A cw uv copper hollow cathode laser in the 260 nm region

A cw uv copper hollow cathode laser is described, which could be operated for a longer time duration with an output power of 7 mW in the 260 nm region. A double-cathode configuration with a protection for the mirrors from metal-vapour deposition is presented. Characteristics of the laser output power, the spontaneous emission, and the ion densities in the negative glow were measured as depending on the discharge current, the neon gas pressure, and the size of the cathode slit. The observed saturation of the laser output power at high discharge current (1 A/cm²) and the optimum slot size are discussed.     

UV-CuII-laser with cylindrical hollow cathodes

The UV-performance of a CuII-laser with cylindrical hollow cathodes has been investigated. The output power was measured in dependence of the neon pressure and the discharge current. By disconnecting cathode segments from the power supply, the active discharge length could be varied and the threshold and saturation currents were determined in dependence of the length of the active medium. The lowest threshold current amounted to 7 A. The laser emission saturates at current densities of 0.4 A/cm².     

Simultaneous oscillation on UV and IR transitions of the copper ion laser

Simultaneous oscillation of UV (248–270 nm) and IR lines (773–785 nm) in the copper ion laser with helical hollow cathode has been observed using high reflectivity combination mirrors. The output power characteristics of these laser lines are measured as functions of the discharge current and fill-gas pressure. A total laser power of about 100 mW with equal UV and IR contributions was obtained.     

CW Cu II laser in a hollow anode-cathode discharge

CW laser operation on near infrared transitions of Cu II was investigated in a high voltage hollow cathode discharge tube of 19 cm active length. The high voltage was obtained by a special anode system placed inside the cathode. Threshold current for the strongest 7808 Å laser line was 0.4 A. At a discharge current of 2.4 A a multiline output power of 30 mW was obtained on six transitions between 7404 and 7896 Å.     

Beam parameters,mode structure and diffraction losses of slab lasers with unstable resonators

The properties of unstable resonators in on-axis and off-axis geometry were investigated both theoretically and experimentally. Diffraction loss, mode structure, beam quality and misalignment sensitivity were measured in single-shot operation with a gas-cooled Nd: YAG slab laser (4×12×100 mm³) and compared with theoretical results obtained by solving the Fresnel integral equation numerically. The excellent agreement allowed detailed resonator optimization. Furthermore, the resonator performance in high-power operation was investigated with two water-cooled Nd: YAG slab lasers (6×25×163 mm³ and 7×26×191 mm³) capable of 670 W of output power. Beam quality near the diffraction limit and a maximum output power of 475 W was achieved with an on-axis unstable resonator with variable-reflectivity mirror.     

Enhancement of laser power at 7588 Å in HeZn hollow cathode laser by the addition of xenon

The effects of inert gas additives on the laser output power in the HeZn hollow cathode laser are investigated. The increase of nearly 50% in the laser power at 7588 Å has been observed when a small amount of xenon was mixed into the HeZn hollow cathode discharge tube. The mechanisms of the enhancement of the 7588 Å laser output by the addition of xenon are discussed.     

Numerical modeling of a He-Kr coil hollow cathode laser

A theoretical study of a He-Kr laser (KrII, 469.4 nm line) pumped by a helical hollow cathode discharge is presented. A detailed kinetic model of plasmachemical reactions and radiative processes including the influence of gas heating on the active medium is developed. In the process of numerical calculations the dependence of the plasma parameters (electron and gas temperature, electron and metastable density, upper and lower laser level density) and laser characteristics (output power and gain coefficient) on the variations of discharge pumping, gas-mixture partial pressures and geometry of the coil hollow cathode, are investigated. The results of the numerical calculations are in a good agreement with the experimental data.     

Side-wall emitting ZnSe/AlN waveguide CO2 laser

A side-wall emitting ZnSe/AlN waveguide CO₂ laser, which is able to extract the output power from the waveguide wall, is proposed. In the proposed scheme, four polished AlN plates are cemented to form a 16 cm long waveguide with 1.9×1.9 mm² cross section. One of the AlN plates is partially replaced by the ZnSe plate. This part is used as an output window. To confirm the workability of the proposed scheme, a trial laser was constructed and tested. The output power of several milliwatts was observed from the ZnSe waveguide wall.     

