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.     

CO2 Laser Discharge Influenced by a Rotating Magnetic Field

This paper deals with experimental investigations of the effect of a rotating magnetic field on a diffusion cooled CO₂ laser discharge. Some properties relevant to laser activity are discussed, e.g. neutral gas temperature, magnetically driven gas rotation, pumping rate, and distribution of small signal gain within the discharge tube. By means of an intracavity method the radial distribution and the time behavior of the laser output power were measured.     

Investigations to the increase of the specific energy of a gasdynamic CO-laser

The input power density and hence the output power of electrically excited gasdynamic lasers is limited by instabilities of the glow discharge. The application of theoretical results, which have been obtained with respect of convection or flow lasers, to the discharge region of an electrically excited gasdynamic CO-laser shows, that especially thermal instabilities cause this glow collapse. An increased convection of local heat concentrations in front of the anode surface results in an improved stability behaviour. Input power densities of up to 100 W/cm³ are now accessible to operate the glow discharge and hence specific laser output powers of 57 kJ/kg are obtained.     

Investigation of Gas Degradation in CO2 ? N2 Pulse Discharges I. Long Term Behaviour of Pulsed Laser Discharges in CO2 — N2 Gas Mixtures

The correlation between the plasma resistance and the laser output parameters has been investigated in pulsed CO₂ — N₂ discharges. The strong increase of the discharge resistance during gas degradation can be explained on the basis of strong attaching gas components. In degraded mixtures a supression of discharge instabilities together with the restoration of the laser pulse energy is possible by increasing the reduced electric field E/N temporarily.     

The effect of an axial external magnetic field on the output power of a small-bore CuBr laser

In this work, the effect of an axial external moveable magnetic field on the output power of a CuBr laser with small-bore tube has been investigated. In all experiments, by applying an EMF along the tube axis, the laser output power has been decreased and by moving the EMF toward the cathode region, more substantial decrease of output power has been observed. The effect is more significant at a magnetic field intensity of 1100 G, Ne gas pressure of 35 Torr, frequency of 19 kHz and voltage of 3.8 kV, such that there was no laser emission when the EMF was placed around the cathode.     

Improvement of the performance of cw CO lasers by using externally ribbed wall cooled discharge tubes

 We describe a modified design of a continuous-flow cw CO laser with longitudinal electric discharge using an externally ribbed wall cooled discharge tube. The transverse ribbed discharge tube provides a more intense heat exchange of the CO-laser gas with the walls. With this configuration it was possible to obtain about 50% more output power from an all-line CO Δv=1 laser. For a CO-overtone Δv=2 laser we were able to improve both the output power and the number of lines as compared to a conventional smooth tube. Received: 23 April 1996     

Voltage current and power relation in an arc plasma in a variable axial magnetic field

The variation of voltage, current and output power in a mercury arc plasma has been investigated in an axial magnetic field (0–1350 G) for three values of discharge current namely 3, 4 and 5 A. The voltage increases and current decreases almost linearly and the output power also increases with increase of the magnetic field. The conductivity value in magnetic field has been calculated and an analytical expression presented to represent the variation of conductivity in the magnetic field. Utilizing this expression the variation of output power with magnetic field can be explained.     

Enhancement of soft X-ray emission from a pinch plasma using a rotating plasma for pre-ionization

An experimental study on the enhancement of soft X-ray emission from a pinch plasma has been carried out by using a rotating plasma for pre-ionization. The rotating plasma is produced by a pulsed J×B cross-field discharge between coaxial electrodes, and subjected to a pinch discharge. Under an optimized discharge condition, it has been observed that UV emission of 251.6 nm (Ar III) soft X-ray intensity increases with increasing applied axial magnetic field B. At 400 G, the X-ray intensity is enhanced by a factor of 3 compared to that without the rotating plasma. It is considered that this result is due to the improved characteristics of the pre-ionization rotating plasma, which influences the uniformity and stability of subsequent pinch plasma.     

