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Introduction

Analysis of LCLS data from Nearly all imaging experiments requires precise coordinate definition of the photon detection spotconducted at LCLS require a precise description of the experimental geometry, especially how one or more area detectors are arranged with respect to the x-ray beam and interaction site.  In pixel array detectors photon energy is usually deposited in a single pixel and hence a description of the experimental geometry should aim to provide the pixel location to a precision should be comparable with or better than its size, for the CSPAD about 100μm.  Apparently, calibration

Determination of the detector and entire experimental setup geometry with to such a precision is a challenging task for many reasons; :

• position of the detector sensors relative to interaction point (IP)  of the photon beam with target is not well known,
• in some cases detector is a composition of other sub-detectors arranged together and consisting of other sub-detectors and so on for a few layers in depth,
• sub-detectors of each layer may have stable positions or be moved by stepping motor relative to each other,
• final level sub-detector is represented by precisely engineered sensor(s) of particular type(s) which geometry needs to be tabulated.

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FIG. 2: Coordinate frame of CSPAD 2x1 sensor. Note that a right-handed rule is used for the coordinate system, so the z-axis is coming out of the page. This "native" sensor frame is initially aligned with the global coordinate system; the sensor is then positioned by applying translations and rotations relative to that native frame.

The CSPAD 2x1 tile has

• 185 rows and 388 columns of pixels,
• regular pixel size is 109.92 × 109.92 μm²,
• pixel size in two middle columns (193 and 194) is 274.80 × 109.92 μm².

The pixel index and coordinates in the tile memory block of size 185×388 can be evaluated as

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