High-Order Harmonic Analysis of Anisotropic Petahertz Photocurrents in Solids

Ultrashort laser pulses can give rise to extremely brief' finely sculpted pulses of electric current in a solid [1]. 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 E d making an angle ψ with the ΓΚΧ 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.