Stefan Hild for the GEO600 team October 2007 LSC-Virgo meeting Hannover Homodyne readout of an...
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Transcript of Stefan Hild for the GEO600 team October 2007 LSC-Virgo meeting Hannover Homodyne readout of an...
Stefan Hild for the GEO600 team
October 2007
LSC-Virgo meeting Hannover
Homodyne readout of an interferometer with Signal Recycling
Stefan Hild LSC-Virgo Meeting 10/2007 Slide 2
Motivation for DC-readout (1)
Increased coupling of laser power noise.
Usually an output mode cleaner (OMC) is required.
Very sensitive to imbalances of the interferometer arms.
Stefan Hild LSC-Virgo Meeting 10/2007 Slide 3
Motivation for DC-readout (2)
Reduced shot noise (no contributing terms from 2 times the heterodyne frequency)Reduction of oscillator phase noise and oscillator amplitude noiseStronger low pass filtering of local oscillator (due to PR cavity pole) Simplify the GW detector
Simpler calibration (GW-signal in a single data-stream, even for detuned SR) Simpler circuits for photodiodes and readout electronics Possibility to use photodiodes with larger area => reduced coupling of pointing Reduced number of beating light fields at the output photodiode => simpler
couplings of technical noiseRequires less effort for injecting squeezed light (=> useful precursor for GEO-HF)LO and GW pass the same optical system (identical delay, filtering, spatial profile) => This advantage is especially important for detectors with arm cavities.
Stefan Hild LSC-Virgo Meeting 10/2007 Slide 4
DC-readout without OMC
102
103
10-10
10-9
10-8
10-7
Frequency (Hz)
Op
tica
l P
ow
er @
da
rkp
ort
(W
att
/ H
z1/2)
nfft/fs = 2.00 : navs = 60 : enbw = 0.75 : nsecs = 120
reference S5
10% MI midx
10% MI midx + TEM00 carrier
Turning down the radio frequency modulation (stable operation is possible with 10 times lower sidebands)
Dark port is dominated by carrier light (TEM00) from a 50 pm dark fringe offset
Disadvantage: Still some shot noise contribution from RF-sidebands.
Frequency [Hz]
Da
rkp
ort
po
we
r [W
/sq
rt(H
z)} Red. MI modulation
Heterodyne 550 Hz
Red. MI modulation+ carrier from dfo
Stefan Hild LSC-Virgo Meeting 10/2007 Slide 5
Simulated shot noise: Homodyne vs Heterodyne detection
102
103
10-22
10-21
Frequency [Hz]
Str
ain
[1
/sq
rt(H
z)]
Homodyne, tuned SRHeterodyne, tuned SR
DC-readout with tuned Signal-Recycling: - shape stays constant - overall level is reduced
Stefan Hild LSC-Virgo Meeting 10/2007 Slide 6
102
103
10-22
10-21
Frequency [Hz]
Str
ain
[1
/sq
rt(H
z)]
Homodyne, 550HzHeterodyne, 550Hz
Simulated shot noise: Homodyne vs Heterodyne detection
DC-readout with detuned SR: - better peak sensitvity- shape is rotated => better at low freqs, worse at high freqs.
Stefan Hild LSC-Virgo Meeting 10/2007 Slide 7
Simulated shot noise: Homodyne vs Heterodyne detection
102
103
10-22
10-21
Frequency [Hz]
Str
ain
[1
/sq
rt(H
z)]
Homodyne, 1kHzHeterodyne, 1kHz
DC-readout with detuned SR: - better peak sensitivity- shape is rotated => better at low freqs, worse at high freqs.
Stefan Hild LSC-Virgo Meeting 10/2007 Slide 8
Simulated shot noise: Homodyne vs Heterodyne detection
102
103
10-22
10-21
Frequency [Hz]
Str
ain
[1
/sq
rt(H
z)]
Homodyne, tuned SRHeterodyne, tuned SRHomodyne, 550HzHeterodyne, 550HzHomodyne, 1kHzHeterodyne, 1kHz
1st Question: Can we confirm the rotation of the shape in our measurements?
Stefan Hild LSC-Virgo Meeting 10/2007 Slide 9
‚Rotation‘ of the optical gain
102
103
105
Frequency [Hz]
Op
tical G
ain
[a.u
.]
