Experimental observation of polarization-resolved nonlinear Thomson scattering of elliptically polarized light

Colton Fruhling, Junzhi Wang, Donald Umstadter, Christoph Schulzke, Mahonri Romero, Michael Ware, and Justin Peatross

Phys. Rev. A 104, 053519 – Published 17 November 2021

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.

Received 2 December 2020
Revised 26 October 2021
Accepted 28 October 2021

DOI:https://doi.org/10.1103/PhysRevA.104.053519

Physics Subject Headings (PhySH)

Light-matter interaction Nonlinear optics Polarization of light Second order nonlinear optical processes Strong electromagnetic field effects

Nonperturbative methods Optical spectroscopy Optical techniques Time-resolved light scattering spectroscopy

Atomic, Molecular & OpticalNonlinear Dynamics

Authors & Affiliations

Colton Fruhling ^*, Junzhi Wang , and Donald Umstadter

Department of Physics and Astronomy, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, USA

Christoph Schulzke , Mahonri Romero, Michael Ware, and Justin Peatross^†

Department of Physics and Astronomy, Brigham Young University, Provo, Utah 84602, USA

^*colton.fruhling@huskers.unl.edu
^†peat@byu.edu

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Vol. 104, Iss. 5 — November 2021

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Images

Figure 1
Calculated radiation patterns for the fundamental (left column) and second-harmonic (right column) NTS with $a_{0} = 0.5$ in a plane perpendicular to laser propagation. The calculation is repeated for elliptical laser polarization states $δ = 0, 0.38, 0.52$ . The dashed lines show approximations in Eqs. (3a) and (3b) (only the first terms in square brackets). The units are arbitrary, but the right column was multiplied by 14 to put it on scale with the left column. Blue lines are for perpendicularly polarized light and green lines are for z-polarized light.
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Figure 2
Calculated radiated electric fields scattered at $90^{\circ}$ from the laser propagation. The red arrows are the electric field vector which traces the blue line through time. The top row shows that, for the linear case, the polarization of scattered light is linear regardless of incoming polarization orientation. The bottom row shows complex electric fields generated in a nonlinear interaction.
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Figure 3
Experimental setup. A linearly polarized laser pulse passes through an approximate quarter-wave plate (aQWP), introducing an ellipticity in the polarization, then proceeds through a half-wave plate (HWP) to rotate the polarization. The beam was focused into the interaction region with an off-axis parabola (OAP). The scattered radiation is collected at the equator of the radiation sphere by an imaging system comprising a wire-grid polarizer and a 1:1 lens pair. The collection system is coupled to an optical fiber, where the signal is guided through a bandpass filter and then into a single-photon counter (SPC). The interaction geometry and coordinate system is displayed in the center. Insets (a) and (b) show the electron 3D trajectory for a single cycle of the laser in blue, with respective ellipticities. The labeled yellow, red, and black curves are projections along the $x - y, x - z$ , and $y - z$ planes, respectively. The axes are scaled to the laser wave vector $k$ .
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Figure 4
Number of photons counted per 1000 laser shots in the wavelength range $900 \pm 20 nm$ emitted in the plane perpendicular to laser propagation. Measurements of $⊥$ polarization for different elliptical laser polarization states are shown, all with peak laser field strength $a_{0} = 0.76 \pm 0.04$ . The data are compared with theoretical simulations (solid line) using the model described in Ref. [18] with an ensemble of 10 000 electrons randomly positioned in the laser focus.
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Figure 5
Number of photons counted per 1000 laser shots in the wavelength range $450 \pm 20 nm$ emitted in the plane perpendicular to laser propagation. Measurements of $⊥$ polarization for different elliptical laser polarization states are shown, all with peak laser field strength $a_{0} = 1.52 \pm 0.08$ . The data are compared with theoretical simulations (solid line) using the model described in Ref. [18] with an ensemble of 10 000 electrons randomly positioned in the laser focus.
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Figure 6
Number of photons counted per 1000 laser shots in the wavelength range $450 \pm 20 nm$ emitted in the plane perpendicular to laser propagation. Measurements of $z$ polarization for different elliptical laser polarization states are shown, all with peak laser field strength $a_{0} = 1.52 \pm 0.08$ . The data are compared with theoretical simulations (solid line) using the model described in Ref. [18] for an ensemble of 10 000 electrons randomly positioned in the laser focus.
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