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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
TL;DR: In this article, it was shown that all the ideas essential to making a laser were known before 1930, but there was no operating laser before 1960. So why didn't the laser come sooner?
Abstract: All the ideas essential to making a laser were known before 1930, but there was no operating laser before 1960. So why didn't the laser come sooner? There are several reasons. One important impedim...

5 citations

Proceedings ArticleDOI
TL;DR: The Infrared Spatial Interferometer (ISI) is a three telescope interferometer system that operates near 11 microns wavelength using heterodyne detection with CO 2 lasers as local oscillators as mentioned in this paper.
Abstract: The Infrared Spatial Interferometer (ISI) is a three telescope interferometer system that operates near 11 microns wavelength using heterodyne detection with CO 2 lasers as local oscillators. Stellar measurements have been made using consistent instrumentation for 20 years, allowing comparisons of stellar sizes of red giant and Mira stars over time intervals which are long in comparison to stellar luminosity periods. Recent visibility and clos ure phase measurements of the star Betelgeuse have been fitted to simple image models and these results have been added to the 17 year record of stellar observations. A new area of investigation of stellar properties at very high spectral resolution will begin in the 2010-2011 observing season. The design of a new digital spectrometer-correlator system is discussed. This system will obtain visibility measurements on-and-off individual spectral lines and the continuum, simultaneously. Keywords: stellar interferometry, in terferometry instrumentati on, mid-infrared astronomy

5 citations

Journal ArticleDOI
TL;DR: A very brief overall account of the progress of microwave spectroscopy, its present capabilities and problems, and some of the directions in which it can be expected to progress are given.
Abstract: Microwave spectroscopy may be defined broadly as the study of interactions between matter and radio waves of wavelengths between a few meters and a few tenths of a millimeter. Although microwave spectroscopy has become prominent since the second world war, in this broad sense it goes back to the nineteenth century, a t least as early as the experiments of Drude on the dielectric properties of matter with Herzian waves. An important step towards the modern form of microwave spectroscopy was the measurement of a broad absorption line in ammonia a t atmospheric pressure in the region near one centimeter wavelength by Cleeton and Williams.' This was in 1934, before the advent of radar and the extensive technical developments in microwave generation and techniques which came with the war. In 1946, after the war-time radar techniques had become available, the possibility of a very high resolution spectroscopy of gases a t low pressure was realized and the NH, spectrum resolved into a large number of fine and hyperfine structure line^.^-^ This high resolution and the availability of surplus radar equipment launched the present, very active investigation of resonance absorption in gases, a field which is sometimes regarded as synonymous with microwave spectroscopy in a more limited sense than that used above. Also in 1946, the first successful observation of a ferromagnetic resonance was made in the microwave regione6 Paramagnetic resonances a t microwave frequencies had been discovered just one year before,6 and several other smaller branches of microwave spectroscopy developed a t about this same time. The conference which resulted in this monograph, then, may be regarded as a celebration of the fifth anniversary of modern microwave spectroscopy. Individual papers in this monograph give excellent summaries of many of the important areas of microwave spectroscopy. This paper will attempt to give a very brief overall account of the progress of microwave spectroscopy, its present capabilities and problems, and some of the directions in which it can be expected to progress. Since most of the participants in the symposium are interested in gas spectroscopy, and since this is the only branch of microwave spectroscopy in which I have very direct experience, primary attention will be given to microwave spectroscopy in gases, with minor reference to paramagnetic resonance and quadrupole resonances in solids. Microwave spectroscopy of gases has been most widely used to obtain information in two general areas, molecular structure and nuclear structure. For molecular structure it gives molecular moments of inertia of one or more isotopic species and hence interatomic distances and bond angles. I t also provides information on electric dipole moments, rotation-vibration interactions, hindered molecular motions, molecular magnetic moments, intermolecular interactions, and hyperfine structure. Hyperfine structure in molecular

5 citations

Book ChapterDOI
TL;DR: In this article, it was shown that failure to detect these radicals does not necessarily imply that these radicals are excessively rare in interstellar space, since various unfavorable factors make the search difficult.
Abstract: Some time ago, optical astronomy was successful in detecting the first molecular species in interstellar space. However, these have been limited to the three diatomic molecules CH, CH+, and CN. Consideration of this list made it rather natural, after the development of microwave astronomy, for some attention to be given to a search for OH, which has a rather strong microwave transition. This molecule was first detected, after a considerable search, by Weinreb et al. [1]. The analogous Λ-doublet transitions in SH and CH have since been searched for assiduously; failure to detect them does not necessarily mean these radicals are excessively rare in interstellar space, since various unfavorable factors make the search difficult.

5 citations

Proceedings ArticleDOI
TL;DR: The U.C. Berkeley Infrared Spatial Interferometer (ISI) as discussed by the authors is a two-to-three-star interferometer operating in the 9-12 micron atmospheric window with CO2 laser local oscillators.
Abstract: The U.C. Berkeley Infrared Spatial Interferometer is a two telescope stellar interferometer operating in the 9-12 micron atmospheric window, utilizing heterodyne detection with CO2 laser local oscillators. Science with the ISI has been focused on the measurements of the spatial distribution of dust and molecules around mass-losing late type stars, and more recently precision measurements of stellar diameters in the mid-infrared avoiding molecular lines. During the past few years, a National Science Foundation sponsored program of expansion from two to three telescopes has been underway. This expansion will allow the ISI to make visibility observations on three simultaneous baselines and a measure a closure phase. The third telescope was completed last year and shipped to Mt. Wilson, and more recently a Central Control Facility and Master Laser Oscillator Facility were also completed and recently shipped to Mt. Wilson. In this paper we report progress on this program and highlight some of the most recent astrophysical results.

5 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