Laser Resonance Fluorescence Research Articles

Hyperfine magnetic anomaly in atomic spectra of rare-earth elements

The constants of the hyperfine splitting in the atomic optical spectra of the rare-earth elements - Nd, Eu, Gd and Lu - were measured. The method of laser resonance fluorescence in the parallel atomic beam was used. The values of the hyperfine magnetic anomaly were determined from the comparision of magnetic dipole constant ratios of the neighbouring odd Z or N isotopes for the different atomic levels. The connection of these values and the parameters of atomic and nuclear structure is discussed.

Production of heavy atomic clusters upon interaction of laser radiation with matter

The results of an investigation of the formation of Pb, Th, and U clusters over a broad range of numbers of atoms (from a few atoms to macroparticles) upon interaction of high-power pulsed laser radiation with matter are presented. Clusters of fissionable elements are studied for the first time. A setup for determining the yield of clusters and the number of atoms in them, which is based on the use of several different methods (laser resonance fluorescence, time-of-flight measurements, and counting the number of tracks of fission fragments from the cluster nuclei), is described. The dependence of the yield of clusters with various numbers of atoms on the conditions for their formation is discussed.

First collinear laser spectroscopy measurements of radioisotopes from an IGISOL ion source

The standard Doppler-free technique of collinear laser spectroscopy has been successfully applied to radioisotopes from the ion-guide isotope separator (IGISOL) at the University of Jyväskylä. The laser resonance fluorescence signals for the 140,142,144Ba radioisotopes show that the ion beam energy spread is less than 6 eV, allowing the laser technique to have both high resolution and a sensitivity comparable with the best obtained at conventional facilities.

Measurement of tropospheric OH by long‐path laser absorption at Fritz Peak Observatory, Colorado, during the OH Photochemistry Experiment, fall 1993

The determination of the concentration of hydroxyl (OH) in the Earth's troposphere is of fundamental importance to an understanding of the chemistry of the lower atmosphere. This paper describes the results from the laser long‐path spectroscopic OH experiment used in the Tropospheric OH Photochemistry Experiment (TOHPE) held at Fritz Peak, Colorado, in fall 1993. A primary goal of TOHPE was to compare the OH concentrations measured using a variety of different techniques: a long‐path spectroscopic instrument [Mount, 1992], an in situ ion‐assisted chemical conversion instrument (Eisele and Tanner, 1991, 1993), a laser resonance fluorescence instrument [Stevens et al., 1994), and a liquid scrubber instrument (X. Chen and K. Mopper, unpublished data,; 1996), all with sensitivities at or below 1×106 molecules cm−3. In addition to the OH measurements, a nearly complete suite of trace gas species that affect the OH concentration were measured simultaneously, using both in situ and/or long‐path techniques, to provide the information necessary to understand the OH variation and concentration differences observed. Measurements of OH, NO2, CH2O, SO2, H2O, and O3 were made using long‐path spectroscopic absorption of white light or laser light and OH, NO, NO2, NOy, O3, CO, SO2, CH2O, j(O3), j(NO2), RO2/HO2, HO2, H2O, SO2, PAN, PPN, HNO3, and aerosols (size and composition) and ozone and nitrogen dioxide j‐values were measured using in situ instruments. Meteorological parameters at each end of the long path and at the Idaho Hill in situ site were also measured. The comparison of the long‐path and in situ species from this set of complementary measurements provides an effective way of interpreting air masses over the long path with those at the in situ site; this is a critical issue since the long‐path spectroscopic OH determinations provide a nonchemical and well‐calibrated measurement of OH which must be compared in a meaningful manner with the in situ determinations. Over the period of the TOHPE experiment, OH concentrations were typically low during periods of clean and clear airflow, averaging about 4×106 molecules cm−3 at noon. In contrast, during the well‐defined pollution episodes which occurred during the campaign, OH concentrations rose as high as 15×106 molecules cm−3.

The nuclear magnetic moment of by atomic beam laser spectroscopy

The magnetic dipole moment has been deduced for the nuclear ground state of the self-conjugate nucleus from the hyperfine splitting of the atomic ground state. The hyperfine structure of the 308.2 nm transition was measured by laser resonance fluorescence of an atomic beam. The tunable ultraviolet light was generated by frequency doubling using a lithium iodate crystal within the cavity of a dye laser. The result of fits well with the systematics of neighbouring -subshell nuclei and its small difference from the pure Schmidt value is satisfactorily described by a shell-model calculation in the full 2s1d shell.

He(43P) sublevel quenching by electron collision

The quenching by electron collisions of the He(43P) sublevel has been studied by a laser resonance fluorescence method. The sublevel is optically pumped by a dye laser tuned to the transition 23S-43P, and the fluorescence from 43P itself and from the 43D state is observed and analysed. The measurement is performed at various times in the post discharge of a pulsed RF discharge, and it is correlated to the decay of the electron random flux. The latter is measured simultaneously by a time resolved Langmuir probe technique. Combination of the two results allows the measurement of the electron collision rate constants kel(43P)=(1.23+or-0.34)*10-4 cm3 s-1, for the total quenching of 43P, and kel(43P to 44D)=(1+or-0.24)*10-4 cm3 s-1. Such rate constants turn out to be constant, within the experimental accuracy, in the range 0.2-0.6 eV of electron average energy. A good agreement is obtained with theoretical calculations. The importance of electron collisions is also demonstrated by a qualitative analysis of the fluorescence from 53D, 41D states.