High-power transverse flow CW CO2 laser for material processing applications

A transverse flow transversely excited (TFTE) CW CO₂ with a maximum output power about 15 kW has been developed. This is excited by pulser sustained DC discharge applied between a pair of multi-pins anodes and a common tubular cathode. Though the laser power in convective cooled CO₂ laser scales proportionally with the volumetric gas flow, it did not increase in this laser when the volumetric gas flow was increased by increasing the electrode separation keeping the flow velocity constant. The discharge voltage too remained almost unchanged with increase of the electrode separation. These observations are explained considering the electrical discharge being controlled by ionization instability. Laser materials processing applications often demand programming facilities for laser power modulation. A four-stage cascaded multilevel DC–DC converter-based high-frequency switch mode power supply has been developed to modulate the output power of the laser. Laser was operated up to 15 kW output power in four different modes viz. continuous wave mode, pulse periodic mode, single shot mode and processing velocity-dependent power mode with 1.2 kHz modulation bandwidth. We describe briefly the laser system, the SMPS, and the temporal behavior of laser beam.     

Laser capabilities of CuBr mixture excited by RF discharge

Our investigations demonstrated that utilizing copper bromide (CuBr) mixture as a source of Cu atoms in a RF-excited discharge can be a promising alternative to the Cu sputtered system, when the development of Cu ion gas laser is considered. Both spectroscopic and laser investigations showed that the threshold input power for lasing was reduced about 5 times using the CuBr-based system instead of the Cu-sputtered system. Pulsed and CW laser oscillation on Cu⁺ transitions in the near IR spectral region was obtained in RF-excited He-CuBr discharge operated at 13.56 MHz and 27.12 MHz. At input RF power of 800 W, a laser output power of 10 mW at the 780.8 nm Cu ion laser line was achieved. An increase of laser output power by a factor of two, as well as better Cu vapour axial distribution and better discharge stability, was attained when DC discharge was superimposed on the RF discharge. Laser gain on 11 UV Cu ion lines was observed in RF-excited Ne-CuBr discharge. basing on the obtained results, we consider the CuBr laser system excited by RF discharge capable of generating UV laser radiation at relatively low input power. Received 4 January 1999     

气体激光中的对流效应

介质流动对于气体激光功率输出的大幅度提高,起着决定性的作用。分析表明:表征连续波激光的饱和强度和光功率密度(或小信号增益系数)均随流速而非线性地增大,并趋向各自的极限值;饱和强度的增加量约不超过10倍;光功率密度的大幅度增加起因于激励能在气流中的累积。这些结论与常用理论关于饱和强度随流速线性且无限地增大,光功率密度增大起因于饱和强度增大的结论并不相同。本文关于饱和强度随气流渡越时间变化的定量结果与流动CO₂气体激光饱和强度的测试结果相符。 关键词：     

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.     

Optimization of the UV CuII laser

The cw output power of the uv CuII laser has been optimized with respect to the hollow cathode geometry, the discharge current, the fill gas pressure and the resonator mirror parameters. A maximum laser output power of 900 mW for multiline operation at 248.6, 259.1, 260.0, and 270.3 nm was achieved with 100 A discharge current, 260 V voltage and 16 mbar fillgas pressure, when a hollow cathode of 1.2 m length and 2×6 mm² cross section was employed. The single-pass pain gl has been estimated to 7%. A hollow cathode cross section of 1.5×4.5 mm² is suggested as an optimum geometry. In addition, some investigations on the mechanism of the laser power decay in Ne–Cu-discharges are presented.     

Cold-hollow-cathode arc discharge in crossed electric and magnetic fields

A crossed-field cold-hollow-cathode arc is stable at low working gas pressures of 10⁻²–10⁻¹ Pa, magnetic-field-and gas-dependent arcing voltages of 20–50 V, and discharge currents of 20–200 A. This is because electrons come from a cathode spot produced on the inner cathode surface by a discharge over the dielectric surface. The magnetic field influences the arcing voltage and discharge current most significantly. When the plasma conductivity in the cathode region decreases in the electric field direction, the magnetic field increases, causing the discharge current to decline and the discharge voltage to rise. The discharge is quenched when a critical magnetic field depending on the type of gas is reached. Because of the absence of heated elements, the hollow cathode remains efficient for long when an arc is initiated in both inert and chemically active gases.     

