Abstract
Efficient transport of fast electrons driven by intense laser solid interaction depends crucially on optimal target design. We demonstrate a hybrid target design that incorporates two important features---efficient generation of relativistic electrons and their unimpeded transport in dense media. The target was fabricated on a porous alumina base consisting of an array of sublambda cylindrical holes partially filled with Cu nanorods, such that light field propagates in the hollow channels, located ahead of the metallic fillings. The hollow array acts as an efficient source of hot electrons when driven by relativistically intense, femtosecond laser pulses and shows a 60-fold enhancement in electron flux compared to a solid target. This enhancement is ascribed to an increased penetration of laser through subwavelength pores and enhanced local electric fields. The metal doped part facilitates efficient transport of the generated electrons, due to its large background conductivity. A 4-fold enhancement in target rear side electron flux is observed compared with unfilled porous alumina.
Highlights
The development of intense ultrashort laser pulses has opened up exciting research areas such as high-energydensity science [1], fast ignition scheme of inertial confinement fusion [2,3], compact high-energy particle accelerators [4], and ultrashort x-ray sources [5]
After demonstrating the nanochannel PAA template as an efficient source for hot electron enhancement, we have studied the transport of fast electrons in media of similar geometry but of different conductivity, namely, hollow and metal-filled PAA templates
The penetration depth (L) of fast electrons [26] inside media due to electrical inhibition alone is given as L 1⁄4 3 Â 10À3ðThÞ2ðIabsÞÀ1 m, where is the conductivity in units of 106 ð mÞÀ1, Th is the temperature of fast electrons in keV, and Iabs is the absorbed laser intensity into the target in units of 1017 W=cm2
Summary
The development of intense ultrashort laser pulses has opened up exciting research areas such as high-energydensity science [1], fast ignition scheme of inertial confinement fusion [2,3], compact high-energy particle accelerators [4], and ultrashort x-ray sources [5]. The interaction of intense p-polarized light pulses with solid targets leads to generation of relativistic fast electrons via various collisionless mechanisms [6,7,8]. These fast electron bunches [9] serve as carriers of laser energy from the critical surface to deep inside the target [10]. The realization of an efficient carrier depends crucially upon two aspects: (i) enhanced generation and (ii) unimpeded propagation of fast electrons through the dense plasma. Nanostructuring the surface of the target can lead to an enhancement in the coupling efficiency by almost 100% [11] as surface plasmon excitation and lightning rod effect locally intensify the incident electric field.
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