The kinetic effects of HBr partial pressure and gas-flow rate in Cu HyBriD lasers

Abstract

In Cu 'HyBrID' lasers (also referred to as Cu-Ne-HBr lasers), the lasant Cu atoms are generated in situ as byproducts of discharge and surface reactions involving solid Cu pieces placed in the tube bore and a controlled amount of HBr gas additive. Though the principal role of the HBr additive is to generate free Cu, the HBr additive also has important positive effects on the plasma kinetics. Cu HyBrlD lasers have yielded several fold increases in laser efficiency (>3%), high beam quality output power (>100W) and optimal operating pulse rate (>17 kHz) compared to conventional copper vapour lasers. These enhancements are primarily attributed to the acceleration of charge neutralisation during the interpulse period via the large HBr cross-section for dissociative electron attachment. We have investigated the effects of HBr partial pressure and buffer-gas flow rate on the kinetics by measuring their effects on the time behaviour of the Cu ground-state density. These density measurements present a powerful method for investigating the key kinetic effects of gas flow since the prepulse ground state density is essentially equal to the free Cu density in the plasma, and the rate of ground state density regrowth is representative of the interpulse rate of neutralisation and quenching of atoms.