The target geometry plays an important role in the laser-to-electron conversion efficiency, the electron transport in the dense target plasma, as well as the properties of the generated hot electron beam. The cone target design for enhancing both the energy coupling and electron yield has attracted much attention.

Researchers at Shanghai Institute of Optics and Fines Mechanics (SIOM/China) and Institute of Applied Physics and Computational Mathematics have been investigated the dependence of the laser-target energy coupling, conversion efficiency and characteristics of the hot electrons on the laser intensity, laser pulse duration, interlayer vacuum spacing, and the width and length of nanolayers.[PHYSICS OF PLASMAS 18, 054501 (2011)] 

Two-dimensional PIC simulations show that the use a cone-nanolayer target can improve the efficiency of laser absorption and enhance the yield of hot electrons. The enhanced absorption can be attributed to the much increased regions for laser-plasma interaction and thus the total absorption area, as well as the nonlinear deflection/reflection induced focusing of laser energy in the cone. The nanolayer structure acts like a reduced-mass solid target offering much deeper laser penetration. The hot electrons generated by the cone-nanolayer target are still confined to near the center of the cone tip, resulting in enhanced electron yield and reduced transverse divergence. With the proposed composite target, one can generate controllable hot electron beams by tailoring the parameters of the laser, cone, and nanaolayers. It can thus be useful as a source of collimated energetic electron beams for various applications.