Hollow Cathode Discharge Tube Research Articles

Investigation of the Zeeman—hyperfine structure of atomic niobium

Laser spectroscopy was used for the investigation of the Zeeman-hf structure of 22 lines of atomic niobium in the visible region between 573.7 and 649.4 nm. We used two methods of laser absorption spectroscopy: laser induced fluorescence (LIF) method and optogalvanic spectroscopy (OG). The source of niobium atoms was a hollow cathode discharge tube. The magnetic field of approximately 800 G was generated by a permanent neodymium magnet. We determined experimentally for the first time the Lande gJ factors for 10 levels. We also verified earlier experimental data on the hf structure as well as data from the NIST database regarding Lande gJ factors.

Landé gJ - factors of Nb I levels determined by laser spectroscopy

Laser spectroscopy methods were used in the investigation of the Zeeman-hyperfine structure of 14 lines of atomic niobium in the visible region 585.279–637.481 nm. We used the laser induced fluorescence (LIF) method and for higher lying states the fluorescence depletion spectroscopy (FDS). The magnetic field of approximately 800G was generated by a permanent neodymium magnet. The source of niobium atoms was a hollow cathode discharge tube. We determined experimentally for the first time the Lande gJ-factor values for six levels. We also verified earlier experimental data on the hf structure as well as the experimental data from the NIST database regarding Lande gJ-factors. For four levels we have obtained more accurate results.

Laser spectroscopy used in the investigation of the Zeeman - hyperfine structure of vanadium

Laser spectroscopy methods were used in investigations of the Zeeman - hf structure of 17 lines of atomic vanadium in the visible green - red region 568.3 - 648.1 nm. We used two methods of laser spectroscopy: the laser induced fluorescence (LIF) and fluorescence depletion spectroscopy (FDS). A hollow cathode discharge tube was the source of vanadium atoms. Zeeman structure measurements were carried out using a permanent neodymium magnet generating a field of approximately 800 G. We determined A hfs constants for 7 levels and values of the Lande gJ factors for 10 levels. We also verified the previously determined gJ factors for 12 levels and 18 hfs constants.

Observation of even-parity autoionization states of uranium by three-colour photoionization optogalvanic spectroscopy in U–Ne hollow cathode discharges

Three-colour three-step photoionization spectroscopy of uranium has been performed in a U–Ne hollow cathode discharge tube by temporally resolving three-colour photoionization optogalvanic (PIOG) signal from the normal optogalvanic (OG) signal using three tunable pulsed dye lasers. U–Ne hollow cathode discharge tube has been used as a source of uranium atomic vapours and photoionization detector. Using this technique, photoionization spectra of uranium have been investigated systematically in the energy region 52,150–52,590cm−1, through three different excitation pathways, originating from its ground state, 0cm−1(5Lo6). By analysing the three-colour photoionization spectra sixty new even-parity autoionization resonances of uranium have been identified and their probable total angular momentum (J) values have been assigned according to the J-momentum selection rule. The J-value of five autoionization resonances, which have been observed either through all three excitation pathways or through two different excitation pathways where J-value of the second excited levels differs by two, has been assigned uniquely.

Atomic-hydrogen Balmer line's abnormal broadening of argon and hydrogen plasma in hollow cathode

In the study of new energy resource, hydrogen energy has become a green energy the same as solar energy and wind energy. Under the action of certain catalytic materials (such as Ar+), the hydrogen atom of fractional hydrogen plasma can transit from the ground state to the fractional principal quantum number energy levels lower than the ground level, meanwhile the energy is largely released. By the study of the law of Balmer line's abnormal broadening of atomic hydrogen in argon and hydrogen plasma, the possibility of hydrogen plasma reaction with such a large amount of releasing energy is discussed. The research is in two aspects: by using hollow cathode discharge tube, the existence of fast hydrogen is confirmed and the relationship between the abnormal broadening and the ratio of argon to hydrogen is found to be consistent with the feature of catalytic reaction; by the comparative approach and experiments of strengthening reaction of fractional hydrogen plasma, we have obtained the broader Balmer line's abnormal broadening (the half height broadening reaches 0.245 nm).

