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Laser &Optics of LCGT 2011/10/5(Wed) Norikatsu Mio Photon Science Center University of Tokyo EGO-ICRR 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 MC 1 MC 3 MT 1 Schematic View of LCGT Optical System ETMY Laser MC 1 MC 3 MT 1 PRM PR 1 ITMY ITMX ETMX MT 2 BS PR 2 SR 1 MC 2 SR 2 EGO-ICRR Meeting 2011/10/4 -5 SRM 2

Laser EGO-ICRR Meeting 2011/10/4 -5 Laser EGO-ICRR Meeting 2011/10/4 -5

Requirements for the laser • • • Power > 180 W Single frequency Linear Requirements for the laser • • • Power > 180 W Single frequency Linear polarization Single transverse mode Wide-band control for stabilization systems – About 1 MHz for frequency control – About 100 k. Hz for intensity control EGO-ICRR Meeting 2011/10/4 -5 4

Injection Lock or MOPA • Single frequency laser output over 100 W CW can 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), 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 EGO-ICRR Meeting 2011/10/4 -5 particular, a high-power fiber laser. 6

Schematic diagram Mitsubishi laser modules 200 W 80 W Fiber laser amplifiers 40 W Schematic diagram Mitsubishi laser modules 200 W 80 W Fiber laser amplifiers 40 W NPRO(500 m. W) 40 W EGO-ICRR Meeting 2011/10/4 -5 7

Commercial fiber amplifier EGO-ICRR Meeting 2011/10/4 -5 8 Commercial fiber amplifier EGO-ICRR Meeting 2011/10/4 -5 8

Laser module (Mitsubishi) Two rods and rotator Diffusive reflector +LD EGO-ICRR Meeting 2011/10/4 -5 Laser module (Mitsubishi) Two rods and rotator Diffusive reflector +LD EGO-ICRR Meeting 2011/10/4 -5 9

Laser • Most of the main elements will be obtained by the end of 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

Current Status Chiller Power Supply 200 W Mitsubishi laser modules 80 W Fiber laser Current Status Chiller Power Supply 200 W Mitsubishi laser modules 80 W Fiber laser amplifiers 40 W NPRO(500 m. W) 40 W EGO-ICRR Meeting 2011/10/4 -5 Light Green: Obtained Green: Ordered 11

Schedule 2010 i. LCGT laser b. LCGT laser (2 nd) 2011 2012 2013 2014 Schedule 2010 i. LCGT laser b. LCGT laser (2 nd) 2011 2012 2013 2014 2015 Evaluation of basic parts Preparation 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 EGO-ICRR Meeting 2011/10/4 -5 12

TODO • Performance of the fiber amplifier – 10 -W one is OK but 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

Optics EGO-ICRR Meeting 2011/10/4 -5 Optics EGO-ICRR Meeting 2011/10/4 -5

Mirror Core optics of LCGT ETMY f 10 cm Laser MC 1 MC 3 Mirror Core optics of LCGT ETMY f 10 cm Laser MC 1 MC 3 Mirrors for Main cavities Initial: Silica Final: Sapphire MT 1 PRM ITMY PR 2 ITMX MT 2 PR 3 BS SR 2 MC 2 f 38 cm SRM SR 3 f 25 cm EGO-ICRR Meeting 2011/10/4 -5 ETMX

Optics • Substrates(Silica, Sapphire) • Polish & Coating & Measurement • i. LIGO Mirrors Optics • Substrates(Silica, Sapphire) • Polish & Coating & Measurement • i. LIGO Mirrors EGO-ICRR Meeting 2011/10/4 -5 16

Substrate (Silica) • Asahi Glass Company (AGC), AQ and AQ 2 will be used. Substrate (Silica) • Asahi Glass Company (AGC), AQ and AQ 2 will be used. • BS (f 38 cm x t 12 cm, AQ 2): obtained! • MC (f 10 cm x t 3 cm, AQ 2 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 (f 25 cm x t 10 cm, AQ 2) have been ordered. EGO-ICRR Meeting 2011/10/4 -5 17

AGC: AQ 2 IR performance of AQ 2 is comparable to Sprasil. At UV, AGC: AQ 2 IR performance of AQ 2 is comparable to Sprasil. At UV, its performance is better than Sprasil. EGO-ICRR Meeting 2011/10/4 -5 18

Substrate (Sapphire) • A-axis crystal (f 25 cm x t 15 cm) has been Substrate (Sapphire) • A-axis crystal (f 25 cm x t 15 cm) has been ordered. • Max size of C-axis crystal is now f 22 cm x t 15 cm; 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: f 20 cm x t 15 cm • A-Plane mirror: f 25 cm x t 15 cm “With time we feel can develop larger C-axis sapphire slabs to achieve your goal of 25 cm x 15 cm 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. EGO-ICRR Meeting 2011/10/4 -5 19

Photo-thermal deflection method C-axis f: 100 mm x t: 60 mm Z=50 mm, 53. Photo-thermal deflection method C-axis f: 100 mm x t: 60 mm Z=50 mm, 53. 4 ppm/cm Z=40 mm, 45. 5 ppm/cm Z=30 mm, 47. 3 ppm/cm Z=20 mm, 46. 1 ppm/cm Z=10 mm, 54, 2 ppm/cm EGO-ICRR Meeting 2011/10/4 -5 Z=30 mm (2005) 20

