Laser Optogalvanic Spectroscopy Research Articles

Laser optogalvanic spectroscopy of lead lines — Isotope shifts and hyperfine structure studies

Six atomic lines of Pb I in the 569–612 nm wavelength range and two lines of Pb II in the wavelength range of 560-608 nm were examined using optogalvanic spectroscopy. A hollow cathode discharge lamp was the source of Pb atoms and ions. Hyperfine structure constants were measured for levels associated with the observed transitions. The result of the research was also the determination of isotope shifts in the studied lines. The experimental data we have obtained complement or correct the existing database. We determined six values of the A constants of the hyperfine structure of Pb I, including one value determined for the first time and clarified one value of the A constant for Pb II. We determined seven new values of isotopic shifts between individual isotopes for two Pb I lines and one Pb II line. Furthermore, ab-initio MCDHF calculations of the observed isotope shifts and hyperfine structure constants were performed. Theoretical results are in good agreement with experimental data.

Optogalvanic spectroscopy of the Zeeman structure of argon energy levels close to the ionization limit

The Lande gJ factors for high lying states of the argon atom by laser optogalvanic spectroscopy were measured, in most cases with an uncertainty of less than 0.005. The Zeeman structure of 12 argon lines with wavelengths in the range 598.7-612.8 nm was investigated. We determined Lande gJ factors for 9 odd parity levels and verified the data for several other levels.

The Puzzle of the La I Lines 6520.644 Å and 6519.869 Å

The strong La line 6520.644 ? is present in a Fourier Transform Spectrum (signal to noise ratio of 240), but its wavelength in commonly used tables (e.g. [1]) is given as 6520.770 ?, while in [2] the wavelength is given as 6520.74 ?, unclassified, with the remark “h” (hazy). The line could not be classified using known energy levels of the La atom (La I) and its first ion (La II). It appears as a single broadened peak. By a combination of laser optogalvanic spectroscopy, laser-induced fluorescence and Doppler-reduced saturation spectroscopy we could introduce a new even parity La I energy level, 35449.041 cm -1, J = 13/2, with hyperfine (hf) constants A = ?8.0(5) MHz, B = 10(10) MHz. For a second, up to now unknown neighbouring La I line (wavelength 6519.869 ?) we introduced another even parity energy level involved in the formation of the line, 41207.994 cm -1, J = 13/2, A = 91.6(5) MHz, B = 170(50) MHz. We tried also to explain why in old tables the wavelength given was so different.

Hyperfine structure investigations of atomic niobium with optogalvanic and laser-induced fluorescence spectroscopy in the near-infrared wavelength range

Aims. The aim of this work is to increase the amount of hyperfine structure data of atomic niobium (Nb I), which is needed for astrophysicists for the detailed analysis of new stellar spectra. Particular emphasis was placed on the investigation of energy levels with unknown hyperfine structure constants. Methods. The hyperfine structure in the spectrum of Nb I was studied using laser-induced fluorescence spectroscopy and laser optogalvanic spectroscopy with a tuneable single-mode cw Ti:Sa laser in the wavelength range from 750 nm to 865 nm. The Nb atoms were produced and excited in a liquid-nitrogen-cooled hollow-cathode plasma. Results. We measured and analysed 81 spectral lines, 19 of which are not previously known from the literature. In total, the magnetic dipole hyperfine structure constants A were determined for 28 energy levels of even and 53 energy levels of odd parity. The electric quadrupole hyperfine structure constants B were only determined in a few cases, when the spectra were clearly resolved and/or when a level was found from several transitions. The magnetic dipole hyperfine structure constants A of 13 even and 11 odd levels as well as the electric quadrupole hyperfine structure constants B of 13 even and 17 odd levels are presented for the first time. For the other levels, improved values of hyperfine structure constants are given. Conclusions. The hyperfine structure can have a significant effect on stellar absorption line profiles, and the corresponding abundances can be substantially overestimated if these effects are not taken into account. Therefore, a detailed consideration of the hyperfine structure is important for stellar abundance determinations. The present work substantially increases the knowledge of hyperfine structure of Nb, which plays an important role in investigating the nucleosynthesis of heavy elements.

