An alkali metal vapor laser amplifier
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An Alkali Metal Vapor Laser Amplifier A. I. Parkhomenko and A. M. Shalagin Institute of Automation and Electrometry, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630090 Russia Novosibirsk State University, Novosibirsk, 630090 Russia email: [email protected]; email: [email protected] Received December 29, 2013
Abstract—The operation of a transversely diodepumped alkali metal vapor laser amplifier is theoretically studied. The amplifier operation is described by a rather intricate system of differential equations, which can be solved in the general case only numerically. In the case of intense incident radiation, an analytic solution is obtained which makes it possible to determine any energy characteristics of the laser amplifier and to find the optimal parameters of the active medium and pump radiation (temperature, buffer gas pressure, and intensity and width of the pump radiation spectrum). DOI: 10.1134/S106377611407005X
1. INTRODUCTION Currently, studies of a new class of gas lasers, diodepumped alkali metal vapor lasers, are attracting considerable attention (see [1, 2] and references therein). The advantages of such lasers are the high pump–laser radiation conversion efficiency, the high energy extraction per unit volume, their simple design, and ease of operation. The physical principle of operation of alkali metal vapor lasers is very simple (Fig. 1). The pump radiation is resonantly absorbed on the transition from the ground n2S1/2 state of an alkali metal atom to the n2P3/2 state (the D2 line; n = 2, 3, 4, 5, 6 for lithium, sodium, potassium, rubidium, and cesium, respectively). In buffer gases at sufficiently high enough pressures (on the order of a few hundred millimeters of mercury), collision transitions between the fine structure com ponents n2P3/2 and n2P1/2 occur so fast that an equilib rium Boltzmann population distribution is established during the lifetime of these levels. According to this distribution, the population of the n2P1/2 level is higher than that of the n2P3/2 level by the Boltzmann factor exp(ΔE/kBT), where ΔE is the energy difference between the n2P3/2 and n2P1/2 levels, T is temperature, and kB is the Boltzmann constant. If now we provide the pump radiation intensity so high that it will equal ize the populations of the ground level and the n2P3/2 level, the population of the n2P1/2 level will exceed that of the ground level by the same Boltzmann factor. Thus, the population inversion is produced on the n2P1/2–n2S1/2 transition, which can result in lasing at this transition. Lasing by this mechanism was first observed in potassium [3] and sodium [4, 5] vapors. Potassium and sodium vapors in the buffer helium gas atmosphere at a pressure of about few hundred torr produce lasing at the D1 line (the 2P1/2–2S1/2 transition) upon laser
pumping into the D2 line. In [5], this effect was also described theoretically. It was shown later in experi ments with rubidium vapors [6] that lasing was consid erably enhanced when a buffer molecular gas (meth
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