Zhijiang Wang

An improved pulse-line accelerator-driven, intense current-density, and high-brightness pseudospark electron beam

A high-voltage (200 kV), high current-density, low-emittance (23/spl pi//spl middot/mm mrd), high-brightness (8/spl times/10/sup 10/ A/(mrd)/sup 2/) electron beam was generated in a pseudospark chamber filled with 15 Pa nitrogen and driven by a modified pulse line accelerator. The beam ejected with /spl les/1-mm diameter, 2.2-kA beam current, 400-ns pulse length, and about 20 cm propagation distance. Exposure of 10 shots on the same film produced a hole of 1.6-mm diameter at 7 cm downstream of the anode, and showed its good reproducibility. After 60 shots, it was observed that almost no destructive damage traces were left on the surfaces of the various electrodes and insulators of the pseudospark discharge chamber. It was experimentally found that the quality of the pseudospark electron beam remains very high, even at high voltages (of several hundred kilovolts), similar to low voltages, and is much better than the quality of the cold-cathode electron beams.

Role of interface absorption in laser-induced local heating of optical coatings

Considering the interface absorption in optical coatings, we propose a model to simulate interface absorption. Calculations are made and the temperature field of several kinds of thin film multilayers, including those of partial reflectivity, high-reflectivity, and antireflectivity coatings are analyzed. The interface absorption is found to greatly influence the temperature distribution within multilayer coatings and to weaken the laser damage resistance of the samples. The real-time results of the photothermal deflection technique for laser induced damage to samples supports the model

Experiments of a Raman free electron laser with distributed feedback cavity

Abstract A design of a free electron laser with distributed feedback has been proposed. Experiments of a Raman free electron laser with a Bragg cavity have made progress in SIOFM. Results of producing 14 MW peak power at 7.7 mm wavelength with 4.4% extraction efficiency using a 400 keV/800 A electron beam of 60 ns duration are reported. The radiation spectrum is measured and a bandwidth narrower than typical superradiation indicated that there is an oscillation in our device.

A new beam source for free electron lasers

Abstract A high power, high current density and high voltage electron beam was generated with the pseudospark discharge (PS). This is a new approach to high brightness beam source for free electron lasers. The design and construction of the pseudospark discharge is described. The device has low cost and is easy to fabricate. The experimental results are presented, the configuration of the modified pulse line accelerator (PLA) is described. The intense electron beams with a voltage of 200 keV, a current of 2kA, a beam diameter of less than 1 mm, a beam pulse duration of 400 ns and beam emittance of 48 mm mrad were measured. The compact free electron laser with a table size is discussed.

Design of high-voltage and high-brightness pseudospark-produced electron beam source for a Raman free-electron laser

The design of a pseudospark chamber, a high-voltage (.100 kV), high-current density, low-emittance and high-brightness electron beam source which can provide high-quality beams for free-electron la- sers (FELs), driven by a modified pulse line accelerator, is presented. Based on the hollow cathode (HC) effect and the pseudospark (PS) empirical formula, the HC parameters, the cathode-anode separation, and the working gas pressure region are determined. The general ex- perimental setup of the high-brightness PS-produced electron beam source is shown.

The grazing incidence, ring resonator for a free-electron laser

Abstract The grazing incidence, ring resonator for a free-electron laser has been investigated. Using the telescope construction of a hyperboloid with large half-axis a = 312.5 mm and short half-axis b = 100.0 mm , a paraboloid with focal length f p = 3500 mm . grazing incidence angle θ = 83.5° , the cross section of the beam in cavity is expanded approximately by a factor of six. This ability of resonator film against laser damage reduces the laser fluence on the multilayer resonator mirrors. The effect of the beam expansion, the parameters of aspheric mirrors, the length of cavity and the spot size of grazing incidence on the optical quality of the system are discussed.

Effects of thin film production parameters on laser-induced damage in optical coatings

Laser induced damage in optical coatings is a complicated problem, which is attributed to a lot of factors, including environment parameters, laser parameters and thin film production parameters. Among the three factors, production parameters interest us most. We produce a series of samples with different roughness levels of the substrates, thin film material and vacuum environment within the chamber, etc. Using 1.06 micrometers Nd:YAG laser as our test laser, we make 1- on-1 laser damage test to these samples. Some interesting phenomena are found. We calculate the laser induced local heating within the thin film multilayers, and make analysis to the experimental phenomena. Conclusions are given.

A novel small-period wiggler and simulations of its free-electron laser

A small-period wiggler constructed of edgy-wound bifilar-helical conducting sheets with ferromagnetic cores, which is intended for free-electron lasers, is presented. The performance characteristics of the wiggler fields with a 100 mm period are measured. A field as high as 1500 G has been obtained. Free-electron lasers with this small-period wiggler have been investigated numerically with a three-dimensional nonlinear theory. Simulation results estimated that a radiation power of 20.2 MW and a frequency of 170 GHz with an efficiency of 5.1% can be obtained. It is feasible to make Raman free-electron lasers with this type of wiggler operating in the millimeter and submillimeter wavelength range with a relatively low electron energy ( >

A novel small‐period wiggler for free‐electron lasers

A novel small‐period wiggler constructed of edgy‐wound bifilar‐helical conducting sheets with ferromagnetic cores, intended for free‐electron lasers (FELs), is presented, and the performance characteristics of the wiggler prototype with 10‐mm period are measured. A field as high as 500–1000 G has been obtained. It is feasible to make a Raman FELs with this type of wiggler operating in the wavelength range of millimeters and submillimeters with a low electron energy (<500 keV) beam.

The Efficiency Improvement Of A Raman Free Electron Laser (FEL)

We have developed a first Raman FEL in China [1]. A recent experiment for improving the efficiency is reported. The wiggler length has been enlarged from 79 cm to 119 cm, the efficiency of 3.7% was obtained.