High efficient continuous wave operation of diode-double-passing-pumped Tm:YAP laser

A high efficient continuous wave diode-pumped Tm:YAP laser at room temperature was presented in this paper. Tm:YAP crystal with doped concentration of 4 at % was c-cut and had a cross section of 3 × 3 mm² and length of 5 mm. Using double-passing-pumped cavity structure, under the pump power was 25.5 W, the highest output power reached 8.5 W by use of 10% output coupling, corresponding to optical conversion efficiency was 33.3% and the slope efficiency was 44.5%. The laser wavelength was 1936 nm with FWHM of 4 nm.     

CW HCN laser gain in a hollow dielectric rectangular cross-section discharge tube

This paper describes a 1 m-long CW HCN discharge laser with a hollow dielectric rectangular discharge tube of 5×20 cm² cross-section. For optimum working conditions, the characteristics of the amplifying medium have been made constant over the cross-section, by using an additional magnetic field. Then, the unsaturated gain for the 337 μm line is 6.8% m⁻¹. It is shown to be dependent on the smaller dimension of the cross-section rather than on the other dimension. By using the tube as a waveguide, laser output power of 1 Watt might be obtained with a discharge length of 4 m, instead of the 12m-long discharge required to get the same output power from a cylindrical waveguide laser.     

Plasma cathode TEA Ar laser development

The plasma cathode design concept is applied to an Ar laser for the first time. The sliding discharge is used as a plasma cathode for the main laser discharge. The laser operates at atmospheric pressure with a gas mixture of Ar/He/SF₆. Results concerning the dependence of the laser performance on the gas mixture flow rates and charging voltage are presented. The temporal behavior of the laser output is also presented. Output energies as high as 2 mJ, efficiency and specific energy extraction values up to 1.3×10⁻²% and 0.02 J/l respectively, at atmospheric pressure, are obtained. The spectroscopic examination of the output shows that lasing at 1.79 and 1.27 μm is obtained with approximately equal line intensities.     

Hollow cathode fall field strength measured by Doppler-free two-photon optogalvanic spectroscopy via Stark splitting of the 2S level of hydrogen

It has recently been demonstrated that Doppler-free two-photon optogalvanic spectroscopy is very well suited to measure the strong electric field strength (0.4 kV/cm to 4 kV/cm) present in the cathode fall of hollow cathode discharges, via the Stark splitting of the 2S level of atomic hydrogen and its isotopes. Based on an improved reliability and precision of the measurements, the aim of the present study is to analyze more deeply the dependence of the cathode fall behaviour for a hydrogen discharge on the usual discharge parameters like gas pressure and discharge current; and for changes of the discharge geometry using two different cathode diameters of 10 mm and 15 mm.     

Some Investigations of the Ignition and Development of Breakdown in Cylindrical Hollow Cathode Glow Discharges

The breakdown behaviour of a hollow cathode glow discharge is investigated in a cylindrical, hollow cathode structure having an internal diameter of 2 cm. The anode is a plane electrode across one end of the cathode cylinder. Pressures of argon between 20 and 107 Pa were used (0.15 to 0.80 torr), and applied voltages between 800 and 2500 V. It is shown that the statistical time lag for breakdown is in the range of ～ 1 ms and depends on the applied voltage, the gas pressure, and the history of operation of the discharge tube. The rise time of the discharge current ranges from about 10 ns at high pressure and voltage to about 200 ns at the lowest pressure and voltage used. The discharge propagates along the cathode axis at a speed of about 10⁸ cm s^?1. From the obtained data, a qualitative model of the first stage of the discharge is derived. Based on this model, a simple calculation gives values of Townsend modified first coefficient η at high values of E/N, 10⁴ < E/N < 8 · 10⁴ Td which fit well at the lowest E/N, where they approach the data of PENNING and KRUITHOF in argon. In contrast to the extremely short initial current-rise times, in the submicrosecond range, the discharge currents reach steady-state values only after about 300 μs.     

Experimental Study with LaB6 Cathode on DCN Laser

A new LaB₆ cathode has been developed on DCN laser in this experiment. The LaB₆ cathode is expected with long-life time at high current discharge. Optimization of various parameters for maximum output power with the LaB₆ cathode at the DCN laser were performed and reported in this paper.     