Design considerations and scaling laws for high power convective cooled CW CO2 lasers

Various criteria for designing high power convective cooled CO₂ lasers have been discussed. Considering the saturation intensity, optical damage threshold of the optical resonator components and the small-signal gain, the scaling laws for designing high power CW CO₂ lasers have been established. In transverse flow CO₂ lasers having discharge of square cross-section, the discharge lengthL and its widthW for a specific laser powerP (Watt) and gas flow velocityV (cm/s) can be given byL = 1.4 x 10⁴ p ^1/2 V ^-1 cms andW = 0.04P ^1/2 cms. The optimum transmitivity of the output coupler is found to be almost constant (about 60%), independent of the small signal gain and laser power. In fast axial flow CO₂ lasers the gas flow should be divided into several discharge tubes to maintain the flow velocity within sonic limit. The discharge length in this type of laser does not depend explicitly on the laser power, instead it depends on the input power density in the discharge and the gas flow velocity. Various considerations for ensuring better laser beam quality are also discussed.     

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 s 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. PACS 42.55.Lt; 42.60.Lh; 52.80.-s     

Simple single-frequency He-Ne laser

For a (0.5–0.6)m long He–Ne laser tube, single longitudinal mode 632.8 nm generation is obtained, using a higher gas-mixture pressure and application of an axial magnetic field. An efficient and very simple mode selection is obtained by gas-mixture pressure increase only. A multimode power to single-mode power conversion coefficientk=0.75 is obtained by increasing the tube pressure. A further increase tok=0.85 is possible with optimum magnetic field and gas pressure.     

Laser on nitrogen-electronegative gas mixtures, pumped by inductive energy storage generator: Experiment and theoretical model

The advantages of inductive energy storage (IES) generators for increasing the pulse energy, power, and duration for nitrogen laser pumped by self-sustained transverse discharge have been experimentally demonstrated. A theoretical model is developed and the operation of IES-pumped laser on nitrogen-electronegative gas mixtures is numerically simulated. It is shown experimentally and theoretically that, adding electronegative gases, one can control the pulse shape of lasing on the C³II _u -B³II _g transition in nitrogen. The increase in the electric field strength in the laser gap in N₂-NF₃ and N₂-SF₆ mixtures produced 337.1-nm laser pulses consisting of two spaced peaks and 40–50-ns pulses close to rectangular. The increase in the laser active volume to 6 l (discharge cross section to 6×10 cm²) in N₂–SF₆ mixtures made it possible to obtain the maximum output energy (Q=110 mJ) and UV power (P _las =6 MW). In N₂-NF₃ mixtures, the laser pulse duration was up to ∼100 ns with an energy up to Q=30 mJ.     

Optimization and Maximum Output Power of CW DCN Laser

A high power CW 195 m DCN laser has been developed for fusion plasma diagnostics. Optimization of various parameters (such as the rate of N₂:CD₄:He gas mixture, the gas pressure and the discharge current, the wall temperature and the output couple) for maximum output power at the DCN laser were performed and reported in this paper. Output power of about 220 mW on the 195 m line has been obtained with 3.4 m long and 54 mm inner diameter discharge-pumped wave-guide laser. A new mixture gas of N₂:CD₄:D₂ was used in producing a stable high-power discharge and preventing the deposition of brown polymer with lower wall temperature and discharge current.     

Der Einfluß axialer Magnetfelder auf den ArII-Hochleistungslaser

The influence of axial magnetic fields on ion-laser discharges of large diameter (tube radiusR=0.6 cm) has been investigated. At modest power levels (jR<50A/cm,j: current density) laser output could be increased by about a factor of 2. The optimum magnetic field was found to follow the relation: [Gcm]. At high power levels (jR>150 A/cm) axial magnetic fields cannot increase the laser output.