Magnetic scattering experiments with an ultrashort pulsed soft X-ray source using iLGADs

Abstract

Inverse Low Gain Avalanche Diode (iLGAD) sensors developed at the Paul Scherrer Institute (PSI) in collaboration with the Fondazione Bruno Kessler (FBK) have demonstrated an excellent Signal-to-Noise Ratio (SNR) and Quantum Efficiency (QE) in the soft X-ray range. In the current batch, single-photon detection is achievable at 400 eV with an SNR > 5, while the QE surpasses 85 % at 250 eV. Combined with the high frame rates of CMOS readout ASIC, iLGAD sensors make the hybrid pixel detectors excellent candidates for time-resolved magnetic Small Angle X-ray Scattering (mSAXS) experiments in the soft X-ray energy range. In this contribution, we evaluated ILGAD sensors bump-bonded to 25 μm pitch charge-integrating MÖNCH chips at a laser-driven soft X-ray source. During the experiments, we measured energy-dispersed radiation between 600 eV and 1500 eV. These measurements were performed for the iLGAD sensor, as well as for the standard silicon sensor. Using the high-precision electronic trigger of the X-ray source, we were able to synchronise the detector with the X-ray source delivering few-picosecond pulses and optimise the timing parameters for the acquisition. Finally, we successfully performed the mSAXS experiment probing the magnetic domain pattern of a FeGd heterostructure, demonstrating better performance than a MÖNCH detector with a standard silicon sensor. ILGAD sensors achieved a significantly higher photon detection efficiency and, consequently, a higher sensitivity compared to standard silicon sensors under the same conditions, particularly for the lower-energy Fe L3 edge.