Performance of an x‐ray optical time delay line with synchrotron radiation

We describe pump‐probe experiments in the x‐ray region using synchrotron radiation to supply both the pump and probe beams. The time between pump and probe is adjustable on the nanosecond time scale by means of an optical delay line operating in the x‐ray region. With the ‘‘third generation’’ sources presently under construction around the world it should be practicable to study optical excitations using similar techniques to those described here. The initial studies we describe were carried out at the National Synchrotron Light Source. A 30‐μm‐thick silicon [110] crystal was irradiated by white light from a bending magnet. The radiation passing through this sample was monochromated by two silicon [660] reflections in such a way that the monochromatic beam was directed onto the first surface of the thin crystal sample. The surface of this thin crystal was probed by recording the symmetric (220) reflexion 2.78 ns after illumination by the white beam. Techniques for overcoming the background problem resulting from scattering of the white beam by the sample crystal are discussed.