Optogalvanic spectroscopy of the hyperfine structure of weak La I lines: discovery of new even parity fine structure levels

The hyperfine structure of weak La I lines was experimentally investigated using laser optogalvanic spectroscopy in a hollow cathode discharge lamp. More than 100 La I lines were investigated and 40 new energy levels were discovered, most of them having even parity. The magnetic hyperfine interaction constants A and in some cases the electric quadrupole interaction constants B for these levels were determined. All the newly discovered levels were confirmed either by additional laser excitations (from other known levels) or by lines in a Fourier transform spectrum which could now be classified.

Reference lines in the optogalvanic spectra of uranium and thorium in the wavelength range 422 to 462 nm

The spectra of uranium and thorium are convenient sources of reference lines for wavelength calibration at the level of a few parts in 108. We observed these spectra by laser optogalvanic spectroscopy in commercial hollow-cathode lamps using a single-frequency cw dye laser operating over the wavelength range 422 to 462 nm. Ten uranium and eight thorium lines were measured with an estimated uncertainty of 0.0003  cm−1 by using our Fabry–Perot wavemeter. The results are compared to previous measurements of these lines and are found to be in good agreement with, and 1 order of magnitude more accurate than, values determined by Fourier-transform spectroscopy.

Laser optogalvanic spectroscopy of neon at 659.9 nm in a discharge plasma and nonlinear least-squares fitting of associated waveforms

Laser optogalvanic spectroscopy of neon has been studied in the discharge environment of a hollow cathode discharge lamp. We illustrate the fitting of the time-resolved optogalvanic waveforms by focusing on the 1s 2–2p 2 transition of neon at 659.9 nm and employ a nonlinear least-squares Monte Carlo approach to determine the pertinent amplitude coefficients, decay rates and the instrumental time constant.

One- and two-photon laser optogalvanic spectroscopy of neon in the 570–626 nm region

Eleven two-photon transitions originating from the 2p 53s[3/2] 2, 2p 53s′[1/2] o, 2p 53s[3/2] 1, and 2p 53s′[1/2] 1 states to the 2p 54d configuration states have been investigated in the optogalvanic spectrum of neon in the visible region (570–626 nm) for the first time. The two-photon assignments are confirmed by evaluating the temporal evolution, power dependency, and line widths of the optogalvanic signals. The time evolution of the optogalvanic signals for the two-photon transition originating from the metastable 2p 53s[3/2] 2 state to the 2p 54d′[3/2] 2 state has also been studied at different discharge currents.

A study of Stark effects of Rydberg p states of noble gas atoms

We have studied the Stark effect for Rydberg p states of noble gas atoms using laser optogalvanic spectroscopy. The measurements were performed in the sheath region of noble gas glow discharges. Laser excitation from metastable states to np states was monitored by optogalvanic spectroscopy. Clear Stark shifts were observed and the experimental results were compared with a theoretical calculation based on solving the Schrödinger equation of noble gas atoms in an electric field. There was good agreement between the calculation results and the experimental results. The analysis shows that the Stark shift of np states of noble gas atoms can be used for electric field measurements. This method can be a useful alternative to electric field methods based on excitation to nf states because of the higher transition probability of np states.

Optogalvanic effect and measurement of gas temperature in an abnormal glow discharge

Axial distribution of the gas temperature in an abnormal glow discharge in argon is simultaneously determined by laser optogalvanic and absorption spectroscopy methods. Temperature distributions obtained by two different methods are in a fair agreement except in the boundary region between the cathode fall and the negative glow. Systematically lower temperature in this region obtained by optogalvanic spectroscopy is a consequence of the nature of optogalvanic effect, which, in some circumstances, cannot be identified with spectral line profile.

A comparative study of RF and dc discharge based laser optogalvanic spectroscopy of helium Rydberg states

We present a detailed optogalvanic spectroscopic study of the characteristics of the 1s2s 1S0 → 1snp 1P1 Rydberg series of atomic helium using three different discharge geometries, a RF discharge cell, a dc discharge cell and a commercial see-through hollow cathode lamp. In the dc discharge, the series termination of the 1snp 1P1 Rydberg series has been studied as a function of applied voltage at a constant gas pressure and as a function of gas pressure at a constant applied voltage. The electric field in the dc discharge has been determined from the series termination and the observed energy shift as a function of the radial distance from the electrode axis. A comparison of the electric field distribution in the three different discharges is presented based on the series termination, Stark shift, line broadening and relative intensities of the observed spectral lines.

