P Camus

Two-Step Optogalvanic Spectroscopy of Neutral Barium: Observation and Interpretation of the Even Levels Above the 6s Ionization Limit Between 5.2 and 7 eV

Even parity levels of neutral barium above the 6s ionization limit have been investigated by using a two-step pulsed laser excitation with optogalvanic detection. From the metastable states, 5d6s, populated by a d.c. discharge in a heat-pipe vapour, we reach the 5dnl even Rydberg series with J values ranging from 0 to 5, the 6p2 1S0 state and the low-lying members (n = 7 and 8) of the 6pnp series above the 5d limits. The 5dnd configurations (18 levels for each n member) are observed from n = 8 up to n = 45 using optogalvanic spectra recorded from five intermediate 5d6p levels: 3P1,20, 3F3,40 and 1P10. These eighteen series are observed for the first time. Fine structure is resolved up to n = 25 and has been analyzed using Slater-Condon parametric calculations. In addition, the 5d3/2ns J = 1 and 5d5/2ns J = 3 series are observed up to n = 38 and 42 respectively, as well as sharp resonances interpreted as 5d3/2ng7/2 J = 2 and 5d5/2ng J = 1, 2 series up to n = 27 and n = 28 respectively. In conclusion, the energies of 636 new levels between 6s and 5d limits are given with their term and configuration identifications. Above the 5d5/2 limit, broad resonances observed from the 5d6p 1P10, 6s7p 1P10 and 3P0,1,20 intermediate levels have been identified with levels of the 6p7p and 6p8p configurations using parametric calculations based on the Slater-Condon theory.

Ultraviolet optogalvanic laser spectroscopy of iron for reference wavelengths

We present a preliminary study of a UV optogalvanic spectrum obtained by using a see-through iron hollow cathode and a tunable pulsed laser in the 240-260-nm range. The hollow cathode used and described is a homemade device that can be run in static- or dynamic-flow gas regimes. Spectra have been recorded with argon and neon buffer gases, and many classified Fe I lines have been identified. The accuracy of the measured wave numbers is limited at present to 0.05 cm(-1) by the spectral width of the UV laser. This iron optogalvanic spectrum is proposed for reference-wavelength calibration in UV laser spectroscopy, and an application to the study of Ba(+) Rydberg levels is reported. Possibilities for future developments of such a device are analyzed.

Highly excited levels of neutral ytterbium. I. Two-photon and two-step spectroscopy of even spectra

Highly excited even levels of ytterbium have been investigated using both a two-photon absorption, and a two-step process from the 6S2 1S0 ground state. Resonances are detected by the thermoionic-diode method. Most of the observations are between the J=O and J=2 even levels: the series 6sns1S0, and 6snd1D2 and 6snd 3D2 have been observed from n=10 to n=65, n=8 to n=80 and n=10 to n=61 respectively. Several levels of the 4f135d6s6p and 6p2 configurations have been identified. In the autoionising region lines showing a Fano profile have been observed and analysed. The authors observed many lines corresponding to absorption from the excited levels 6s6p 1P1 degrees , 5d6s3D2 and 5d6s3D3. Some J=2, 3 and 4 odd levels have been observed with this method.

Transient frequency shift in a single-mode quasi-continuous diode-pumped Nd:YAG laser

The transient frequency shift of a quasi-continuous single-mode frequency-doubled diode-pumped Nd:YAG ring laser has been measured using a confocal spherical Fabry-Perot. At a rate of 50 Hz, a quasi-linear shift of 5.4 MHz at the fundamental 1.06-/spl mu/m wavelength has been measured during the 150-/spl mu/s laser pulse duration. The doubled frequency, which is obtained by an intracavity LBO crystal, shows also a similar but doubled linear shift. This observed frequency shift is interpreted as due to thermal effects in the rod and fits well a modeling of the pulsed laser diode pumping. Introducing intracavity compensation, a piezoceramic transducer mounted cavity mirror, has limited the observed shift to less than /spl plusmn/1 MHz. Such a quasi-continuous Nd:YAG single-mode and frequency stabilized device should be a very suitable single-mode laser source to pump optical parametric oscillator systems.

