Dispersive XAS at third-generation sources:: strengths and limitations

The experience of two years of operation of the ESRF Dispersive XAS beamline is reviewed. The examples of experiments performed show that the advent of third generation sources has given a new perspective to the field of X-ray absorption in the dispersive mode. The achievement of an aberration-free horizontal focal spot of similar to 20 mu m FWHM has opened up unique possibilities for performing X-ray absorption studies in extreme conditions of temperature and pressure. The implementation of quarter wave plates has allowed extremely accurate XMCD and nanosecond-resolved XMCD using the pump-probe scheme to be recorded. However, the reduction of source size combined to the lengthening of beamlines have introduced new problems related to the much higher sensitivity to beam instabilities amplified by phase contrast phenomena. Possibilities for the future have been investigated and shall be discussed.