“Solar pumping” in this context means that solar radiation directly and immediately makes the lasant material lase. The power output of solid state lasers is limited by the rate at which the laser rod can be cooled. Gas-dynamic solar-powered lasers (GDLs) use solar radiation to heat the lasant gas rather than make it lase directly. Consequently, equipment is required for the heating and recirculation of the lasant gas which makes GDL systems heavier and more complex than equivalent direct solar-pumped laser systems. The gas is stationary in a direct solar-pumped laser: solar radiation photodissociates the lasant gas to form excited atoms which emit coherent radiation upon de-excitation [8].
Recent researches have been directed towards the identification and assessment of lasant materials with pumping thresholds which are low enough to allow the use of parabolic trough concentrators (PTC). Such concentrators allow unrestricted laser gain length, are relatively simple to construct and enlarge and are thus being proposed for large-scale solar power systems in space [8].
The relative merits of parabolic dish, parabolic trough and conical concentrators for solar-pumped laser applications are summarized in Table 1-3.
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