Relativistic light synthesis of femtosecond sawtooth pulses

Formation of femtosecond sawtooth pulses by high harmonic generation from relativistic oscillating mirrors is studied. For oblique incidence of $p$-polarized laser pulse, one can efficiently control the intensity of the first few harmonics by modifying the plasma density gradient at the plasma-vacuum interface. With appropriate choice of the laser amplitude and incidence angle, the generated harmonics can form a millijoule femtosecond sawtooth pulse. The scheme does not rely on phase manipulation and/or pulse synchronization as in the state-of-art methods. It is also shown that such a sawtooth pulse can boost the generation of ultrashort terahertz pulses in laser-plasma interaction by one order of magnitude, as compared with that from the conventional two-color laser pulse.