Doppler-free frequency-modulation spectroscopy of atomic erbium in a hollow-cathode discharge cell

The erbium atomic system is a promising candidate for an atomic Bose-Einstein condensate of atoms with a non-vanishing orbital angular momentum ($L \neq 0$) of the electronic ground state. In this paper we report on the frequency stabilization of a blue external cavity diode laser system on the 400.91 $nm$ laser cooling transition of atomic erbium. Doppler-free saturation spectroscopy is applied within a hollow cathode discharge tube to the corresponding electronic transition of several of the erbium isotopes. Using the technique of frequency modulation spectroscopy, a zero-crossing error signal is produced to lock the diode laser frequency on the atomic erbium resonance. The latter is taken as a reference laser to which a second main laser system, used for laser cooling of atomic erbium, is frequency stabilized.

Changes in the Optogalvanic Signal Amplitude in a Hollow Cathode Discharge

The spatial distribution of the optogalvanic (OG) signal in argon at the 801.489 nm (<TEX>$1s_5-2p_8$</TEX> transition at the metastable level in Paschen notation) was investigated in the radial direction of a hollow cathode discharge tube. The results of this experiment showed that the OG signal amplitude decreases in accordance with the following two conditions; first, the level of discharge current and second, the distance from the cathode dark space. These results can be quantified by analyzing the electron density profile along the discharge regions, which can directly influence the collisional ionization induced by electron impact.

Measurement of electron density in atmospheric pressure small-scale plasmas using CO2-laser heterodyne interferometry

CO2-laser heterodyne interferometry was applied to measure electron density ne in three different types of high pressure (including atmospheric pressure) small-scale plasma sources: a short hollow cathode (HC) discharge tube, a pulsed dc plasma jet and a micro-HC plasma jet. The interfering contribution of the gas density reduction due to Joule heating of the measured phase shift was separated from the electron component based on these different temporal dependences. The typical values of ne measured in the short HC discharge tube with helium gas were on the order of 1013 cm−3 at a discharge current that varied from 25 to 225 mA and the pressure from a few tens to hundreds of Torr; the values measured in argon gas were further increased by a factor of five to six. For the dc He plasma jet ejected into open air, the radial profile of ne on the order of 1014 cm−3 presented a hollowed distribution based on the tubular cathode structure. The micro-HC structure allowed us to evaluate ne in both the parallel and the perpendicular directions with respect to the plasma jet axis, and the derived values of ne from both directions were consistent. Thus, we verified that this diagnostic technique can be applied to measure ne in various sub-millimeter scale plasmas operated at atmospheric pressure in pulsed operation modes with a sensitivity of about 1013 cm−3 (at an optical length of 1 mm) and a spatial resolution better than 100 µm.

Two-color photoionization spectroscopy of uranium in a U–Ne hollow cathode discharge tube

A U–Ne hollow cathode discharge tube is used as a source of uranium atomic vapors as well as a photoelectron/photoion detector for carrying out two-color three-photon photoionization spectroscopy of uranium. Using the uranium excitation transition 0 cm−1 (5L60) → 16 900.38 cm−1 (7M7) at 591.5-nm laser wavelength as a first step transition and scanning the wavelength of a second laser from 558 to 568 nm, high-lying odd-parity atomic levels of uranium are studied in the energy region 34 500–34 813 cm−1. All the expected 21 odd-parity atomic levels identified by various researchers in this region are observed in a single spectrum, demonstrating the high sensitivity achieved therein. In addition to this, we have identified eight autoionization resonances of uranium starting from its odd-parity atomic level at 33 801.06 cm−1 pumped by two-photon excitation. Four out of these eight autoionization resonances are observed for the first time.

The Optogalvanic Line Shapes of Neon Transitions in a Hollow Cathode Discharge Tube

The optogalvanic line shapes are observed in a commercial hollow cathode discharge tube containing neon buffer gas. Anomalous optogalvanic line shape is particular for transition originating from the 3P 2 (1S 5 in Paschen notation) metastable level of neon. The anomalous line shape is interpreted as being due to two competing atomic processes, which are the collisional ionization and the depletion of metastable atoms. When the competition is almost comparable at discharge current of 15 mA, the differences in the polarity and the magnitude of the optogalvanic signal of the transition result in the anomalous line shape.

