Impact of oblique reflections on the generation of isolated attosecond pulses by polarization gating

Isolated attosecond pulses are often generated via sub-optical-cycle polarization gating. This technique, based on the precise control of the time-dependent polarization of the infrared driver pulse, enables strong temporal confinement of the extreme ultraviolet (XUV) emission from high-order harmonic generation (HHG) in gases. In this work, we study the influence of pulse propagation between the position where the polarization gate is created and the nonlinear HHG medium on the generation of isolated attosecond pulses. Oblique reflections on mirrors, in particular, lead to a significant polarization-dependent carrier phase shift and group delay. In our experiments, seven reflections of the few-cycle infrared driver pulse on metallic mirrors at 45° lead to a delay of 2.8 fs, which is large enough to destroy the polarization gate. When these effects are precompensated, efficient XUV confinement via sub-cycle polarization gating is evidenced by continuous XUV spectra which strongly depend on the carrier-envelope phase (CEP).