Fig. 2. XUV phase manipulation.

a Scheme of timing and phase control of the XUV pulse pair (violet) by manipulation of the seed pulse (blue) parameters. In this scheme, manipulation of pulse delay τ and phase difference ϕ₂₁ = ϕ₂ − ϕ₁ are decoupled, in contrast to previous work^10,12,15. b Demonstration of XUV phase control in Ramsey-type interference fringes for fixed delay τ = 250 fs and two different phase values ϕ₂₁ recorded for the seed (blue) and its 5th harmonic (violet), respectively. The fringe spacing is inversely proportional to the pulse delay τ, while the fringe phase is directly proportional to the phase difference ϕ₂₁. c Shot-to-shot phase manipulation of XUV pulses for different high harmonics for fixed delay τ = 250 fs. Shown are Ramsey-type fringes of the seed (1H) and harmonic FEL pulses (5H–10H). ϕ₂₁ was incremented by 15 mrad steps between each laser shot leading to a quasi-continuous phase sweep. Full phase rotations of several periods of 2π are demonstrated without modification of τ. At the 10th harmonic, the spectrometer resolution is on the order of the fringe spacing, compromising the data quality slightly. All Ramsey-type fringes correspond to normalized single-shot events with no additional data processing applied.