Transcript 2013_1205_OptLev_agatsumax

Local control sensors for iKAGRA
payloads and perspective
(Optical lever)
Kazuhiro Agatsuma
2013/Dec./5
2013/Dec./5
ELiTES meeting at Tokyo
1
Contents
Optical lever (OpLev) development for
KAGRA
• Selection of components
• Performance test
• Layout
• Toward bKAGRA (cryo-condition)
2013/Dec./5
ELiTES meeting at Tokyo
2
OpLev is used for
• Local angular control for each mirror
• Alignment control to lead to lock the interferometer
• Monitoring drift motion
Light source
Position sensor
mirror
Objectives
• To decide detail design of OpLev
• Engineering test (prototype test)
2013/Dec./5
ELiTES meeting at Tokyo
3
Requirement (spectrum)
To lock IFO
RMS: 0.1 urad
(for cavity)
RMS: 1 urad
(for BS mirror)
Requirement
Intensity noise,
shot noise
by Michimura and Sekiguchi,
(※) In this calculation, following parameters are assumed
JGW document (2012/4/27)
• Intensity noise of light source: RIN ~ 1e-7 /rtHz
• Shot noise or dark noise： ~1e-11 m/rtHz (as the spot fluctuation)
2013/Dec./5
ELiTES meeting at Tokyo
4
Requirement (drift)
To be locked by referring to optical lever
3 cm / 3km = 10 urad
remaining fringe
3 km
3 cm
10 urad/week?
10 urad/day?
10 urad/h?
If commissioning phase is assumed
=>
2013/Dec./5
ELiTES meeting at Tokyo
To hold fringe for a day
Drift: 10 urad/day
5
Selection of components
• Light source
–
–
–
–
SLD (Super Luminescent Diode)
Wave length: 670-680 nm
Thermal control
Power: 1 - 2 mW
• Collimator lens
– Beam-spot size： it affects the linear range and sensitivity
⇒ 0.5 - 2 mm for PSD (c.f. 2mm in case of aLIGO)
• Photo receiver (Rec.)
– PSD
– Φ: 9 mm x 9 mm
2013/Dec./5
ELiTES meeting at Tokyo
6
Light source
• Selected parameters
– Fiber coupled SLD： to avoid interference with a reflection from cladding
– Center of wave length: 650-680 nm
• Visible is useful at the installation and commissioning phase
• Tradeoff with lifetime (switchable to IR SLD, which has longer
lifetime)
– Power: 1~2 mW
– Thermal control (to avoid the mode hop)
– PM fiber (to keep polarization because of high incident angle)
– FC/APC (to avoid reflected light)
2013/Dec./5
ELiTES meeting at Tokyo
7
Measured RIN and lifetime
from LIGO document
This is much lower than the requirement
2013/Dec./5
ELiTES meeting at Tokyo
8
Position sensors
Performance has been checked for below candidates
PSD (Position Sensitive Detector)
• Large linear dynamic range
• Low speed response
• Spot-size-independent sensitivity
QPD (Quadrant Photo Detector)
• Small linear dynamic range
• High speed response
• Spot-size-dependent sensitivity
(※ Spot size affects the linear dynamic range)
2013/Dec./5
ELiTES meeting at Tokyo
9
Calibration factors
X-Y stage
Φ 2mm: linear range: 7mm
Φ 0.5mm: linear range: 8mm
PSD: 7 mm (Φ 2 mm)
QPD: 0.5-1.5 mm (Φ 2-6 mm)
Sensitivity is independent on the spot size => easy adjustment
Linear range of PSD (7mm) is much larger than that of QPD (0.5mm)
2013/Dec./5
ELiTES meeting at Tokyo
10
Collimator lens and launcher
Selected lenses
Spot size is 1-2 mm with the
working distance of 4m
• Adjustable-focus lens for PSD
2013/Dec./5
ELiTES meeting at Tokyo
11
Layout design
Length coupling
Light source
θ
Position sensor
mirror
mirror
Large θ causes length coupling
mirror
Turning mirror
2013/Dec./5
ELiTES meeting at Tokyo
12
Comprehensive drift
~1m
Thermometer
Paper box was used as windshield
PSD
2013/Dec./5
ELiTES meeting at Tokyo
13
Comprehensive drift
