Heidi Fearn

Quantum theory of the lossless beam splitter

Abstract The electromagnetic fields associated with a beam splitter having two input arms and two output arms are quantized in terms of the spatial modes of the complete optical system. The continuum mode operators employed conveniently describe the flow of light through the beam splitter from sources to detectors. The formalism is used to determine the photocount fluctuations in difference detection of the two outputs, the effect of beam splitting on squeezed input light, and the distribution of output photocounts for a definite number of input quanta.

Theory of two-photon interference

The interference effects that can be observed in the two output arms of a lossless beam splitter are calculated for incident light in the form of a photon-pair excitation in the two input arms. The output state that occurs when the photon pair is excited in a single input arm resembles that expected for independent classical particles, whereas quantum interference effects occur when the photon pair is divided between the two input arms. Detailed output photocount correlation functions are calculated for two-photon input states produced by a two-atom light source, a degenerate or nondegenerate parametric oscillator in a high-Q cavity, and an atomic cascade emission light source.

Theory of continuous-wave excitation of the sodium beacon

We extend our previous analysis of the sodium beacon [J. Opt. Soc. Am. A15, 217 (1998)] to the case of continuous-wave excitation. Various effects that could be ignored in the case of pulsed excitation, such as the geomagnetic field, the recoil of the sodium atoms upon absorption and emission, and collisions of the sodium atoms with other mesospheric species, are included. Spin-relaxation collisions are among the most important of these effects for the cases considered. Analytical approximations to numerical results are presented, and using a semi-empirical estimate for Na-O2 spin relaxation, we compute photon returns in good agreement with recently reported measurements at the Steward Observatory.

Microscopic approach to reflection, transmission, and the Ewald–Oseen extinction theorem

We describe how the reflection and transmission of light at a dielectric interface can be understood starting from the fact that dielectrics are collections of molecules. More precisely, we consider from the microscopic perspective the interpretation and significance of the Ewald–Oseen extinction theorem of classical optics. The usual interpretation of the theorem is that an incident field is extinguished by the dipoles on the boundary and replaced by transmitted and reflected fields consistent with the Maxwell equations for the media. However, the extinction theorem is more appropriately regarded simply as a boundary condition effected by all the molecular scatterers, not just those at the boundary. To demonstrate this we take a microscopic approach to three familiar problems: (1) the electrostatic interaction of a point charge with a dielectric wall; (2) the reflection of a monochromatic plane wave at a dielectric interface; and (3) diffraction by an aperture. We show that the extinction of the incident...

Fizeau’s experiment and the Aharonov–Bohm effect

The electromagnetic wave equations in a moving medium may be approximated by a form similar to that of the Schrodinger equation for a particle in an electromagnetic field, with the velocity v of the medium and the vorticity ∇×v playing the roles of the vector potential and magnetic field, re‐ spectively. A purely classical optical analogue of the Aharonov–Bohm effect follows by consider‐ ation of the interference pattern produced by two beams, each of which propagates in a region with zero vorticity, but such that the flux of the vorticity through the closed loop defined by the optical paths does not vanish. Fizeau’s experiment (1851) on the velocity of light in moving media may be regarded as an example of such a situation.

Of some theoretical significance: implications of Casimir effects

We will describe some aspects of Casimir effects that appear to be of particular significance now, more than half a century after Casimirs famous paper.

Lasing without inversion in a simple model of a three-level laser with microwave coupling

Abstract We consider the linear nondegenerate Λ quantum beat laser, and investigate the possibility of lasing without inversion when coherence is established between the lower levels by applying a strong microwave field. Saturation terms are considered qualitatively for a steady state analysis. For the most favorable case of maximum coherence between the two lower levels we investigate phase locking and noninversion gain on both optical transitions.

Lasing without inversion

We present a nonlinear theory for lasing without inversion in three-level atomic systems by utilizing initial atomic coherence between two closely spaced lower levels. We discuss nondegenerate and degenerate cases for closed and open atomic systems. The equations of motion for the laser fields, and the steady state intensities of the fields are obtained. The realization of lasing without inversion is due to the absorption cancellation by the atomic coherence, i.e., the quantum interference. The quantum interference can bring about gain enhancement in the nondegenerate cases.

Gain and threshold in noninversion lasers

Abstract In this paper we study the influence of the atomic lifetime and Raman field strength on the gain and laser threshold in noninverted atomic systems. Our results show that to obtain a useful gain in such a system, it is necessary to use a sufficiently intense Raman field, atoms with a long lifetime for the lower active levels, and a small cavity loss.

Mach’s Principle, Action at a Distance and Cosmology

Hoyle and Narlikar (HN) in the 1960’s [1] 08D0C9EA79F9BACE118C8200AA004BA90B02000000080000000E0000005F005200650066003400310031003900330036003000340034000000 -[3] 08D0C9EA79F9BACE118C8200AA004BA90B02000000080000000E0000005F005200650066003400310031003900330036003000340037000000 developed a theory of gravitation which was completely Machian and used both retarded and advanced waves to communicate gravitational influence between particles. The advanced waves, which travel backward in time, are difficult to visualize and although they are mathematically allowed by relativistic wave equations, they never really caught on. The HN theory reduced to Einstein’s theory of gravity in the smooth fluid approximation and a transformation into the rest frame of the fluid. Hawking [4] 08D0C9EA79F9BACE118C8200AA004BA90B02000000080000000E0000005F005200650066003400310031003900330036003000350030000000 in 1965 pointed out a possible flaw in the theory. This involved integrating out into the distant future to account for all the advanced waves which might influence the mass of a particle here and now. Hawking used infinity as his upper time limit and showed the integral was divergent. We point out that since the universe is known to be expanding, and accelerating, the upper limit in the advanced wave time integral should not be infinite but is bounded by the Cosmic Event Horizon. This event horizon He represents a barrier between future events that can be observed and those which cannot. We show that the advanced wave integral is finite when He/C, is used as the upper limit of the advanced wave integral. Hawking’s objection is no longer valid and the HN theory becomes a working theory once again.