Spectrally encoded optical/x-ray relative delay with $\sim$10 fs RMS resolution*

We present a spectral encoding technique that measures the single-shot relative delay between optical and x-ray laser pulses at the Linac Coherent Light Source. The technique has now been shown capable of resolving relative delays with an RMS accuracy down to 10 fs for both soft and hard x-rays. We sort the single-shot measurements into time-ordered traces and construct a scanning spectrogram representation of the x-ray/optical cross-correlation reminiscent of frequency resolved optical gating. We will discuss how such measurements can be used to reconstruct the ultrafast material response to the x-ray pulses. Once the material response is known, it may be possible to reverse the algorithm to reconstruct the average temporal shape of the x-ray pulses.