Two-photon laser optogalvanic spectroscopy of the Rydberg states of mercury by RFdischarge

We present new experimental data on the highly excited levels in mercury using thelaser optogalvanic detection technique in conjunction with RF discharge. The6s np 3P0 (), 6s np 3P2 () and 6s nf 3F2 () Rydberg series have been observed via two-photon excitation from the6s6p 3P0 intermediate level, which is collisionally populated in the discharge. The6s nf 3F2 Rydberg seriesto such high n-values is reported for the first time. The first ionization potential of mercury is determined from the unperturbed6s nf 3F2 Rydbergseries as 84 184.15 ± 0.05 cm−1.

Analysis of collisional sheath structure in an argon DC discharge

The electric fields of the sheath region in an argon DC discharge were measured using a laser optogalvanic spectroscopy in a pressure range from 0.88 to 10 torr, where collisions are significant in the sheath region. The sheath width is estimated as the position where the electric field becomes zero, and the pressure dependence of the measured sheath width was obtained to be (pressure)/sup -1/3/. The measured electric fields agree well with two-dimensional simulation results but are slightly different from collisional sheath theory in the mobility limited region. The discrepancy of the theory from the experiment and simulation results was found to be caused by the change of ion current density due to ion collisions in the sheath region.

Study of Even-Parity Autoionization States of Samarium Atom by Laser Optogalvanic Spectroscopy

Two-color two-step laser resonance ionization spectroscopy (RIS) was used to study autoionization states of neutral samarium atom (Sm I). Optogalvanic signals were detected from a Sm hollow cathode lamp which was used as an atomic source. Several metastable states of the ground state term were populated from the heated hollow cathode. The six intermediate states which had mutually different total angular momentum ( J ) values from 1 to 6 were excited using the first step dye laser from the ground state ( J =0) and three metastable states having J values of 3, 4 and 5. These six excitation channels were used to study systematically the autoionization states having the probable J values from 0 to 7. The 359 even-parity autoionization states were found and their J values were estimated. The 357 states among the 359 autoionization states were newly found in this experiment.

Time- and space-resolved electric potentials in a parallel-plate radio-frequency plasma

A low-input capacitance emissive probe heated by a CO2 laser has been used to investigate frequency-modulated electric potentials in a radio-frequency (rf) glow discharge plasma. An excellent time-response ability of our probe system to a sharp potential change was confirmed by potential measurements with applying a step function voltage to the plasma. The electric field distribution as the first derivative of the potential distribution obtained by the probe method was compared with that by the laser optogalvanic spectroscopy to ensure the reliability of the measurements in the sheath region. The probe method was applied to directly monitor a temporal variation of axial potential and electric field distributions between two parallel-plate electrodes in a rf argon plasma. The formation of ion sheath regions on both electrode surfaces was confirmed at any phase in a rf cycle. The results were consistent with a one-dimensional model for potential and electric field distributions in the sheath region.

Method to measure the electric field vector in an argon glow discharge using laser polarization spectroscopy.

A method for measurement of the direction of the electric field in a glow discharge is reported. This method uses the dependence of the electronic excitation spectrum of argon atoms on the polarization of the laser radiation. In this research, laser radiation was used to excite argon atoms in a plasma from the 4s [3 / 2](2) metastable level to Rydberg levels, and excitation spectra were measured using laser optogalvanic (LOG) spectroscopy. In addition, LOG spectra of argon atoms interacting with an electric field were calculated by solving the Schrödinger equation. Good agreement was found between experimental and theoretical LOG spectra obtained for different polarizations of the laser radiation.

