Simulation of FEL pulse length calculation with THz streaking method

Abstract

Having accurate and comprehensive photon diagnostics for the X-ray pulses delivered by free-electron laser (FEL) facilities is of utmost importance. Along with various parameters of the photon beam (such as photon energy, beam intensity, etc.), the pulse length measurements are particularly useful both for the machine operators to measure the beam parameters and monitor the stability of the machine performance, and for the users carrying out pumpprobe experiments at such facilities to better understand their measurement results. One of the most promising pulse length measurement techniques used for photon diagnostics is the THz streak camera which is capable of simultaneously measuring the lengths of the photon pulses and their arrival times with respect to the pump laser. This work presents simulations of a THz streak camera performance. The simulation procedure utilizes FEL pulses with two different photon energies in hard and soft X-ray regions, respectively. It recreates the energy spectra of the photoelectrons produced by the photon pulses and streaks them by a single-cycle THz pulse. Following the pulseretrieval procedure of the THz streak camera, the lengths were calculated from the streaked spectra. To validate the pulse length calculation procedure, the precision and the accuracy of the method were estimated for streaking configuration corresponding to previously performed experiments. The obtained results show that for the discussed setup the method is capable of measuring FEL pulses with about a femtosecond accuracy and precision.

Dipole phase and photoelectron group delay in inner-shell photoionization

“…The same idea of the THz streak camera allows for a high-precision measurement of the arrival time of an FEL pulse [19][20][21]. The photoionization time delay is also needed for understanding the energy spectra of the photoelectrons created by the FEL pulses [22]. These spectra do not exactly mimic the spectrum of the photon pulse, rather they have contributions from the photon pulse spectrum and the emission spectrum corresponding to the ionization time.…”

Real-Time Tomography of Gas-Jets with a Wollaston Interferometer

“…In this device, the X-ray pulses ionise xenon atoms, and the photoelectrons are streaked by an externally applied Terahertz field [25]. For the X-ray pulse length measurement of SwissFEL, the knowledge of the gas jet diameter determines the maximum interaction length, which is used to assess the Guoy phase shift of the Terahertz wave [26].…”

Approaching the Attosecond Frontier of Dynamics in Matter with the Concept of X-ray Chronoscopy

“…The relationship between the streaked photoelectron spectra and the complicated SASE pulse temporal structure has already been studied (see, e.g., Refs. [24,25]). Herein, we invoke the basis of terahertz streaking method and assess its capability to measure timedependent X-ray pulse profiles at XFELs.…”