Temporal X-ray Reconstruction Using Temporal and Spectral Measurements

Transverse deflecting structures (TDS) are widely used inaccelerator physics to measure the longitudinal density ofparticle bunches. When used in combination with a dispersivesection, the whole longitudinal phase space density canbe imaged. At the Linac Coherent Light Source (LCLS), theinstallation of such a device downstream of the undulatorsenables the reconstruction of the X-ray temporal intensityprofile by comparing longitudinal phase space distributionswith lasing on and lasing off. However, the resolution ofthis TDS is limited to around 1 fs rms (root mean square),and therefore, in most cases, it is not possible to resolvesingle self-amplified spontaneous emission (SASE) spikeswithin one photon pulse.By combining the intensity spectrum from a high resolutionphoton spectrometer and the temporal structure fromthe TDS, the overall resolution is enhanced, thus allowingthe observation of temporal, single SASE spikes. The combineddata from the spectrometer and the TDS is analyzedusing an iterative algorithm to obtain the actual intensityprofile.In this paper, we present the reconstruction algorithm aswell as analyzed data obtained from simulations which showsthe reliability of this method. Real data will be published ata later stage