition (917.23 nm). The selectivity gained through resolving specific hyperfine transitions allows for a photon detector that is both spectrally tunable and narrow. We report the sub-Doppler linewidths achieved through various laser beam orientations. We also describe how these beam geometries can be applied to spectrally narrow and tunable image detection.
ABSTRACT
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.
ABSTRACT
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.
ABSTRACT
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.
ABSTRACT
A new method for laser-enhanced ionization detection of mercury atoms in an inert gas atmosphere is described. The method, which is based on the avalanche amplification of the signal resulting from the ionization from a selected Rydberg level reached by a three-step laser excitation of mercury vapor in a simple quartz cell, can be applied to the determination of this element in various matrices by the use of conventional cold atomization techniques. The overall (collisional + photo) ionization efficiency is investigated at different temperatures, and the avalanche amplification effect is reported for Ar and P-10 gases at atmospheric pressure. It is shown that the amplified signal is related to the number of charges produced in the laser-irradiated volume. Under amplifier noise-limited conditions, a detection limit of â¼15 Hg atoms/laser pulse in the interaction region is estimated.
ABSTRACT
An experimental set-up for the detection of elemental chlorine in chlorinated hydrocarbons (CHCs) is described based on a miniaturized system, which could be used for on-line monitoring of chlorinated compounds. With an optimized time-resolved detection chlorine from CHCs like CCl(4) can be determined by Laser-Induced-Breakdown-Spectroscopy (LIBS) with microg/g-detection limits in the gas phase. The application of a miniaturized Nd : YAG laser resulted only in a minor loss in performance, hence it could be used for designing a rugged and small on-line sensor. In addition, preliminary results for the detection of chlorine via the formation of CuCl in the plasma formed by focussing the laser on a copper surface are reported. Utilizing the luminescence of the CuCl D-system at 440 nm, a tenfold improvement in the detection limits was obtained. It appears that the formation of "ad hoc" selected, small molecules in a laser plasma could be a promising alternative for the selective and sensitive analysis of gaseous chlorinated and other species.
ABSTRACT
A method of measuring atomic-absorption factors by means of a photon detector based on stepwise atom photo-ionization is proposed for the first time. This method can be widely used in laser analytical spectroscopy.
ABSTRACT
Detection of single atoms Yb has been achieved using the method of electric-field ionization from the high-lying Rydberg states. Atoms of Yb in a beam were excited in three steps to a 17-p state by radiation of three pulsed dye lasers. The statistics of an atom's appearance in the interaction volume have been studied in the single-ion-counting regime at low beam density.
