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Charles H. Townes

Bio: Charles H. Townes is an academic researcher from University of California, Berkeley. The author has contributed to research in topics: Infrared Spatial Interferometer & Interferometry. The author has an hindex of 62, co-authored 345 publications receiving 19318 citations. Previous affiliations of Charles H. Townes include University of California & University of California, Santa Cruz.


Papers
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TL;DR: The techniques of quantum electronics allow interesting new ways to generate and explore most of the acoustic spectrum and much of the electromagnetic domain, and we can look forward to another decade of rapid development in this field from the time when man first saw the sunlight until very recently.
Abstract: The techniques of quantum electronics allow interesting new ways to generate and explore most of the acoustic spectrum and much of the electromagnetic domain. We can look forward to another decade of rapid development in this field From the time when man first saw the sunlight until very recently, the light which he has used has come predominantly from spontaneous emission, like the random emission of incandescent sources. So have most other types of electromagnetic radiation — infrared, ultraviolet, or gamma rays. The maximum radiation intensities, or specifically the power radiated per unit area per unit solid angle per unit frequency bandwidth, have been controlled by Planck's black-body law for radiation from hot objects. This sets an upper limit on radiation intensity — a limit which increases with increasing temperature, but we have had available temperatures of only a few tens of thousands or possibly a few millions of degrees.

8 citations

01 Jan 2002
TL;DR: In this article, it was shown that more extensive corrections can be made by measurements of backscattered lidar radiation sent along the direction of the direction in which a substantial fraction of path length is affected by atmospheric seeing distortions within 20¨30 m of ground level.
Abstract: Adaptive optics provides a method for improving telescope imaging aUected by atmospheric seeing distortions, but the diUerences in path length —uctuations through the atmosphere to two or more separate telescopes continues to limit the quality of stellar interferometry, and unfortunately is not ameliorated by adaptive optics. Some corrections to such —uctuations can be made by atmospheric density measurements near the ground, particularly since in some cases a substantial fraction of path length —uctuations occur in the atmosphere within 20¨30 m of ground level. It is shown that more extensive corrections can be made by measurements of backscattered lidar radiation sent along the direction

8 citations

Journal ArticleDOI
TL;DR: In this paper, three-baseline interferometry data from a linear array of telescopes is used to create a one-dimensional image of the star and circumstellar dust, which yields some insight into the two-dimensional structure of IRC +10216.
Abstract: The unusual source IRC +10216 is the brightest stellar object at mid-infrared wavelengths in the northern hemisphere. Adding to its distinctiveness, the dust around IRC +10216 almost completely enshrouds the star and has an extremely complex distribution. We report the imaging of IRC +10216 at 11.15 μm with three telescopes and the closure phase at two different stellar phases. Three-baseline interferometry data from a linear array of telescopes is used to create a one-dimensional image of the star and circumstellar dust. The two epochs over which data have been taken provide information at different position angles, which yields some insight into the two-dimensional structure of IRC +10216. Specifically, we observe two areas of peaked intensity. The first is 66 ± 4 mas to the west and 160 ± 51 mas to the south of the star, and the second is 227 ± 8 mas to the east and 94 ± 57 mas to the south. These two features can explain most of the observed asymmetry.

8 citations

Journal ArticleDOI
TL;DR: In this paper, the MPE/UCB Far Infrared Fabry-Perot Imaging Spectrometer (FIFI) images of galaxies have been made using the FIFI on the KAO with 55" resolution.

8 citations

Journal ArticleDOI
TL;DR: Visibility data and analyses for 16 late-type stars observed with the Infrared Spatial Interferometer (ISI) of the University of California, Berkeley are discussed in this article.
Abstract: Visibility data and analyses are discussed for 16 late-type stars observed with the Infrared Spatial Interferometer (ISI) of the University of California, Berkeley.

8 citations


Cited by
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[...]

08 Dec 2001-BMJ
TL;DR: There is, I think, something ethereal about i —the square root of minus one, which seems an odd beast at that time—an intruder hovering on the edge of reality.
Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

33,785 citations

Journal ArticleDOI
TL;DR: In this paper, the authors consider the atomic dynamics and the optical response of the medium to a continuous-wave laser and show how coherently prepared media can be used to improve frequency conversion in nonlinear optical mixing experiments.
Abstract: Coherent preparation by laser light of quantum states of atoms and molecules can lead to quantum interference in the amplitudes of optical transitions. In this way the optical properties of a medium can be dramatically modified, leading to electromagnetically induced transparency and related effects, which have placed gas-phase systems at the center of recent advances in the development of media with radically new optical properties. This article reviews these advances and the new possibilities they offer for nonlinear optics and quantum information science. As a basis for the theory of electromagnetically induced transparency the authors consider the atomic dynamics and the optical response of the medium to a continuous-wave laser. They then discuss pulse propagation and the adiabatic evolution of field-coupled states and show how coherently prepared media can be used to improve frequency conversion in nonlinear optical mixing experiments. The extension of these concepts to very weak optical fields in the few-photon limit is then examined. The review concludes with a discussion of future prospects and potential new applications.

