Report on future detector requirements at ESRF

Spatial resolution:
A 2D detector is necessary to record both the direct image and the diffracted spots in all the
directions perpendicular to the beam (a maximum of spots is necessary to reconstruct the
shape of the grains, one quadrant is not enough).
Spatial resolution is used both for direct imaging of the sample and localisation of the
diffraction spots around the image (centroid, area, intensity,…). A pixel size of 1 to 3 µm is
required for imaging. A large field of view is needed to collect the widest possible part of the
diffraction pattern. The image is recorded in parallel beam but the distance between the
sample and the detector can be varied in order to adapt the solid angle of collection of the
diffracted signal. A field of view of 4kx4k pixels (that is 4 x 4 mm 2 with 1 µm pixel size)
would be appreciated. Since the symmetrical diffraction spots (Friedel pairs) are studied, the
useful field of view is square and not rectangular.
Efficiency:
Efficiency should be improved, particularly at high energy. The problem is that the diffracted
beams do not reach the scintillator normally to the surface but with an angle that broadens the
spot. Thus the scintillator should be as thin as possible, even more than for other high
resolution applications.
Dynamic range:
Since the number of photons per pixel is approximately 10 to 100 times higher in the sample
image than in the diffracted spots, dynamic range is a important issue. It should be at least as
it is now: 14 bits.
Linearity:
Current linearity obtained with the FReLoN camera is satisfactory.
Flux on detector:
Flux will be highly dependant on the beamline hosting this detector. It will be at least
comparable to the one currently obtained at ID19, that is between 10 8 and 10 9 photons/s/mm 2 .
Fluxes foreseen on MIA are 10 10 to 10 13 photons/s/mm 2 for the transmitted beam. Thus, one
can foresee 10 8 to 10 11 photons/s/mm 2 for the diffracted spots.
Particular operating conditions:
Since this set-up will be installed on different beamlines, lightness and ease of installation on
any experimental environment would be useful. It should be thought, for example, to separate
even more than in the current FReLoN camera the cooled sensor head from the rest of the
detector.
Required detector
The required detector is a high resolution 2D detector.
Existing detectors
For this application, FReLoN detectors (Atmel 2k14 and Kodak 4M) are currently used.
Short term possibilities
A 4kx4k sensor could be used in frame transfer mode to increase the duty cycle.
Main required improvements
The main expected improvements concern the efficiency and the field of view.
40