Download BeamScope™-P5

Introduction
1.2 FUNCTIONAL DESCRIPTION
BeamScope-P5 implements slit profiling in accordance with the ISO 11146 standard
by using a linear slit scan probe to sample the beam. The following is a brief description
of the working principle.
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The BeamScope scans a slit, slit pair or pinhole in a plane orthogonal to the beam
axis. The energy transmitted by the aperture(s) falls upon a silicon detector and is
measured as a function of lateral slit position. (Germanium and Indium Arsenide
detectors are employed for the longer wavelengths.) In Slit Mode, the normal mode
of operation, the slit is much smaller than the beam diameter. In Knife-Edge Mode
the slit must be wider than the beam diameter.
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The pinhole, single slit, or X-Y slit pair, sits in a fixed position in front of the
detector. All the energy, whether passing through one slit/pinhole or two slits, falls
upon a single detector or upon two detectors connected in parallel.
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The slit plus detector is carried on a rectangular moving carriage which rides on
precision linear bearings in a plane set orthogonal to the beam axis.
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The carriage is driven by a taut stainless steel band. The center section of the band
wraps round and is locked to a capstan on the shaft of a 5-phase stepper motor.
(Similar drive principles are employed in some disk drive heads.)
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The stepper motor is driven in micro-stepping mode at 51,200 steps per revolution
resulting in sub-micron linear steps of the moving carriage. The minimum scanned
range is 120 µm.
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The probe is driven to scan region(s) defined by the search routine. The search
routine actively centers the scanned region about the centroid of the beam profile(s)
and automatically adjusts the width(s) of the scanned region(s).
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For each scanned profile, the amplified detector output amplitude is digitized in 2048
levels using a 12-bit ADC (Analog to Digital Converter), at 2048 intervals spaced
equally across the scanned region.
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The software processes the digitized profile to give the data required for display and
data logging, and feeds back some information to the automatic search routine
above.
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The user configures screen functions to implement the measurements in the desired
manner.
BeamScope-P5
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