Temporal X-ray Reconstruction using Temporal and Spectral Measurements at LCLS

TL;DR

This paper enhances X-ray temporal profile reconstruction at LCLS by combining TDS and spectral data, improving resolution to observe individual SASE spikes within photon pulses.

Contribution

It introduces improved algorithms for combining TDS and spectral measurements, enabling higher-resolution X-ray temporal reconstructions at LCLS.

Findings

Enhanced resolution allows observation of single SASE spikes.

Improved reconstruction algorithms increase accuracy.

Real data demonstrates practical effectiveness.

Abstract

Transverse deflecting structures (TDS) are widely used in accelerator physics to measure the longitudinal density of particle bunches. When used in combination with a dispersive section, the whole longitudinal phase space density can be imaged. At the Linac Coherent Light Source (LCLS), the installation of such a device downstream of the undulators enables the reconstruction of the X-ray temporal intensity profile by comparing longitudinal phase space distributions with lasing on and lasing off. However, the resolution of this TDS is limited to around 1 fs rms (root mean square), and therefore, it is not possible to resolve single self-amplified spontaneous emission (SASE) spikes within one X-ray photon pulse. By combining the power spectrum from a high resolution photon spectrometer and the temporal structure from the TDS, the overall resolution is enhanced, thus allowing the observation of temporal, single SASE spikes. The combined data from the spectrometer and the TDS is analyzed using an iterative algorithm to obtain the actual intensity profile. In this paper, we present some improvements to the reconstruction algorithm as well as real data taken at LCLS.