Segmented Hollow Cathode Discharge Research Articles

Self-induced optogalvanic effect in a segmented hollow-cathode discharge

Optogalvanic (OG) interaction is simulated and studied in a segmented hollow-cathode discharge (SHCD). HCD-lamps are used to induce an OG signal by their own emission or by that of another lamp. The efficiency of the OG of a Ne/Cu HCD lamp in the range 320-380 nm is estimated theoretically. An irregular galvanic peak arising near the inflection point in the i-V curve (∂V/∂i<0) is detected. Its origin is related to Penning ionization of the sputtered cathode material.

224 nm segmented hollow-cathode silver ion laser

The segmented hollow-cathode discharge arrangement is used the first time to excite the 224 nm Ag II laser transition. Quasi-continuous output power of 45 mW is obtained during the 300 μs current pulses at optimal discharge conditions (10 hPa of He+4% Ar buffer gas) for discharge current of 3 A. No power saturation is observed up to this current value. An average output power of 0.75 mW is reached using pulse repetition frequency of 190 Hz. The longitudinal mode structure of the TEM00 transversal mode is measured by means of a scanning confocal Fabry–Perot interferometer. Two-mode operation is found to be dominant at high current values. Attempts and suggestions are made to prolong the lifetime of the laser tube.

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.

Operation characteristics of the Au-II 690-nm laser transition in a segmented hollow-cathode discharge

Single-mode operation at the Au-II 690-nm transi- tion was obtained in a segmented hollow-cathode discharge laser without the use of any additional frequency-selective device. The pressure of the helium buffer gas, which is re- sponsible for the significant homogeneous broadening of the laser line, was varied between 10 and 20 mbar. The discharge was excited with rectangular current pulses (up to 3A )s ix times exceeding the threshold value. The time dependence of the laser output during the 1-ms-long discharge pulses is ex- plained on the basis of the temperature and pressure changes in the tube. The highest small-signal gain at optimal discharge conditions was 11%m 1 .

High-gain ultraviolet Cu-II laser in a segmented hollow cathode discharge

We report measurements of the discharge and laser characteristics of an ultraviolet (UV) copper ion laser radiating on the 248.6- and 270.3-nm transitions. Our 50-cm active length laser operates in a high-voltage segmented hollow cathode discharge with Brewster windows and external mirrors. The lowest threshold currents were 7.3 and 5.6 A for the above transitions, respectively. The threshold current was found to increase with decreasing active length. We obtained superior gain characteristics (to 11.2 and 8.8%/m gain for the 248.6-and 270.3-nm transitions, respectively, at 0.3 A/cm linear current density) compared with previous studies on UV Cu ion lasers in conventional hollow cathode discharges.

Spectral-Interferometry Measurements of Copper Atom Concentration in a Segmented Hollow Cathode Discharge

Abstract We report spectral-interferometry measurements of the concentration and the spatial distribution of copper vapor in a high voltage, segmented hollow cathode discharge, which is an efficient source for laser light generation. The concentration of sputtered copper atoms was found to be in the order of 1014 cm-3 at currents of 0.6-1.0 A in a 5 cm long, 4 mm bore diameter discharge tube, operating in argon buffer gas. At high pressures and relatively low current densities the sputtered metal concentration forms two maxima near the cathode surface. With increasing current and decreasing pressure these two maxima move towards the center of the discharge. This result may account for the fact that at certain discharge parameters the segmented hollow cathode lasers operate in higher order transverse modes near the threshold. The measurements of copper vapor concentration show increased sputtering compared to conventional hollow cathodes, which is considered to be one of the reasons for segmented hollow cathode metal ion lasers being more efficient.

The spatial distribution of small signal gain in a segmented hollow cathode discharge laser

We present measurements of the spatial distribu- tion of the small signal gain in the cross section of a lon- gitudinally segmented hollow cathode discharge. This con- figuration proved to be the most efficient for pumping dif- ferent cathode sputtered metal ion laser transitions excited by thermal energy charge transfer reactions. We performed the measurements for the Cu-II 780: 8n mtransition for dif- ferent currents and buffer gas pressures. At higher pressures there are two peaks in the gain distribution nearer to the cath- ode surface. With increasing current the gain increases faster in the center of the discharge and the gap between the two separate peaks tends to disappear. At the optimum pressure (where the gain is the highest), the gain has a maximum in the center of the discharge. Our results are generally valid for the charge transfer excited cathode sputtered UV metal ion lasers as well. The measured gain values are proportional to the gain of possible continuous VUV laser transitions around 150- 160 nm, where the upper level is common with the upper level of the 780: 8n mtransition.

