laser &optics of lcgt
DESCRIPTION
Laser &Optics of LCGT. 2011/10/5(Wed) Norikatsu Mio Photon Science Center University of Tokyo. Schematic View of LCGT Optical System. ETMY. Laser. MC1. MC3. ITMY. MT1. PRM. PR1. ITMX. ETMX. MT2. BS. PR2. SR1. MC2. SRM. SR2. Laser. Requirements for the laser. Power > 180 W - PowerPoint PPT PresentationTRANSCRIPT
Laser &Optics of LCGT
2011/10/5(Wed)Norikatsu Mio
Photon Science CenterUniversity of Tokyo
EGO-ICRR Meeting 2011/10/4-5
Laser MC1
MC2
MC3PRM PR1
PR2
BS
SR2
SR1
SRM
ITMX
ITMY
ETMX
ETMY
MT1
MT2
Schematic View of LCGT Optical System
EGO-ICRR Meeting 2011/10/4-5 2
Laser
EGO-ICRR Meeting 2011/10/4-5
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.EGO-ICRR Meeting 2011/10/4-5 5
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
Fiber laser amplifiers
NPRO(500mW)
40 W
40 W
80 W
200 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
Mitsubishi laser modules
Fiber laser amplifiers
NPRO(500mW)
40 W
40 W
80 W
200 W
Power Supply
Chiller
Light Green: Obtained Green: OrderedEGO-ICRR Meeting 2011/10/4-5 11
Schedule
2010 2011 2012 2013 2014 2015
iLCGT laser
Evaluation of basic parts
Stabilization system
Installation preparation
Operation
bLCGT laser
Preparation of basic parts
Evaluation of basic parts
Assembly Evaluation of the laser system
Installation preparation
Operation preparation
bLCGT laser(2nd)
Assembly Evaluation of the laser system
Installation preparation
EGO-ICRR Meeting 2011/10/4-5 12
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
Laser MC1
MC2
MC3PRM PR2
PR3BS
SR3
SR2
SRM
ITMX
ITMY
ETMX
ETMY
MT1
MT2
25cm
38cm
10cm
Mirror
Mirrors for Main cavitiesInitial: Silica
Final: Sapphire
Core optics of LCGT
EGO-ICRR Meeting 2011/10/4-5
Optics
• Substrates(Silica, Sapphire)• Polish & Coating & Measurement• iLIGO Mirrors
EGO-ICRR Meeting 2011/10/4-5 16
Substrate (Silica)
• Asahi Glass Company (AGC), AQ and AQ2 will be used.
• BS (38cm x t12cm, AQ2): obtained!• MC (10cm 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 (25cm x t10cm, AQ2) have been ordered.
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AGC:AQ2
18
IR performance of AQ2 is comparable to Sprasil.
At UV, its performance is better than Sprasil.
EGO-ICRR Meeting 2011/10/4-5
Substrate (Sapphire)
• A-axis crystal (25cm x t15cm) has been ordered.• Max size of C-axis crystal is now 22cm 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: 20cm x t15cm• A-Plane mirror:25cm 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.”
Absorption is still unclear; new small samples are being tested.
Optical Absorption <20 ppm/cm (10 ppm/cm is preferable
EGO-ICRR Meeting 2011/10/4-5 19
Photo-thermal deflection method
(2005 )
AB29
Z = 10 mm
Z = 50 mm
Z = 20 mm
Z = 30 mm
Z = 40 mm
5
Y
X0
C-axis 100 mm x t: 60 mm
Z=10mm, 54,2 ppm/cm
Z=20mm, 46.1 ppm/cm
Z=30mm, 47.3 ppm/cm
Z=40mm, 45.5 ppm/cm
Z=50mm, 53.4 ppm/cm
Z=30mm
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Sapphire absorption at cryogenic temperature
By Tomaru @ KEK in 2000
EGO-ICRR Meeting 2011/10/4-5
Lock-in AmplifierLock-in Amplifier
PZT
PD
Mirror
Sample
Laser : 1064nmPower : 10W
120Hz
Chopper
BS(R=98%)
BPFBPF
PZT driverPZT driver
LPFLPF
FilterFilter
15kHz
Chopped light is incident on a sample.Chopped light is incident on a sample.
Dark fringeDark fringeAbsorbed light powerAbsorbed light power
Sample tempature changeSample tempature change
Refraction Index, length changeOptical path length change
Refraction Index, length changeOptical path length change
Absorption measurement@UT
Signal is lock-in detected.Signal is lock-in detected.
22EGO-ICRR Meeting 2011/10/4-5
Interferometer
Laser light2010/9/14 23EGO-ICRR Meeting 2011/10/4-5
Sapphire sample
C-axis rod (diameter: 10mm, length: 40mm)
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Results of Sapphire
80ppm/cm 87ppm/cm
Measurement in last year Measurement in this year
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!EGO-ICRR Meeting 2011/10/4-5 25
AA149 48 47
AC150 229 138 682 687
P401 34 32 65 67
Name Absorption [ppm/cm]
10 Samples
Preliminary results
• 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• Total Integrated Scattering
• Spatial spectrum of surface roughness
24
nm6.0μm1
Spatial distribution of the surface roughness can be express as a function of spatial wave number.
nm2.0mm2
nm5.0mm2
s
s
AdvLIGO
cm5.10d
28
Hiro Yamamoto@ LIGO Is kindly collaborating about this issue.
EGO-ICRR Meeting 2011/10/4-5
Example of Superpolished Surface done by Japanese Company
Substrate: ZerodurDiameter: 25 cmThickness: 4cm
Surface roughness: 0.12 nm rmsSize: 0.14mm x 0.1mm
Requirement: 0.5 nm within 12cm
29 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???
30EGO-ICRR Meeting 2011/10/4-5 30
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.
Laser MC1
MC2
MC3PRM PR2
PR3BS
SR3
SR2
SRM
ITMX
ITMY
ETMX
ETMY
MT1
MT2
LIGO mirrors(re-polishing and re-coating)25cm x t10cm
38cm x t12cm
10cm
New mirrors25 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 2012 2013 2014 2015BS Substrate Polish
&coating
MC Substrate Polish &coating
PRMs SubstratePolishing
Coating
SRMs SubstratePolishing
Coating
ITMs &ETMs(iLCGT)
Substrate Polishing Coating
ITMs &ETMs(bLCGT)
Substrate R&DPolishing R&D
SubstratePolishing R&DCoating R&D
PolishingCoating R&D
Coating
33EGO-ICRR Meeting 2011/10/4-5 33
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.
EGO-ICRR Meeting 2011/10/4-5 34
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.
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In particular, collaborations from VIRGO/EGO