Applications Of Lasers To Magnetic Confinement Fusion Plasmas

In the drive toward achieving controlled thermonuclear fusion using magnetic confinement of high temperature plasmas, there is a critical need for detailed knowledge of essential plasma parameters such as electron density and temperature. Lasers have made significant contributions to the magnetic confinement fusion program by providing nonperturbing measurements of almost all desired parameters with high spatial and temporal resolution. A wide variety of lasers have been utilized with wavelengths covering the range from the vacuum ultraviolet (-1200 A) to millimeter regions of the spectrum. To illustrate the impact that lasers have made in plasma diagnostics, this paper reviews the selected techniques of laser interferometry, Thomson scattering, and laser resonance fluorescence, together with the relevant laser require-ments. The current state of the art is described, and future needs are projected. The successes already achieved will ensure an expanding role for lasers in the fusion energy program.

Optical isotope shifts of146Sm and151Sm

We have measured the optical isotope shifts of146Sm and151Sm by laser resonance fluorescence. From these measurements the changes in the mean square nuclear radii are: Δ〈r2〉 (A=144 to 146)=0.266(10) fm2, and Δ〈r2〉 (A=151 to 152)=0.262(10) fm2. These results, together with those of the stable isotopes, show that the average nuclear expansion of samarium can be accounted for by the liquid drop model with deformations.

Measurement of total decay rates of excited states in a deuterium plasma by laser-resonance fluorescence

In a deuterium plasma with an electron density of 2.8 × 10 13 cm -3 and an electron temperature of 1850 K, the n = 2 level is coupled to the n = 6 level by absorption of short-pulsed laser light. Due to inelastic and superelastic electron collisions, the enhanced n = 6 population density is distributed to its neighbouring levels, i.e., n = 5 and n = 7. The laser-resonance fluorescences of the Balmer lines D 5, D 6, and D 7 were measured with time resolution. The transient behaviour of the fluorescence is compared with numerical calculations, which are based on the rate equations for population densities of a system with 5 states. It is observed that the rate coefficients of Johnson cannot explain our experimental data. The coefficients of Vriens and Smeets compare favourably with the measurements within experimental errors.

The presence of NO 2 in premixed flames

Previous findings that a substantial proportion of the NO x in the gases withdrawn from a premixed CH 4 or H 2 flame by a suction probe may be present as NO 2 are confirmed. Strong evidence is provided, however, that this result is an artifact of the probe system and that the proportion of NO 2 actually present in the flame is quite small. The evidence is of two kinds: (1) A 50-reaction kinetic model of reactions of the flame radicals was used to calculate the concentrations of NO and NO 2 emerging from the probe. The results showed first, that the NO 2 /NO ratio calculated for the most rapid sampling procedure used experimentally is close to that measured but second, that the ratio is independent of the initial NO 2 /NO ratio assumed to be present in the flame. This indicates that the measured NO 2 concentration in the sample gas bears little relation to the NO 2 concentration in the flame. (2) A laser-resonance fluorescence technique was used to measure NO 2 in situ in the flame. The NO 2 was also measured simultaneously by the probe technique. The true concentration of NO 2 in the flame as indicated by fluorescence was considerably less than that recorded by the probe technique. It is concluded that the results of probe measurements as hitherto conducted do not reflect even approximately the true NO 2 /NO ratios in the flames; the true ratios are in fact much smaller than those indicated by the probe technique.

Measuring the velocity of individual atoms in real time

It is proposed that the thermal velocity of a single atom could be measured in real time using a laser time-of-flight velocimeter (LTV) operating on the principle of laser resonance fluorescence. Theoretical data are presented for several atomic species that have resonances within the range of available dye-laser systems. It is shown that measurements in the subsonic region are certainly feasible. The atoms could be either in vacuum or in a buffer gas, e.g., at atmospheric pressure. Measurements in the transonic and supersonic region also appear possible. One potential application is the measurement of flow speeds in wind tunnels, perhaps as high as Mach 45.

Local measurement of population densities and effective depolution rates by laser resonance fluorescence

An experimental method is described, which facilitates the determination of local population densities of the n = 2 state of hydrogen in an inhomogeneous plasma that is not in thermodynamic equilibrium. Moreover a measurement of effective electronic collision rates that give rise to a depopulation of the state n = 3 was possible.

Absolute measurement of very low sodium-vapor densities using laser resonance fluorescence*

By use of a cw dye laser, the resonance-fluorescence method is used to make absolute density measurements of sodium vapor from 102 atoms/cm3 at −28 °C to 1011 atoms/cm3 at 144 °C. The results are compared with other measurements at higher temperature by a thermodynamic analysis. A new vapor-pressure curve is derived, which is slightly different from previous curves based on the higher-temperature measurements. The application of laser resonance fluorescence to other species is also discussed. In particular, a scheme for detecting sodium-quark atoms, if they exist, with a sensitivity of nq/nB ~ 10−15, is proposed.