An investigation of gas lasers.
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Date
1999
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Abstract
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.
Description
Thesis (M.Sc.)-University of Natal, Durban, 1999.
Keywords
Gas lasers., Theses--Physics.