Anomalous behavior of optogalvanic signal in a miniature neon discharge lamp

A strong optogalvanic effect has been observed in a negative glow of a miniature neon discharge lamp using tunable pulse dye laser pumped by a copper vapor laser. A comparative study on temporal evolution of optogalvanic signal in a positive and negative dynamic resistance region of the discharge is described. Dye laser beam was tuned to various neon transitions 1s_i → 2p_j (Paschen notations) within 570-617 nm wavelength range. Anomalous behavior of optogalvanic signal was observed at 588.2 nm for (1s₅ → 2p₂) neon transition at low discharge current (<220 μA). This anomalous behavior is the attributes of damped oscillations of optogalvanic signal that correlate with negative dynamic resistance (dV/di < 0) of the discharge. Penning ionization at low discharge current and small energy mismatch is assumed to be the main cause of the negative dynamic resistance. Penning ionization process has been explained by resonantly ionizing energy transfer via collisions between neon buffer gas atoms in the lowest metastable state (1s₅) and electrode sputtered atoms in ground state using their partial energy level diagram.     

Intermodulated optogalvanic Zeeman spectroscopy in a hollow cathode discharge

The Zeeman and hyperfine structures of various transitions of calcium, copper, and neon are investigated by means of Doppler-free optogalvanic spectroscopy. This work demonstrates the suitability of the hollow cathode discharge to high resolution Zeeman spectroscopy of refractory and reactive elements.     

CW laser oscillation in a hollow cathode He-Kr discharge

CW laser oscillation on the 4694 Å transition of Kr II has been observed in a hollow cathode He-Kr discharge.     

Modification of spectral characteristics and optogalvanic response in neon hollow cathode under laser excitation

The changes in emission characteristics of a neon hollow cathode discharge by resonant laser excitation of 1s ₅→2p ₂ and 1s ₅→2p ₄ transition have been studied by simultaneously monitoring the optogalvanic effect and the laser induced fluorescence. It has been observed that resonant excitation causes substantial variation in the relative intensities of lines in the emission spectrum of neon discharge.     

CW laser oscillation in a hollow cathode HeAr discharge

CW laser oscillation was observed at the 4765 Å transition of Ar II in a hollow cathode HeAr discharge.     

CW aluminum ion laser in a high voltage hollow cathode discharge

Laser oscillation on transitions of Al II was investigated in a large diameter hollow cathode discharge where Al vapour was produced by cathode sputtering. The special internal anode system used considerably increased the tube voltage and resulted low threshold currents.     

Systematic trends in optogalvanic signals of some transitions in a uranium hollow cathode discharge

A study of optogalvanic (OG) signals in a uranium hollow cathode discharge using a tunable pulsed dye laser with intensities above saturation revealed certain systematic trends. The peaks of OG signals, for a given hollow cathode current, due to all transitions involving the ground state are within a certain range of values. The same is true of the OG signals due to transitions involving the 620 cm^-1 and 3800 cm^-1 lower metastable levels. For all transitions involving the same lower state, the peaks of OG signal vary linearly with the discharge current. The slopes of such straight lines are different for transitions involving different lower levels of uranium. Effects of radiation trapping are seen in the OG signals due to transitions involving the ground state of uranium at currents above 60 mA. Details of our observations are presented and discussed.     

Temperature of neutral copper and neon atoms in a hollow cathode laser discharge

From measurements with a Fabry-Perot interferometer it was found that neon and copper neutrals in the active part of a hollow cathode charge transfer laser discharge have kinetic temperatures of 1000 K and 2100 K, respectively.     

Spatial variation of the linewidth of Kr atomic lines as observed on optogalvanic signals in cathode fall region of hollow cathode discharge

An abrupt change in the spectral width of optogalvanic (OG) signals of Kr atomic lines has been observed at a distance from the cathode wall where the signal itself changes its sign, by using a hollow cathode lamp whose cathode has its both ends open. The width is broader near the cathode wall with its magnitude varying by discharge current while the narrower width which is obtained on passing the laser beam in the central region of cathode cylinder is independent of the current. It is suggested that a well-defined region, where the particles of larger cross section of collisions with Kr atom are confined, is present in front of the cathode wall.     