102
103
-200
-100
0
100
200
Ph
ase [
deg
]
Frequency [Hz]
DC-readoutHeterodyne
Rotated shape of optical response confirmed by measurement:
Rotated shape of optical response can be understood by looking at the phases of the contributing light fields. => change of the optical demodulation phase.
Stefan Hild LSC-Virgo Meeting 10/2007 Slide 10
Simulated shot noise: Homodyne vs Heterodyne detection
102
103
10-22
10-21
Frequency [Hz]
Str
ain
[1
/sq
rt(H
z)]
Homodyne, tuned SRHeterodyne, tuned SRHomodyne, 550HzHeterodyne, 550HzHomodyne, 1kHzHeterodyne, 1kHz
2nd Question: Can we confirm the change of the relative shape of tuned and detuned SR with DC-readout ?
Stefan Hild LSC-Virgo Meeting 10/2007 Slide 11
Simulated shot noise: Homodyne vs Heterodyne detection
102
103
10-22
10-21
Frequency [Hz]
Str
ain
[1
/sq
rt(H
z)]
Homodyne, tuned SRHomodyne, 1kHz
2nd Question: Can we confirm the change of the relative shape of tuned and detuned SR with DC-readout ?
Stefan Hild LSC-Virgo Meeting 10/2007 Slide 12
102
103
10-22
10-21
Frequency [Hz]
Str
ain
sen
siti
vit
y [
1/s
qrt
(Hz)
]
Simulated shot noise, DC 1000Hz1/Optical Gain, DC 1000Hz, measuredSimulated shot noise, DC 0Hz1/Optical Gain, DC 0Hz, measured
Comparison of measured and simulated optical transfer function for DC-readout
The simulated optical transfer function for tuned and detuned SR wit DC-readout is reproduced by our measurements.
Stefan Hild LSC-Virgo Meeting 10/2007 Slide 13
102
103
10-22
10-21
10-20
10-19
Frequency [Hz]
Str
ain
[1/s
qrt
(Hz)
]
Simulated shotnoise, DC-readout 550HzSimulated shotnoise, heterodyne 550Hzh(f), heterodyne 550 Hzh(f), DC-readout 550 Hz
Best sensitivity so far with DC-readout and a SR detuning of 550 Hz
Shot noise Increased at high freqs in DC-readout (with detuned SR)
Peak sensitivity roughly same as with heterodyne (2e-19m/sqrt(Hz))
Increasedtechnical
noise
Stefan Hild LSC-Virgo Meeting 10/2007 Slide 14
Noise budget for DC-readout (detuned SR)
102
103
10-7
10-6
10-5
10-4
10-3
10-2
Frequency [Hz]
AS
D [V
/sqr
t(H
z)]
Noise projection for DC-readout with detuned SR
Mid visMID AA FB RotMID AA FB TiltSignal recycling longitudinal noiseLaser amplitude noise (BS ar)PR errorDark noiseModelled shot noiseSum of the noise
Laser power noise (LPN):
• is partly limiting at low frequencies
• overall seems to be less of a problem than initially expected
3rd Question: Do we understand the laser power noise coupling?
Stefan Hild LSC-Virgo Meeting 10/2007 Slide 15
Understanding the LPN in DC-readout
Good agreement between measurement and simulation !!
102
103
100
Ma
g [
a.u
.]
Frequency [Hz]
measured data, SR 550 Hz
Simulation, SR 550 Hz
Stefan Hild LSC-Virgo Meeting 10/2007 Slide 16
Summary
Demonstrated DC-readout with tuned and detuned Signal-Recycling (without OMC)
Going to DC-readout changes the optical demodulation phase (rotated shape of optical response)
Measurements and simulations agree pretty well:Optical responseLaser intensity noise coupling
Achieved a displacement sensitivity of 2e-19m/sqrt(Hz) (currently worse sensitivity than in heterodyne readout)
Laser power noise is not as bad as rumors suggest (due to filtering of PR cavity pole)
Stefan Hild LSC-Virgo Meeting 10/2007 Slide 17
Where to go in future ??
Best shot noise at low and high frequencies.