Fitting: Y = α + β*T + γ*(x – t)
T: temperature, β: temperature response
x: time,
γ: constant drift
t: time delay
To hold fringe for a day
Drift: 10 urad/day
X direction: β = 8 um/℃, γ = 14 um/day => 2 urad/day
Y direction: β = 50 um/℃, γ = 170 um/day => 30 urad/day (3m OpLev length)
Origin of this drift is in investigation
2013/Dec./5
ELiTES meeting at Tokyo
14
Layout design
Option 1 (Mixed signal)
Chamber for Type-B SAS
Range:
8mm/(2*1m)
= 4 mrad
BS
Default
Option 2 (Broad range & length)
BS
PSD
Turning port
lens
Input port
Range:
8mm/(2*3m)
= 1.3 mrad
2013/Dec./5
ELiTES meeting at Tokyo
15
Turning port
Option 1 (Mixed signal or Length information)
Subtraction of angular signal (input port) from the mixed
PSD output produces the longitudinal signal
BS
Merit: Cheap and simple
Demerit: Direct coupling between longitudinal and
angular motion
lens
Option 1.5 (Broad range or Length information)
To adjust the focal or image plane by adding a lens
Option 2 (Broad range & Length)
BS
PSD
Merit: Clear separation between longitudinal and angular
motion
Demerit: Extra optics (PSD, lens and their sliders)
increase total cost.
lens
2013/Dec./5
PSDs have to be placed on the focal plane and image
plane using sliders with about 10-um accuracy
Option 1
Option 1.5
Option 2
Cost
Low
Middle
High
Information
Mix or Length
Broad or Length
Broad and Length
ELiTES meeting at Tokyo
16
Layout design for Type B (preliminary)
Breadboard
Drown by Gianni Gennaro
2013/Dec./5
ELiTES meeting at Tokyo
17
Toward bKAGRA
(perspective for cryogenic system)
2013/Dec./5
ELiTES meeting at Tokyo
18
Layout
test mass chamber
for bKAGRA
~15 m
test mass chamber
for iKAGRA
2013/Dec./5
ELiTES meeting at Tokyo
19
Layout for iKAGRA
OpLev length: 3m
Optical path length: 4m
Range:
8mm/(2*3m)
= 1.3 mrad
~1m
Input port
2013/Dec./5
ELiTES meeting at Tokyo
Turning port
Pylon
20
Layout for bKAGRA
OpLev length: 15 m
Optical path length: 30 m
Range:
8mm/(2*15m)
~ 0.3 mrad !
~ 15 m
Detection port
aLIGO
Design of collimator lens is needed
Pylon
Observable range becomes small (1.3 mrad => 0.3 mrad)
2013/Dec./5
ELiTES meeting at Tokyo
21
Additional OpLev
Merit inside cryostat
Observing Intermediate mass
Short length OpLev (broad
range)
Technical misc.
・No optical window
・Fiber coupled SLD is useful
・Cryo-compatible PD
What should be the reference?
- Cryostat => deformation by
changing temperature
- Making special pylon (super
invar?) => difficult…
2013/Dec./5
ELiTES meeting at Tokyo
22
Summary
Selection and prototype test for the OpLev of iKAGRA
Laser source: Superlum SLD (670 nm) with PM fiber, Position sensor: PSD (9mm x
9mm), Collimator lens: Adjustable-focus lens is selected for PSD (Φ2 mm at 2-m
WD, Φ1 mm at 4-m WD)
Comprehensive drift
• Three times worse (30 μrad/day) than the requirement (10 μrad/day)
=>Now in investigation
Layout
• Current range (PSD, 8mm range, and input port) is 1.3 mrad for the angular motion
of mirrors. It is useful to detect the signal at not only input port but also the turning
port. (It is said that 10 mrad range is sufficient for SA in VIRGO)
Perspectives
• Long-length OpLev have a high sensitivity but small range
• Additional OpLev inside cryostat has some merits (broad range and seeing
intermediate mass)
2013/Dec./5
ELiTES meeting at Tokyo
23
Acknowledgements
•
•
•
•
•
Riccardo DeSalvo
Ettore Majorana
Ryutaro Takahashi
Takanori Sekiguchi
all member of VIS, AOS, and QND group.
2013/Dec./5
ELiTES meeting at Tokyo
24