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Novel Semi-Transparent Optical Position Sensors for high-precision alignment monitoring applications Sandra Horvat, F.Bauer, V.Danielyan, H.Kroha Max-Planck-Institute for Physics, Munich,Germany 13.06.2002. Orlando, Florida Slide 2 Introduction ATLAS detector @CERN End-Cap Octant Sandra Horvat 1/13 MPI for Physics,Munich ALMY System: high-precision alignment monitoring designed for high energy physics experiments laser beam along the alignment line ALMY sensors measure its position Requirements: high position resolution high transmittance insensitivity to high magnetic fields long term illumination radiation hardness 23 m Slide 3 ALMY Optical Monitoring System Sandra Horvat 2/13 MPI for Physics,Munich Multi-point measurement of the laser beam position : collimated laser beams (690 nm and 780 nm) single mode fibers (SMF), gaussian beam profile semi-transparent silicon sensors for 2D position measurement, from the induced photo current distribution Slide 4 ALMY Optical Position Sensors Transparent active surface: chemical vapour deposition of a-Si:H layer (0.3-1.0 m) from the plasma phase 2 layers of ITO electrodes (50-100 nm) glass substrate (0.5-1.0 mm) anti-reflective coating Custom designed readout electronics: analog signal multiplexed, amplified (I-V converter), digitized, transmitted to PC for online analysis readout speed: 10 ms up to 30 sensors serially to PC port only commercial components laser controler 64x64 diodes, 312.5 m pitch, 20x20 mm 2 6 cm Sandra Horvat 3/13 MPI for Physics,Munich Slide 5 Setup for the Sensor Tests Scan of the sensor surface with a laser beam, using stepping motors of 1 m positioning accuracy position resolution photo current response laser beam deflection transmittance long term illumination ~200 sensors Sandra Horvat 4/13 MPI for Physics,Munich Slide 6 Transmittance transmittance @780 nm: 80-90% transmittance @690 nm: 70-75% Minimized reflectivity: optimized thicknesses of a-Si:H and ITO layers anti-reflective coating on the back side of the glass up to 10 sensors along the 780 nm beam Sandra Horvat 5/13 MPI for Physics,Munich Slide 7 Photo Current Response Finite wedge angle of the glass substrate can cause the interference patterns, due to the reflected light. Efficiently suppresed! anti-reflective coating laser diodes with short coherence length uniform distribution over the whole surface laser beam profile remains undistorted Sensitivity: 0.1 A/W @690 nm 0.01 A/W @780 nm Saturation (strip current 1 A): 1 mW/cm 2 @690 nm 10 mW/cm 2 @780 nm Sandra Horvat 6/13 MPI for Physics,Munich Slide 8 Position Resolution 5.012 m 5.746 m Typical production batch: S/N>1000 local resolution: 1 m overall resolution: 5 m uniform distribution Sandra Horvat 7/13 MPI for Physics,Munich Slide 9 Laser Beam Deflection specially polished glass wafers parallel surfaces remain undeformed during the antireflecive coating deflection