The individual polarization components of nonlinear Thomson scattering arise from the separate dimensions of electron figure-8 motion caused by a linearly polarized laser field. We present the first measurements of nonlinear Thomson scattering in both emission hemispheres. In the electron average rest frame, the shape of the electron figure-8 path is symmetric about the laser polarization dimension. However, the periodic electron velocity is intrinsically asymmetric. The full scattering emission pattern reveals this asymmetry and the direction that electrons move around the figure-8 path.

We measured correlated X-ray photons from parametric down conversion as a means of creating entangled X-rays. Using a Laue diffraction geometry, we measured the efficiency of this process from single crystal diamond samples.

Measurements of first and second harmonic radiation from nonlinear Thom- son scattered light as a function of laser polarization ellipticity are reported. Polarization-resolved patterns were observed and connected to the underlying electron motion, confirming half-century old theoretical predictions.

We report experimental results from a study of nonlinear Thomson scattering of elliptically polarized light. Polarization-resolved radiation patterns of the scattered light are measured as a function of the elliptical polarization state of the incident laser light. The relativistic electron trajectory in intense elliptically polarized fields leads to the formation of unique radiated polarization states, which are observed by our measurements and predicted by a theoretical model. The polarization of Thomson scattered light depends strongly on the intensity of the incident light due to nonlinearity. The results are relevant to high-field electrodynamics and to research and development of light sources with novel capabilities.

Photophoresis can trap opaque microscopic particles in a focused laser beam surrounded by a gas such as air. The particle is heated by the laser, and in turn, interactions with the ambient gas provide a stabilizing force that holds the particle in a specific region of the beam. The particles can stay trapped while the beam ismoved side to side up to 2 m/s, enabling three-dimensional images to be traced out in a display application. Structure in the laser beam is associated with the trapping phenomenon, but the fundamental mechanism for stability of the trap remains mysterious. Particles prefer regions of the beam with diffraction features such as those that arise from spherical aberration. Nevertheless, the ability of near-unidirectional light, albeit light that undergoes focusing and exhibits structure, to provide a restoring force to trapped particles in the direction opposite to beam propagation needs to be explained. Through repeated trials of capturing particles in a well characterized beam, we map out the preferred locations for particle capture and correlate them with diffraction features of the beam. The specific beam locations that host trapped particles, when compared with neighboring regions that do not, can offer insight into the stability mechanism. We analyze the Poynting vector in the vicinity of trapped particles. The flow of light energy can provide important clues into the trapping mechanism.

We measure polarization-resolved fundamental, second, and third harmonic nonlinear Thomson scattering out the side of a laser focus with 1018 W/cm2. The separate measured polarization components are each associated with a distinct dimension of predicted electron figure-8 motion. Taken together, the measured angular emission patterns for the two polarizations unambiguously confirm the figure-8 motion. Electrons are donated from lowdensity helium (10−3 to 1 Torr) ionized early during the laser pulse. Time-resolved single-photon detection is used to distinguish signal from noise.

Lasers are ubiquitous in modern society. They transmit the vast bulk of all information on the internet through fiber optics, are commonly used for medical tasks from dentistry to surgery, play crucial roles in everyday technologies like printing and manufacturing, and are common in almost all disciplines of scientific inquiry. The collimated beam serves as a reference to reveal the phase of the focused beam through interference. Getting a basic understanding of how to manipulate and control them is an essential task for most experimental disciplines. A wave plate is made from a birefringent crystal wherein the index of refraction that light experiences depends on the orientation of its polarization. Wave plates have the appearance of thin windows and do not absorb light. Rather, a wave plate introduces a relative phase delay between field components oriented along the slow axis and the fast axis. These two axes are associated with higher and lower refractive indices, respectively.

We report an all-solid-state gamma-ray scintillation detector comprised of a NaI(Tl) crystal and a scientific-grade CMOS camera. After calibration, this detector exhibits excellent linearity over more than three decades of activity levels ranging from 10 mCi to 400 nCi. Because the detector is not counting pulses, dead-time correction is not required. Compared to systems that use a photomultiplier tube, this detector has similar sensitivity and noise characteristics on short time scales. On longer time scales, we measure drifts of a few percent over several days, which can be accommodated through regular calibration. Using this detector, we observe that when high activity sources are brought into close proximity to the NaI crystal, several minutes are required for the measured signal to achieve a steady state.

