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 EGO-ICRR Meeting 2011/10/4-5 4
Slide 5
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
Slide 6
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. EGO-ICRR Meeting 2011/10/4-5 6
Slide 7
Schematic diagram Mitsubishi laser modules Fiber laser
amplifiers NPRO(500mW) 40 W 80 W 200 W EGO-ICRR Meeting
2011/10/4-57
Laser module Mitsubishi Two rods and rotator Diffusive
reflector +LD EGO-ICRR Meeting 2011/10/4-5 9
Slide 10
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. EGO-ICRR Meeting 2011/10/4-5
10
Slide 11
Current Status Mitsubishi laser modules Fiber laser amplifiers
NPRO(500mW) 40 W 80 W 200 W Power Supply Chiller Light Green:
ObtainedGreen: Ordered EGO-ICRR Meeting 2011/10/4-511
Slide 12
Schedule 201020112012201320142015 iLCGT laser Evaluation of
basic parts Stabilization system Installation preparation Operation
bLCGT laser Preparation of basic parts Evaluation of basic parts
AssemblyEvaluation of the laser system Installation preparation
Operation preparation bLCGT laser (2 nd ) AssemblyEvaluation of the
laser system Installation preparation EGO-ICRR Meeting 2011/10/4-5
12
Slide 13
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) EGO-ICRR Meeting 2011/10/4-5 13
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 ( ). New
substrates for ITMs ( 25cm x t10cm, AQ2) have been ordered.
EGO-ICRR Meeting 2011/10/4-5 17
Slide 18
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
Slide 19
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
Results of Sapphire 80ppm/cm87ppm/cm Measurement in last
yearMeasurement 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
Slide 26
AA1494847 AC150229138682687 P40134326567 NameAbsorption
[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? EGO-ICRR Meeting 2011/10/4-5 26
Slide 27
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. EGO-ICRR Meeting 2011/10/4-5 27
Slide 28
Requirements for Roughness Allowable loss of main mirrors: 45
ppm Scattering loss < 30 ppm Total Integrated Scattering Spatial
spectrum of surface roughness Spatial distribution of the surface
roughness can be express as a function of spatial wave number.
AdvLIGO 28 Hiro Yamamoto@ LIGO Is kindly collaborating about this
issue. EGO-ICRR Meeting 2011/10/4-5
Slide 29
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 29 EGO-ICRR Meeting 2011/10/4-5
Slide 30
Requirement for coating Main mirrors Absorption: 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??? 30 EGO-ICRR
Meeting 2011/10/4-5 30
Slide 31
iLCGT mirrors from iLIGO For iLCGT, the size of the mirrors is
chosen as that of iLIGOs mirror. BS and ITMs will be newly
fabricated from Japanese Silica. LIGO kindly donates the mirrors to
us. EGO-ICRR Meeting 2011/10/4-531
Slide 32
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. EGO-ICRR Meeting
2011/10/4-532
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
Slide 35
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. EGO-ICRR
Meeting 2011/10/4-5 35 In particular, collaborations from
VIRGO/EGO