Transcript Variable reflectivity signal-recycling mirror and control

Variable reflectivity signal-recycling
mirror and control
Stefan Goßler
for the experimental team of
The ANU
Centre of Gravitational Physics
Outline
• Tuned and detuned signal recycling
• Introduction of VRSM
• Layout of the initial experiment
• Error signals
• First results
• Carrier/Subcarrier offset phase-locking control scheme
• Summary
David Rabeling, Malcolm Gray, David McClelland
Control and VRSM
Signal Recycling I
Signal recycling can be used to enhance SNL sensitivity
of gravitational wave detectors within certain bandwidth:
•
Tuned SR: SRC is tuned on resonance with carrier
Requires broadband mode: low finesse of SRC
•
Detuned SR: SRC is detuned from resonance with carrier
Enables narrowband mode: high finesse of SRC
Microscopic tuning of SRM position alters the tuning
Changing the reflectivity of SRM alters the bandwidth
Control and VRSM
Signal Recycling II
Control and VRSM
125W input
10 -20
Detuned quant T=0.1%
h(f) [1/sqrt Hz]
10 -21
Detuned total
T=0.1%
Tuned total
T=7%
Tuned quant
T=7%
10 -22
10 -23
10 -24
10-25
101
102
103
Frequency [Hz]
104
Complication
Rotational stage
Cantilever
springs
360 µm
420 mm
Coilholder for Activ
local control stack
isolator
200 µm
Upper masses
Cantilever
springs
Steel wire loops
162 µm
Intermediate
masses
Mirror 2,9 kg
150 mm
Magnet-coil
actuator
3 mm
180 mm
280 mm
Complicaton:
Changing the reflectivity of the
signal-recycling mirror causes
a down-time of the GWD for
a substantial period of time!
Solution:
A mirror with a reflectivity
that can be varied on demand:
a VRSM
Control and VRSM
VRSM
Can be realised by:
Thermal tuning of an etalon
Kawabe, Hild et al.
Michelson interferometer
Downside: Slow and lateral thermal
gradients the substrate
Downside: Very complex system
deVine, Shaddock, McClelland
Fabry-Perot cavity
Downside: Complex reflectivity
Strain, Hough
Control and VRSM
Simplification of Layout
Arm-cavity
Michelson
interferometer
Power-recycling
mirror
Signal-recycling
mirror
`Michelson´
mirror
`Michelson´
mirror
Dual recycled
Michelson interferometer
with arm cavities
Signal-recycling
mirror
Variable reflectivity
signal-recycling
mirror
Control and VRSM
Simplification of Layout
Arm-cavity
Michelson
interferometer
Power-recycling
mirror
Signal-recycling
mirror
`Michelson´
mirror
Signal-recycling
mirror
Collapse
`Michelson´
Michelson mirror
interferometer
into one mirror
Variable reflectivity
signal-recycling
mirror
Control and VRSM
Introduction of VRSM
Arm-cavity
Michelson
interferometer
Power-recycling
mirror
Signal-recycling
mirror
`Michelson´
mirror
Signal-recycling
mirror
`Michelson´
mirror
Variable reflectivity
signal-recycling
mirror
Control and VRSM
Experimental Layout
Laser
Phase
l/2
Isolator modulator
PBS
l/4
R1 R2 SRC
R3
= 380 MHz
FSR
Isolator
Signal
Laser
= 30 GHz
VRSM
FSR
RF output
In-phase
errror signal
Quadrature
errror signal
Lowpass
filter
190 MHz
Local
Oscillator
Servo
Lowpass
filter
~
Phase
shifter
Servo
Phase
shifter
Control of SRC via in-phase error signal
Control of VRSM via in-quardature error signal
Control and VRSM
Error Signals
Amplitude and phase response of a narrow linewidth cavity
Amplitude and phase response of a broad linewidth cavity
1.0
1.0
0.8
Amplitude
0.8
0.6
Phase
0.6
Phase
0.4
0.2
[Arb. units]
[Arb. units]
0.4
Amplitude
0.0
-0.2
-0.4
0.2
0.0
-0.2
-0.4
-0.6
-0.6
-0.8
-1.0
-200
-0.8
-1.0
-200
-150
-100
-50
0
50
100
150
200
-150
-100
Frequency [MHz]
0
50
100
150
200
150
200
Frequency [MHz]
PDH error signal for a narrow linewidth cavity
PDH error signal for a broad linewidth cavity
0.5
0.4
0.4
In quadrature
0.3
In phase
0.3
In quadrature
0.2
In phase
[Arb. units]
0.2
[Arb. units]
-50
0.1
0.0
-0.1
-0.2
0.1
0.0
-0.1
-0.2
-0.3
-0.4
-0.5
-200
-0.3
-150
-100
-50
0
50
Frequency [MHz]
100
150
200
-0.4
-200
-150
-100
-50
0
50
100
Frequency [MHz]
Control and VRSM
Experimental layout
Laser
Phase
l/2
Isolator modulator
PBS
l/4
R1 R2 SRC
R3
= 380 MHz
FSR
Isolator
Signal
Laser
= 30 GHz
VRSM
FSR
RF output
In-phase
errror signal
Quadrature
errror signal
Lowpass
filter
190 MHz
Local
Oscillator
Servo
Lowpass
filter
~
Phase
shifter
Servo
Phase
shifter
Control of SRC via in-phase error signal
Control of VRSM via in-quardature error signal
Control and VRSM
First results...
...of a linear three mirror coupled cavity when varying the reflectivity of the VRSM from
R=93% over R=87% to R=63%
Experimental frequency response
1.0
1.0
0.9
0.9
0.8
0.8
0.7
0.7
0.6
0.6
T/Tmax
T/Tmax
Theoretical frequency response
0.5
0.4
0.5
0.4
0.3
0.3
0.2
0.2
0.1
0.1
0.0
370
0.0
370
375
380
385
390
Frequency [MHz]
395
400
405
410
375
380
385
390
395
400
405
Frequency [MHz]
Control and VRSM
410
Carrier/Subcarrier
Phase
modulator
Carrier
laser
In quadrature
~
Frequency
offset
Power recycled
Michelson
interferometer
VRSM
cavity
In phase
Output
modecleaner
Sub-carrier
laser
Phase
modulator
Readout
Control and VRSM
Frequency Offsets
Norm. Refl.
VRSM reflectivities for some carrier-subcarrier offsets
Norm. Trans.
Effect on signal cavity
Control and VRSM
Frequency Offsets II
1.0
0.9
0.8
Norm. SRC reflection
0.7
Norm. VRSM reflection
0.6
0.5
0.4
0.3
0.2
0.1
Broadband mode
Norm. refl.
Norm. refl.
Narrowband mode
Control and VRSM
Summary VRSM and Control
• The use of a VRSM eases the change of bandwidth,
avoiding long down-times of the detector
• A new way to control the SRC including a VRSM by using
an auxiliary laser that is offset phase locked to the carrier laser
• This control scheme is compatible with the injection of squeezed light
• First experiments using a linear three mirror cavity are carrried out
• A more complex experiment using a dual-recycled Michelson
interferometer with arm cavities is in preparation
Control and VRSM