Studies of copper halide lasers

Abstract

Copper Halide lasers are discussed and the results of experiments reported. It is found that the presence of small quantities of an electron attaching gas (such as bromine) cause discharge instability. Specially designed electrodes which remove excess bromine cure this problem and yield a stable discharge. A 4W copper bromide laser is operated, sealed-off, for 100 hours. This laser has an apertured discharge tube with side-arm reservoirs to control copper bromide vapour pressure, a feature essential to stable operation. The addition of small amounts of hydrogen changes the beam from an annular to a gaussian-like profile. The estimated lifetime of this laser tube is 1,000 hours. Exploiting the theory of metallic walls for discharge confinement, it is found that metal segments shorter than about 1m can support a stable discharge at high pulse repetition rates (5 - 20kHz). On the basis of this, a novel copper halide laser containing cylindrical copper segments is demonstrated. Neon and halogen gases flow through the tube. The reaction between the halogen and the copper segment walls forms copper halide in-situ. Hydrogen bromide, bromine and chlorine have been used. Hydrogen bromide proves to be the most suitable. A one metre long laser tube of this design produces 40W. Pulsed power supplies for metal vapour lasers are discussed. The conventional form of the capacitor-transfer circuit has the peaking capacitor value around one half of the storage capacitor value. It is found that equal capacitor values produce the best results for the gold vapour laser system we describe. The reliability of a gold vapour laser is improved by replacing the hollow anode thyratron (which has a high latch rate) with a solid anode thyratron. The replacement thyratron, in combination with a saturating charging choke, significantly reduces the latch rate. The laser is used for studies of photodynamic therapy of cancer in a local hospital.