Isolated attosecond pulses generated from a relativistic plasma mirror via noncollinear gating

A train of intense attosecond pulses can be obtained through relativistic high harmonic generation when an intense laser field is reflected on a plasma surface. Separating a single isolated attosecond pulse from the train is critical not only for applications such as time-resolved pump-probe experiments but also for studying laser-plasma interactions with attosecond temporal resolution. Various methods have been developed for an isolated attosecond pulse generation in gas. However, they require ultrashort laser pulses, which are difficult to apply with high-power lasers typically employed in relativistic high harmonic generation. Here, we demonstrate that an isolated attosecond pulse can be obtained through relativistic high harmonic generation using noncollinear temporal gating. Our approach also provides direct access to each attosecond pulse in the train, allowing us to diagnose the laser-plasma interaction, such as plasma denting and reflection positions, in a time-resolved manner. Thus, it offers breakthroughs in attosecond pulse generation at relativistic laser intensities.