Edge Sensors for the Schwarzschild-Couder Telescopes David Hanna McGill University UCLA AGIS Meeting...
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Transcript of Edge Sensors for the Schwarzschild-Couder Telescopes David Hanna McGill University UCLA AGIS Meeting...
![Page 1: Edge Sensors for the Schwarzschild-Couder Telescopes David Hanna McGill University UCLA AGIS Meeting June 26-27, 2008.](https://reader031.fdocuments.in/reader031/viewer/2022032104/56649c8b5503460f94945c8b/html5/thumbnails/1.jpg)
Edge Sensors for the Schwarzschild-Couder Telescopes
David HannaMcGill University
UCLA AGIS MeetingJune 26-27, 2008
![Page 2: Edge Sensors for the Schwarzschild-Couder Telescopes David Hanna McGill University UCLA AGIS Meeting June 26-27, 2008.](https://reader031.fdocuments.in/reader031/viewer/2022032104/56649c8b5503460f94945c8b/html5/thumbnails/2.jpg)
The Requirement:
facets on the S-C telescopes need to be positioned to a tolerance of the order of 10 microns
light-weight optical support structure will undergodeformations of at least this scale while tracking sources
a system of actuators to dynamically correct the facets’ positions and orientations is planned
a related system to measure the facets’ positions and orientations must be developed
![Page 3: Edge Sensors for the Schwarzschild-Couder Telescopes David Hanna McGill University UCLA AGIS Meeting June 26-27, 2008.](https://reader031.fdocuments.in/reader031/viewer/2022032104/56649c8b5503460f94945c8b/html5/thumbnails/3.jpg)
Edge Sensors
to measure the displacement of one mirror facet with respect to its neighbour we plan to use a system of position-sensitive detectors (PSDs) illuminated by diode lasers or collimated LEDs.
relative motion of the two facets causes the position of the beam spot on the PSD to be displaced; the job of the actuatorsis to move the facets in order to put the spot back to itsnominal position
light sourcePSD
beam
Mirror 1 Mirror 2
![Page 4: Edge Sensors for the Schwarzschild-Couder Telescopes David Hanna McGill University UCLA AGIS Meeting June 26-27, 2008.](https://reader031.fdocuments.in/reader031/viewer/2022032104/56649c8b5503460f94945c8b/html5/thumbnails/4.jpg)
for the PSD, we are evaluating a lateral-effect photodiodeof the pin-cushion type ( Hamamatsu S5991).
- electrodes on the edges of the silicon photodiodecollect charges produced by the illumination of the PSD.
- ratios of currents from electrodes on opposite sides are used to calculate the centroid of the light pool.
- thus the device is non-imaging.
- shaped electrodes increase linearity near the edges and produce the pin-cushion-shaped sensitive area.
figure from Circuit Cellar(www.circuitcellar.com)
Position Sensitive Detectors (PSDs)
![Page 5: Edge Sensors for the Schwarzschild-Couder Telescopes David Hanna McGill University UCLA AGIS Meeting June 26-27, 2008.](https://reader031.fdocuments.in/reader031/viewer/2022032104/56649c8b5503460f94945c8b/html5/thumbnails/5.jpg)
15 mm
- this PSD model is available for $30 each in large quantities.
- resolution is 1.5 m
Hamamatsu S5991
![Page 6: Edge Sensors for the Schwarzschild-Couder Telescopes David Hanna McGill University UCLA AGIS Meeting June 26-27, 2008.](https://reader031.fdocuments.in/reader031/viewer/2022032104/56649c8b5503460f94945c8b/html5/thumbnails/6.jpg)
Light Sources:
we have two options: laser diode and light-emitting diode (LED)
LED – blue(465 nm) Optek Technology ~ $0.70
(shown here with collimator, 1 mm diameter 10 mm long)
LASER diode- red (650 nm) BEA lasers ~ $60
The LED can be made bright enough for our purposes but the forward current(80 mA) is larger than the suggested maximum (20 mA)
Probably OK since - collimator acts as a very effective heat sink- we can use the LED in a low-duty-cycle mode (needs study)
![Page 7: Edge Sensors for the Schwarzschild-Couder Telescopes David Hanna McGill University UCLA AGIS Meeting June 26-27, 2008.](https://reader031.fdocuments.in/reader031/viewer/2022032104/56649c8b5503460f94945c8b/html5/thumbnails/7.jpg)
Hamamatsu provides a circuit for reading out the PSD.
We have carried out tests on accuracy and stability using the setup shown at the right;
the collimated LED is attachedto an X-Y-Z translation devicewhich is used to make controlledscans across the PSD
- the blue spot below the PSDshows the size of the beam spot obtained using the simple collimator
System Evaluation
![Page 8: Edge Sensors for the Schwarzschild-Couder Telescopes David Hanna McGill University UCLA AGIS Meeting June 26-27, 2008.](https://reader031.fdocuments.in/reader031/viewer/2022032104/56649c8b5503460f94945c8b/html5/thumbnails/8.jpg)
Scan in x and y
use micrometer translator to change laser spot position on PSD
compare PSD reading with translator position
repeat to test for reproducibility
![Page 9: Edge Sensors for the Schwarzschild-Couder Telescopes David Hanna McGill University UCLA AGIS Meeting June 26-27, 2008.](https://reader031.fdocuments.in/reader031/viewer/2022032104/56649c8b5503460f94945c8b/html5/thumbnails/9.jpg)
Overnight Stability Test
leave LED on for 16 hours
record x, y and current
sunrise
+/- 10 um
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Electronics Developments
single PSD circuit
op-amps turn currents into voltages for ADCsto digitize
![Page 11: Edge Sensors for the Schwarzschild-Couder Telescopes David Hanna McGill University UCLA AGIS Meeting June 26-27, 2008.](https://reader031.fdocuments.in/reader031/viewer/2022032104/56649c8b5503460f94945c8b/html5/thumbnails/11.jpg)
4-PSD op-amp board
![Page 12: Edge Sensors for the Schwarzschild-Couder Telescopes David Hanna McGill University UCLA AGIS Meeting June 26-27, 2008.](https://reader031.fdocuments.in/reader031/viewer/2022032104/56649c8b5503460f94945c8b/html5/thumbnails/12.jpg)
Present status and future plans
PSDs and op-amp circuits now at UCLA awaiting tests on mechanical setup
new circuit which puts ADC near the op-amp (ie send digital information over cables to improve noise rejection) to be developed this summer at McGill