Temporal characterization of individual harmonics of an attosecond pulse train by THz streaking

We report on the temporal pulse characteristics of individual harmonics in an attosecond pulse train by means of photoelectron streaking in a strong low-frequency transient. The scheme allows one to retrieve the pulse durations and first-order chirp of individual harmonics without the need for temporal scanning. The measurements were performed using an intense THz field generated by a tilted phase front technique in ${\mathrm{LiNbO}}_{3}$. We compared the performance of Xe clusters and atomic He as a detection medium and retrieved the temporal properties for harmonics of order 19, 21, 23, 25, and 27. Our measurements confirm that the individual pulse durations and linear chirp decrease by harmonic order.