Latest measurements with Tor Vergata pre-amps

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Latest measurements with Tor Vergata pre-amps

Post  Alessio on Wed Jul 22, 2009 5:45 pm

In the last days, E. Tusi modified the pre-amps to remove almost completely the DC offset. Around +50mV to +90mV of offset are still present depending on the pre-amp.

Together with Viviana, we rebuilt the intensity stabilization loop. We made the usual scheme, putting 15% reflecting beam splitters to shine the PDs. We were able to increase the power on the In-Loop PD almost to saturation. With the present setup, there are 830mW on the In-Loop PD and 640mW on the Out-Of-Loop PD.

I now show the graph comparing the noise spectra measured with two different powers on the PDs. The improvement in the performances of the loop is evident.



It is also clear that with higher power, some structures and peaks, that were buried into noise, have now appeared.
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Re: Latest measurements with Tor Vergata pre-amps

Post  mdipaolo on Wed Jul 29, 2009 12:49 pm

I report some measure about this outline







I have inserted also the integrator; i don't report the noise because it is very high. I have observed that:
- Decrease the Gain of the Filter the noise (out loop) decrease but it is always high for the our limitation
- Changing the parameter of the integrator the noise doesn't change.

First of all i have tried the integrator with a general signal, it seems works well.

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Re: Latest measurements with Tor Vergata pre-amps

Post  mdipaolo on Mon Aug 03, 2009 1:49 pm

I have tried to insert the Integrator: PD ---- Amplificator ----- Integrator ---- PAR .
The noise is very high...I didn't see an changing of the noise to the change the offset of the integrator and the band of the filter.

I have tried to change the setup: PD----Amplificator ---- PAR ---- Integrator : I have seen that the power onto PDs decrease...there is an increased of the power on the first order. The noise is decreased...but...the noise nel setup with no integrator is better than noise in this setup.

The problem, i think, is the offset of the integrator...We must fixed exactly this offset for don't have a oscillation of the integrator.

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Re: Latest measurements with Tor Vergata pre-amps

Post  mdipaolo on Mon Aug 03, 2009 5:30 pm

I used a function generator to understand the integrator:

1) If the signal has offset zero it is very easy to integrate the signal.

2) If the signal has a offset not zero it is very difficult to integrate the signal. Changing the offset i haven't observed positive results.

I think that we must insert the integrator after the filter for cut the DC. In this case we must increase the power onto PD, so decrease the efficinety of the AOM. In this case the noise level is not good, it is better not use the integrator.

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Re: Latest measurements with Tor Vergata pre-amps

Post  mdipaolo on Tue Aug 11, 2009 6:40 pm

In these measurement i put 2 polarizer first the PDs. The goal of this is to compensate the polarizazion introduced by beam splitter.
In total there are 2 polarizer.





Perhaps the better thing is put another polarizer after the waveplate.
So, i think that we can works also without polarizer first the PDs.

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