Polarization Gating in Relativistic Laser-Solid Interactions

High order harmonic generation from relativistic laser-solid interactions (focused intensity of > 10(18) Wcm(-2)) has the potential to serve as a source of bright attosecond radiation. One key mechanism that can generate such radiation is the Relativistically Oscillating Mirror (ROM) where the overdense plasma surface oscillates at relativistic velocities leading to a Doppler upshift of the reflected laser radiation. A major obstacle to the application of such a harmonic source is that the radiation is emitted as a periodic pulse train with the frequency of the driving laser. One route to limiting this emission to a single pulse is to exploit the ellipticity dependence of these mechanisms by forming a pulse whose polarisation varies from circular to linear to circular-a technique known as polarization gating. At small angles of incidence it is expected that the efficiency of the ROM mechanism drops dramatically for circular polarization. Here we present a novel method of implementing this technique for high power laser pulses along with proof of principle experimental results.