I'm trying to think hard with my small brain how the distortion would affect the PDH functioning and inject noise in the frequency of the laser. I have a line of reasoning which starts with a question.:

• The two RF sidebands of laser that fall on the cavity, upon reflection, do they destructively interfere? Because the calculation I did in CTN:2481 suggests that the power at second harmonic (2-Omega frequency) is so high because of the sidebands beating with each other.
• In case they do not destructively interfere, the generated second-order harmonic (2-Omega) will have laser amplitude noise on it. This when it mixes with the (1-Omega) signal which actually carries the cavity length noise at the inputs of MAX4107, the distorted 1-Omega created would have laser amplitude noise on it.
• This might be the reason why FSS loops get overwhelmed with seeing a lot of laser amplitude noise which ideally it is not supposed to see. And it tries to correct this noise in phase quadrature making the situation worse.
• Since Andrew left, I increased the laser power reaching the cavities to go above the shot-noise limit of the photodiodes. Maybe, this increased light level increased this effect to a point where we are witnessing the problem.

Of course, all this depends on the RF sidebands interfering constructively upon reflection. I remember (I don't know from where) that it is the opposite. Either there is a fault in my calculations or this is indeed what is happening. I need to understand this properly to go further. Need help.