Mirror Coatings for Next Generation Detector

Transcription

1 Mirror Coatings for Next Generation Detector Prof. Shiuh Chao (Member of LSC) Institute of Photonics Technologies (IPT) National Tsing Hua University (NTHU) Hsinchu, Taiwan, R.O.C. The 3rd KAGRA International Workshop (KIW3) May 21-22, 2017 Academia Sinica (NTU campus), Taipei Contents of this presentation havepartly been presented at Workshop on Gravitational Wave activities in Taiwan (GWTW) January 15, 2017 Academia Sinica, Institute of Physics and LVC meeting, Mar. 14,2017,Pasadena,Ca, USA (LIGO-G ) 1

2 LIGO-T v4 2

3 Noise Spectrum GW Dominant noise sources: Coating Brownian thermal noise Quantum noise shot noise and radiation pressure noise Thermal noise for mirror: Reducing thermal noise of the mirrors is therefore to reduce its mechanical loss, to operate at cryogenic and go for larger beam (i.e. larger mirror). Optically, the mirror needs to have excessively low absorption and low scattering loss to avoid effects such as thermal-lensing and phase disturbance

4 Challenges for coatings of future detectors Lower mechanical loss (i.e. thermal noise) room temp and cryogenic. Lower optical loss absorption and scattering. Large area uniform coating process.

5 Current coating technologies for a-ligo

6 Current mirror coatings for a-ligo -- material Snipview.com Currently for a-ligo: - Fused silica substrate (34 cm in diameter 20 cm in thickness and 40 Kg ) - Ta 2 O 5 -TiO 2 mixed film for high index layer, and SiO 2 film for low index layer coatings

7 Current mirror coatings deposition method Ion Beam Sputter (IBS) Production type IBS at LMAà Two aligo mirrors are coated simutaneously with planetary rotation and masking to ensure the thickness uniformity (all Zernike poly terms <0.5nm was achieved for a-ligo) But, need to scale-up to larger area coatings for future detectors.

8 Mirror Substrate

9 Cryogenic loss leak for IBS SiO 2 films at different annealing temperatures. R. Robie et al., Brief update of crygoenic coating mechanical loss measurements at the University of Glasgow, LIGO document:ligo-g (2016)

10 Cryogenic loss peak of Ta 2 O 5 and Ta 2 O 5 -TiO 2 films I W Martin et al., Comparison of the temperature dependence of the mechanical dissipation in thin films of Ta2O5 and Ta2O5 doped with TiO2, Class. Quantum Grav (2009)

11 Some potential improvement for future coatings Crystalline coatings -- AlGaAs Multi-material coatings amorphous silicon Nano-meter layers structure Chemical Vapor Deposition (CVD) Silicon nitride 11

12 AlGaAs Crystalline Coatings Need to transfer the coatings to large area substrate. Currently 100-mm diameter GaAs on silica G. D. Cole, W. Zhang, M. J. Martin, J. Ye, and M. Aspelmeyer, Nature Photonics (2013) G. D. Cole LIGO-G (2015) 12

13 Multi-materials coatings Conventional Ta 2 O 5 /SiO 2 QW stack has lower optical loss but higher mechanical loss than the amorphous silicon/sio 2 QW stack Multi-materials QW stack : lower optical loss but higher mechanical loss materials in the front layers and higher optical loss but lower mechanical loss in the back layers Jessica Steinlechner, Iain Matin, LIGO-P

14 IBS nano-meter layers (collaboration between NTHU and U. Sannio (Prof. Innocenzo Pinto) Room Temperature H. W. Pan, S. J. Wang, S. Chao et al, OPTICS EXPRESS, vol 22, (2014). LIGO-G Cryogenic (LIGO-G ) SiO 2 (As-deposited) x10 Bending mode: Torsional mode: x10 SiO 2 (Anneal 600 oc 24hr) Bending mode: x Hz Hz Hz Hz Tors ional mode: TiO 2 (As-deposited) Hz Hz Hz Hz Bending mode: 1.4x10-3 T orsional mode: 1.2x x H z Hz Hz Hz x x x10 Coating loss Coating loss Coating loss x10 8.0x x x x x x x10-4 No cryogenic peaks!! x10 5.0x x Temperature(K) Temperature(K) Temperature(K) Currently, we are measuring the cryogenics loss of the 19-layer nano-layer 14

