Selected Publications

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By Christoph Schulzke, Mahonri Romero, Michael Ware, and Justin Peatross (et al.)
Abstract:

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.

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By Michael Ware, Aaron Peatross, Daniel Smalley, Daniel Tveten, and Justin Peatross
Abstract:

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 is moved 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 restor-ing 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 Poynt-ing vector in the vicinity of trapped particles. The flow of light energy can provide important clues into the trapping mechanism.

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By Brittni Pratt, Nicholas Atkinson, Daniel Hodge, Mahonri Romero, Christoph Schulzke, Yance Sun, Michael Ware, and Justin Peatross
Abstract:

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 low-density helium (10−3 to 1 Torr) ionized early during the laser pulse. Time-resolved single-photon detection is used to distinguish signal from noise.