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Journal of Physics B Atomic and Molecular Physics

A study of the transients in resonance fluorescence following a step or a pulse of magnetic field

John N. Dodd, Weston J. Sandle, O M Williams

Published Feb 1, 1970• 31 citations
Publisher

Abstract

Following (i) a sharp step or (ii) a pulse of applied magnetic field, the resonance fluorescence of an atomic vapour exposed to steady linearly polarized resonance radiation undergoes transient behaviour until a new steady state is reached; the form of the transient will be (i) modulation of the intensity with an exponential envelope, or (ii) simple exponential decay. From the modulation period the gJ value of the excited state is obtained. From the exponential decay the lifetime for the relaxation of atomic alignment is obtained directly. The technique, applied to the 63P1 state of mercury, gives 117.4+or-1.0 ns for the natural mean life.

DOI
10.1088/0022-3700/3/2/019

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Line Shapes in the Method of Intersecting Energy Levels

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The first part of this work is a study of the changes of intensity of the resonance fluorescence from mercury vapour as a small magnetic field H is applied either parallel or anti-parallel to the direction of the incident light. The changes follow either a Lorentzian or a dispersion-type function of the Zeeman splitting of the excited state, according to the orientations of polarizer and analyser in the beams of light. In an experiment with an additional oscillatory field at a frequency ω 0 , similar curves are observed in the region H = H 0 /2. ( H 0 is the field for which ω 0 is the Larmor frequency.) The observations are relevant to a recently developed technique in which intensity changes of this sort are used to make precision measurements in spectroscopy. The Lorentzian line shape is usually observed. The possibility of obtaining line profiles of other shapes was pointed out by Franken.

Proceedings of the Physical Society•Jul 1, 1961•9 citations
Following (i) a sharp step or (ii) a pulse of applied magnetic field, the resonance fluorescence of an atomic vapour exposed to steady linearly polarized resonance radiation undergoes transient behaviour until a new steady state is reached; the form of the transient will be (i) modulation of the intensity with an exponential envelope, or (ii) simple exponential decay. From the modulation period the gJ value of the excited state is obtained. From the exponential decay the lifetime for the relaxation of atomic alignment is obtained directly. The technique, applied to the 63P1 state of mercury, gives 117.4+or-1.0 ns for the natural mean life.
A Stark effect experiment is presented, which involves the recording of transients in radiation resonantly scattered by a vapour, following the sudden application of an electric field pulse. The theory of this effect is developed from the case where a general step-function perturbation is applied. The transients have the form of damped sinusoidal oscillations: the damping is determined by the rate of radiative decay; the modulation frequencies depend directly on the energy-level splittings caused by the applied field. This technique has been to measure the magnitude and sign of the differential Stark shifts in the 6 3 P 1 level of 198 Hg and 199 Hg. These lead to a value for the tensor polarizability which is in good agreement with recent measurements. Results are presented of a calculation of the polarizabilities of the 6 3 P 1 and 6 1 S 0 levels based on experimental oscillator strengths.
Frequency-modulated light was generated by the application of a magnetic field oscillating at frequencies in the range 1-10 MHz to mercury vapour undergoing resonance fluorescence. The characteristics of the fluorescent light have been studied. When the primary illumination in the plane perpendicular to the field is anisotropic the sigma components are coherently excited. The light emitted along the field is then polarization-modulated. It becomes intensity-modulated if it is passed through a linear analyser. The light emitted obliquely to the magnetic field is intensity-modulated without passing through an analyser. The amplitudes of these modulations show resonance behaviour under the application of an additional static field parallel to the oscillating field. The polarization-modulated light was used to excite resonance fluorescence in a second cell of mercury vapour. The fluorescent light is intensity-modulated. The amplitude of modulation shows resonance behaviour when harmonics of the driving frequency coincide with Zeeman intervals in the excited atoms. These resonances have been explored in detail. They are satisfactorily interpreted by a theory given in an accompanying paper.
The first part of this work is a study of the changes of intensity of the resonance fluorescence from mercury vapour as a small magnetic field H is applied either parallel or anti-parallel to the direction of the incident light. The changes follow either a Lorentzian or a dispersion-type function of the Zeeman splitting of the excited state, according to the orientations of polarizer and analyser in the beams of light. In an experiment with an additional oscillatory field at a frequency ω 0 , similar curves are observed in the region H = H 0 /2. ( H 0 is the field for which ω 0 is the Larmor frequency.) The observations are relevant to a recently developed technique in which intensity changes of this sort are used to make precision measurements in spectroscopy. The Lorentzian line shape is usually observed. The possibility of obtaining line profiles of other shapes was pointed out by Franken.