This page describes the design of a new quadrant photodetector.
The main applications are for DC beam sensing and optical lever servos. These are non-critical applications.
The DC beam sensing ones are mainly for beams on the PSL and IO optics. We should also add a QPD to each of the ISC readout paths.
The basic idea is to make an updated version of Jay's circuit ([http://www.ligo.caltech.edu/%7Ejay/drawings/d980325-c1.pdf D980325-C1]):
- Use a voltage regulator
- Maybe use a different op-amp. The OP497 in Jay's circuit is a good part, but not modern. We want to use something that's not going obsolete soon.
- Use metal film resistors.
- Allow for whitening in the head via some jumpers. Possibly also give slow DC ouputs.
Useful Links
- Application note attachment:AN_940.pdf on selection of low noise opamps.