An investigation of gas lasers.
Jugessur, Agnivesh Sharma.
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Pulsed lasers have a wide range of applications in industry, medicine and for scientific research. Many of these devices are expensive and have delicate optics. The nitrogen laser is robust and inexpensive to build and maintain. A short review of the experimental nitrogen lasers is given. A major part of this thesis covers work on increasing the energy output (from30 µJ to 0.3 mJ). The one design of nitrogen laser consists of a pc board etched on the sides and at the centre for the laser discharge. The separated sections are rectangular in shape. However, in the new design the discharge section of the nitrogen laser has a parabolic shape and an inclined laser channel was used instead of a horizontal one to observe the effect on the energy output. Parameters such as the distance between the top and bottom plates, the area of the bottom plate, the area of the parabola and the flow velocity of nitrogen were varied. Both nitrogen gas and cold nitrogen vapour were used as the lasing medium. The substitution of vapour for gas increased the energy 2 fold. Liquid nitrogen was tried unsuccessfully as the medium in the discharge channel. Two large lasers were built giving increased laser energy. A multilayer nitrogen laser was also built increasing the output by a factor of 2.5. The multilayer idea was also tried on the large lasers. The multilayer laser behaves like a small capacitor bank, discharging in parallel into the laser channel. The low pressure electrodes which were used on the large parabolic laser consisted of a pair of flat copper electrodes enclosed in a plexiglass housing and the latter being connected to a vacuum pump. The effect of using the low pressure electrodes on the laser energy output was investigated. Three nitrogen lasers made of aluminium foil were also constructed where transparencies and mylar were used as the dielectric insulator. In addition, a multilayer parabolic N2 laser was made using the same materials. A water wave simulation experiment of the parabolic laser was done which showed that due to the parabolic form, circular waves are converted into planes wave. The spark gap which acts as a fast nanosecond switch must be precisely located at the focus of the parabola. Otherwise the laser does not lase. Michelson Interferometry was carried out to measure the coherence length of the laser Which was found to be longer than that mentioned in the literature. The improved parabolic nitrogen laser was used to obtain fringes in a Mach Zehnder experiment. The laser is now being used by the Durban laser group as a diagnostic tool to measure the refractive index of the gas lens created in a Colliding Shock wire experiment. Carbon dioxide lasers have numerous industrial applications. The Laser group at the Atomic Energy Corporation(AEC), Pretoria are looking into possible industrial applications such as carbon isotope separation, paint-stripping and de-rusting. The author spent sometime at the centre to investigate how the beam quality and energy output of the laser can be improved since a near gaussian profile is very important for many applications. The carbon dioxide laser system basically consists of an oscillator and two amplifiers in series. Measurements of the beam parameters (waist size, pulse shape, divergence angle) along different sections of the laser chain were taken. The laser beam was double passed through one of the amplifiers to observe the effect on the energy output. Burn patterns at several places were taken to observe the beam profile. An investigation into the optical energy losses along the laser chain was made. A device called the Three Element Detector invented by the Laser Group, AEC, was also used to analyse the laser beams.