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Quantum Electronics

Use of cavity as a multipass system in laser isotope separation

Aleksei N Tkachev, Sergei I Yakovlenko

Published Aug 31, 1997• 3 citations
Publisher

Abstract

It is proposed to use a multipass cavity to increase the efficiency of multistage selective photoionisation of atomic vapours. A simple analytic model is used to describe the efficiency of utilisation of radiation in a zero-dimensional cavity filled with a two-level absorbing medium. A numerical calculation is made of the kinetics of multistage selective ionisation of 168 Yb in a zero-dimensional cavity, taking account of 10 energy levels of different isotopes. It is shown that the use of a cavity can increase the yield of the selectively ionised isotope by an order of magnitude.

DOI
10.1070/qe1997v027n08abeh001019

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It is proposed to use a multipass cavity to increase the efficiency of multistage selective photoionisation of atomic vapours. A simple analytic model is used to describe the efficiency of utilisation of radiation in a zero-dimensional cavity filled with a two-level absorbing medium. A numerical calculation is made of the kinetics of multistage selective ionisation of 168 Yb in a zero-dimensional cavity, taking account of 10 energy levels of different isotopes. It is shown that the use of a cavity can increase the yield of the selectively ionised isotope by an order of magnitude.
Analytical solutions of the Schr?dinger equations for coherent excitation of an atom in the scheme of two- and three-stage photoionization are obtained as applied to the problem of laser isotope separation. A feature of the study is the introduction of laser excitation from an additional initial state to increase the fraction of the atoms involved in the separation process. The optimal from the points of view of photoion ratios of radiation intensities at individual photoionization stages are found. Key words: laser photoionization, laser isotope separation.
Propagation of short ($\ensuremath{\lesssim}{T}_{2}$, where T2{T}_{2}T2​ is the phase relaxation time) light pulses through absorbing media consisting of two ensembles of two-level systems of slightly different transition frequency is considered here. It is shown that one group of absorbers can be totally excited (inverted) while the other is returned to ground state. The effect of inhomogeneous broadening is illustrated by examples of propagation (numerical simulation) of properly shaped pulses through media having a linewidth equal to 1/5 of the frequency separation between the two transitions. The initial proportion of the two-level mixture is: 5% of the element to be excited, 95% of the element to be kept in ground state. The selective excitation capabilities of a Gaussian pulse and a zero-area pulse are compared.
Isotope separation by laser deflecting an atomic beam is analyzed theoretically. Interacting with a tilted one-dimensional optical molasses, an ytterbium atomic beam is split into multi-beams with different isotopes like 172 Yb, 173 Yb, and 174 Yb. By using the numerical calculation, the dependences of the splitting angle on the molasses laser intensity and detuning are studied, and the optimal parameters for the isotope separation are also investigated. Furthermore, the isotope separation efficiency and purity are estimated. Finally a new scheme for the efficient isotope separation is proposed. These findings will give a guideline for simply obtaining pure isotopes of various elements.
A numerical study is made of the interaction of laser radiation with different isotopic forms of potassium, 39K and 40K, for time intervals shorter than the relaxation times. The quantum efficiency and selectivity of the process are determined. The behavior of the atoms is considered using the Schrodinger equations for the probability amplitudes. Account is taken of the effects associated with hyperfine splitting of the levels, their degeneracy, and the Doppler effect. Excitation by a single traveling wave and by two oppositely traveling waves is considered and the excitation characteristics of the two regimes are compared.
The pulse deformation and time delay, which appear when the laser propagates in a thick atom vapor, influence the ionization yield and selectivity of atomic multi-step photoionization process directly. In this paper, we study the propagation of laser pulse and atomic photoionization in a thick atom vapor medium according to the atom vapor laser isotope separation. The process of atomic multi-step photoionization and the propagation of laser in a thick medium are described by density matrix equation and Maxwell equations, respectively. The medium consists of target isotope and non-target isotope, which is non-resonantly excited. Through numerical solution of the coupled equations we illustrate the propagation characteristics of laser and the influences of atom vapor parameters and laser parameters on average ionization yield and average selectivity in a thick medium. The important results of calculation are as follows:when the atom vapor medium is rather thick, the average ionization yield increases while average selectivity decreases with the increase of laser power. When the atom vapor is relatively thin, the average ionization yield and average selectivity increase with the decrease of laser power simultaneously. Besides, there is a positive time delay between two laser pulses in which case the average ionization yield of target isotope reaches its maximum value. Moreover, when the parameters of atom vapor are constant, extending the width of laser pulses as great as possible can not only increase average ionization yield and average selectivity simultaneously, but also loosen the control accuracy of time delay between laser pulses.
We present a procedure for treating coherent selective excitation (and subsequent ionization) of atomic vapour in a radiation-filled cavity. Specifically, we describe a technique for solving the coupled Maxwell-Bloch equations for atoms in a one-dimensional cavity by means of a spatial quasi-Fourier expansion that introduces a sequence of increasing spatial harmonics for atomic populations and coherences. We discuss the resulting coupled equations and present examples of solutions for a simple model of stationary and moving two-state atoms in the limit of very low density. The atomic excitation exhibits a travelling wave behaviour, but with significant modulation.