We placed a power meter after the fiber collimator, 75mm focal length lens and HR mirror at 45 degrees - basically, we placed the power meter immediately before the input window to the cryo chamber after all the intervening optics from the fiber output.
For a series of laser diode current levels, we measured the power on the power meter and the corresponding voltage on the reference photodetector that is monitoring a 10% pick-off from the laser. The calibration is as follows:
| Diode current (mA) |
REF PD (V) |
Laser Power (mW) |
| 100.83 |
1.048 |
1.171 |
| 90.75 |
0.941 |
1.043 |
| 80.66 |
0.827 |
0.904 |
| 70.56 |
0.708 |
0.763 |
| 60.47 |
0.596 |
0.627 |
| 50.45 |
0.48 |
0.485 |
| 39.92 |
0.357 |
0.338 |
| 29.82 |
0.237 |
0.191 |
| 19.73 |
0.117 |
0.045 |
| 9.64 |
0.080 |
0.000 |
| 0.00 |
0.080 |
0.000 |
|