Outlook
The ET-LF Sensing and Control System Vaishali Adya1,2, Sean Leavey3, Christian Gräf3, Stefan Hild3 and Harald Luck1,2
1Max-Planck-Insitut für Gravitationsphysik (Albert-Einstein-Institut), Hannover, Germany 2Institut für Gravitationsphysik, Leibniz Universität, Hannover,Germany, 3SUPA, University of Glasgow, UK
Dual recycled Fabry Perot Michelson with 4 km arm cavities1064 nm TEM00 light withfused silica opticsMirror temperature: 300 KFinesse of arm cavities: 12500.83 MW power in the arm cavities
Advanced LIGO
Einstein Telescope
Underground facility, equilateral triangle with 10 km between corner stationsSix dual recycled Fabry Perot interferometers in total, two main BS per corner stationCryogenic silicon mirrors for three out of six interferometers (LF)'Xylophone' concept: two IFOs with parallel arms, optimized for low and high frequency detection, respectively1064 nm TEM00 light (HF),1550 nm LG33 light (LF)3 MW, 18 kW in the arms for HF and LF respectively
Optical Lengths
The sidebands must be resonant within the recycling cavitiesThe first sideband must be resonant only within the PRCThe second sideband must be resonant within both the PRC and SRCBoth sideband frequencies must not resonate in the arm cavitiesChosen sideband frequencies: 11 MHz and 57 MHz
PRC length: 310 m, SRC length: 312.634 m, changed from 310 m due to clash of sideband resonancesSchnupp asymmetry: 5 cm
References
These degrees of freedom must be sensed and controlled in order to bring the interferometer to a locked state and keep it there.
[1] R. Abbott, et al. "Advanced LIGO Length Sensing and Control Final Design", LIGO Document T1000298
[2] G.Vajente "Requirements for Advanced VIRGO Length Sensing and Control system", VIR-083A-08
BS
from inputoptics
PRM
SRM
Y-arm cavity
X-arm cavity
AS
POPREFL
to output
101
102
10−24
10−23
Frequency [Hz]
Str
ain
[1/√H
z]
Gravity GradientsQuantum noise: no signal recycling (1 FC)Quantum noise: tuned signal recycling (1 FC)Quantum noise: detuned signal recycling (2 FC)
2G vs 3G Detectors
Modulation Frequencies
Preliminary ResultsOptimisation of control matrix for ET-LF with detuned signal recycling cavityNoise budget for sensing and control of ET-LFInvestigate control signals at small signal recycling cavity detunings
0 0.2 0.4 0.6 0.8 1
10−5
100
Schnupp Asymmetry [m]
Sid
eban
d P
ower
[W]
Sidebands in Recycling CavitiesPRC Sideband 1PRC Sideband 2SRC Sideband 1SRC Sideband 2
308 310 312 314 316 318 320 322 32410−5
10−4
10−3
10−2
10−1
Side
band
pow
er [W
]
Sideband 1Sideband 2
Sideband power in SRC vs SRCL
SRCL [m]
CARM DARM MICH PRCL SRCLREFL I1 3.37E+08 3.38E+04 1.65E+02 5.87E+05 6.45E-01REFL Q1 1.08E+08 1.08E+04 5.15E+01 1.89E+05 2.42E-01REFL I2 1.55E+08 1.55E+04 5.20E+03 2.93E+05 5.60E+03REFL Q2 4.69E+07 4.67E+03 7.52E+03 9.17E+04 3.03E+03POP I1 6.01E+07 5.99E+03 3.68E+02 9.59E+04 3.46E+00POP Q1 7.58E+07 7.79E+03 4.55E+03 1.41E+05 2.85E+01POP I2 1.35E+08 1.37E+04 1.13E+05 3.98E+04 6.19E+04POP Q2 8.34E+07 7.81E+03 2.23E+05 1.79E+04 2.31E+04AS I1 2.39E-01 7.77E+08 1.37E+06 5.50E+00 4.05E-02AS Q1 1.75E-01 8.16E+06 1.44E+04 4.09E+00 1.54E-01AS I2 9.86E+00 4.87E+10 8.56E+07 3.40E+03 7.33E+02AS Q2 8.14E+00 4.30E+10 7.55E+07 2.85E+03 5.91E+02
Optickle and FINESSE models developed with good agreement
Sensitivity curves match the design study reasonably well - work still ongoing
Preliminary control matrix obtained
Optical gain from each degree of freedom to each probe
Ly
Lx
lylxlp
ls
CARM = (Ly + Lx) / 2DARM = (Ly - Lx) / 2DARM = ly - lxPRCL = lp + (ly + lx) / 2SRCL = ls + (ly + lx) / 2
