0191-9067/83 $3.00 + .00 Copyright ® 1984 SUNSAT Energy Council KINETIC MODELING OF AN IBr SOLAR PUMPED LASER W. L. HARRIES Old Dominion University Norfolk, Virginia 23508, USA W. E. MEADOR NASA/Langley Research Center Hampton, Virginia 23665, USA Abstract — The possibility of using an IBr laser as a solar energy converter is examined theoretically, and reasons for its choice are given. Broadband absorption results in dissociation with the formation of excited Br* atoms, some of which then lase to the ground state Br. The ground state is depopulated by three-body recombination and, more importantly, by exchange reactions which more than compensate for the high quenching in heteronuclear halogen systems. Kinetic modeling indicates lasing is possible in the pulsed mode and possibly in the steady state with a cooled gas flow system. Temperature effects are discussed. The efficiency of the laser approaches 1.2% at optical thicknesses large enough for complete absorption of the photons. I. INTRODUCTION The concept of collecting solar radiation in large mirrors on orbiting space stations, and then transmitting the energy via laser beams has been considered previously (1-3). The efficiency of the system is expected to be highest if the laser could be directly pumped by the solar radiation. The criteria for an efficient solar pumped laser are as follows: • There must be broadband absorption; • Peak absorption should occur near the peak of the solar spectrum; • High quantum yield into a long-lived (metastable) state which serves as the upper laser level; • In general, quenching of the excited state should be small, but, as will be pointed out later, this condition is alleviated if • The lower level is rapidly depopulated to maintain inversion; • The upper and lower levels must be sufficiently separated to yield a reasonable quantum efficiency; • The process must be reversible; if not the components must be reconstituted by flow methods. Gas lasers are advantageous because of uniformity of medium and because size is not a limitation. Two classes of laser can be considered: [1] where the absorbing medium is distinct from the lasant, and [2] where one material performs both functions. The first solar pumped laser examined theoretically was type [1] above, namely a
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