Natural Science Forum / Physics / Optics / September 2005

There's a reason for that:  LIGO is a bright-field interferometer, so
they use photodiodes--see
http://apex.ligo-wa.caltech.edu/~fjr/SPIE/P040019-00-R.pdf.

Cheers,

Phil Hobbs

Had to look this one up in my old schematics. Is this a recent inquiry?
Anyway I have a response if you care to forward it.

The photodiode used for the LIGO Length Sensing and Control System (LSC) is
an InGaAs photodiode (C30642) that was made by EG&G. I believe they are
currently made by Perkin Elmer. I used a precision cutting device that I
think came from Thor Labs to cut the window off of the tops of the TO-5
cans. This allowed us to use the diode at the Brewster angle from the
laser. This all took place between 1996 and 2000 when I was principal
design engineer on the LSC and GPS Timing System at LIGO. But I'm sure from
recent publications that they are still using the same diodes.

Regards,
Dale Ouimette