Improvement of the efficiency of a glow discharge-based ion emitter with oscillating electrons

Ion emission from the plasma of a low-pressure (≈5×10⁻² Pa) glow discharge with electrons oscillating in a weak (≈1 mT) magnetic field is studied in relation to the cold hollow cathode geometry. A hollow conic cathode used in the electrode system of a cylindrical inverted magnetron not only improves the extraction of plasma ions to ≈20% of the discharge current but also provides the near-uniform spatial distribution of the ion emission current density. The reason is the specific oscillations of electrons accelerated in the cathode sheath. They drift in the azimuth direction along a closed orbit and simultaneously move along the magnetic field toward the emitting surface of the plasma. A plasma emitter with a current density of ≈1 mA/cm² over an area of ≈100 cm² designed for an ion source with an operating voltage of several tens of kilovolts is described.     

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.     

High power continuous wave Tm:YAP laser dual-end-pumped by laser diode at 795 nm

A high power continuous wave diode-pumped Tm:YAP laser at room temperature was presented in this paper. The Tm:YAP crystal with doped concentration of 3 at % for the experiment was c-cut with dimensions of 3 × 3 × 8 mm³. A 795 nm continuous wave laser diode in dual-end-pumped geometry was used to generate 1.94 μm laser output. At the pump power of 38.9 W, the highest output power reached 12.3 W by use of 15% output coupling, corresponding to optical conversion efficiency was 31.6% and the slope efficiency was 38.2%.     

On the excitation mechanism of the He-Ar hollow cathode laser

Investigations were carried out on the Ar-II 476.5 nm laser to obtain information on possible excitation mechanisms. The He-Ar hollow cathode discharge was excited by square wave current pulses. From the results of measurements it could be concluded that collisions of the second kind between He 2³ S metastable atoms and ground state Ar ions are dominant in the excitation of the upper laser level. This is also supported by results obtained in the case of the He-Kr hollow cathode laser, where the upper level of the Kr-II 469.4 nm laser is excited by a similar collision process.     

Analysis of a hollow-cathode reflex discharge in a hydrocarbon flow

Variation of parameters of a reflex discharge with a hollow cathode operating continuously in propane with a flow rate of 1.3–5.6 (m³ mPa)/s and a discharge current of 0.1–0.4 A is analyzed. It is shown that for a hydrocarbon flow rate of 2.4 (m³ mPa)/s and higher, an increase in the discharge voltage takes place after a time interval depending on the discharge current and gas pressure; this is explained by the formation of coating of the dissociation products of hydrocarbon molecules on the electrodes of the discharge chamber. An increase in the thickness of the carbon coating of the cathodes with time and their charging with ions lead to electric breakdown of coatings and the formation of cathode spots. The oscillograms of the discharge current and voltage indicate a short-term transformation of the glow discharge into the arc discharge. The energy spectra of ions emerging from the discharge are measured, and the effect of the discharge current and the gas flow rate on the energy spread of ions is analyzed. The operation time of the discharge in hydrocarbon after which the cleaning of the discharge chamber is required is determined. The possibility of using an ion source based on the reflex discharge with a hollow cathode for technological purposes is established.     

Use of a Glow Discharge in a Magnetic Field for Production of Broad Ion Beams for Technological Applications

The results of investigations of the conditions of existence and ion-emission properties of a plasma of the high-current variety of a low-pressure glow discharge with a hollow cathode in a magnetic field are given. It has been shown that an applied weak magnetic field (10^–3 T) not only reduces the minimum threshold gas pressure, but also makes the radial distribution of the plasma density more uniform (10%). A decrease in statistical straggling of the delay time to breakdown (10² times) and in discharge formative time (10 times) with increasing pulse repetition rate has been revealed to occur as a result of the transition to multielectron discharge initiation. The mass constitution of the discharge and the charge state of ions have been investigated and ways of lowering the content of the basic types of impurities have been determined. The influence of the parameters of the space charge cathode layer on the beam formation by electrostatic ion optics was investigated. The design of a source of gas ions possessing an increased lifetime and high reliability is described. The source is capable of producing an ion beam of cross section 100 cm² with an energy of ions of up to 40 keV at an average current density of up to 1 mA/cm².