Laser optogalvanic and jet spectroscopy of germylene (GeH2): New spectroscopic data for an important semiconductor growth intermediate

The à 1B1–X̃ 1A1 electronic transition of germylene has been reinvestigated. A room temperature absorption spectrum of the central portion of the 000 band of GeH2 has been obtained using the technique of laser optogalvanic spectroscopy. A rotationally resolved spectrum of the 000 band of jet-cooled GeD2 has been recorded with a pulsed discharge source. Analysis of these spectra has yielded ground and excited state rotational constants for the GeH274, GeH272, GeH270, GeD276, GeD274, GeD272, and GeD270 isotopomers and approximate equilibrium structures of: r″(Ge–H)=1.5883(9) Å, θ″(H–Ge–H)=91.22(4)°, r′(Ge–H)=1.5471(6) Å, and θ′(H–Ge–H)=123.44(2)°. The ground state ν1 and ν2 vibrational frequencies have been determined from wavelength-resolved fluorescence spectra of jet-cooled GeH2 and GeD2. There is good evidence that GeH2 rotational levels with Ka′>1 are so strongly predissociated that lifetime broadening makes them diffuse, severely restricting the information that can be obtained from absorption and laser-induced fluorescence experiments.

Measurement method for electric fields based on stark spectroscopy of argon atoms

We report the development of a method for the measurement of electric fields in glow discharge plasmas, based on Stark spectroscopy of argon atoms. The method is based on laser excitation of transitions in atomic argon. The key feature of the method is that the electric field is determined by matching experimentally obtained absorption spectra to theoretically calculated spectra. The dependence of the positions of energy levels of argon atoms on the strength of the electric field was calculated by solving the Schrodinger equation for the argon atom. Measurements of Stark spectra were made in the sheath region of a glow discharge using laser optogalvanic spectroscopy. The wavelength of the laser radiation was tuned to the transitions 4s-->nf (n=7,8,ellipsis,14) of the argon atom. For n=11, the lower limit for electric field measurements was estimated to be 14 V/mm.

Laser assisted ratio analyser 13C-urea breath testing, for the detection of H. pylori: A prospective diagnostic European multicentre study.

Novel technology based on laser optogalvanic spectroscopy called the LARA (Laser Assisted Ratio Analyser) system was developed to measure 12C/13C ratios in breath samples using stable 13C isotopes, to detect Helicobacter pylori infection. To determine the sensitivity and specificity of the 13C-LARA-urea breath test in the detection of H. pylori infection in a prospective European multicentre trial; FDA-and EMEA-approved. Consecutive dyspeptic patients underwent diagnostic gastroscopy with biopsies for culture and histopathology, to detect H. pylori infection (gold standard). Subsequently, the LARA-urea breath test was performed using either a system without a cold trap (part I) or a system with a cold trap (part II). In both instances baseline, 30-min and 60-min breath samples were collected. The optimum cut-off level for 12C/13C ratios was determined by Receiver Operator Characteristics analysis. In part I, 544 out of 604 patients were evaluable (low CO2: 47; withdrawn: 13). 284 out of 544 patients (52%) were H. pylori-positive according to the gold standard. The sensitivity of the LARA-urea breath test was 95% and the specificity 94%. In part II, 257 out of 272 were evaluable (low CO2: 14; withdrawn: 1). Sensitivity and specificity were 93% and 96%, respectively. The LARA-technology represents an accurate and non-invasive testing system for the detection of H. pylori infection. Its major advantages are the use of stable 13C isotope, the high throughput of samples and the easy means of collecting, storing and transporting the samples, thus making the system convenient to both patient and clinician.

Laser optogalvanic spectroscopic studies of xenon

We report new data on the bound odd-parity Rydberg series of xenon using single-colour two-photon laser optogalvanic spectroscopy. These series are excited from the metastable level. A total of eight odd-parity , , , , , , and Rydberg series are observed with an accuracy of . The , and series for high-n values are reported for the first time. We have also observed an even-parity (two-photon parity-forbidden) Rydberg series excited from the metastable level by focusing the laser in the region (10 mm away from the cathode) of discharge where the electric field is stronger. The multichannel quantum defect theory analysis for the odd-parity bound levels of J = 0, 2 and 3 has been performed. Besides these two-photon Rydberg series we also report a number of single-photon transitions. Some of them can be grouped into Rydberg series .