This combination of SR tuning and DC-readout would allow an ‚easy‘ implementation of squeezed light (no filter cavity necessary to get full benefit)
See talk by S.Chelkowski @ QND-meeting
Stefan Hild LSC-Virgo Meeting 10/2007 Slide 18
Additional slides
Stefan Hild LSC-Virgo Meeting 10/2007 Slide 19
positive dfodark fringenegative dfo
Output mode for positive and negative dfo: observation vs simulation
Stefan Hild LSC-Virgo Meeting 10/2007 Slide 20
Output mode for positive and negative dark fringe offset (dfo)
positive dfo
negative dfo
Wave front radii of returning beams @ beam splitter:
horizontal: north > eastvertical: north < east
Stefan Hild LSC-Virgo Meeting 10/2007 Slide 21
Realisation of tuned signal recycling For tunings < 250 Hz we cannot achieve a reasonable control signal.
Developed a new technique: We ‘kick‘ MSR in a controlled way to jump to tuned SR, where a reasonable control signal can be obtained again.
MSR is caught at the tuned operating point again.
-10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 1010
0
Sig
na
l a
mp
litu
de
[a.u
.]
Position of MSR [nm]
-4 -3 -2 -1 0 1 2 3 4
0
Sig
na
l a
mp
litu
de
[a.u
.]
Position of MSR [nm]
SR Mod = 9017065 Hz,tuning = 330 HzSR Mod = 9017195 Hz,tuning = 200 HzSR Mod = 9017395 Hz,tuning = 0 Hz
SR Mod = 9016395 Hz,tuning = 1000 HzSR Mod = 9017065 Hz,tuning = 330 Hz
Stefan Hild LSC-Virgo Meeting 10/2007 Slide 22
2 different possibilities for going totuned signal recycling
1. Keep the modulation frequency and jump to center zerocrossing.2. Change the modulation frequency (corresponding to 0 Hz tuning)
=> only a single zerocrossing exists.
Stefan Hild LSC-Virgo Meeting 10/2007 Slide 23
Laser intensity noise coupling for tuned and detuned SR
102
103
100
101
Ma
g [
a.u
.]
Frequency [Hz]
measured data, SR 550 HzSimulation, SR 550 HzSimulation, tuned SRSimulation, tuned SR,adjusted mod freq
Simulation, tuned SR,adjusted mod freq,lower mod index
Stefan Hild LSC-Virgo Meeting 10/2007 Slide 24
Tuned DC with various dark fringe offsets
102
103
105
Frequency [Hz]
Op
tica
l G
ain
[]
102
103
-100
-50
0
50
100
150
Ph
ase
[deg
]
Frequency [Hz]
Tuned DC, data set 3
Tuned DC, data set 2b
Tuned DC, data set 4
Tuned DC, data set 5
data set 2b:small –dfo
data set 3: large –dfo
data set 4: small +dfo
data set 5:large +dfo
Stefan Hild LSC-Virgo Meeting 10/2007 Slide 25
Comparison of heterodyne 550 Hz, tuned heterodyne and tuned DC
102
103
10-22
10-21
10-20
10-19
Frequency [Hz]
ST
RA
IN [
1/sq
rt(H
z)]
DER_DATA_H (nominal S5= 550 Hz, heterodyne) 2007-05-16 03:20:30 -
TUNED SR, heterodyne readout (P-quad), (Sept 2006)
TUNED SR, DC-readout (4513)DC 0Hz (simulated shot noise)
Hetero 0Hz (simulated shot noise)
Hetero 550Hz (simulated shot noise)
While in the two heterodyne cases the sensitivity is close to simulated shot noise at 2 kHz,
this is not the case for tuned DC.
Stefan Hild LSC-Virgo Meeting 10/2007 Slide 26
Combination of tuned SR and squeezing– an option for GEO HF?
• Squeezed light is available for injection
• Tuned Signal-Recycling operation was demonstrated
No need for long filter cavity !
„Demonstration and comparison of tuned and detuned Signal-Recycling in a large scale gravitational wave detector“ , S Hild et al, CQG. 24 No 6, 1513-1523.
“Coherent Control of Vacuum Squeezing in the Gravitational-Wave Detection Band“, Vahlbruch et al, PRL 97, 011101 (2006)