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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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Journal ArticleDOI
01 Dec 1974-Icarus
TL;DR: In this paper, the rate of evolution of CO from Comet Kohoutex was investigated and shown to be less than that of CH3CN observed before perihelion, and the observations were made approximately two months after perohelion.

1 citations

Book ChapterDOI
01 Jan 1989
TL;DR: In the last two decades, the refinement of radio and infrared techniques, as well as work in space, have provided a remarkable amount of information about the center of our galaxy as mentioned in this paper.
Abstract: Over the last two decades, the refinement of radio and infrared techniques, as well as work in space, have provided a remarkable amount of information about the center of our galaxy. Much of it fits into a more or less understandable and increasingly well-defined pattern. However, some of this information seems to represent phenomena we do not yet understand, and still other measurements appear to challenge us with inconsistencies. Much of the material to be presented at this conference represents new results which will add both to our information and our understanding. It is hoped this first discussion will properly introduce the overall subject, paying particular attention to those areas which are still puzzling or under debate. Because of the wealth of material, the complexity of the subject, and my own limitations, not all of the many important points and questions will be treated, nor treated equally. Fortunately, the many gaps which I must leave will be filled by others, since there are review talks on most of the various, more specific aspects of the field.

1 citations

01 Mar 1981
TL;DR: In this article, the advantages of multiple telescope infrared interferometry are discussed in detail, using the 10 micron region as a specific example, taking into account analytically the distorting effect of turbulent air and discussing the effect of water vapor on seeing.
Abstract: The advantages of multiple telescope infrared interferometry are discussed in detail, using the 10 micron region as a specific example Scale and seeing considerations are addressed, taking into account analytically the distorting effect of turbulent air and discussing the effect of water vapor on seeing The usefulness of fringe phase determination to determine the intensities in the radiation field, and the effect of atmospheric fluctuations on their use, are considered Astrometry by means of interferometry is extensively covered, with examples such as a plot of the fringe phase of o Ceti as a function of time compared with a theoretical fringe phase of the star with a fixed best-fit baseline The sensitivity of an interferometer involving two receiving telescopes is considered Finally, an example of a telescope design for 10-micron interferometry is described and depicted

1 citations

Proceedings ArticleDOI
15 Apr 1987
TL;DR: In this paper, the authors present new measurements of CO submillimeter (J = 7..-->..6) and far-infrared lines in the Galactic center and derive the physical conditions of the dense, warm molecular gas at different positions in the Sgr a circum-nuclear ring.
Abstract: We present new measurements of CO submillimeter (J = 7 ..-->..6) and far-infrared (J = 14 ..-->.. 13, J = 21 ..-->.. 20) lines in the Galactic center. The new data, together with earlier CO measurements, are used to derive the physical conditions of the dense, warm molecular gas at different positions in the Sgr a circum-nuclear ring. From the inner edge of the ring at Rapprox.1.7 pc to Rapprox.6 pc the gas pressure decreases proportional to R/sup -1.6//sup +- //sup 0.4/. The best fit excitation curves indicate that both density and temperature decrease with distance from the center. There is also an azimuthal excitation gradient in the ring. If the molecular gas is directly heated from the center by UV radiation or mass outflow the decrease of excitation is a natural consequence of the R/sup -2/ dependence of the energy density. In the more likely scenario of shock heating fed by the large turbulence of the gas throughout the ring, the excitation gradient may reflect variations in gas density and heating efficiency.

1 citations


Cited by
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Journal ArticleDOI

[...]

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