James Hayden Brownell

Anomalies in electrostatic calibrations for the measurement of the Casimir force in a sphere-plane geometry

Dipartimento di Fisica “Galileo Galilei”, Universit`a di Padova, Via Marzolo 8, Padova 35131, Italy(Dated: December 1, 2008)We have performed precision electrostatic calibrations in the sphere-plane geometry, and observedanomalous behavior. Namely, the scaling exponent of the electrostatic signal with distance was foundto be smaller than expected on the basis of the pure Coulombian contribution, and the residualpotential found to be distance dependent. We argue that these findings affect the accuracy of theelectrostatic calibrations and invite reanalysis of previous determinations of the Casimir force.

Detectability of dissipative motion in quantum vacuum via superradiance

We propose an experiment for generating and detecting vacuum-induced dissipative motion. A high frequency mechanical resonator driven in resonance is expected to dissipate mechanical energy in quantum vacuum via photon emission. The photons are stored in a high quality electromagnetic cavity and detected through their interaction with ultracold alkali-metal atoms prepared in an inverted population of hyperfine states. Superradiant amplification of the generated photons results in a detectable radio-frequency signal temporally distinguishable from the expected background.

Reply to "Comment on 'Anomalies in electrostatic calibrations for the measurement of the Casimir force in a sphere-plane geometry' "

In a recent Comment, Decca et al. [Phys. Rev. A 79, 026101 (2009)] discussed the origin of the anomalies recently reported by us in Phys. Rev. A 78, 036102(R) (2008). Here we restate our view corroborated by their considerations that quantitative geometrical and electrostatic characterizations of the conducting surfaces (a topic not discussed explicitly in the literature until very recently) are critical for the assessment of precision and accuracy of the demonstration of the Casimir force and for deriving meaningful limits on the existence of Yukawian components possibly superimposed to the Newtonian gravitational interaction.

On electrostatic and Casimir force measurements between conducting surfaces in a sphere-plane configuration

We report on measurements of forces acting between two conducting surfaces in a spherical-plane configuration in the 35 nm-1 μm separation range. The measurements are obtained by performing electrostatic calibrations followed by a residuals analysis after subtracting the electrostatic-dependent component. We find in all runs optimal fitting of the calibrations for exponents smaller than the one predicted by electrostatics for an ideal sphere-plane geometry. We also find that the external bias potential necessary to minimize the electrostatic contribution depends on the sphere-plane distance. In spite of these anomalies, by implementing a parametrization-dependent subtraction of the electrostatic contribution we have found evidence for short-distance attractive forces of magnitude comparable to the expected Casimir-Lifshitz force. We finally discuss the relevance of our findings in the more general context of Casimir-Lifshitz force measurements, with particular regard to the critical issues of the electrical and geometrical characterization of the involved surfaces.

A new far infrared free-electron laser

Abstract The operation of a new ultra compact diffraction grating coupled free-electron laser (FEL) has been demonstrated. The basic elements of the device which is termed a grating coupled oscillator (GCO) are the beam in a scanning electron microscope (SEM) and a diffraction grating which is mounted in the e-beam focal region of the SEM. The e-beam is controlled by the SEMs electron optical system and distributed feed back is provided by the grating itself. Recent experimental results are presented and techniques for extending the wavelength and power coverage are discussed.

Designing a grating based free electron laser

A compact far-infrared free electron laser (FEL) driven by a moderate energy beam would have many applications in academic and industrial research. Our goal is to find the optimal operating parameters producing the highest gain for a grating FEL with either a SASE or oscillator configuration. The basic structure consists of a grating bounded above by a roof extending over a portion of its length. The dispersion relation for such a system can be found by expanding the electromagnetic fields in a series of resonant modes. When the fields and the beam have near-synchronous velocities, the fields grow at a rate determined by the imaginary component of ω (k for spatial growth) and group velocity. Relations between gain and beam energy, roof height, tooth depth and angle of curve intersection have been investigated.

SMITH-PURCELL RADIATION FROM A 50 MEV BEAM

Abstract A 50 MeV electron beam and a 1 mm period, 5° blaze, echelle grating have been used to produce radiation in the mid-infrared spectral region. The emission is highly collimated and forward-directed. The intensity level in the few ps pulse (2 nJ/sr) indicates a degree of coherent enhancement.

Modelling superradiant amplification of Casimir photons in very low dissipation cavities

Recent advances in nanotechnology and atomic physics may allow for a demonstration of the dynamical Casimir effect. An array of film bulk acoustic resonators (FBARs) coherently driven at twice the resonant frequency of a high-quality electromagnetic cavity can generate a stationary state of Casimir photons. These are detected using an alkali atom beam prepared in an inverted population of hyperfine states, with an induced superradiant burst producing a detectable radio-frequency signal. We describe here the results of the simulations of the dynamics of superradiance and superfluorescence, with the aim to optimize the parameters for the detectability of Casimir photons. When the superradiant lifetime is shorter than the dissipation time, we find superradiant evolution to be similar in character but dramatically slower than in the usual lossy case.

A new type of high-resolution position sensor for ultra-relativistic beams

The radiation emitted through the interaction of an ultrarelativistic particle with a metallic grating (Smith-Purcell radiation) could be used as a very sensitive position sensor for a future Linear Collider or X-ray FEL, with position resolution of m µ 1 , or better. This article discusses the physical principles underlying the operation of such a device and concludes with some of the practical issues in its implementation.

Coherent tunable FIR source

The operation of a new type of tunable, coherent, ( FIR) source has been demonstrated [1J. The device which may be characterized alternatively as either a grating coupled oscillator (GCO) or a Smith-Purcell free-electron laser (SP-FEL) uses the beam in a scanfling electron microscope (SEM) and a diffraction grating mounted in the e-beam focal region of the SEM to produce the radiation. The device, although new , has many antecedents. Sources which use diraction gratings driven by electron beams to produce both incoherent and coherent radiation have a long history {3—9J. A brief review of the relationship of the present work to earlier devices has been presented elsewhere [2}. The uniqueness of the present source is a consequence of the very bright electron beam in the SEM. Because it is bright. the beam supports collective modes of oscillation that are destabilized by the distributed feedback on the grating and coherent Smith-Purcell radiation is generated. In the present note, recent data will be summa.rized and used as a frame work for discussing theoretical limits to device performance.