Spatially resolved common-path high-order harmonic interferometry

In this letter we report on interference between high harmonic emission from two longitudinally separated sources driven by the same laser pulse. Compared with previous implementations of in-line interferometry we demonstrate that by analysing the spatially-resolved harmonic signal as a function of longitudinal separation quantum trajectory-dependent interference can be identified. The inline geometry demonstrated here offers a high degree of stability, since both harmonic sources are generated from the same driving pulse, as opposed to pulse replicas, which has typically been the case in other interferometric schemes. The inherent synchronization and high timing stability afforded by this approach offers a new route for the measurement and timing of ultrafast processes