Transcript Laser and Optical system of LCGT

Laser &Optics of LCGT
2011/10/5(Wed)
Norikatsu Mio
Photon Science Center
University of Tokyo
EGO-ICRR Meeting 2011/10/4-5
Schematic View of LCGT Optical System
ETMY
Laser
MC1
MC3
MT1 PRM
PR1
ITMY
ITMX
ETMX
MT2
BS
PR2
SR1
MC2
SR2
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SRM
2
Laser
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Requirements for the laser
•
•
•
•
•
Power > 180 W
Single frequency
Linear polarization
Single transverse mode
Wide-band control for stabilization systems
– About 1MHz for frequency control
– About 100kHz for intensity control
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Injection Lock or MOPA
• Single frequency laser output over 100 W CW can be
realized by using injection-locking and MOPA.
– Injection locking has many advantages compared with
MOPA.
– However, an injection locking system is more complex than
a MOPA system; this is quite critical for easy operation.
– We have a 10-year history developing a prototype based
on the injection-locking scheme.
– We recognized that the injection-locking system is quite
sensitive to the alignment and it seemed to be difficult to
keep the best performance without a well-trained operator.
– MOPA is easy for assembly and maintenance.
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Design for the system
• An amplifier system consisting of a seed laser (NPRO),
fiber amplifiers and solid-state amplifiers will be used.
– Fiber laser technology is rapidly progressed and its power
level may arrive at the requirement soon even though the
current fiber amplifiers have some problems.
– Combination of the fiber laser technology and the solid
state laser technology is our current choice.
– If high-power, long life-time and narrow line-width fiber
amplifiers are available, solid-state amplifiers can be
replaced.
• Korean Group (Prof. Yoon @ Korea University) is
willing to develop a part of the laser system, in
particular, a high-power fiber laser.
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Schematic diagram
Mitsubishi laser modules
200 W
80 W
Fiber laser amplifiers
40 W
NPRO(500mW)
40 W
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Commercial fiber amplifier
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Laser module （Mitsubishi）
Two rods and rotator
Diffusive reflector +LD
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Laser
• Most of the main elements will be obtained by the
end of this FY.
• Discussion will start with a company that will
assemble the laser system using Mitsubishi modules
and fiber amplifiers, soon.
• The first laser will be hopefully completed at the end
of FY 2012 (March, 2013).
• Green lasers used for “GREEN-LOCK” will be
prepared at the end of this FY.
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Current Status
Chiller
Power
Supply
200 W
Mitsubishi laser modules
80 W
Fiber laser amplifiers
40 W
NPRO(500mW)
40 W
EGO-ICRR Meeting 2011/10/4-5
Light Green: Obtained
Green: Ordered
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Schedule
2010
iLCGT
laser
bLCGT
laser
bLCGT
laser
(2nd)
Preparation
of basic parts
2011
2012
2013
2014
2015
Evaluation of
basic parts
Stabilization
system
Installation
preparation
Operation
Evaluation of
basic parts
Assembly
Evaluation of
the laser
system
Installation
preparation
Operation
preparation
Assembly
Evaluation of
the laser
system
Installation
preparation
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TODO
• Performance of the fiber amplifier
– 10-W one is OK but 40-W one has not been tested.
• Performance of the coherent addition system
– The fringe contrast, phase stability and so on.
• Performance of the laser module when used as an amplifier.
– Optimization of the beam profile for obtaining the best amplification
performance.
– Polarization stability, noise level should be tested.
• Fix the specifications for the control system (interfaces to a PC
and other systems)
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Optics
EGO-ICRR Meeting 2011/10/4-5
Mirror Core optics of LCGT
ETMY
f10cm
Laser
MC1
MC3
Mirrors for Main cavities
Initial: Silica
Final: Sapphire
MT1 PRM
ITMY
PR2
ITMX
MT2
BS
PR3
SR2
MC2
f38cm
SRM
SR3
f 25cm
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ETMX
Optics
• Substrates(Silica, Sapphire)
• Polish & Coating & Measurement
• iLIGO Mirrors
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Substrate (Silica)
• Asahi Glass Company (AGC), AQ and AQ2 will
be used.
• BS (f38cm x t12cm, AQ2): obtained!
• MC (f10cm x t3cm, AQ2 and AQ): obtained!
• Delivery was delayed owing to the earthquake
because the factory of AGC is located in
Koriyama (郡山).
• New substrates for ITMs (f25cm x t10cm,
AQ2) have been ordered.
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AGC:AQ2
IR performance of AQ2
is comparable to
Sprasil.
At UV, its performance
is better than Sprasil.
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Substrate (Sapphire)
• A-axis crystal (f25cm x t15cm) has been ordered.
• Max size of C-axis crystal is now f22cm x t15cm; this
size is limited by the height of the boules.
Response from CSI at the beginning of 2011
– Current Max size of
• C-axis mirror: f20cm x t15cm
• A-Plane mirror: f25cm x t15cm
“With time we feel can develop larger C-axis sapphire
slabs to achieve your goal of 25cm x 15cm sapphire
mirrors with our HEM growth process.”
Optical Absorption <20 ppm/cm (10 ppm/cm is preferable
Absorption is still unclear; new small samples are
being tested.
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Photo-thermal deflection method
C-axis f: 100 mm x t: 60 mm
AB29
Z=50mm, 53.4 ppm/cm
Y
Z = 50 mm
0
X
Z=40mm, 45.5 ppm/cm
Z = 40 mm
Z=30mm, 47.3 ppm/cm
Z = 30 mm
Z=20mm, 46.1 ppm/cm
Z = 20 mm
Z=10mm, 54,2 ppm/cm
Z = 10 mm
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Z=30mm
(2005）
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Sapphire absorption at cryogenic
temperature
By Tomaru @ KEK in 2000
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Absorption measurement@UT
Chopped light is
incident on a sample.
120Hz
Laser
l：1064nm
Power：10W
Signal is lockin detected.
Lock-in Amplifier
Chopper
Sample
BS(R=98%)
BPF
LPF
PD
Absorbed light power
Sample tempature change
Dark fringe
Mirror
15kHz
PZT
Refraction Index, length change
Optical path length change
PZT driver
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Filter
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Interferometer
2010/9/14
Laser light
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Sapphire sample
C-axis rod (diameter: 10mm, length: 40mm)
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Results of Sapphire
Measurement in last year
Measurement in this year
80ppm/cm
87ppm/cm
The result was reproduced but the noise level of the
interferometer became worse; the origin of the noise has not
been identified.
Calibration for sapphire has not been done
Absolute values may contain large uncertainty!
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Preliminary results
10 Samples
Name
Absorption [ppm/cm]
AA149
48
47
AC150
229
138
682
687
P401
34
32
65
67
• AA149 and P401 show better performance
compared with the last year sample.
• AC150 shows quite high absorption; why ?
• P401 contains lower and high absorption
pairs. what is the difference?
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Polish & Coating & Measurement
• Members of AIST-NMIJ are collaborating with
us ; a mirror used in LISM (R=30 m) has been
sent to NMIJ to evaluate the absolute value of
its curvature radius.
• Memorandum for the collaboration about the
polishing with Riken group has fixed.
• We are still looking for the facilities for
polishing and coating.
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Requirements for Roughness
• Allowable loss of main mirrors: 45 ppm
• Scattering loss < 30 ppm
Hiro Yamamoto@ LIGO
• Total Integrated Scattering
Is kindly collaborating
 4

