For confirming if the BRDF of the PD (C30665GH) can be measured, the setup as shown in Fig. 1 is established.
For now, incident angle to the PD is 0 deg for simplicity.
The beam size on the PD (C30665GH) is estimated as 215 um in the x direction and 210 um in the y direction.
If the reflected light is incident to the lens, the light is focued at the PD (PDA100A).
For determining theta_s and aligning the lens, metal tube, and PD (PDA100A), the incident angle is set to theta_s/2 temporally and seeing the reflected light they are placed without PD.
Specifically, the reflected light is cented to the lens and the output of the tube.
After that, the PD (PDA100A) is placed and the incident angle is set to 0 deg.
The distance between lens and PD is 31 cm for theta_s>0, and 23 cm for theta_s<0.
These distances are determined by space constraint.
And also for space constraint, the BRDF cannot be measured at the theta_s beteween 40 and 80 deg.
The incident power is also measured by the PD (PDA100A).
The gain of the PD (PDA100A) was 0 dB at the incident power measurement and 70 dB at the scattered light power measurement.
The BRDF is obtained with folloing equation,
where P_S is the power of the scatterd light, P_i is the power of the incident light, theta_i is the incident angle, dOmega is the solid angle of the detector, r_l is the radius of the lens, and d is the distance between the PD (C30665GH) and the lens.
With the setup and the method, the BRDF is measured for P-pol and S-pol as shown in Figs. 2 and 3.
The error of the Figs. 2 and 3 are determined by the systematic error of the PD and the distance error.
When Figs. 2 and 3 are observed, the BRDF looks to be able to be measured.
However the data quality can be improved.
Thus we are going to scan finer angles and change the incident angle from tomorrow.
angle inc(V) zero sca(mV,P) sca (mV) zero dis(cm)
-90 5.43 0.026 330.0 336.9 328.7 23
-80 5.44 0.027 372.2 375.7 309.1 23
-70 5.44 0.026 295.8 295.1 292.9 23
-60 5.45 0.026 294.1 295.9 288.4 23
-50 5.43 0.027 289.1 288.9 285.2 23
-40 5.44 0.027 294.0 293.6 286.4 23
-30 5.44 0.026 296.3 292.8 282.1 23
-20 5.43 0.028 316.7 309.0 290.3 23
-10 5.44 0.026 366.4 365.7 292.9 23
% BRDF @ 0deg
delimiterIn = ' ';
headerlinesIn = 1;
A = importdata(filename,delimiterIn,headerlinesIn);
G0=1.51*10^3; % V/A
EG0= 0.02; % %
G70=4.75*10^6; % V/A