Optical and THz signatures of sub-cycle tunneling dynamics

Abstract We present experimental observation of optical signals induced by tunnel ionization and a theoretical model for the generation of new optical and THz frequencies in media ionized by a high intensity laser field. The emergence of sidebands is treated as an integral part of the same underlying process of electron-plasma emission through tunneling. First, investigating the broadly transparent case of gaseous media, we demonstrate the ability to detect multiple new frequency components in the probe field direction, and describe in detail how such tunnel-ionization induced signals can be reliably separated from concomitant nonlinear responses. Second, we apply the same pump–probe method to transparent dielectrics, thus expanding the field of attosecond physics to systems where direct detection of charged particles is unfeasible. Third, we show that a probe beam with a central frequency tuned close to the half of the pump frequency acquires a tunable sideband with a frequency close to zero.