Cheryl, Rodica
Last Friday we finished the isolation measurements for powers up to 133 W. As we increased the power, we optimized for isolation ratio at 450 mW, 4.70 W and 20 W from the half waveplate and adjusting the pitch/yaw of DKDP, and for powers higher than 20 W we only finetuned from the waveplate's picomotor screw. We measured incident and REFL (using the same water-cooled high power power meter Ophir L250W-SH-ROHS), transmitted (Ophir L300W-LP), forward rejected and isolation beams.
The results are:
| P-inc (W) | Fwd Extinction (dB) | Isolation Ratio (dB) | One way losses (%) |
| 0.45 | 31.35 | 55.85 | 4.55* |
| (*big uncert in PM readings) | |||
| 4.70 | 30.06 | 51.21 | 1.83 |
| 20.90 | 36.07 | 47.73 | 2.13 |
| 54.40 | 34.19 | 37.92 | 1.76 |
| 93.50 | 29.40 | 32.94 | 1.73 |
| 133.30 | 26.45 | 30.11 | 1.55 |
At maximum power we readjusted the orientation of DKDP, returned to 20 W and reoptimized for isolation, and repeated the measurements increasing again to 133 W. Thermal depolarization was higher, but the isolation kept within same levels.
| P-inc (W) | Fwd Extinction (dB) | Isolation Ratio (dB) | One way losses (%) |
| 22.28 | 26.1 | 47.7 | 2.5 |
| 22.28 | 26.2 | 47.6 | 2.5 |
| 55.6 | 27.2 | 41.2 | 2.0 |
| 55.6 | 27.4 | 41.1 | 2.0 |
| 98.7 | 28.4 | 36.1 | 1.8 |
| 98.7 | 28.1 | 35.9 | 1.7 |
| 133.5 | 29.0 | 33.3 | 1.1 |
| 133.5 | 28.9 | 33.4 | 1.3 |
Cheryl took pictures of the DKDP under 140 W incident power with the IR camera, and shows serious scatter on the defects observed predominantly on one side. We will be installing the Faraday with this DKDP piece, but new ones are being purchased to installed at a later date. Picture attached.
