Fig. 7: Attosecond interferometry in transmission and reflection configuration.

Experimental setup in a transmission and b reflection, where high harmonics from two sources interfere in the far field. Reproduced with permission from ref. ¹⁰⁶, Copyright 2019, Springer Nature. A representative interferogram is shown in c. Fringe shift as a function of relative change in laser intensities, in transmission. d and in reflection (e). Reflection geometry closely represents the microscopic effects. Fringe shifts in transmission are overwhelmed by propagation effects. Adapted with permission from ref. ¹⁰⁶, Copyright 2019, Springer Nature.