Yesterday I was asked by Keita to measure the reflectivity of a beam splitter which will be installed in HAM1 next week. This is called M14 in D1000313. I measured it at the OSB optics lab.
According to my measurement :
R = 99.4 +/- 0.1 % for S-polarizing beam at 1064 nm 45 deg.
R = 94.8 +/- 0.9 % for P-polarizing beam at 1064 nm 45 deg.
Some details :
I used the laser which was already setup for the reference cavity and squeezer experiment in the OSB lab. Conveniently there was a PBS already setup after a Faraday on the table and I used it for specifying the polarization of the beam. I put a pick off high reflector in both the transmitted and reflected sides of the PBS so that I don't destroy the existing setup. Then I directed these beams aside and put the BS that I wanted to measure. The incident angle of the beam should be pretty close to 45 deg with an accuracy of 1 deg or so. This was established by comparing the ray trace with the hole locations on the table. Also I put an ND1 attenuator to reduce the power to less than 100 mW so that my power meter can handle.
I measured the power of both reflected and transmitted light of the BS using the Ophir handy power meter. I assumed that loss is very small.
For S -polarization I obtained the following two numbers (also as shown in the attachment ):
R = 42.8 mW / 43.1 mW = 99.3 % and R = 1 - 213.1 uW / 43.1 mW = 99.5 %.Therefore a plausible reflectivity can be
R = (99.3 % + 99.5%) / 2 = 99.4 %.The estimated deviation of this mean value is
sqrt( (99.3 % - 99.4%)^2 + (99.5% - 99.4%)^2 ) / sqrt(2) = 0.1 %.In summary R at S-pol is
99.4 +/- 0.1 %I applied the same procedure for P-pol and obtained
94.8 +/- 0.9 %. This number is close to the specification which is "95 % P-pol".I have added this result in DCC as a supplimental document. See E1000871-v1.