Abstract
Time-resolved resonant inelastic X-ray scattering (RIXS) is one of the developing techniques enabled by the advent of X-ray free electron laser (FEL). It is important to evaluate how the FEL jitter, which is inherent in the self-amplified spontaneous emission process, influences the RIXS measurement. Here, we use a microchannel plate (MCP) based Timepix soft X-ray detector to conduct a time-resolved RIXS measurement at the Ti L3-edge on a charge-density-wave material TiSe2. The fast parallel Timepix readout and single photon sensitivity enable pulse-by-pulse data acquisition and analysis. Due to the FEL jitter, low detection efficiency of spectrometer, and low quantum yield of RIXS process, we find that less than 2% of the X-ray FEL pulses produce signals, preventing acquiring sufficient data statistics while maintaining temporal and energy resolution in this measurement. These limitations can be mitigated by using future X-ray FELs with high repetition rates, approaching MHz such as the European XFEL in Germany and LCLS-II in the USA, as well as by utilizing advanced detectors, such as the prototype used in this study.
Highlights
Time-resolved resonant inelastic X-ray scattering (RIXS) is one of the developing techniques enabled by the advent of X-ray free electron laser (FEL)
While it is possible to increase the readout rate to ~ 100 Hz by binning the 2D image into a 1D spectrum, this could potentially compromise the energy resolution of a RIXS measurement. This method would not meet the demands of future X-ray FEL facilities, such as European XFEL and Linac Coherent Light Source (LCLS)-II, which will operate at much higher FEL repetition rates (~ 30 kHz to 1 MHz)
Microchannel plate (MCP) detectors with Timepix r eadout[29,30] have become available for X-ray detection. These detectors are capable of fast readout operation, allow single photon detection, possess high spatial resolution of ~ 5 to 10 μm limited by the pore size of the microchannel plates, and have high quantum efficiency for soft X-ray as required for RIXS study on quantum materials consist of 3d transition metal elements, such as cuprates and maganites
Summary
Time-resolved resonant inelastic X-ray scattering (RIXS) is one of the developing techniques enabled by the advent of X-ray free electron laser (FEL). Due to the FEL jitter, low detection efficiency of spectrometer, and low quantum yield of RIXS process, we find that less than 2% of the X-ray FEL pulses produce signals, preventing acquiring sufficient data statistics while maintaining temporal and energy resolution in this measurement These limitations can be mitigated by using future X-ray FELs with high repetition rates, approaching MHz such as the European XFEL in Germany and LCLS-II in the USA, as well as by utilizing advanced detectors, such as the prototype used in this study. In order to conduct high resolution RIXS measurements, it is necessary to utilize a two dimensional (2D) detector with fine spatial resolution that can correct and resolve the dispersion of the scattering photon spectrum across the detector These requirements are difficult to meet by commercially available charge coupled device (CCD) detectors for X-rays, whose readout frame rates are usually ~ 1 Hz for low-noise readout with a typical spatial resolution of 20–30 μm. We used such a prototype MCP/Timepix detector to conduct a time-resolved RIXS measurement at LCLS
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