High order modes of intense second harmonic light produced from a plasma aperture

Due to their ability to sustain extremely high amplitude electromagnetic fields and transient density and field profiles, plasma optical components are being developed to amplify, compress and condition high power laser pulses. We recently demonstrated the potential to use a relativistic plasma aperture, produced during the interaction of a high power laser pulse with an ultrathin foil target, to tailor the spatio-temporal properties of intense fundamental and second harmonic light generated [Duff et al., Scientific Reports 10, 105 (2020)]. Here, we numerically explore the interaction of an intense laser pulse with a preformed aperture target to generate second harmonic laser light with higher-order spatial modes. The maximum generation efficiency is found for aperture diameter close to the full width at half maximum of the laser focus and for target thickness on the micron-scale. The spatial mode generated is shown to depend strongly on the polarisation of the drive laser pulse, which enables changing between a linearly polarised TEM01 and a circularly polarised Laguerre–Gaussian, LG01, mode. This demonstrates the use of a plasma aperture to generate intense, higher frequency light with selectable spatial mode structure.