4.3-μm CO₂ Laser

Abstract

<p>The work described in this thesis concerns the investigation of the properties of a new type of CO₂ laser, one which operates in the wavelength region near 4.3 μm rather than in the 9-11-μm region where most CO₂ lasers operate. Lasing at 4.3 μm is achieved by using a 10-μm sequence CO₂ laser to optically pump CO₂ molecules which have been excited in an electrical discharge. The laser is based on existing CO₂ laser technology, and therefore it is potentially a very useful source of coherent radiation in a spectral region where there are presently few lasers suitable for widespread use.</p> <p>Preliminary experiments are described which serve to identify the various physical processes involved in 4.3-μm Iaser action. Efficient optical pumping is demonstrated and peak output powers of 1 kW are observed. A theoretical model of the laser is developed. The model can accurately predict the observed 4.3-μm output and it is shown that the lifetime of the upper laser level is the critical factor in determining the gain dynamics of the laser system.</p> <p>Two principal operating regimes are identified. The first is a high repetition rate Q-switched mode suitable for the production of high average power. A Q-switched 4.3-μm laser is constructed, employing continuous discharge tubes and SF₆ is used to passively Q-switch the sequence oscillator. The average output power at 4.3 μm is 120 mW.</p> <p>The other operating regime is a high power pulsed mode. This involves scaling the laser to higher operating pressures, which requires the use of high levels of sequence pumping power. To this end, a TEA sequence CO₂ laser having output energies of up to 6 J per pulse was developed, and design criteria for such lasers are presented. The scalability of the 4.3-μm laser, using the TEA sequence laser as the pump source, is discussed. The factors which limit the maximum output power attainable are identified, and guidelines for the construction of high power 4.3-μm lasers are presented.</p>