High pulse repetition frequency XeCl laser and its applications
This thesis discusses the development, characterisation and evaluation of a compact, medium power, XeCl laser operating at pulse repetition frequencies (prf) >1kHz. The use of this laser to cut polymer films by ablative etching is also presented. The device uses a closed-cycle gas flow loop, constructed from stainless-steel for corrosive gas compatibility, and a total volume of 6 litres and a working pressure of 4 atmospheres. A magnetically coupled, tangential fan provides the gas flow and, with appropriate flow shaping into the 0.8 x 1.5 x 22.0cm⁻³ discharge region, produces a maximum flow velocity of 40m.s⁻¹. Electrical excitation is provided by a conventional, thyratron switched, capacitor discharge circuit, coupled with an internal, capacitively loaded, uv spark preionisation scheme, resulting in a rapid energy deposition into the discharge. Investigations of the effects of discharge perturbations on the maximum repetition rate capability of this laser, Indicate that repetition rates up to 1800Hz should be feasible. In operation, the laser has proven to be capable of 16W at 1kHz, and 22W at 700Hz, with a 10nF charging capacitor. Qualitative studies of the effect of resonator configuration on the beam profile, have shown that the use of folded cavities will produce more uniform beam profiles. Experiments have been carried out, using this laser, to cut thin polyethylene teraphthalate (PET) film at rates up to 1.3m.s⁻¹. The 8x15mm output beam from the laser, was brought to a 5.4mm long line-focus with a full width of 140µm. It is shown that the effective etch rate, and corresponding cutting efficiency, is markedly dependent on prf due, it Is thought, to cumulative heating.