We installed a 2 inch diameter lens at the NE viewport of IMC tower, followed by a calibrated power meter at its focus.
The angle of scattering was about 15 and the surface of the lens covered a solid angle of ~7e-4 sr.
The wide-angle BRDF measured on LMA give 16ppm and the estimated stored power in the IMC cavity was about 2630W.
So, the expected scattered power is :
P_scat = Solid_Angle*P_stock*BRDF/pi ~ 10 uW
Another calculation using the PSD specification for the IMC gives the same results (~10uW).
The measurements give 74uW scattered light.
Unfortunately it is very difficult to collect measurements at other scattering angles, so it is very difficult to estimate from this one point the total scattering for the IMC end mirror. Nevertheless, the computed power and the measured one does not seem to be dramatically different even if the measured power is higher, maybe due to the mirror pollution (see entry #31362).
