Thesis plan
I'm planning to graduate by the end of 2010.
This are some of the contents of my thesis.
This is just an idea of how the arguments may unfold.
The Gist
Noise in systems like laser, oscillator, sensing photodiodes, demodulation electronics, can affect the control of all the degrees of freedom of the interferometer. Through direct or indirect mechanisms they can also couple in to the gravitational wave channel.
My thesis will focus on studying how such noises are generated, how they add to each other and ultimately how they can affect the signal extraction scheme and the sensitivity of advanced interferometer.
Starting from the Upgraded 40m prototype, I'm going to study the problem of defining requirements in the design of those systems such that they can provide the optimal performances for an interferometer in advanced configuration.
Summary
Contents
Effect of Technical Noises
- laser noise
- oscillator noise
- sensing noise: noise from photodetection and demodulation electronics
- effects of technical noise coupling
- aux DOF control signals
- directly to detection port
- indirectly to detection port through aux DOFs
Couplings to Control Signal
Mechanisms of technical noise coupling to aux DOFs
SNR along the modulation/demodulation chain
We study the effects of:
- SNR in the oscillator
- SNR in the signal distribution and demodulation systems
- calculation of expected power for all sensing photodiodes
From the studies we define:
- optimal modulation depths for f1, f2, fMC (se page 59-60 of Rana's thesis).
- requirements on the SNR degrading along the modulation and demodulation chains
RF System Design
- Defining noise requirements on oscillator, frequency multiplier: phase noise, amplitude noise, higher order harmonics.
- Comparison of oscillator+multiplier vs. two phase locked oscillators strategies.
- RF PDs: determining SNR, signal amplification, off-band attenuation
- SNR after the demodulation stage
Couplings to the Detection Port
- Simulations of laser and oscillator noise couplings in Stable, Detuned/Not-Detuned, DRFPMI IFOs with DC readout.
- The case of the Upgraded 40m
- Simuations of IFO asymmetries. In particular, the role of cavity absolute lengths.
- Defining tolerances in setting cavity lengths.
Cavity Absolute Length Measurement Experiment
- Define required precisions of cavity absolute length measurements.
- Laser injection and signal extraction plans for arms and short cavities.
- Transmitted power estimates. PD Shot noise calculations
- Design of PLL. Simulink model.
- PLL characterization: open loop gain TF, bandwidth, PZT calibration, noise budget, combined lasers frequency noise
3f Signals
3f signals are generated by the beating withing the 3rd order harmonic of the phase modulated light.
Such signals are potential candidates for the first stages of lock acquisition of the IFO, when the arms are not locked yet.
- less dependence on the carrier phase as reflected by the arms, i.e. independent by arm lock status
- low SNR
- ok for the first stages of lock acquisition (CARM offset from 0)
- good to maintain central part locked when CARM offset gets to zero
Lock Acquisition Plan
Here, based on optickle simulations, I propose a step-by-step plan for the first stages of lock acquisition.
- study of sensing matrices
- identification of optimal control signals
PRC and SRC locking: experiment
We try to lock the central part with the 3f signals.
- setup of 3f demodulation systems