Quote: 
I and koji setup the measurement of the QPD response to the pitch and yaw displacements of the beam spot.
We did this using a 100mW 1064nm laser. Its power was attenuated to ~ 1.9mW, and the spot size at the QPD position was 60007000 um .
The QPD was put on a translation stage, using which, the center of teh QPD wrt the beam spot could be moved in pitch and yaw.
Following are the measurements :

The old plots looked horrible, and so here is a new plot
The slopes and other stats are
Pitch
Linear model Poly1:
f(x) = p1*x + p2
Coefficients (with 95% confidence bounds):
p1 = 8550 (7684, 9417)
p2 = 2148 (2390, 1906)
Goodness of fit:
SSE: 9944
Rsquare: 0.9923
Adjusted Rsquare: 0.9907
RMSE: 44.59
Yaw
Linear model Poly1:
f(x) = p1*x + p2
Coefficients (with 95% confidence bounds):
p1 = 8310 (8958, 7662)
p2 = 2084 (1916, 2252)
Goodness of fit:
SSE: 6923
Rsquare: 0.9954
Adjusted Rsquare: 0.9945
RMSE: 37.21 