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.

The Nonspherical Shape of Betelgeuse in the Mid-Infrared

Abstract: Three-telescope interferometric observations from the Infrared Spatial Interferometer (ISI) are reported at spatial frequencies that resolve the size and shape of the star Betelgeuse (α Ori) at a wavelength of 11.15 μm with a bandwidth of 0.18 cm-1. The data include closure phase measurements, the first such measurements of a stellar disk in the mid-infrared. The data indicate a clear asymmetry of the stellar surface at these wavelengths. Mechanisms for generating the observed asymmetry via an elliptical shape or a hot spot near the southern limb of the star are discussed.

Far-infrared spectroscopy of the galactic center: neutral and ionized gas in the central 10 parsecs of the Galaxy

Abstract: The 3P1 - 3P2 fine structure line emission from neutral atomic oxygen at 63 microns in the vicinity of the galactic center was mapped. The emission is extended over more than 4' (12 pc) along the galactic plane, centered on the position of Sgr A West. The line center velocities show that the O I gas is rotating around the galactic center with an axis close to that of the general galactic rotation, but there appear also to be noncircular motions. The rotational velocity at R is approximately 1 pc corresponds to a mass within the central pc of about 3 x 10(6) solar mass. Between 1 and 6 pc from the center the mass is approximately proportional to radius. The (O I) line probability arises in a predominantly neutral, atomic region immediately outside of the ionized central parsec of out galaxy. Hydrogen densities in the (O I) emitting region are 10(3) to 10(6) cm(-3) and gas temperatures are or = 100 K. The total integrated luminosity radiated in the line is about 10(5) solar luminosity, and is a substantial contribution to the cooling of the gas. Photoelectric heating or heating by ultraviolet excitation of H2 at high densities (10(5) cm(-3)) are promising mechanisms for heating of the gas, but heating due to dissipation of noncircular motions of the gas may be an alternative possibility. The 3P1 - 3P0 fine structure line of (O III) at 88 microns toward Sgr A West was also detected. The (O III) emission comes from high density ionized gas (n 10(4) cm(-3)), and there is no evidence for a medium density region (n 10(3) cm(-3)), such as the ionized halo in Sgr A West deduced from radio observations. This radio halo may be nonthermal, or may consist of many compact, dense clumps of filaments on the inner edges of neutral condensations at R or = 2 pc.

Small rotating clouds of stellar mass in Orion molecular cloud 1

Abstract: A region in the Orion molecular cloud containing NH/sub 3/ and 3''.5 north of BN/KL has been examined with the high angular and spectral resolution of the VLA. Observations of the NH/sub 3/(1,1) and (2,2) inverison transitions reveal at least two small cloud fragments about 0.05 pc across that rotate rather rapidly and have masses approximating that of normal stars. Optical depth of the (1,1) transition is tau = 7 and the temperature is about 20 K. These clumps are likely candidates for a stage of cloud development shortly before the formation of low-mass protostars.

A systematic change with time in the size of betelgeuse

Abstract: The diameter of Betelgeuse (α Orionis) has been measured at a wavelength of 11.15 μm using the Infrared Spatial Interferometer over the past 15 years. During this 1993-2009 time period the star's size has decreased systematically by 15%.

I and i

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 …

Electromagnetically induced transparency : Optics in coherent media

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.

Comparison of quantum and semiclassical radiation theories with application to the beam maser

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.

Nonlinear optics

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.

The Confrontation Between General Relativity and Experiment

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.