15 At NTHU, asidefrom IBS for nano-meterlayers with U. Sannio, we also focus on : New deposition method CVD and new material -- SiN 15

16 Large area uniform coating on silicon wafer up to 18 (450mm) by Chemical Vapor Deposition (CVD) is a common practice in Taiwan s silicon-ic industry At National Tsing Hua University (NTHU), we are exploring mirror deposition for GW detector by using CVD method with low loss thin film materials (SiN). 16

17 Fabrication of SiN film on Silicon by Plasma-enhanced CVD (PECVD) Plasma Ref : Donald L. Smith, et al. mechanism of SiN x H y Deposition from NH 3 -SiH 4 plasma. J.Electrochem. Soc. 137, (1990) SiN x Deposit on polished surface Ref : J. N. Chiang, et al Mechanistic Considerations in the Plasma Deposition of silicon nitride film J. Electrochem. Soc. 137, (1990) Adjusting the ratio of the gas flow rate, the composition of the SiN film can be changed With fixed N 2 gas flow at 980 sccm, we used 5 recipes with different gas flow rate : Gas flow rate SiH 4 /NH 3 (sccm) Composition thickness * (nm) Refractive Young s modulus (GPa) * Means QW thckness of 1550nm Extinction coefficient for all 17 The 3rd KAGRA International LIGO-Gxxxxxx Workshop LVC (KIW3) meeting, May Stanford 21-22, 2017, University, Academia Aug. Sinica 25,2014 (NTU campus), Taipei Stress (MPa) Uncoated cantilever frequency Coated cantilever frequency 45/15 SiN ± ± ± ± /22 SiN ± ± ± ± /30 SiN ± ± ± ± /45 SiN ± ± ± ± /48 SiN ± ± ± ±

18 Plasma Enhanced Chemical Vapor Deposition (PECVD) for multi-layer dielectric mirror coating Process chamber 1:SiNx Process chamber 2: SiO 2 Silicon substrate side view 18

19 Plasma Enhanced Chemical Vapor Deposition (PECVD) for multi-layer dielectric mirror coating Process chamber 1:SiNx Process chamber 2: SiO 2 Silicon substrate side view 19

20 Optical and Mechanical Properties of SiNx film Optical properties (measured by ellipsometer) ( LIGO-G ) Refractive 1064 & 1550 nm Young s modulus (measured by nano-indentation) Stress (measured by curvature meter) Young's modulus(gpa) X SiN X ** Optical absorption of low-stress LPCVD silicon nitridemembrane from Norcada were: 213±17 nm (d eff = 2.2 um, α = 0.97±0.1 cm -1 κ = 1.2x10-5 ) 1512±27 nm (d eff = 2.2 um, α = 6.87±0.69 cm -1 κ = 5.8x10-5 ) **J. Steinlechner et al., Optical absorption of silicon nitride membrane at 1064 nm and at 1550 nm, LIGO-P

21 Mechanical loss of single SiNx layer 21

22 10-3 Room Temperature Loss Angle of SiNx Film with Different Compositions Coating loss angle SiN 0.40 (n = 2.30@1064, n=2.28@1550) SiN 0.65 (n = 1.93@1064, n=1.92@1550) SiN 0.87 (n = 1.78@1064, n=1.78@1550) Frequency (Hz) -- Loss of the lowest mode correlated with the trend of stress, Young s modulus and composition. -- Loss of high index SiN 0.40 is lower than that of 14.5% Ti: Ta 2 O 5 ~2000Hz [1][2]) -- Refractive index of SiN 0.40 is higher than that of 14.5% Ti: Ta 2 O 5 (n = 2.07@1064 nm, [1] I. Martin, H. Armandula, C. Comtet, M. M Fejer et al, Class. Quantum Grav. 25, (2008) [2] I. W. Martin, E. Chalkley, R. Nawrodt, et al, Class. Quantum Grav. 26, (2009) 22

