[Yao-Chin, Aritomi]
Testing method was same as entry 1785. However, we changed laser source to infrared light of 1064 nm. Infrared light hit in the first quarter of QPD2 (QPD2 input 1). We connected the corresponding DC output to the oscilloscope to check DC voltage. We also connected the corresponding RF output to a 32 dB amplifier and then check its power spectrum by a spectrum analyzer (Keysight N9320B).
We measured the light power, DC voltage, DC current by using "PuTTY", and RF channel power spectrum with RBW of 1MHz and average 28 times shown in pic. 1. Dark noise of pic.1 included the 32 dB amplifier and instrument when no IR light hit to QPD. In this measurement, when light power goes up, power loss is going down unlike the measurement in entry 1785. Green power in entry 1785 was too much since maximum DC current is 10mA according to specification and calculated DC current is already more than 10mA with 53.5 mW of green.
Pic. 2 shows same measurement in NIKHEF. The result is similar to our result, but we have some peaks around 25MHz, 125MHz, 140MHz.
|
Light Power [mW] |
DC Voltage [mV] |
DC Current [mA] |
calculated DC current (mA) (photosensitivity is 0.55A/W according to specification) |
power loss (%) (ratio of measured DC current/calculated DC current) |
| 0.58 | 248 | 0 | 0.319 | 100 |
| 1.25 | 504 | 0.1 | 0.688 | 85 |
| 2.5 | 1000 | 0.6 | 1.38 | 57 |
| 3.7 | 1500 | 1.1 | 2.04 | 46 |
| 4.5 | 1940 | 1.5 | 2.48 | 40 |
| 7.3 | 3000 | 2.7 | 4.02 | 33 |
| 9.5 | 4000 | 3.7 | 5.23 | 29 |
| 11.7 | 5000 | 4.8 | 6.44 | 25 |
| 13.5 | 5960 | 5.7 | 7.43 | 23 |
| 15.5 | 7040 | 6.8 | 8.53 | 20 |
| 17 | 8000 | 7.7 | 9.35 | 18 |
