**I have a simulated version of the differences that we expect to see between the 2 different sides of the CARM resonance. The point is that we can try to compare these results with Q's measured results (****elog 10594****) to see if we know if we are on the spring or antispring side.**
I calculated the same transfer functions vs CARM offset again, although tonight I do it in steps of 20pm because I was getting bored of waiting forever. Anyhow, this is important because my previous post (elog 10591) didn't have spring side calculations all the way down to 1pm.
This is similarly true for that elog 10591, but here are some notes on how I am currently getting the W/N units out of Optickle. First of all, I am still using old Optickle1. I don't know if there are significant units ramifications for that, but just in case I'll write it down. Nic tells me that to get [W/N] out of Optickle1, I need to multiply sigAC (units of [W/m]) by my simple pendulum (units of [m/N]). Both of these "meters" in the last sentence are "mevans meters", which are the meters you would get per actuation if radiation pressure didn't exist. So, I guess they're supposed to cancel out? I need to camp out in Nic's office until I figure this out and get it untangled in my head.
Plots of transfer functions for both sides of CARM resonance (same as prev. elog), as well as the ratio between the spring and antispring transfer functions at each CARM offset:
The take-away message from the 3rd column is that other than a sign flip, we don't expect to see very much difference between the 2 sides of the CARM resonance, particularly above a few hundred Hz. (Note that we do not see the sign flip in Q's measurements because he is looking at CARM_IN1, which is after the input matrix, and the input matrix elements have opposite signs between the signs of the CARM offsets. So, the sign flip between spring and antispring around the UGF is implied in the measurements, just not explicit).
Also, something that Rana pointed out to me, and I still don't know why it's true: The antispring transfer functions (at least for the transmission) don't have all the phase features that we expect to see based on their magnitudes. If you look at the TRX antispring plot, blue trace (which is about 500pm from resonance), you'll see that the magnitude starts flat at DC, has some slope in an intermediate region, and then at high frequencies has 1/f^2. However, the phase seems to not know about this intermediate region, and magically waits until the 1kHz resonance to flip the full 180 degrees. |