Motohisa Abe

Development of high-power dye laser chain

Copper vapor laser (CVL) pumped dye laser (DL) system, both in a master oscillator power amplifier (MOPA) configuration, has been developed for Atomic Vapor Isotope Separation program in Japan. Dye laser output power of about 500 W has been proved in long-term operations over 200 hours. High power fiber optic delivery system is utilized in order to efficiently transport kilowatt level CVL beams to the DL MOPA. Single model CVL pumped DL oscillator has been developed and worked for 200 hours within +/- 0.1 pm wavelength stability. Phase modulator for spreading spectrum to the linewidth of hyperfine structure has been developed and demonstrated.

Development of high-power copper vapor laser system

A high power copper vapor laser (CVL) system in master oscillator power amplifier configuration has been developed for laser isotope separation program in Japan. Maximum output power of 650 W has been successfully achieved with 9- cm diameter and 350 cm discharge length amplifier. Also MOPA output power of 2.4 kW has been demonstrated in small master oscillator with 4 cm bore and 4 stage power amplifier with 9 cm bore configuration. The authors developed a thermal calculation code to maintain an optimum copper vapor density throughout a large volume and a new thermal insulation structure design method has been proposed to combine two different heat insulators to make longitudinal temperature distribution of the laser tube as flat as possible. A CVL discharge circuit has been improved by applying an excellent magnetic switch which prove a approximately 90 kV-4000 A pulse to a CVL at 4.4 kHz repetition rate. This paper reports such CVL design methods together with the performance of the designed high power CVL system.

Modelling and Simulation of Electron Impingement Pressure.

Pressure due to impingement of high-energy electrons onto the metal surface is considered to have the influence of deforming the molten metal surface, especially in cases where an electron beam is employed as an energy driver to evaporate molten metal. Here, a modelling of such electron impingiment pressure was proposed in terms of relativistic collision theory. By Monte Carlo simulation, electron impingement pressure, which was calculated as momentum transfer of high-energy electrons, was compared with vapor pressure, another factor that mainly influences deformation of the molten metal surface. According to the calculated results, although electron impingement pressure is smaller than vapor pressure in general cases, surface concavity induced by electron impingement pressure in addition to vapor pressure might develop and penetrate into the molten metal when the electron beam is focused and current density is increased to some degree.