Collision-induced amplification of short-wave radiation on transitions to the ground state of atoms
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Collision-Induced Amplification of Short-Wave Radiation on Transitions to the Ground State of Atoms A. I. Parkhomenko, A. N. Usol’tsev, and A. M. Shalagin Institute of Automatics and Electrometry, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630090 Russia Novosibirsk State University, Novosibirsk, 630090 Russia e-mail: [email protected]; [email protected] Received January 31, 2008
Abstract—A new version of obtaining short-wave lasing on transition between highly excited states and the ground state of active atoms in the buffer gas atmosphere is studied theoretically. The mechanism of obtaining population inversion on such a transition is associated with the establishment of the local Boltzmann distribution of populations in a group of highly excited levels due to frequent collisions. If the excitation of the upperlying level is performed by two laser radiation sources with frequencies ω1 and ω2, short-wave lasing can be obtained at a frequency close to the total frequency ω1 + ω2. The conditions for the emergence of population inversion are analyzed and simple analytic formulas are derived. It is shown that collision-induced enhancement of short-wave radiation can occur for pumping intensities on the order of 100 W/cm2. For pumping intensities on the order of 1000 W/cm2, the amplification factor for short-wave radiation may attain values of 3 cm–1(for an active atom concentration of N ~ 1015 cm–3), which is sufficient for the development of lasing per path through an active medium (superradiance condition) for a length of the active medium on the order of 10 cm. PACS numbers: 42.50.Hz, 32.70.-n DOI: 10.1134/S1063776108080013
1. INTRODUCTION This research is devoted to studying a new version of obtaining short-wave lasing on transitions to the ground state, which was proposed for the first time in [1]. The object of investigation is a two-component gas consisting of atoms (which are in a resonant interaction with laser radiation) and buffer particles playing the role of the thermostat. We pay attention to the fact that under certain conditions, the combined effect of optical excitation of atoms and their collision with buffer gas particles may lead to population inversion on the transition from a highly excited state to the ground state. A quantitative description of this phenomenon is the goal of this study.
that these energies ensure leveling out of states n and m and that the frequency of collision-induced transition is so high that the Boltzmann distribution of populations has time to set in over the characteristic times of relaxation between states m and k. In this case, the popula-
Figure 1 showing the diagram of energy levels participating in the process clarifies the idea of the proposed method. Two-quantum excitation by two laser radiation sources transforms atoms from ground state n to a higher-lying level m. State m is chosen in such a way that below this level (within the limits of thermal energy kBT), a level k exists, which is not perturbed by the external field, but is co
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