In situ relative phase measurement of two-color field with terahertz radiation

We perform a joint measurement of terahertz waves, high-harmonics and the second harmonic interference generated by ionizing atomic Argon gas in a thin jet moving along the Releigh range of a phase-locked two-color laser field. The measurements show that the optimal phases for terahertz radiation and even-order harmonics change simultaneously along the focal length but the the relative phase between them is locking perfectly at any jet position. This finding implies that terahertz radiation can be used to the relative phase of the two-color field, even the carrier-envelope phase in situ.