Sound-velocity measurements in gases by laser-induced electrostrictive gratings

Laser-induced electrostrictive gratings have been applied to measure the adiabatic sound velocity in various gases on a single-pulse basis. The gratings are generated by the interference of two parallel polarized, crossed excitation beams arising from a pulsed Nd: YAG laser at 532.1 nm, and are detected by diffracting a probe beam originating from a cw Ar⁺ laser operating single-line at 514.5 nm. Measurements were performed in the overlap volume of unfocused and focused excitation beams. Using unfocused beams, the sound velocities in various gases at pressures of 5 bar were measured with a statistical error for single-pulse measurements of about 0.3%. With focused beams, the accuracy of the measurements is reduced because of the propagation of the sound waves out of the smaller overlap volume of 0.2 mm diameter and 4 mm length. Measurements with focused beams were performed in air and CO₂, with an error of about 1%.     

CW laser oscillation at 8096 Å in Cu II in a hollow cathode discharge

CW laser oscillation at 8096 Å in a He-Cu hollow cathode discharge is reported. Lower thresholds have also been observed for nine previously reported transitions.     

Preparation and antibacterial effect of plasma sprayed wollastonite coatings loading silver

In this work, the plasma sprayed wollastonite coating was soaked in 5 wt% AgNO₃ solution at room temperature to load silver for improving its antibacterial effect. The surface characteristics of the silver-loaded coating were investigated by SEM, EDS and XRD. The release rate of silver from the coating was measured by ICP-OES in deionized water. The osteotoxicity of the silver-loaded coating was evaluated by in vitro cell culturing test. The antibacterial activity against Staphylococcus aureus was examined by Zone of Inhibition test. The results showed that the loaded silver reacted with the wollastonite coating to form silver silicate, which ensured a sustained release of silver in deionized water for as long as 50 days. The antibacterial activity and cell culturing tests confirmed that the silver released from silver-loaded wollastonite coating had strong inhibition against the growth of S. aureus, while they did not exhibit any adverse effects on the osteoblasts proliferation.     

Laser action in an indium hollow cathode discharge

Hollow cathode discharge excitation of indium is shown to produce laser action at 468.1, 689.2, 1342.8, and 1720nm. The cw468.1 nm and 1720 nm ionic lines are excited by charge exchange effect whereas the 689.2 nm cw ionic line is excited by a radiative cascade. The 1342.8 nm atomic line appears in the afterglow of the pulsed discharge and its population inversion is produced by recombination of the indium ions and the electrons. Shanghai Institute of Optics and Fine-Mechanics, Academia Sinica. Research Fellow 1979–1980 of the Alexander-von-Humboldt-Stiftung     

Exact electrostatic solitons in a magnetoplasma with degenerate electrons

Fully nonlinear planar ion-acoustic solitary waves (IASWs) moving obliquely to an external magnetic field are studied in a collisionless magnetoplasma with degenerate electrons. The features of the nonlinear IASWs are investigated through the derivation of an energy balance-like equation involving the Sagdeev-type potential as well as the nonlinear dispersion relation.     

CW laser oscillation observed on visible and near-infrared PbII-transitions in a hollow cathode discharge tube

For the first time CW laser oscillation of the 537.2 nm and 1.32 μm transitions of PbII has been obtained in a hollow cathode discharge tube in which the lead vapor density was created by discharge sputtering of the lead cathode. In addition two new PbII laser transitions at 666.0 nm and at 839.6 nm were observed, operating CW and quasi-CW, respectively.     

Relative densities of hydrogen ion species in a hollow cathode glow discharge

Highly resolved Doppler shifted peaks of the hydrogen Balmer lines, resulting from charge exchange of H⁺, H₂⁺, and H₃⁺ with an H₂ gas target, were obtained without the need for a deconvolution procedure. This enabled the unambiguous determination of the chemistry of these hydrogen species in the units of mTorr pressure range. This was obtained from a gaseous discharge using a biconical hollow cathode that yielded a well collimated and monoenergetic beam.     

Laser action in a gallium hollow cathode discharge

cw laser action was observed for the 6335 and 7199 Å transitions of Ga II in a hollow cathode discharge. Charge exchange and radiative cascade processes are suggested to be responsible for the population of the upper laser levels.     

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 (⁵L ₆ ⁰ ) → 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.     

Atomic nitrogen laser action in a hollow cathode discharge

Near-infrared laser action of nitrogen atoms was obtained in a hollow cathode discharge. Four laser lines at wavelengths of 1358.2, 939.3, 938.7, and 862.9 nm were observed in the cw mode. In addition, the laser line at 904.6 nm was observed in quasi-cw operation in the afterglow for the first time. It is supposed that resonant charge exchange between He⁺ and N₂ followed by predissociation of N ₂ ⁺ is an important way of populating the upper laser levels.     

X-ray emission in the ‘water window’ from a nitrogen gas puff target irradiated with a nanosecond Nd:glass laser pulse

Received: 20 April 1998/Revised version: 19 June 1998