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Physical Review A

Radiation amplification near an autoionizing state: A model in atomic Ca

Jian Zhang, P. Lambropoulos, Xian Tang

Published Aug 1, 1994• 9 citations
Publisher

Abstract

We present an internally consistent theory of amplification near the minimum of the absorption profile of autoionizing states, with a quantitative application to calcium. We have included a completely specified three-photon pumping, and have obtained quantitative results for the gain that reveal certain unusual aspects of this system. Our results and their extensions are also discussed in the context of present-day experimental possibilities.

DOI
10.1103/physreva.50.1935

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We consider laser action on a transition involving an autoionizing state \ensuremath{\Vert}a〉 and an initially unpopulated state \ensuremath{\Vert}f〉, the population of which builds up because of spontaneous emission and Raman processes. The autoionizing state is pumped by a coherent field. We discuss the transient amplification of the probe field on the lasing transition for a range of parameters. The coherent field on the pumping transition leads to minima in the absorption spectra if the atomic population were in the state \ensuremath{\Vert}f〉. Such regions of minima can be used for obtaining gain even for long times.

Physical Review A•May 1, 1990•75 citations
We present an internally consistent theory of amplification near the minimum of the absorption profile of autoionizing states, with a quantitative application to calcium. We have included a completely specified three-photon pumping, and have obtained quantitative results for the gain that reveal certain unusual aspects of this system. Our results and their extensions are also discussed in the context of present-day experimental possibilities.
We present an internally consistent theory of amplification near the minimum of autoionizing states with quantitative application to calcium.We have included a completely specified three-photon pumping and we find certain unusual aspects of the system.We find conditions under which the system remains in a steady state, although being coupled to the continuum.For incoherent pumping we obtain quantitative results for the gain.Our results and their extensions are also discussed in the context of present-day experimental possibifities.
In the present study we have investigated three-photon ionization in Ca in which autoionizing states are engaged. The two-photon resonant process (from the Ca ground state 4s 2 1 S 0 ) occurred through or at least in the vicinity of one of the following states: 4s4d 1 D 2 , 4p 2 3 P 2 , 4s6s 1 S 0 , 4p 2 1 D 2 and 4p 2 1 S 0 , with the third photon either reaching the continuum directly or one of the autoionizing states. The three-photon resonant transitions to 3d m p, m f: 1 P 1 , 3 P 1 and 3 D 1 autoionizing states for m up to 21 have been observed. Some of the autoionizing resonances which we have found had not been observed before in a high-resolution one-photon absorption experiment (for J = 1) and in multiphoton experiments (for J = 3). We have compared the ionization signal as a function of the laser detuning and the laser intensity with theoretical curves obtained within a simple model (three-level atom + one-mode laser field). This gives information about the order of magnitude of the three-photon ionization probability through autoionizing states.
We present a quantitative study of radiation amplification without population inversion based on models recently proposed by Harris [Phys. Rev. Lett. 62, 1033 (1989)]. We discuss both two-level and three-level arrangements in terms of the density matrix. Our calculations, which are fully time dependent, incorporate an incoherent pumping mechanism that is essential for amplification. We discuss in detail the range of and conditions on atomic parameters for which amplification is possible. Its feasibility is demonstrated through the direct calculation of the change of the intensity of a probe beam interacting with the atom.
We consider laser action on a transition involving an autoionizing state \ensuremath{\Vert}a〉 and an initially unpopulated state \ensuremath{\Vert}f〉, the population of which builds up because of spontaneous emission and Raman processes. The autoionizing state is pumped by a coherent field. We discuss the transient amplification of the probe field on the lasing transition for a range of parameters. The coherent field on the pumping transition leads to minima in the absorption spectra if the atomic population were in the state \ensuremath{\Vert}f〉. Such regions of minima can be used for obtaining gain even for long times.