Retrieving characteristic times in high harmonic generation from the spectral phase of the emitted radiation

We present a novel experimental approach to retrieve both the ionization and return times in high harmonic generation from the spectral phases of the radiation generated by a two-color femtosecond field. By performing a detailed characterization of the phases as both the ratio and delay between the two colors of the field are varied, we have unraveled specific conditions under which the electrons emerge in a nearly single-color field. This unique feature in the HHG process allows for retrieval of the return times directly from the phases, and subsequently, the born and tunneling times. In addition, it allows for the referencing of the delay scale, which in turn, permits the evaluation of those times under the condition of maximal contribution of the second color. Our findings pave the way towards accessing sub-cycle electron dynamics under the influence of multi-color laser fields.