Laser measurement of the LAT detector displacement Jerzy Zachorowski

Instytut Fizyki UJ

Wojciech Wierba

Instytut Fizyki Jądrowej PAN

Optical measurements of detector position • Precision requirement: sub m m transverse 10 m m axially.

• Optical sensors non-contact measurements.

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Possible axial displacement sensors • Interferometers: resolution l /2 or better (down to nm), require continueous illumination, • Triangulation detectors: resolution m m, working distance cm • Photonic detectors: m m-resolution, minimal working distance 3

Position sensitive detectors • Position sensitive photodiodes • CCD (Charge Coupled Device) Matrices • Two detectors allow x,y, j tracking 4

Transverse position Proof-of-principle measurements • Simple CCD camera, • He-Ne red laser, • Laser translated in 50 m m steps 5

Camera pictures 6

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Problems • Color camera instead of B&W • Saturation of the detector • Big pixel size • Large beam 8

Position measurement 220 210 200 190 180 170 160 150 140 130 120 110 100 0 Linear Regression for direkt_B: Y = A + B * X Parameter ----------------------------------------------------------- A Value Error 92,57067 0,72927 B 0,12727 0,00128 ----------------------------------------------------------- (1) (2) 100 200 300 400 500 600 camera position [um] 700 800 900 1000 9

Result • Coefficient: 0,12727pixel/ m m • Resolution 1 m m if the accuracy of determination of the center of the light spot is better than 0.1pixel • Possible!

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To be done • Small-pixel camera, • Picture analysis algorithm, • Micro pointing stability of lasers, • Laser MTBF, • Two lasers? System reliability, • Exposure and readout synchronization.

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