Demonstration of attosecond ionization dynamics inside transparent solids

Attosecond science has arisen from intense light pulses interacting with low density gases. We show that the initiating process—sub-cycle ionization—also survives in large band gap condensed media. Using fused SiO2 as an example, we measure the differential nonlinear absorption between the major and minor axis of elliptically polarized light. Through simulations that include ionization and light propagation, we confirm that changes in the ellipticity between the incident beam and the transmitted beam encode sub-cycle absorption dynamics. As the pulse duration is increased, we observe that sub-cycle ionization is masked by collisional processes. We propose a general class of methods for measuring attosecond dynamics in condensed media.