Showing papers on "Flattop published in 2000"

Design and performance of a refractive optical system that converts a Gaussian to a flattop beam.

Abstract: A system of two aspheric lenses is described, which efficiently converts a collimated Gaussian beam to a flattop beam. Departing from earlier designs, both aspheric surfaces were convex, simplifying their fabrication; the output beam was designed with a continuous roll-off, allowing control of the far-field diffraction pattern; and diffraction from the entrance and exit apertures was held to a negligible level. The design principles are discussed in detail, and the performance of the as-built optics is compared quantitatively with the theoretical design. Approximately 78% of the incident power is enclosed in a region with 5% rms power variation. The 8-mm-diameter beam propagates approximately 0.5 m without significant change in the intensity profile; when the beam is expanded to 32 mm in diameter, this range increases to several meters.

Spatial mode control of a diode-pumped Nd:YAG laser by use of an intracavity holographic phase plate.

Abstract: We present a new method of realizing phase plates by phase-volume holography on a photopolymer film. We implement such a component in a diode-pumped Nd:YAG oscillator to control the output spatial beam profile. Flattop super-Gaussian and square-shaped beams are obtained.

Experiments in laser cutting of thick steel sections using a 100-kW CO2 laser

Abstract: Cutting of thinner steels has been an active laser application for many years. As technology advances have enabled available laser output power to increase, the thicknesses of steels that can be cut at competitive feed rates has also increased. This paper will describe a series of laser cutting experiments performed on a 2” thick steel cross-section using a 100-kW CO2 flattop laser. The application driving these experiments was from the salvage industry and the objective was to meet or exceed the cutting rates of the currently used torches but with a cleaner process (i.e. fewer by-products). The paper will discuss the results of these successful experiments including laser parameters used, both with and without oxygen assist, and cutting rates achieved.Cutting of thinner steels has been an active laser application for many years. As technology advances have enabled available laser output power to increase, the thicknesses of steels that can be cut at competitive feed rates has also increased. This paper will describe a series of laser cutting experiments performed on a 2” thick steel cross-section using a 100-kW CO2 flattop laser. The application driving these experiments was from the salvage industry and the objective was to meet or exceed the cutting rates of the currently used torches but with a cleaner process (i.e. fewer by-products). The paper will discuss the results of these successful experiments including laser parameters used, both with and without oxygen assist, and cutting rates achieved.

Inductance calculations and measurements for the cern lhc injection pulse forming network

Abstract: The injection kicker systems for the two LHC beams will each consist of four travelling wave magnets, four pulse forming networks (PFNs), and two resonant charging power supplies (RCPS). Each system must produce a kick of 1.3 Tm with a flattop duration adjustable between 4.25 µs and 7.8 µs, and rise and fall times of less than 900 ns and 3 µs respectively. Ripple in the field flattop must be less than ±0.5%. To achieve this stringent requirement, the PFN inductances are made of a continuous straight and rigid coil with constant and high precision pitch. Frequency dependence of the inductance and resistance of the PFN coil, as well as the effect of distortion during winding, are main issues and have been assessed via electromagnetic simulations. Component selection for the PFN was made on the basis of these theoretical models. A prototype PFN was built at CERN, without trimming of any component values. A system including the PFN, thyratron switches, terminating resistors, and the prototype RCPS built at TRIUMF has been set up. The system has been extensively tested and performs to specification. This paper describes 2D and 3D electromagnetic simulations of the PFN coil and compares the predictions with measurements.

Hollow Beam Electron Gun for Electron Beam Reducing Image Projection System: Computer Simulation

Abstract: A new hollow beam electron gun with an annular emission area is described. A cathode image is focused at the contrast aperture of the projection lens system, and the mask is irradiated by a uniform intensity electron beam which is conjugate to a flattop region near the crossover. The emittance is 7.8 mm mrad for a beam energy of 100 keV. Brightness can be varied from 8×102 to 4.5×103 A/cm2sr by changing only the cathode temperature. The gun crossover, the flattop area and the cathode image axial positions can also be varied widely, without changing gun brightness and emittance, by changing the gun control anode potential. The emission current can be reduced by reducing the "ratio (emission area radial width/maximum emission area radius) of the cathode surface" without changing the emittance and with little brightness change. Using this simulated electron gun, the basic electron optics of an electron beam projection lithography system with a hollow beam is designed.

Design and Construction of the 3.2 Mev Cathode Assembly for Darht II

Abstract: A 3.2 MeV injector has been designed and built for the Darht II Project at Los Alamos Lab. The installation of the complete injector system is nearing completion at this time. The requirements for the injector are to produce a 3.2 MeV, 2000 ampere electron pulse with a flattop width of at least 2-microseconds and emittance of less than 0.15 p cm-rad normalized. A 16.5 cm diameter hot emitter cathode is used. This paper will describe the design and fabrication of major Cathode Assembly components and test performance of subsystems to date. Mechanical and thermal issues will be emphasized. More detailed discussion of the active alignment system used to maintain the stringent cathode alignment requirement.