A time-to-space conversion scheme has been investigated to determine the time interval between laser and x-ray pulses. In future pump-probe experiments using ultrashort x-ray pulses, the precise register of the interval of arrival times of the laser and x-ray pulses can make obtained data with a non-negligible jitter be sorted, providing a precision higher than the jitter. This scheme was tested using the SPring-8 synchrotron radiation pulses with a duration of a few tens ps. A femtosecond pulsed laser beam was guided to a GaAs crystal surface with a shallow glancing angle, while an x-ray beam onto the surface from the opposite direction of the laser beam with the similar glancing angle, giving rise to enlarging asymmetric diffraction. The position where the both pulses meet on the surface was identified by observing the change in the diffraction intensity due to the transient expansion of lattice spacing. Since the position is a function of the interval of arrival times of the pulses, the relative arrival time has been determined with a precision of less than the SR pulse duration from the observed spatial distribution of the diffraction intensity.
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