40m QIL Cryo_Lab CTN SUS_Lab TCS_Lab OMC_Lab CRIME_Lab FEA ENG_Labs OptContFac Mariner WBEEShop | ||||||||||||||||||||||||||||||||||||||||||

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Transimpedance measurements of all RFPDs in PSL were taken at the setup at 40m. All measurement results and data are in the git folder link below. Dark Noise measurement was also attempted but it turned out that the measurement is limited by Agilent 4395A's noise floor and hence this measurement needs to be done again using low noise preamplifiers.
This formula can be derived easily by first taking the ratio of light powers on the two photodiodes at DC and then taking ratio at AC and using photocurrent ratio at DC to substitute for unknown values like power attenuation, the fraction of power falling on PD and ratio of responsivity of the two photodiodes. Note that this circumvents any differences due to the different focusing of light on photodiodes, losses due to mirror and beamsplitter and different responsivities of the two photodiodes. The extra path length () is measured using a ruler. The uncertainty in this measurement and all other measurements are carried forward and described later.
The uncertainty in transfer function measurement is estimated using the method described above. Othe sources of uncertainties are the following: - RFPD DC transimpedance: These are read off from the resistor values in the actual circuit. I have assumed 2% uncertainty in each resistor value in the DC transimpedance circuit. Since transimpedance is created through 3 resistors, the uncertainty is % in the calculated transimpedance.
- Reference Photodiode: Reference Photodiode's marked dc and ac transimpedance are assumed to have 1% error in them. This number came in a discussion with Gautum.
- DC Voltage level: Uncertainty in this value was simply eye-balled during the measurement. Without any amplitude modulation, I just saw how much the 10s averaged value fluctuate and used at as the uncertainty.
- Extra Path Length: Since extra path length of light was measured quite crudely with a ruler, I took uncertainty in this measurement as 1 cm.
- All RFPDs have roughly the intended peaks in their transimpedance and the notches are close to 2 value.
- North and South Cavity Relfection PDs have an almost similar response. This is good to have equivalent paths. So I think we solved the problem which initiated this whole project.
- North and South PMC Reflection PDs are quite different primarily dude to different frequencies at which they will be operated at. The low peak frequency in South path has resulted in a very high transimpedance at the peak. But since PMCs only affect the mode shape, this should not affect the equivalency of the two paths.
Edit Tue Oct 9 09:54:40 2018 (awade): Narrowed table width to prevent horizontal scrolling. Edit Wed May 15 19:48:20 2019: See https://nodus.ligo.caltech.edu:30889/ATFWiki/doku.php?id=main:experiments:psl:rfpd for the latest changes in RFPD. | ||||||||||||||||||||||||||||||||||||||||||

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