Attenuator for Central Heating

We have tested the attenuator. It works well. In attachment the calibration curve. In this moment we have changed the angle by hand. The motor isn't still mounted. We have positioned the Attenuator after the polarizer. and the laser has worked in maximum power but with power in input to the attenuator of about 4.4 W.

It seems to me there is something strange in these data. First of all, I don't think the numbers on the side of the attenuator are the rotation angle, but rather the transmittivity precentage. According to the manual, the range of the transmitted power should go from a minimum of 0.04% to a maximum of 98% of the incident power. If these measurements are correct, then these limits are 2% to 25%, much less than what reported in the manual.

I have observed that using polarizer the Pout/Pin % decreasing. If we dont' use the polarizer, the % is:

0.04 (trasmission factor) -----> around 29 %
98 (trasmission factor) -------> around 1 %

I have tried to rotate the attenuator in order to have:

0.04 ----> around 1 %
98 -------> around 29 %

But the % is always the same; it is different from manual.

This morning we (Maurizio and I) repeated the measurements. We changed the setup:
Laser--->Polarizer--->Manual attenuator--->Power meter
To get the maximum transmittance we proceeded this way:
- we set the gear to 0.98 (maximum)
- we rotated the whole attenuator body until a maximum power is measured.
We added the polarizer in order to be sure that the light entering the Manual attenuator is totally (or at least as much as possible) P polarized.
With a power of 13.86W entering the Manual attenuator, we get the following output power limits of 4.2W (30%) and 9mW (0.06%). We noticed that the attenuator body becomes warm also when the gear is set to maximum transmittance. This is clear since more than 9W are dissipated inside the attenuator.
We repeated the measurement decreasing the input power to 2.8W, in this case we get Pmax=850mW (30%) and Pmin=1mW (0.04%).
The minimum transmittance is compliant with the specifications found in the manual, while the maximum transmittance is lower by a factor of 3 (it should be 98%).
This will be a problem in the Central Heating telescope, since this will limit the maximum power to about 85-100mW, while when the YAG laser power will be 25W, the required CH power for the WI bench should be about 130mW.
We should check if also the other attenuator behaves this way, but unfortunately we left it in Cascina...

We have done the same measurement with the 2nd attenuator. The setup is

Laser--->Polarizer--->Manual attenuator--->Power meter

The laser works to the maximum power (14,20 W).
The maximum power trasmitted is 6.05 W...around 45 % (Pou/Pin) instead 98 % as indicate in the graduate scale. In the next attenuator this value was around 30 %.

The power trasmitted changed with the input power.