23 Bending mode: x10-4 Cryogenic Loss Angle of SiNx Film with Different Compositions ~664 Hz x10-4 ~1854 Hz Coating loss angle SiN 0.87 SiN 0.65 SiN0.40 Coating loss angle SiN 0.87 SiN 0.65 SiN0.40 Cryo peak No cryo peak and low loss Torsional mode: x10-4 Temperature (K) ~1269 Hz x10-4 Temperature (K) ~3845 Hz Coating loss angle SiN 0.87 SiN 0.65 SiN 0.40 Coating loss angle SiN 0.87 SiN 0.65 SiN 0.40 Temperature (K) Temperature (K) -- SiN 0.40 and SiN 0.65 have no cryogenic peak and low loss, but SiN 0.87 shows a about 40K -- We are investigating annealing effect on loss angle and optical absorption of SiNx films. 23

24 Mechanical loss of PECVD Quarter-wave SiN 0.40 /SiO 2 Stacks 24

25 Room Temperature Loss Angle of QW SiN 0.40 /SiO 2 Stack (LIGO-G ) Coating loss angle From 1-pair sample From 2-pair sample From 3-pair sample From 4-pair sample Frequency (Hz) -- The coating loss angles are in 10-5 range at 100 Hz. -- The coating loss does not increase with pair number, indicating that there is no significant loss in SiN 0.40 /SiO 2 interface. 25

26 Thermal Noise Estimation of SiN 0.40 /SiO 2 QW HR at Room Temperature aligo [1] A + [1] SiN 0.40 /SiO 2 on silicon (max.) SiN 0.40 /SiO 2 on silicon (min.) Strain (1/ Hz) Frequency (Hz) SiN 0.40 /SiO 2 HR : 18 pairs of QW SiN 0.40 /SiO 2 + one λ/2 SiO 2 protective layer. (total thickness=8.57 um, transmittance =0.26 ppm) Strain of SiN 0.40 /SiO 2 QW HR is 3 ~ 4 times lower than that of the aligo specification and 1.5 ~ 2 times lower than the A + specification. 26 [1] LIGO white paper LIGO-T15TBI-v1 The 3rd KAGRA July, International 2016 Workshop (KIW3) May 21-22, 2017, Academia Sinica (NTU campus), Taipei

27 Cryogenic Loss Angle of QW SiN 0.40 /SiO 2 Stack Bending mode: x10-4 ~671 Hz x10-4 ~1873 Hz Coating loss angle Torsional mode: SiO 2 SiN 0.40 /SiO 2 (calculated) SiN 0.40 /SiO 2 (experimental) Temperature (K) SiN 0.40 x10-4 ~1221 Hz Coating loss angle SiO 2 SiN 0.40 /SiO 2 (calculated) SiN 0.40 /SiO 2 (experimental) SiN Temperature (K) x10-4 ~3705 Hz Coating loss angle Temperature (K) SiO 2 SiN 0.40 /SiO 2 (calculated) SiN 0.40 /SiO 2 (experimental) SiN 0.40 Coating loss angle SiN 0.40 /SiO 2 (calculated) SiN 0.40 /SiO 2 (experimental) Temperature (K) SiO2 SiN The cryogenic loss is boosted by the cryogenic peak of SiO The experimental values are lower than the calculated values that were obtained from the individual layers. 27

28 Conclusion Challenges for coatings of the future detector low mechanical loss in room temp. Low mechanical loss in cryogenics Low optical absorption and scattering Larger area uniform coatings CVD deposition process for large area coatings is promising. SiNx films deposited by CVD have low mechanical loss at room temp and cryogenic. Optical absorption measurement by PCI is ongoing. Quarter-wave stacks of SiNx/SiO 2 deposited by CVD have low mechanical loss at room temp and cryogenic. 28

29 Major In-house Facilities at NTHU - Ion Beam Sputter coater - Room temp. cantilever ring-downq measurement - Cryogenice cantilever ring-downq measurementfacilities - Photothermal common path interferometer (PCI) for ultra-low optical absorption measurement Facilities at National Nano-Devices Lab (NDL) accessible to us - Full silicon IC process facilities - CVD coaters - Elcetron microscopes, TEM, SEM, XED - X-ray diffractometer - ESCA for compisition analysis - Nano-indentor for Young s modulus measurement - Stressmeter forthin film stress measurement - Ellipsometer - Welcome collaborations with people in KAGRA and Virgo 29