On Tuesday, I tried reproducing Pooja's measurements (https://nodus.ligo.caltech.edu:8081/40m/13986). The table below shows the values I got. Pictures of LED circuit, schematic and the setup are attached. The powermeter readings fluctuated quite a bit for input volatges (Vcc) > 8V, therefore, I expect a maximum uncertainity of 50µW to be on a safer side. Though the readings at lower input voltages didn't vary much over time (variation < 2µW), I don't know how relaible the Ophir powermeter is at such low power levels. The optical power output of LED was linear for input voltages 10V to 20V. I'll proceed with the CCD calibration soon.
| Input Voltage (Vcc) in volts |
Optical power |
| 0 (dark reading) |
1.6 nW |
| 2 |
55.4 µW |
| 4 |
215.9 µW |
| 6 |
0.398 mW |
| 8 |
0.585 mW |
| 10 |
0.769 mW |
| 12 |
0.929 mW |
| 14 |
1.065 mW |
| 16 |
1.216 mW |
| 18 |
1.330 mW |
| 20 |
1.437 mW |
| 22 |
1.484 mW |
| 24 |
1.565 mW |
| 26 |
1.644 mW |
| 28 |
1.678 mW |
|