Ultrashort laser pulses can give rise to extremely brief, finely sculpted pulses of electric current in a solid . Recently, full reconstruction of energy band structure of a crystal has been demonstrated using high-order harmonic generation (HHG) [2,3]. Here, we show that polarization maps of high-order harmonics can serve to fully characterize vectorial properties of petahertz electron currents generated in crystalline solids by an ultrashort optical driver. Our HHG experiments were performed with a 200-µm-thick zincblende ZnSe crystal. The [1,1,1] axis crystal was oriented along the wave vector of the driver, with the driver field Ed making an angle ψ with the ΓKX axis of the ZnSe Brillouin zone (Figs. 1a, 1b). The driver 160-fs-pulse with a central wavelength 3.6 µm and energy up to 100 µJ was generated as idler beam in 3 stages KTA-based optical parametric amplifier pumped by 1-kHz Yb-regenerative amplifier. The driver field intensity kept below 0.5 TW/cm2 in all experiments, to avoid a laser damage of the crystal.
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