Sapphire absorption at cryogenic temperature By Tomaru @ KEK in 2000 EGO-ICRR Meeting 2011/10/4 Sapphire absorption at cryogenic temperature By Tomaru @ KEK in 2000 EGO-ICRR Meeting 2011/10/4 -5

Absorption measurement@UT Chopped light is incident on a sample. 120 Hz Laser l: 1064 Absorption [email protected] Chopped light is incident on a sample. 120 Hz Laser l: 1064 nm Power: 10 W Signal is lockin detected. Lock-in Amplifier Chopper Sample BS(R=98%) BPF LPF PD Absorbed light power Sample tempature change Dark fringe Mirror 15 k. Hz PZT Refraction Index, length change Optical path length change PZT driver EGO-ICRR Meeting 2011/10/4 -5 Filter 22

Interferometer 2010/9/14 Laser light EGO-ICRR Meeting 2011/10/4 -5 23 Interferometer 2010/9/14 Laser light EGO-ICRR Meeting 2011/10/4 -5 23

Sapphire sample C-axis rod (diameter: 10 mm, length: 40 mm) EGO-ICRR Meeting 2011/10/4 -5 Sapphire sample C-axis rod (diameter: 10 mm, length: 40 mm) EGO-ICRR Meeting 2011/10/4 -5 24

Results of Sapphire Measurement in last year Measurement in this year 80 ppm/cm 87 Results of Sapphire Measurement in last year Measurement in this year 80 ppm/cm 87 ppm/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! EGO-ICRR Meeting 2011/10/4 -5 25

Preliminary results 10 Samples Name Absorption [ppm/cm] AA 149 48 47 AC 150 229 Preliminary results 10 Samples Name Absorption [ppm/cm] AA 149 48 47 AC 150 229 138 682 687 P 401 34 32 65 67 • AA 149 and P 401 show better performance compared with the last year sample. • AC 150 shows quite high absorption; why ? • P 401 contains lower and high absorption pairs. what is the difference? EGO-ICRR Meeting 2011/10/4 -5 26

Polish & Coating & Measurement • Members of AIST-NMIJ are collaborating with us ; 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

Requirements for Roughness • Allowable loss of main mirrors: 45 ppm • Scattering loss Requirements for Roughness • Allowable loss of main mirrors: 45 ppm • Scattering loss < 30 ppm Hiro [email protected] LIGO • Total Integrated Scattering Is kindly collaborating about this issue. • Spatial spectrum of surface roughness Spatial distribution of the surface roughness can be express as a function of spatial wave number. Adv. LIGO EGO-ICRR Meeting 2011/10/4 -5 28

Example of Superpolished Surface done by Japanese Company Substrate: Zerodur Diameter: 25 cm Thickness: 4 Example of Superpolished Surface done by Japanese Company Substrate: Zerodur Diameter: 25 cm Thickness: 4 cm Surface roughness: 0. 12 nm rms Size: 0. 14 mm x 0. 1 mm Requirement: 0. 5 nm within 12 cm 29 EGO-ICRR Meeting 2011/10/4 -5

Requirement for coating • Main mirrors – Absorption: < 1 ppm=> Heating problem – Requirement for coating • Main mirrors – Absorption: < 1 ppm=> Heating problem – Scattering: < 30 ppm • Beam splitter and Recycling Mirrors – Loss < 0. 01 % • Thermal noise issue is out of scope for i. LCGT. • This issue seems to be taken into consideration seriously even for cryogenic mirrors of b. LCGT ; Ta and Ti co-doping? ? ? EGO-ICRR Meeting 2011/10/4 -5 30

i. LCGT mirrors from i. LIGO • For i. LCGT, the size of the i. LCGT mirrors from i. LIGO • For i. LCGT, the size of the mirrors is chosen as that of i. LIGO’s mirror. • BS and ITMs will be newly fabricated from Japanese Silica. • LIGO kindly donates the mirrors to us. EGO-ICRR Meeting 2011/10/4 -5 31

Telescope used in i. LIGO arrived The mode reducing telescope used in i. LIGO Telescope used in i. LIGO arrived The mode reducing telescope used in i. LIGO arrived at ICRR on August 22, 2011. The Mirrors used in i. LIGO will be sent to Japan, soon. EGO-ICRR Meeting 2011/10/4 -5 32

Schedule 2010 2011 BS Substrate 2013 2014 2015 Polish &coating MC 2012 Polish &coating Schedule 2010 2011 BS Substrate 2013 2014 2015 Polish &coating MC 2012 Polish &coating PRMs Substrate Polishing Coating SRMs Substrate Polishing Coating ITMs &ETMs (i. LCGT) Substrate Polishing Coating ITMs &ETMs (b. LCGT) Substrate R&D Polishing R&D Substrate Polishing R&D Coating R&D Polishing Coating R&D EGO-ICRR Meeting 2011/10/4 -5 Coating 33

Miscellaneous on Optics • We need further R&D for sapphire. • Members of AIST-NMIJ 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 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 EGO-ICRR Meeting 2011/10/4 -5 35