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Japanese Journal of Applied Physics

Magnetic Field Effect on Laser Isotope Separation Based on Polarization Selection Rules

Hideaki Niki, Iwao Kitazima, Yasukazu Izawa

Published Jun 1, 1998• 14 citations
Publisher

Abstract

Excitation dynamics of atoms by linearly polarized lasers were analyzed for J=2→2→1→0 multistep transition under a magnetic field. The time evolution of the population in each magnetic substate was calculated by solving the rate equations under the condition where the atomic alignment is gradually destroyed by the precession motion of the angular momentum around the magnetic field. Isotopic selectivity in the laser isotope separation based on the polarization selection rules was discussed. It has been found that a relatively small magnetic field may cause a degradation of selectivity in the case of Gd and the magnetic field should be kept as small as the terrestrial magnetic field when the laser polarization is perpendicular to the magnetic field.

DOI
10.1143/jjap.37.3343

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Acta Physica Sinica•Jan 1, 1984•4 citations
Excitation dynamics of atoms by linearly polarized lasers were analyzed for J=2→2→1→0 multistep transition under a magnetic field. The time evolution of the population in each magnetic substate was calculated by solving the rate equations under the condition where the atomic alignment is gradually destroyed by the precession motion of the angular momentum around the magnetic field. Isotopic selectivity in the laser isotope separation based on the polarization selection rules was discussed. It has been found that a relatively small magnetic field may cause a degradation of selectivity in the case of Gd and the magnetic field should be kept as small as the terrestrial magnetic field when the laser polarization is perpendicular to the magnetic field.
The effect of an external magnetic field on the isotopic selectivity in a two-color three-step polarization-based isotope-selective photoionization of atomic samarium has been studied. Isotope-selective photoionization of samarium is realized through a level scheme having total angular momentum ( J ) sequence 0-1-1-continuum by using two lasers linearly polarized in the same direction and the isotopic selectivity is measured by varying the magnetic field strength perpendicular to the laser polarization axis while keeping the delay between the laser pulses fixed and vice versa. The experimental data have been analyzed and compared with the results of the numerical calculations. The magnetic field perpendicular to the laser polarization axis present in the laser-atom interaction region has been found to degrade the isotopic selectivity. Further, the Lande factor ( ) of the excited energy level 16 690.76 cm −1 ( J = 1) of samarium has been determined from the observed oscillation in the isotopic selectivity. The value of thus obtained, is in good agreement with that reported in the literature.
Isotope selective photoionization of ⁶⁷Zn is demonstrated with broadband excitation light (∼ 3.4 GHz), temporally separated laser pulses in the presence of a weak external magnetic field. Starting with natural zinc metal (∼ 4% ⁶⁷Zn) the ion sample was enriched to ∼ 90% ⁶⁷Zn. Efficient suppression of the ionization of the even-mass isotopes was achieved by intermediate state alignment in the excitation scheme 4𝑠2 ¹𝑆₀ → 4𝑠4𝑝 ³𝑃₁ → 4𝑠4𝑑 ³𝐷₁, followed by nonresonant photoionization. The first excitation pulse was linearly polarized parallel to the transverse component of the external magnetic field and the linear polarization of the second excitation pulse was rotated to compensate for Larmor precession of the quantization axis during the temporal delay between the two excitations. This is the first systematic study, in the context of resonance ionization, investigating the independent and continuous rotation of the polarizations of the excitation pulses and demonstrating efficient compensation for the presence of an external magnetic field that has an arbitrary direction. Experimental results are supported by a vector model combined with rate equations.
Isotope selective photoionization of ⁶⁷Zn is demonstrated with broadband excitation light (∼ 3.4 GHz), temporally separated laser pulses in the presence of a weak external magnetic field. Starting with natural zinc metal (∼ 4% ⁶⁷Zn) the ion sample was enriched to ∼ 90% ⁶⁷Zn. Efficient suppression of the ionization of the even-mass isotopes was achieved by intermediate state alignment in the excitation scheme 4𝑠2 ¹𝑆₀ → 4𝑠4𝑝 ³𝑃₁ → 4𝑠4𝑑 ³𝐷₁, followed by nonresonant photoionization. The first excitation pulse was linearly polarized parallel to the transverse component of the external magnetic field and the linear polarization of the second excitation pulse was rotated to compensate for Larmor precession of the quantization axis during the temporal delay between the two excitations. This is the first systematic study, in the context of resonance ionization, investigating the independent and continuous rotation of the polarizations of the excitation pulses and demonstrating efficient compensation for the presence of an external magnetic field that has an arbitrary direction. Experimental results are supported by a vector model combined with rate equations.
Isotope selective photoionization of 67 Zn is demonstrated with broadband excitation light (∼3.4GHz), temporally separated laser pulses in the presence of a weak external magnetic field. Starting with natural zinc metal (∼4% 67 Zn), the ion sample was enriched to ∼90% 67 Zn. Efficient suppression of the ionization of the even-mass isotopes was achieved by intermediate state alignment in the excitation scheme 4 s 2 1 S 0 →4 s 4 p 3 P 1 →4 s 4 d 3 D 1 , followed by nonresonant photoionization. The first excitation pulse was linearly polarized parallel to the transverse component of the external magnetic field and the linear polarization of the second excitation pulse was rotated to compensate for Larmor precession of the quantization axis during the temporal delay between the two excitations. This is the first systematic study, in the context of resonance ionization, investigating the independent and continuous rotation of the polarizations of the excitation pulses and demonstrating efficient compensation for the presence of an external magnetic field that has an arbitrary direction. Experimental results are supported by a vector model combined with rate equations.
The evolution of the populations of the magnetic sublevels of the cesium atom (133Cs isotope) in resonant laser fields with linear polarization is analyzed using the equations for the density matrix. Analytic expressions are derived for stationary populations resulting from laser-induced optical transitions on the hyperfine structure components F g = 3 ↔ F e = 2, 3 and F f = 4 ↔ F e = 3, 4 of lines D1 (62S1/2 → 62P1/2) and D2 (62S1/2 → 62P3/2) depending on the initial values of the populations. The numerical solution of the evolution equations gives the characteristic times of stabilization of the steady regime as functions of laser field intensities and detuning from optical resonance. We determine the sequences of optical transitions increasing (by more than an order of magnitude) the population of the lower sublevel 62S1/2F g = 3 M = 0 of the “clock” microwave transition F g = 3 M = 0 ↔ F f = 4 M = 0 in the cesium frequency standard, which increases the signal intensity in the recording system by the same proportion.
We describe a novel method to enrich isotopes and isomers via magnetic deflection of optically polarized atomic beam. High electronic polarization with opposite signs for atoms of both isotopes respectively is achieved by selective optical pumping using lasers with different frequencies and polarizations and then the isotopes are enriched by deflecting the oppositely polarized isotopes along different directions by the inhomo-geneous magnetic field in the spin selective magnet. Separation selectivity and throughput are evaluated and the advantages, disadvantages and prospects of possible application of the present method are discussed in comparison with other existing methods. Experimental scheme with lithium or potassium is suggested.