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PART I: INTENSITY CORRELATIONS IN ELASTIC SCATTERING EXPERIMENTS. PART II: THEORY OF QUANTUM BEAT AND LEVEL CROSSING EXPERIMENTS UTILIZING ELECTRONIC EXCITATION

Robert L. Kelly

Published Nov 10, 1966• 0 citations
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Abstract

IMeasurements of space-time correlations in the intensity of a beam of scattereq particles yield information about the scatterer.Goldberger and Watson have developed a theory of such measl~ementG appropriate to the case of ne~rly elastic scattering; in this paper we extend their theory to the case of inelastic scattering.The main result of our work is that under certain experimental conditions the correlated counting rate in an inelastic scattering experiment is of a form equivalent to the correlated counting rate for an incoherent beam of particles emitted by a source.This result applies, in particular, to Raman or Brillouin scattering of light by phonons in an extended target.However, estimates of the signal to noise ratio for this case indicate that it may not be possible to observe intensity correlations in Raman or Brillouin lines using presently available light sources. ABSTRACT OF PART IIThe coherent excitation of several atomic status by inelastic electron' scattering and their subsequent radia ti ve decay is considered.General expressions for the photon counting rate in a quantum beat experiment, and the total number of photons counted. in a le,vel crossing experiment are d.erived.The general results are used to calculate the phase of the oscillatory part of the photon counting rate in the Radeishi-Nierenberg quantum beat experiment.

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Proceedings of the Royal Society of London A Mathematical and Physical Sciences•Jul 5, 1966•87 citations
IMeasurements of space-time correlations in the intensity of a beam of scattereq particles yield information about the scatterer.Goldberger and Watson have developed a theory of such measlementG appropriate to the case of nerly elastic scattering; in this paper we extend their theory to the case of inelastic scattering.The main result of our work is that under certain experimental conditions the correlated counting rate in an inelastic scattering experiment is of a form equivalent to the correlated counting rate for an incoherent beam of particles emitted by a source.This result applies, in particular, to Raman or Brillouin scattering of light by phonons in an extended target.However, estimates of the signal to noise ratio for this case indicate that it may not be possible to observe intensity correlations in Raman or Brillouin lines using presently available light sources. ABSTRACT OF PART IIThe coherent excitation of several atomic status by inelastic electron' scattering and their subsequent radia ti ve decay is considered.General expressions for the photon counting rate in a quantum beat experiment, and the total number of photons counted. in a le,vel crossing experiment are d.erived.The general results are used to calculate the phase of the oscillatory part of the photon counting rate in the Radeishi-Nierenberg quantum beat experiment.
The results of electron-photon coincidence experiments have given a new insight into the excitation of atoms by electron impact. This article reviews the way in which this new experimental technique has provided an exacting and fundamental test for the theory of the excitation process. The basic experimental method is first described, and a comprehensive treatment of excitation of the n 1 P states of helium is given. The extension of the technique to the study of excitation of the n=2 states of atomic hydrogen is then presented. Coincidence measurements also provide information on the role of spin in the collision, and this subject is treated in detail for excitation of heavy atoms by both unpolarised and spin-polarised beams of electrons. Finally, the electron-photon coincidence method permits observation of the time evolution of excited atomic states, and this review describes the attempts made to observe quantum beats in the radiative decay.
Abstract A theoretical and experimental study has been made of the intensity of forward scattered light in conditions of radio-frequency double resonance and level-crossing. The main conclusions are (i) that the magnetic resonance and level-crossing effects which are familiar in the laterally scattered light are to be found also in the forward scattered light, but (ii) that the resonance curves are Doppler-broadened, and the strength of the oscillatory field necessary to generate them is correspondingly increased, and (iii) that coherence narrowing is much more pronounced in forward than in lateral scattering. The differences derive from the coherence between the radiation from different atoms which is present in forward, but not in lateral scattering, and which is implicitly recognized in the classical theory of the propagation of light in polarizable media. The equations of electromagnetism form the basis of the present analysis. In the presence of the oscillatory magnetic field the polarization tensor is complex and time-dependent. The time dependence leads to the result that the number of eigenwaves necessary to describe propagated waves in the medium is four, as against the usual two. An arbitrary wave is resolved into a superposition of the four eigenwaves, all of which have different propagation constants. The analysis is very general, and is applicable to experiments with lasers. The components of the polarization tensor are derived by finding first the polarizability of individual atoms from a semi-classical theory of their interaction with light and magnetic fields. The macroscopic polarization, obtained by summing over individual atoms, is then given by folding the individual polarizabilities with the Doppler distribution of resonance frequencies. In the particular case studied in detail (the inter-combination resonance line, 2537 A, in mercury), the Doppler width is much greater than the radiation width, and the imaginary (absorptive) part of the polarizability is Gaussian. Expressions are derived in a ‘weak scattering’ approximation for the intensity of the forward scattered light. They are magnetic resonance functions which are found to be the Doppler-broadened equivalents of the familiar functions, based on Lorentzians, characteristic of scattering by a single atom. In the case of double resonance the forward scattered light is strongly modulated, as is the laterally scattered light. To investigate coherence narrowing, the zero-field level-crossing has been studied with the restriction of ‘weak scattering’ removed. The result is obtained that the width of levelcrossing curves is inversely proportional to the vapour density for magnetic fields such that the Zeeman splitting is small in relation to the Doppler width. This analytical result has been verified experimentally.