The standard method for approaching quantum electrodynamic (QED) field theory uses a perturbative $S$-matrix approach. This approach is explicitly nondynamical and provides only a one-time, static map between an initial state to be evolved by the ``full propagator'' of a bona-fide interacting field theory and an asymptotically equivalent effective initial state to be evolved by the ``free propagator'' of the corresponding noninteracting field theory. We provide a detailed derivation of a nonperturbative and dynamical approach to QED that allows one to study the space-time dynamics of electron-photon interactions directly. As an example of this method, we compute the time-resolved dynamics of Compton scattering for a system with a nontrivial spatial structure in only one dimension while restricting to the case of a single electron and at most one photon. This approach retains the massless photon of quantum electrodynamics in contrast to previous approaches that resorted to using massive bosons [T. Cheng, E. R. Gospodarczyk, Q. Su, and R. Grobe, Ann. Phys. 325, 265 (2010)] to represent the photon. The dynamics of Compton scattering are illustrated using joint probability distributions that evolve in time. This information is compared to that provided by the $S$ matrix.

We demonstrate the linearity and stability of a gamma-ray scintillation detector comprised of a NaI(Tl) crystal and a scientific-grade CMOS camera. After calibration, this detector exhibits excellent linearity more than three decades of activity levels. Because the detector is not counting pulses, no dead-time correction is required. When high activity sources are brought into close proximity to the NaI crystal, several minutes are required for the scintillation to achieve a steady state. On longer time scales, we measure drifts of a few percent over several days. These instabilities have important implications for precision determinations of nuclear decay rate stability.

We assess several widely used vector models of a Gaussian laser beam in the context of more accurate vector diffraction integration. For the analysis, we present a streamlined derivation of the vector fields of a uniformly polarized beam reflected from an ideal parabolic mirror, both inside and outside of the resulting focus. This exact solution to Maxwell's equations, first developed in 1920 by V. S. Ignatovsky, is highly relevant to high-intensity laser experiments since the boundary conditions at a focusing optic dictate the form of the focus in a manner analogous to a physical experiment. In contrast, many models simply assume a field profile near the focus and develop the surrounding vector fields consistent with Maxwell's equations. In comparing the Ignatovsky result with popular closed-form analytic vector models of a Gaussian beam, we find that the relatively simple model developed by Erikson and Singh in 1994 provides good agreement in the paraxial limit. Models involving a Lax expansion introduce a divergences outside of the focus while providing little if any improvement in the focal region. Extremely tight focusing produces a somewhat complicated structure in the focus, and requires the Ignatovsky model for accurate representation.

We develop a model that reduces quantum electrodynamics (QED) in time plus three spatial dimensions to time plus a single spatial dimension, making it is possible to numerically calculate the dynamic behavior of simple QED systems. The dimensionality is restricted in such a way as to preserve the influence of spin and angular momentum. In contrast to the S-matrix scattering approach, these calculations are not perturbative within the zero-and one-photon sector of the relevant Hilbert space. The model restricts the electron occupation number to one and the photon occupation number to zero or one. We use this model to calculate the dynamics of a so-called bare electron that dresses itself by a photon field.

We present calibrated measurements of single-photon Thomson scattering from free electrons driven by a laser with intensity 1018  W/cm2. The measurements demonstrate that individual electrons radiate with the strength of point emitters, even when their wave packets spread to the scale of the driving-laser wavelength. The result agrees with predictions of quantum electrodynamics.

In support of an experiment designed to measure the strength of radiation scattered from low-density free electrons in an intense laser focus, we model a variety of physical parameters that impact the rate of scattered photons. We employ a classical model to characterize duration of electron exposure to high-intensity laser light in a situation where the electrons are driven by strong ponderomotive gradients. Free electrons are modeled as being donated by low-density helium, which undergoes strong-field ionization early in the pulse or during a prepulse. When exposed to relativistic intensities, free electrons experience a Lorentz drift that causes redshifting of the scattered 800 nm light. This redshift can be used as a signature to discern light scattered from the more intense regions of the focus. We characterize the focal volume of initial positions leading to significant redshifting, given a peak intensity of 2 x 10(18) W/cm(2). Under this scenario, the beam waist needs to be larger than several wavelengths for a pulse duration of 35 fs. We compute the rate of redshifted scattered photons from an ensemble of electrons distributed throughout the focus and relate the result to the scattered-photon rate of a single electron. We also estimate to what extent the ionization process may produce unwanted light in the redshifted spectral region. (C) 2015 Optical Society of America

Provo — We report the result from an experimental measurement of light scattered by individual free electrons in an intense laser focus. This system becomes particularly interesting when the electron wavepacket spreads to the scale of an optical wavelength, as naturally happens dur-ing the ionization process of helium in a high-intensity laser focus. As the different parts of the wavepacket oscillate out of phase, the question naturally arises whether the different parts of the wave packet can interfere with each other in the radiative process. If this interference were possible, radiation from an electron wavepacket would be strongly suppressed as it gets larger.