X-ray–optical cross-correlator for gas-phase experiments at the Linac Coherent Light Source free-electron laser

Abstract

X-ray–optical pump–probe experiments at the Linac Coherent Light Source (LCLS) have so far been limited to a time resolution of 280 fs fwhm due to timing jitter between the accelerator-based free-electron laser (FEL) and optical lasers. We have implemented a single-shot cross-correlator for femtosecond x-ray and infrared pulses. A reference experiment relying only on the pulse arrival time information from the cross-correlator shows a time resolution better than 50 fs fwhm (22 fs rms) and also yields a direct measurement of the maximal x-ray pulse length. The improved time resolution enables ultrafast pump–probe experiments with x-ray pulses from LCLS and other FEL sources.

Probing nucleobase photoprotection with soft x-rays

“…1), which is strongly localized at the oxygen atoms (see n orbital in Fig.1). The jitter between the UV laser pump and SXR probe pulse was measured for every shot via a transient reflection [6]. We then resorted our data according to this jitter leading to relative delay accuracy below 100 fs.…”

Single-shot pulse duration monitor for extreme ultraviolet and X-ray free-electron lasers

“…Furthermore, we show a solution allowing the XUV beam to be reused for a simultaneous pump-probe experiment. This novel temporal diagnostic tool can also be applied at X-ray FELs, as recently demonstrated for arrival time monitoring 20,21 .…”

“…High-resolution pump-probe experiments require a precisely characterized FEL pulse and precise synchronization to an external optical pump-probe laser. While so far different schemes for arrival time measurements have been developed [11][12][13][14][15][16][17][18][19][20][21][22][23] , insufficient characterization of the XUV or X-ray FEL pulse duration at the experimental station remains the main handicap of single pass free-electron lasers that rely on self-amplified spontaneous emission (SASE).…”

“…Direct and indirect techniques for XUV and X-ray pulse duration measurement [22][23][24][25][26][27][28][29][30][31][32] and pulse arrival time monitoring [11][12][13][14][15][16][17][18][19][20][21][22][23] are subjects of active research and most are already implemented in the FEL machine environment. In particular for XUV pulses, the experiments must be realized under vacuum conditions.…”

“…Additionally, the synchronization drift of the pump-probe laser to the master clock of the accelerator is also not considered. Another category of diagnostics is to directly measure the timing of the XUV pulses [14][15][16][17][18][19][20][21][22][23] . Most of those measurements, such as X-ray optical cross-correlators, are highly invasive and cannot be performed simultaneously with other pump-probe experiments.…”