Monte Carlo analysis of the electrons' motion in a segmented hollow cathode discharge

We have investigated the motion of electrons in a new, high voltage segmented hollow cathode discharge, which is known to be an efficient pumping source for charge-transfer excited UV metal ion lasers. We have studied the spatial distribution of ion production, electron energy distributions, statistics of electron avalanches, the fraction of oscillating electrons, and the distribution of the fast electrons' current on the anode surface in a helium discharge having four electrode segments. We have found that the ion production is strongly peaked in the centre of the discharge due to the focusing cathode geometry. The effect of magnetic field on the characteristics of the discharge was also studied. With increasing magnetic field the peak of the spatial distribution of ionization was split into two regions of high ionization rate. Furthermore, due to the magnetic field, at fixed discharge current the number of high-energy electrons absorbed on the anode increased considerably, and a higher number of primary electrons were absorbed by the anode without making any ionization. At constant discharge voltage the fraction of oscillating electrons was found to decrease, due to the applied longitudinal magnetic field. The magnetic field dependence of the spatial distribution of ion production, the energy distribution of electrons absorbed by the anode and the fraction of oscillating electrons at different discharge conditions were also studied in a discharge having six electrode segments.

Simulation of the Electrons' Motion in a Segmented Hollow Cathode Discharge: Effects of Magnetic Field, Number of Electrode Segments and Cathode-Anode Surface Ratio

Simulation of the Electrons' Motion in a Segmented Hollow Cathode Discharge: Effects of Magnetic Field, Number of Electrode Segments and Cathode-Anode Surface Ratio

The segmented hollow cathode discharge: a pumping source for UV metal ion lasers

We have investigated the operation of a high-voltage segmented hollow cathode discharge which is an efficient pumping source for ultraviolet metal ion lasers. We present the photographically recorded visual appearance of the discharge and the spatial distribution of the ionization source obtained from Monte Carlo simulation of the electrons' motion. Both results show that the high voltage of the segmented hollow cathode discharge and the curved cathode surfaces result in a strong focusing of the fast electrons even at the relatively high operating pressure.

High-gain hollow-cathode metal ion lasers for the UV and VUV

The segmented hollow-cathode pumping discharge gives a higher gain on the He-Cu/sup +/ 781, He-Au/sup +/ 282, and Ne-Cu/sup +/ 270-nm lines at lower discharge current and input power than do the conventional hollow-cathode, hollow anode cathode and helical hollow-cathode discharges. The segmented hollow-cathode offers the prospect of compact low-cost repetitively pulsed UV laser for applications to biomedical and other spectroscopically-based instrumentation. The projections for increasing the gain on the He-Cu/sup +/ VUV lines indicate that laser action on one or more of these lines may be achieved. >

Dependence of gain and laser power for Cu-II 780.8-nm transition on the diameter of a segmented hollow cathode discharge

The dependence of laser performance and discharge characteristics on the diameter of a segmented hollow cathode discharge for the Cu-II 780.8 nm transition is presented. This transition has a special importance since its upper level is common to potential CW VUV laser transitions (150-170 nm). Laser tubes with internal diameters of 2, 3, 4, and 5 mm were investigated. Decreasing the diameter resulted in an increased gain for a given current (up to 100 %/m in the 2-mm diameter, 5-cm-long tube at 1-A current). The highest output power was obtained from the large-diameter tubes (20 mW from a 5-cm-long, 5-mm-diameter tube at 2-A current, without optimizing the output coupler). This work is a part of a series of investigations aimed at the optimization of the segmented hollow cathode discharge which has already been found to be the most efficient type of discharge for cathode sputtered metal ion lasers. >

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. >