Ultra-short, ultra-intense laser irradiation of wavelength-scale wires
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We present the data for electron heating by ultra-short, ultra-intense laser irradiation of wavelength-scale wires on the GHOST Laser. The goal of this experiment is to study how the laser couples energy to an isolated, wavelength-scale structure and to compare it with previous results, which demonstrate enhanced heating for planar targets when they have a surface layer of sub-wavelength structures. The unique cylindrical target geometry, as opposed to spherical, freed us from the complications of floating a sub-wavelength particle into the focus of a single pulse of light. Additionally, the lack of spherical symmetry allowed us to study the effect of aligning the cylinder axis parallel or perpendicular to the laser polarization. The targets were made from Wollaston wire, which comes in a large spool and has a silver sheath that can be etched away to reveal a platinum core of a fixed diameter. We used 0.6 micron, 1 micron, 2 micron, and 5 micron and irradiated with a 1 micron, 120 femtosecond laser pulse with a peak intensity on the order of 10¹⁹ watts per square centimeter. Three identical electron spectrometers were placed at three different angles while the target diameter and angle relative to the laser's polarization were varied. The data suggest an increased heating along the laser forward direction for the smallest diameter wires. Specifically, their hot electron distribution has a forward-folded component.