For measuring the polarization, the setup as shown in Fig. 1 was prepared.
The angle of the HWP #2 was 30 degree.
Rotating the angle of the HWP #3, I measured the laser power with a power meter and a PD.
And I fitted the measured data to the function, .
Here \theta is the angle of the HWP #3.
The result was shown in Fig. 2 and the paremeters were determined as
(with the power meter) a = 7.965 +/- 0.0005 mW, b = -0.002 +/- 0.003 mW, phi = -40.65 +/- 0.01,
(with the PD) a = 1373 +/- 3, b = -1 +/ 2, phi = 40.52 +/- 0.03.
Accoding to this result, the S-pol. and the P-pol are obtained at 40.6 degree and 85.6 degree of the angle of the HWP #2, respectively.
And the calbration constant of the PD from voltage to power is determined roughly as 5.8*10^(-3) W/V. (Systematic errors have not yet been concerned.)