Double-Rydberg spectroscopy of the barium atom

Methods of excitation and analysis of double-Rydberg states of the neutral barium atom are discussed. Spectra of 9dn′d double-Rydberg series of barium are studied and interpreted in a two-channel quantum-defect model. An example of stabilization for the 9d5/227d state is shown. We propose a new investigative method for Rydberg levels of the Ba+ ion that is based on a microwave-ionization process coupled with a double time-of-flight mass spectrometer. This novel setup permits us to obtain initial experimental evidence of highly excited double-Rydberg states, 26dn′p and 27sn′p (n′ ≳ 45), of the barium atom.

Multichannel Quantum Defect Analysis of the Autoionized Even-parity Spectrum of Neutral Barium below the 5d2D3/2 Limit

Extensive new data on the even-parity autoionized spectrum of Ba has been provided by two-step optogalvanic spectroscopy. The spectral range below the 5d3/2 ionization limit presents a complicated scheme of interacting levels, which is analyzed using the multichannel quantum defect theory (MQDT). The analysis concerns the 5d3/2nd and 5d3/2ns series converging on the 5d3/2 limit and their perturbers belonging to 5d5/2nd and 5d5/2ns series converging on the higher 5d5/2 limit. This is a favourable case for MQDT since the number of perturbing levels is very large: for each 5d5/2nl perturbing series, nine levels are located below the 5d3/2 limit. A J by J treatment of the energies of the spectra with J value ranging from 0 to 5 was carried out taking into account the 5dnd-5dns mixing. The analyses only concern the position of autoionized levels. In fact the 5dnl autoionized lines observed in this range are relatively narrow and we can neglect the coupling of 5dnl levels with 6sl continua. The MQDT treatments presented here allow us to improve the identification of levels and to describe accurately the behaviour of perturbed series. The lower 5dnl levels are bound, i.e. below the 6s limit and the MQDT treatment of their mixing with the 6snl principal Rydberg series has been previously published. The comparison of the MQDT parameters fitted to the bound or autoionized spectra confirms the large energy dependence of the parameters. This point is discussed and shows the difficulties of extrapolation procedures. For the first time the MQDT parameters are closely related to semi-empirical values of Slater integrals.

Observation and theoretical analysis of the odd J=3 autoionising spectrum of Sr up to the 4d threshold

The odd J=3 autoionising spectrum of Sr between the 5s and the 4d thresholds has been observed. In a Sr atomic beam, the ionised atoms produced by a two-step excitation scheme have been analysed via a time-of-flight spectrometer. A theoretical approach based on the R-matrix method combined with multichannel quantum defect theory calculations provided a good description of the position of the observed lines. Analysis of the observed profiles gave qualitatively good results although the intermediate 5p2 1D2 level is not perfectly described in the model.

High angular momentum 6pnl and 6dnl doubly excited Rydberg states of barium

6p32/nl (n=11 to 15, l=5 to n-1) and 6d52/nl (n=11 to 14, l=6 to n-1) doubly excited Rydberg states of barium have been studied using a multistep laser excitation technique. The excitation is via the bound 6s12/nl states which are populated using an electric-field switching method which allows the selective population of high-l angular momentum states. The resulting spectra clearly demonstrate the presence of dielectronic correlation. The authors show that this correlation is well described in terms of the (j-l)K coupling scheme, taking into account in a perturbative way the dipole and quadrupole interaction terms.

Laser-microwave ionisation mass spectroscopy of ion Rydberg states: Ba+ spectrum

The authors present a novel instrument for the analysis of highly excited Rydberg states of ions. This set-up is applied to study the ns and nd Rydberg levels of Ba+ produced in an atomic beam with values of n varying between 19 and 65. The selective excitation is provided by a two-UV-laser-photon process. The excited Ba+ ions are ionised by a microwave field and detected by a double time of flight mass spectrometer. A UV optogalvanic spectrum, resulting from an iron hollow-cathode discharge, is used as a reference for calibration. The accuracy of the energy level wavenumber determination is +or-0.1 cm-1. These measurements lead the authors to a revised value for the Ba II ionisation limit of 80 686.25+or-0.10 cm-1.

Two-photon absorption spectroscopy in ytterbium

Highly excited levels of ytterbium have been investigated using two-photon absorption spectroscopy and space-charge detection. The authors tuned the 0.2 cm-1 dye laser radiation over the range 3900-4100 AA and observed the even-parity states J=0 and J=2 belonging to the series 4f146s ns 1S0, 4f146s nd 1D2, 4f146s nd 3D2 from n=13-62, from n=11-64 and from n=11-21, respectively. Many strong perturbations appear due to configurations with a 4f13 core.