Transcript Deci-hertz Interferometer Gravitational Wave Observatory

Space Gravitational Wave Antenna
DECIGO Project
3rd TAMA Symposium
February 7, 2003
@ Institute for Cosmic Ray Research, Japan
Seiji Kawamura
National Astronomical Observatory of Japan
Contents
1.
2.
3.
4.
5.
6.
Introduction
What is DECIGO?
Science obtained by DECIGO
Sensitivity of DECIGO
Current Status of DECIGO
Summary
Laser Interferometer in Space
• Signal increased
- Due to longer interaction between GW and light
- Cancellation of signals at higher frequencies
• Noise reduced
- Lower seismic noise and gravity gradient noise
Sensitivity improved
at lower frequencies
LISA
Laser Interferometer Space Antenna
• Joint Project by NASA and ESA
• Aiming at 0.1mHz - 100mHz
• To be launched in 2011
Gap between Terrestrial
Detectors and LISA
Strain [Hz-1/2]
10-18
LISA
10-20
Gap
10-22
10-24
10-4
10-2
100
Terrestrial Detectors
(e.g.
LCGT)
102
Frequency [Hz]
104
Importance of Bridging
the Gap
New window brings new science!

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Observe inspiral sources that have moved
above the LISA band
Observe inspiral sources that have not yet
moved into the ground-based detector band
Cosmological background could be detected
Completely new sources could be detected
Completely new science could be obtained
What is DECIGO?

Deci-hertz Interferometer Gravitational Wave Observatory
Space Antenna with shorter arm length
10-18
Strain [Hz-1/2]

LISA
10-20
10-22
10-24
DECIGO
Terrestrial Detectors
(e.g. LCGT)
(Sensitivity: Arbitrary)
10-4
10-2
100
102
Frequency [Hz]
104
DECIGO

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
Named by T. Nakamura in the PRL
paper by N. Seto, S. Kawamura, and
T. Nakamura
Potential candidate for the future
Japanese space GW antenna
Study of DECIGO just started
Relationship between
Sensitivity and Arm Length
Strain [Hz-1/2]
10-18
x100
f-2
LISA
10-19
10-20
10-21
Force Noise:
XFN/L∝1/L
f1
DECIGO
f0
f0:1/L f0
(Arm Length:
1/100 of LISA)
x100
Shot Noise (f<f0): XSN/L∝P-1/2/L∝(L-2) -1/2/L=L/L
10-4
10-2
100
Frequency [Hz]
102
Advantages of DECIGO
No confusion limiting noise above 0.1Hz
(From the LISA report)
Acceleration of Expansion of
the Universe
Expansion ＋Acceleration?
DECIGO
GW
NS-NS (z～1)
Output
Strain
Template (No Acceleration)
Real Signal ?
Phase Delay～1sec (10 years)
Time
Seto, Kawamura, Nakamura, PRL 87, 221103 (2001)
Ultimate Sensitivity of DECIGO
10-18
Strain [Hz-1/2]
10-20
DECIGO
(LISA Technology
L=5×107m)
LISA
Terrestrial Detectors
(e.g. LCGT)
10-22
10-24
Ultimate DECIGO × 1000
(Necessary for
acceleration measurement)
10-26
Ultimate DECIGO
(Quantum noise limited
M=100kg, L=5×108m)
10-4
10-2
100
102
Frequency [Hz]
104
In the Paper, we said…
The ultimate sensitivity of a space antenna in
the far future could be, however, 310-27 around
0.1 Hz in terms of strain, assuming the quantum
limit sensitivity for a 100 kg mass and an arm
length of 1/10 of LISA. We name this detector
DECIGO.
This requires an enormous amount of effective
laser power, and also requires that the other noise
sources, such as gravity gradient noise, thermal
noise, practical noise, etc. should be all suppressed
below the quantum noise. Here we assume that
such an antenna may be available by the end of
this century.
Necessary Technologies for
DECIGO
Three Satellite
Formation Flight
Solar Radiation
Drag-free Satellite
Deflection of Light
Reflection with phaselocking
Gravity Gradient
Heterodyne
Detection
How to Improve Sensitivity?

Increase effective power
- Increase the laser power
- Increase the diameter of mirror
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Use shorter wavelength?
Reduce other sensing noise
Reduce force noise
DECIGO Working Group
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Convened in 2002 as one of WGs to study
the future project candidates for NAOJ
1st Meeting held on May 9, 2002
80+ members currently involved
R&D experiments to be started very soon
Two R&D Experiments to be
Started Very Soon
• Constructing a satellite-satellite tracking
simulator for Earth environmental
monitoring by CRL, Niigata Univ., and
NAOJ
• Collaboration work between NASAGoddard (LISA) and NAOJ (DECIGO)
on ground test on force noise
Conceptual Design of Satellite-Satellite
Tracking Simulator
Angular
Perturbation
Simulator
Low Thermal-Expansion
Optical Table
Intensity
Stabilization
System
Laser
Equal Path Lengths
(with Delay Line or
Optical Fiber Later)
Angular
Feedback Signal
Quadrant
Photodetector
AOM
Alignment
Sensing
System
AOM
Length
Sensing
System
Frequency
Stabilization
System
Photodetector
Displacement
Signal
Doppler
Simulator
One Idea of Ground Test on
Force Noise
 Low Resonant Frequency
 Low Thermal Noise
Wire
 Good Sensing System
Bar
Laser
Test Mass/
Mirror
Capacitance
Sensor etc.
Conclusions
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It is important to bridge the gap between
terrestrial detectors and LISA.
DECIGO is a candidate for the Japanese
space GW antenna.
DECIGO-WG has just started investigating
the possibility.
Two R&D experiments will be started very
soon.