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AdV-DET (Photodiodes + demodulation boards (longitudinal control))
mwas - 20:58 Tuesday 31 January 2023 (58653) Print this report
present B1 photodiode dark noise projection

Figure 1 shows the dark noise of the B1 photodiodes that are used right now, compared to the O4 low noise curve (115Mpc range) assuming 10mW on the B1 beam (5mW per photodiode)

FIgure 2 show the measured dark noise of these photodiodes that was used as input to figure 1. And an estimate of the flicker noise was added to it. Assuming 200 Ohm resistor for the total resistance load for the Audio channel. The flicker noise is actually negligible, because the resistor load is 10 times smaller than during O3. So with 10 times lower flicker noise, and 3 times higher thermal resistor noise. So the thermal resistor noise is dominating, and easily measured without light on the PD.

In terms of range, keeping the present photodiodes would cost at 15 Mpc in range, if the detector would be at 115Mpc of BNS range. But for 60Mpc of range it cost only 2.5Mpc of less range, and at 40Mpc it cost 0.8Mpc. So replacing the photodiode is motivated from BNS range perspective once we have a range of at least 40 Mpc. Although it could mean as much as 50% less sensitivity in any shot noise limited region of the noise curve.

 

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mwas - 10:35 Wednesday 01 February 2023 (58663) Print this report

Figure 1. To provide more context, adding also the O4 high noise curve, and one of the measured O3b sensitivity curves to the present B1 photodiode electronic noise.

Figure 2 is a copy of slide 14 of (VIR-0630A-20) which shows the noise level of the B1 photodiodes used during O3b onto the O4 sensivitiy curve. The O3b photodiodes have about 3 times less noise that the ones which are installed right now. Compared to an ideal situation, the O3b photodiodes noise has a minor impact (in that example with technical noises lowering the range from 108 Mpc to 107 Mpc), and a ~5% sensitivity loss at high frequency in the shot noise limited region (assuming 4dB of squeezing).

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mwas - 15:42 Wednesday 01 February 2023 (58671) Print this report

Figure 1 adds more information into a single figure. So including the PD dark noise of the PD installed right now, and the noise if we put back the O3b B1 photodiodes. And also the noise curve of 12 Mpc we have achieved last Friday is superposed.

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