Optimization of error signal

[NekSadam]

Hello,

I am currently trying to use Linien in order to numerically obtain an error signal. After plugging in my AC spectroscopy signal, I am getting a error signal that I cannot optimize the way I would like to. I tried to modify the filters parameters on my own but without success...

So if anyone has the error signal calculation code or has any idea what is going on, feel free to give me a hand !

Thank you !

[NekSadam]

I should mention that this error signal comes from this spectroscopy signal :

[NekSadam]

EDIT : I placed a charging resistor after the photodiode (in parallel) and after adjusting the parameters I ended up with what looks like a decent error signal error. I used a 50 kHz modulation.
Turns out the modulation might have been diminished by the photodiode.

Thank you for having taken the time to try to answer my questions !

I hope this discussion will be useful to some in the future :)

[bleykauf]

Happy that it works now!

Thanks for coming back and reporting your solution :)

[zhpshi]

Hello! It seems that I encountered the same problem. I modulated the strength of the B field around the rubidium cell. Then I observed the error signal same with the 3rd picture in this dialogue. Could you please tell me that the function of the charging resistor and the type of the PD you are using ? Thank you so much.

[NekSadam]

Hello zhpshi !

I don't know what is the B field you are refering to but I'll describe what did the trick for me.

At first, my setup worked as follows : simple rubidium 85/87 cell -> photodiode (-> AC filtor) -> FAST IN 1/2 | FAST OUT 1 (modulation + sweep) -> laser diode (through a LD controller). Which gave me the 3rd picture you are talking about.
Then, I put in between the photodiode and the FAST IN 1/2 a 10 kOhm in parallel configuration. It worked afterwards with a 50 kHz modulation frequency, 120 mVpp modulation amplitude and a 1.9 Hz frequency - filtering at 1 kHz.

Feel free to keep asking me questions about my setup should you need further information.

Good luck !

[zhpshi]

Hi Nek Sadam,

Thank you so much for your suggestions. We have observed the error signal after many times of trying.