Au-II 282 nm segmented hollow-cathode laser-parametric studies and modeling

Laser operation on the Au-II 282.3 nm ultraviolet transition is obtained using a high-voltage segmented hollow-cathode discharge tube. The metal vapor is produced by means of cathode sputtering. A small amount of argon is added to the helium buffer gas in order to achieve higher sputtering yield. Measurements of the laser power and small signal gain indicate that the optimal partial concentration of argon is in the range of 0.25%–0.75%. Quasi-continuous wave output power of 100 mW is obtained from a 34-cm-long active region while the highest small-signal gain is 52% m−1. To explain the basic features of the laser operation we present a model of the segmented hollow-cathode discharge. All the discharge characteristics are calculated in a self-consistent way except the temperature of slow electrons. The trajectories of fast electrons emitted from the cathode are followed by Monte Carlo simulation. Rate equations of ion, metastable and metal atom densities are solved in the negative glow, while another Monte Carlo code is applied for the fast heavy particles in the cathode sheath. The spatial distribution of the gas temperature and the thermalization of sputtered metal atoms are calculated as well. The laser characteristics predicted by the model are in reasonable agreement with the experimental results.

Optogalvanic effect sign change of the 667.8 nm He line in a hollow cathode discharge plasma

The optogalvanic signals (OGS) at the 667.8 nm He line are investigated with low power diode lasers in a longitudinal hollow cathode discharge tube in pure He and in a He:Ne=1:1 gas mixture. A simple model for explaining the dependence of the OGS signal amplitude and sign on pressure is applied. The values obtained for the pressure where the OGS sign changes in pure He are in good agreement with the model calculations. A qualitative explanation of the zero point dependence on current is made. An explanation of the decrease of the OGS in a He:Ne=1:1 mixture discharge is proposed.

Linewidth studies on Cd+ 636.0 nm and 537.8 nm lines excited in a He-Cd hollow cathode discharge

Hollow cathode (HC) lasers usually operate in a single axial mode without any optical selection. This is attributed to the large homogeneous linewidth of the gain curve due to the relatively high filling pressure of these lasers. Collisional and Doppler broadening (ΔνC and ΔνD) of the Cd+ 636 nm and Cd+ 538 nm lines (laser transitions of the HeCd+ laser) excited in a HC discharge tube were determined using a Fabry–Perot interferometer technique. It was found that in the pressure range 7–25 mbar ΔνD was nearly constant, while, as expected, ΔνC increased linearly with pressure. The broadening constants were α(636 nm)= (47±2) MHz/mbarand α(538 nm)=(11.8±0.5) MHz/mbar. The first constant is large enough to explain single-mode operation of the red HeCd+ laser; but in the case of the green laser, the exact reason for the single-mode operation remained unclear.

The Comet-Tail (A2Πi–X2Σ+) System of 12C16O+: A Reinvestigation

The emission spectrum of the comet-tail (A2Πi–X2Σ+) system of 12C16O+ produced in the cathode glow of a hollow-cathode discharge tube and photographed in the spectral region 3345–8500 Å at high resolution was reinvestigated. Detailed rotational analysis of 10 bands involving 5 vibrational levels v = 0 to 4 of each of the A and X states was carried out. Spin-splitting of the rotational levels was observed for the analyzed bands. The observed intensity distribution of the branches is found to be in good agreement with theoretical calculations. Molecular constants for both the A and X states were obtained from a global fit of the present data of the A–X system and the infrared and microwave data available from the literature for v = 0, 1, 2, 3, and 4 of state X, using effective Hamiltonian for the A2Π state and matrix elements for both A and X states. The present work suggests that the A2Πi state changes from Hund's case (a) at low J values to Hund's case (b) at high J values.

Fourier transform emission spectroscopy of the second negative (A2Piu - X2Pig) system of the O+2 ion

The second negative (A2Πu- X2Πg) system of the O2 + ion was produced in a tungsten hollow cathode discharge tube using oxygen in neon. This spectrum was recorded with the McMath-Pierce Fourier transform spectrometer of the National Solar Observatory. A total of ten bands with ν″ = 0 and 1 and ν′ = 6 to 12 in the range 15 945-30 218 cm-1 were observed and rotationally analysed. The line positions of all these bands, along with those of a few additional bands available in the literature, were combined in a global least-squares fit. Many molecular parameters for the various vibrational levels and the equilibrium molecular constants for the X and A states were estimated. RKR potential energy curves were constructed and Franck-Condon factors were calculated for the vibrational bands of the second negative (A-X) system. Some additional information obtained from threshold photoelectron spectroscopy was used to extend the X2Πg potential curve up to ν = 24.