4,218 citations

Journal ArticleDOI
01 Jan 1963
TL;DR: In this article, it was shown that the semiclassical theory, when extended to take into account both the effect of the field on the molecules and the effects of the molecules on the field, reproduces the same laws of energy exchange and coherence properties as the quantized field theory, even in the limit of one or a few quanta in the field mode.
Abstract: This paper has two purposes: 1) to clarify the relationship between the quantum theory of radiation, where the electromagnetic field-expansion coefficients satisfy commutation relations, and the semiclassical theory, where the electromagnetic field is considered as a definite function of time rather than as an operator; and 2) to apply some of the results in a study of amplitude and frequency stability in a molecular beam maser. In 1), it is shown that the semiclassical theory, when extended te take into account both the effect of the field on the molecules and the effect of the molecules on the field, reproduces almost quantitatively the same laws of energy exchange and coherence properties as the quantized field theory, even in the limit of one or a few quanta in the field mode. In particular, the semiclassical theory is shown to lead to a prediction of spontaneous emission, with the same decay rate as given by quantum electrodynamics, described by the Einstein A coefficients. In 2), the semiclassical theory is applied to the molecular beam maser. Equilibrium amplitude and frequency of oscillation are obtained for an arbitrary velocity distribution of focused molecules, generalizing the results obtained previously by Gordon, Zeiger, and Townes for a singel-velocity beam, and by Lamb and Helmer for a Maxwellian beam. A somewhat surprising result is obtained; which is that the measurable properties of the maser, such as starting current, effective molecular Q, etc., depend mostly on the slowest 5 to 10 per cent of the molecules. Next we calculate the effect of amplitude and frequency of oscillation, of small systematic perturbations. We obtain a prediction that stability can be improved by adjusting the system so that the molecules emit all their energy h Ω to the field, then reabsorb part of it, before leaving the cavity. In general, the most stable operation is obtained when the molecules are in the process of absorbing energy from the radiation as they leave the cavity, most unstable when they are still emitting energy at that time. Finally, we consider the response of an oscillating maser to randomly time-varying perturbations. Graphs are given showing predicted response to a small superimposed signal of a frequency near the oscillation frequency. The existence of "noise enhancing" and "noise quieting" modes of operation found here is a general property of any oscillating system in which amplitude is limited by nonlinearity.

3,928 citations

01 Oct 1966
TL;DR: In this method, non-linear susceptibility tensors are introduced which relate the induced dipole moment to a power series expansion in field strengths and the various experimental observations are described and interpreted in terms of this formalism.
Abstract: Recent advances in the field of nonlinear optical phenomena are reviewed with particular empphasis placed on such topics as parametric oscillation self-focusing and trapping of laser beams, and stimulated Raman, Rayleigh, and Brillouin scattering. The optical frequency radiation is treated classically in terms of the amplitudes and phases of the electromagnetic fields. The interactions of light waves in a mterial are then formulated in terms of Maxwell's equations and the electric dipole approximation. In this method, non-linear susceptibility tensors are introdueed which relate the induced dipole moment to a power series expansion in field strengths. The tensor nature and the frequency dependence of the nonlinearity coefficients are considered. The various experimental, observations are described and interpreted in terms of this formalism.

3,893 citations

Journal ArticleDOI
TL;DR: Tests of general relativity at the post-Newtonian level have reached high precision, including the light deflection, the Shapiro time delay, the perihelion advance of Mercury, the Nordtvedt effect in lunar motion, and frame-dragging.
Abstract: The status of experimental tests of general relativity and of theoretical frameworks for analyzing them is reviewed and updated. Einstein’s equivalence principle (EEP) is well supported by experiments such as the Eotvos experiment, tests of local Lorentz invariance and clock experiments. Ongoing tests of EEP and of the inverse square law are searching for new interactions arising from unification or quantum gravity. Tests of general relativity at the post-Newtonian level have reached high precision, including the light deflection, the Shapiro time delay, the perihelion advance of Mercury, the Nordtvedt effect in lunar motion, and frame-dragging. Gravitational wave damping has been detected in an amount that agrees with general relativity to better than half a percent using the Hulse-Taylor binary pulsar, and a growing family of other binary pulsar systems is yielding new tests, especially of strong-field effects. Current and future tests of relativity will center on strong gravity and gravitational waves.

3,394 citations