Stéphanie Hustache-Ottini S LEIL SYNCHROTRON iWoRID 2011 – 140 – July 5 th Towards ps and fs diffraction with the XPAD detector S. Hustache-Ottini 1, J.-C. Clemens 2, C. Laulhé 1, K. Medjoubi 1, S. Ravy 1 12

Stéphanie Hustache-Ottini S LEIL SYNCHROTRON iWoRID 2011 – 140 – July 5 th XPAD3 features Hybrid pixel detector for X-ray applications Photon counting electronics X-ray Similar to Pilatus or Medipix

Stéphanie Hustache-Ottini S LEIL SYNCHROTRON iWoRID 2011 – 140 – July 5 th XPAD3 features COUNTERCOUNTER LIFTLIFT LOCALMEMORYLOCALMEMORY Detector Input CfCf CSA OTA Test Input C test Low level threshold gnd V dd XPAD3S / XPAD3C pixel layout Global threshold: 8 bits Local threshold: 6 bits Detection substrate : Si (S) or CdTe (C) Submicron technology (IBM 0.25 µm) Pixel size : 130 × 130 µm 2 Threshold adjustable : keV (S)/ 60 keV (C) Power consumption : 40 μW / pixel 80 × 120 pixels / chip 1 × 1.7 cm photons/s/mm 2 (random) 12 bit rotating counter (overflow read out) for 28 bit dynamics read out in less than 2 ms

Stéphanie Hustache-Ottini S LEIL SYNCHROTRON iWoRID 2011 – 140 – July 5 th Pump probe experiments Excitation of the sample (laser, electric field, …) : the pump Study of the de-excitation (changes in the diffraction pattern) with Synchrotron Radiation (SR) : the probe Mechanical chopper to select the X-ray bunch : slow, expensive, complicated to synchronize Stroboscopic acquisition to get enough statistics 147 ns 70 ps 8-bunch mode at Soleil 147 ns Laser … Selected SR Pulses Repetition rate up to 10 kHz Repetition rate ∼ 1 kHz Chopper Sample Area detector (several Bragg reflections to solve the structure) Δt electrons undulator X-rays

Stéphanie Hustache-Ottini S LEIL SYNCHROTRON iWoRID 2011 – 140 – July 5 th Pump probe experiments with an electronic chopper In the future : in the sliced mode, with a 100 fs SR bunch To get rid of the slow mechanical chopper : use of an electronic chopper by gating the counters of each pixel of XPAD on a selected SR bunch 147 ns 70 ps 8-bunch mode at Soleil 147 ns Laser … Selected SR Pulses Same repetition rate XPAD Repetition rate up to 10 kHz electrons undulator X-rays Signal locked on the RF of the storage ring

Stéphanie Hustache-Ottini S LEIL SYNCHROTRON iWoRID 2011 – 140 – July 5 th Proof of feasibility Test experiment with a single XPAD3.2 chip (june 2010) 1 bunch 2 bunches 3 bunches 12 keV 24 keV Increasing the width of the gate Repetition rate 847 kHz = revolution frequency of the storage ring 147 ns 70 ps 147 ns Total chip intensity as a function of gate length Teflon® sample Increasing the delay of the gate / RF of the storage ring Repetition rate 847 kHz = revolution frequency of the storage ring It works, but with some limitations …

Stéphanie Hustache-Ottini S LEIL SYNCHROTRON iWoRID 2011 – 140 – July 5 th Proof of feasibility Influence of the sensor 1. Charge sharing Energy threshold Total energy E (keV) Fraction of the total intensity (A.U.) Pixel n Pixel n + 1 The comparator is not a Constant Fraction Discriminator The signal induced on the pixel depends on the position Amplitude of the signal (keV) Transit time of pulses in the pixel (ns) Transit time in the pixel measured with a pulser = delay of an infinite gate / pulser for which half of the pulses are counted

Stéphanie Hustache-Ottini S LEIL SYNCHROTRON iWoRID 2011 – 140 – July 5 th Proof of feasibility Influence of the sensor 2. Depth of interaction Charge induced at t after the interaction Where Φ is the weighting potential : Fraction of the induced charge Time (ns)

Stéphanie Hustache-Ottini S LEIL SYNCHROTRON iWoRID 2011 – 140 – July 5 th Qualitative and simple simulations including both effects Comparison with data Proof of feasibility Remark : same threshold setting for both energies Gate width = 60 ns

Stéphanie Hustache-Ottini S LEIL SYNCHROTRON iWoRID 2011 – 140 – July 5 th First “real” experiment on Cristal XPAD3.2 Single module 1 sensor, 7 chips 6-circle diffractometer Open flow N2 cryostat X-rays Threshold settings : E/2 Nd:YAG Laser Sample: [TPA Fe(III)TCC]PF6 Two beam sessions : 8 bunch mode (end of may 2011) Single bunch (beginning of june 2011)

Stéphanie Hustache-Ottini S LEIL SYNCHROTRON iWoRID 2011 – 140 – July 5 th 002 reflection, Acquisition time 20 s, kphi oscillation 0.35° First “real” experiment on Cristal Preliminary results

Stéphanie Hustache-Ottini S LEIL SYNCHROTRON iWoRID 2011 – 140 – July 5 th Conclusions and perspectives Proof of feasibility of chopperless pump-probe experiments with XPAD3.2 Most important limitation : interaction of incoming X-rays in the silicon sensor 8-bunch mode or hybrid mode at Soleil : 147 ns bunch spacing = limit case to separate bunches November 2011 : 10 kHz Laser on Cristal + XPAD3.2 imager (8 modules, 56 chips) Charge sharing Depth of interaction

Stéphanie Hustache-Ottini S LEIL SYNCHROTRON iWoRID 2011 – 140 – July 5 th Thank you !

Stéphanie Hustache-Ottini S LEIL SYNCHROTRON iWoRID 2011 – 140 – July 5 th Qualitative and simple simulations including both effects Comparison with data Proof of feasibility

Stéphanie Hustache-Ottini S LEIL SYNCHROTRON iWoRID 2011 – 140 – July 5 th

Stéphanie Hustache-Ottini S LEIL SYNCHROTRON iWoRID 2011 – 140 – July 5 th 100 ns 90 ns 75 ns

Stéphanie Hustache-Ottini S LEIL SYNCHROTRON iWoRID 2011 – 140 – July 5 th

Stéphanie Hustache-Ottini S LEIL SYNCHROTRON iWoRID 2011 – 140 – July 5 th

Stéphanie Hustache-Ottini S LEIL SYNCHROTRON iWoRID 2011 – 140 – July 5 th

Stéphanie Hustache-Ottini S LEIL SYNCHROTRON iWoRID 2011 – 140 – July 5 th