A Method for Effective Population Transfer in U Vapor with Doppler Effect and Collision

We proposed a method for effective population transfer in an atomic vapor with Doppler effect and collision. Using this method, we have demonstrated that an efficient population transfer occurs in 238U vapor produced in a hollow-cathode discharge tube. A numerical calculation with density matrix agrees well with our experimental result and indicates that the method can be used to raise the efficiency of atomic vapor isotope separation.

The Gamma (A2Σ+–X2Πr) System of the Nitric Oxide Isotopomers

The gamma (A2Σ+–X2Πr) system of the nitric oxide isotopomers14N16O,15N16O,14N18O, and15N18O, excited in the anode glow of a two-column hollow-cathode discharge tube, was recorded in the spectral region 2140–2730 Å under medium resolution. The gamma system of15N18O and several bands of14N18O of this system in emission are reported here for the first time. The rotational structure of the 0–1, 0–2, and 0–3 bands of15N18O of this system was also recorded under high resolution. The wavenumber data of these three electronic bands and those of the infrared vibration–rotation absorption bands 1–0, 2–0, and 3–0 of theX2Πrstate of15N18O available from the literature were together used in a global fit, using an effective Hamiltonian method for the2Π state, and molecular constants were derived for theAandXstates. These include the following (in units of cm−1) for stateAof15N18O:T0= 44130.244(2),B0= 1.812980(7), andD0= 4.694(6) × 10−6. The present work suggests that theX2Πrstate changes from Hund's case (a) at lowerJto case (b) at higherJ. From the measured bandhead data the vibrational constants of theXandAstates of14N16O,15N16O, and14N18O were also determined.

The Fourth Positive ( A1Π- X1Σ +) System of 12C 18O and 13C 18O: Perturbations in the A1Π State

The fourth positive ( A 1Π- X 1Σ +) system of the carbon monoxideisotopomers 12C 18O and 13C 18O excited in the anode column of a hollow-cathode discharge tube was recorded in the spectral region 1710-1935 Å on a 10.6-m vacuum grating spectrograph. Of the eight bands of the eight bands of 12C 18O observed with v′ = 0 to 2 and v″ = 2 to 6, and three bands of 13C 18O with v′ = 0 and 1 and v″ = 4 and 5, the rotational structure of five bands of the former and two bands of the latter was analyzed. Several perturbations were observed in the A 1Π state of both isotopomers. These include, for 12C 18O, strong perturbations on the order of 2 cm −1 in A, v = 1 caused by a′ 3Σ +, v = 10 and weak perturbations in A, v = 1 by D 1Δ, v = 1 and d 3Δ, v = 5, and in A, v = 2 by I 1Σ −, v = 3, e 3Σ −, v = 4, and d 3Δ, v = 7, and for 13C 18O, weak perturbations in A, v = 1 by a′ 3Σ +, v = 10 and d 3Δ, v = 5. The observed perturbations are in good agreement with those estimated by theoretical calculation. The deperturbed molecular constants were obtained for the A 1Π state of both isotopomers. Perturbation parameters and mixing coefficients which characterize each perturbation were also derived.

A high-voltage hollow-cathode Au-II 282-nm laser

Laser operation on the Au-II 282.3-nm line is obtained from a high-voltage, segmented hollow-cathode discharge tube with external mirrors. Measurements of the laser output power and the small-signal gain demonstrate that, for a given total discharge current, the optimum performance of the laser is obtained for a discharge length for which the linear current density is approximately 65 mA cm/sup -1/. The gain is approximately 2546 m/sup -1/ at this current density and increases with current density up to the highest value used (250 mA cm/sup -1/), at which the gain exceeds 50% m/sup -1/. The threshold current decreases monotonically, with decreasing length, the lowest observed value being 6.28 A for a length of 5 cm. A quasi-CW output power of 20 mW is obtained for a gain length of 20 cm and a discharge current of 3.2 A in a partially optimized tube with unoptimized output coupling. >

Studies of high-lying even-parity levels of Sm i: energies and isotope shifts

Absolute energies and isotope shifts of high-lying even-parity levels of Sm i have been measured by resonantly enhanced Doppler-free two-photon spectroscopy in a hollow-cathode discharge tube. The two-photon transitions in the experiment originate from the levels at 1489.55 cm−1 (7F3) and 2273.09 cm−1 (7F4) of the 4f66s2 configuration and terminate at the high-lying levels ranging from 35 779.26 to 37 054.07 cm−1. Through detection of the laser-induced fluorescence with a monochromator, the J values of these high-lying levels have been partially determined.