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. >

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

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. >

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

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.

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

In a steady-state low-pressure hollow cathode arc (HCA) stabilized by a longitudinal magnetic field, the spatial distribution of the argon plasma parameters are investigated. Densities, temperatures, velocities, and fluctuations of electrons, ions, and neutrals are measured by various local methods such as Thomson and Rayleigh scattering and laser-induced fluorescence (LIF). The experimental results are supported by a theoretical treatment of the plasma using a two-fluid model which gives a good description of the dynamics of HCA's.

Diagnostics of a Steady-State Low-Pressure Hollow Cathode Arc in Argon

Longitudinal sputtering hollow cathode discharge (HCD) used as active medium for lasing is studied by means of numerical modelling. Due to the longitudinal non-uniformities of the discharge, the laser operation could be strongly affected. The non-uniformity of the discharge is mainly influenced by the dimensions of the hollow cathode, in particular by the aspect ratio length/radius. To study the geometrical features, a simulation model for HCDs has been constructed using the Plasimo modelling platform. The model allows in-depth studies of the plasma mechanisms and enables finding the optimum under the working conditions of the HCDs. The model is validated by comparing the results with the experimental observations. The spatial distribution of the plasma density and potential as well as an in-depth discussion of the results and the trends revealed by the model are presented. The proper understanding of the essential geometrical features allowed defining the optimal aspect ratio length/diameter for stable and uniform discharge with high excitation efficiency.

Geometrical features in longitudinal sputtering hollow cathode discharges for laser applications

Operating characteristics of silver, gold and copper vapor hollow-cathode lasers are presented. Dependence of the output power, gain and threshold current on the cathode length, composition of the buffer gas, and mirror transmission is described. Studies of multicomponent hollow cathodes which produce laser lines of several elements simultaneously are also presented.

K. Jain

Papers

Operating characteristics of UV and IR hollow-cathode silver, gold and copper ion lasers