 l





about this issue.
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l  1μm    0.6 nm
• Spatial spectrum of surface roughness
Spatial distribution of the surface
roughness can be express as a function
of spatial wave number.
AdvLIGO
ls  2 mm    0.5 nm
d  10.5 cm
ls  2 mm    0.2 nm
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Example of Superpolished Surface done by Japanese
Company
Substrate: Zerodur
Diameter: 25 cm
Thickness: 4cm
Surface roughness:
0.12 nm rms
Size:
0.14mm x 0.1mm
Requirement:
0.5 nm within 12cm
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EGO-ICRR Meeting 2011/10/4-5
Requirement for coating
• Main mirrors
– Absorption: < 1 ppm=> Heating problem
– Scattering: < 30ppm
• Beam splitter and Recycling Mirrors
– Loss < 0.01 %
• Thermal noise issue is out of scope for iLCGT.
• This issue seems to be taken into
consideration seriously even for cryogenic
mirrors of bLCGT ; Ta and Ti co-doping???
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iLCGT mirrors from iLIGO
• For iLCGT, the size of the mirrors is chosen as that of iLIGO’s mirror.
• BS and ITMs will be newly fabricated from Japanese Silica.
• LIGO kindly donates the mirrors to us.
ETMY
f10cm
Laser
MC1
MC3
MT1 PRM
PR2
ITMY
ITMX
ETMX
MT2
BS
PR3
SR2
MC2
SRM
SR3
f38cm x t12cm
LIGO mirrors
(re-polishing and re-coating)
f25cm x t10cm
New mirrors
f25 cm x t10cm
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Telescope used in iLIGO arrived
The mode reducing telescope used in iLIGO
arrived at ICRR on August 22, 2011.
The Mirrors used
in iLIGO will be
sent to Japan,
soon.
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Schedule
2010
2011
BS
Substrate
Polish
&coating
MC
Substrate
Polish
&coating
2012
2013
PRMs
Substrate
Polishing
Coating
SRMs
Substrate
Polishing
Coating
ITMs &ETMs
(iLCGT)
Substrate
Polishing
Coating
ITMs &ETMs
(bLCGT)
Substrate
R&D
Polishing
R&D
Substrate
Polishing
R&D
Coating R&D
Polishing
Coating R&D
EGO-ICRR Meeting 2011/10/4-5
2014
2015
Coating
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Miscellaneous on Optics
• We need further R&D for sapphire.
• Members of AIST-NMIJ are willing to collaborate with
us concerning the surface profile measurement.
• A few Japanese companies are willing to fabricate
the mirrors of LCGT; they have some experiences for
high precision optics.
• Test facilities for optical absorption and optical
scattering will be kept.
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Summary
• Preparation of the laser system is going well.
• Silica substrates will be obtained soon.
• Preparation of the sapphire crystals needs
further efforts and days.
• Polishing and coating are still issues that
should be solved as soon as possible.
• We would deeply appreciate to the
international collaborations.
In particular, collaborations from VIRGO/EGO
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