Accurate time delay determination for femtosecond X-ray diffraction experiments

We report on a versatile and accurate method for determining the time delay between femtosecond X-ray and optical pulses in an optical pump/X-ray diffraction probe experiment. Upon excitation with moderate pump fluences, Bragg peaks of thin SrTiO3 (STO)/SrRuO3 (SRO) superlattices display 50% changes in diffracted X-ray intensity, followed by a pronounced lineshift (Δθ/θ=0.03°) on a 10 ps time-scale. A parallel time-resolved measurement of the instantaneous all-optical reflectivity change allows for a precise temporal analysis of the fully reversible X-ray response and gives the time delay zero with an accuracy of ±100 fs.

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