Developing the TiO2/SiO2 mixed
films for low optical loss dielectric
mirror --- A retrospect
Prof. Shiuh Chao
Institute of Photonics Technologies
National Tsing Hua University
Taiwan, R.O.C.
2010/8/13 at Caltech
LIGO
Prof. Chao, National Tsing Hua
Univ., Taiwan
LIGO-G1000746
Reflection
Scattering
Absorption
Transmittion
1=R+T+S+A
Total Loss ≡ 1-R-T = S+A
2010/8/13 at Caltech
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Prof. Chao, National Tsing Hua
Univ., Taiwan
RING LASER GYROSCOPE
光腔長度偵測器
數位訊號輸出
曲面鏡
陽極充氣管
陽極
增益氣體
光學共振腔
抖動器
陀螺儀
輸出訊號
腔長控制器
合成稜鏡
薄膜鏡
陰極
輸入訊號
光接收器
順時針光束
逆時針光束
逆時針光束
干涉條紋圖形
干涉條紋圖
High Q resonator  low optical loss for the mirrors
2010/8/13 at Caltech
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Prof. Chao, National Tsing Hua
Univ., Taiwan
LOCK-IN EFFECT IN RLG
  ( 4 A )

L
output frequency
Ψ
ΩL
Ω
input rate
2 c
L  (
)
32dA
s
To avoid lock-in effect => low back-scatter mirror is critical
2010/8/13 at Caltech
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Prof. Chao, National Tsing Hua
Univ., Taiwan
Multi-layer dielectric mirror
H
L
H
nd = 1/2 λ
L
H
H: TIO2, TA2O5
L: SIO2
Substrate
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Prof. Chao, National Tsing Hua
Univ., Taiwan
Coating Apparatus
Ion Beam Sputtering
--- dense film
--- higher refractive index
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Prof. Chao, National Tsing Hua
Univ., Taiwan
2010/8/13 at Caltech
LIGO
Prof. Chao, National Tsing Hua
Univ., Taiwan
Instrumental analysis for mirror characterization
Optical constants and
thickness: Spectrophotometer
Surface roughness:
Atomic Force Microscope
Structure:X-Ray
Diffractometer
Total loss: Cavity
ring-down lossmeter
Optical
Microscope
Optical Damage:
Nd:YAG Laser
Concentration:
Rutherford Backscattering
Spectrometer
2010/8/13 at Caltech
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Prof. Chao, National Tsing Hua
Univ., Taiwan
Chemical bonding:
Electron Spectroscopy
for Chemical
Analysis(ESCA)
Single TiO2 film
Annealing effect on ion-beam-sputtered titanium
dioxide film
Wen-Hsiang Wang and Shiuh Chao
Department of Electrical Engineering, National Tsing
Hua University, Hsin-Chu, Taiwan
September 15, 1998 / Vol. 23, No. 18 / OPTICS
LETTERS 1417
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Prof. Chao, National Tsing Hua
Univ., Taiwan
Anatase A(101)
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Prof. Chao, National Tsing Hua
Univ., Taiwan
(A) as-deposited
(B) annealed 200 oC
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Prof. Chao, National Tsing Hua
Univ., Taiwan
(C) annealed 225 oC
(D) annealed 300oC
2010/8/13 at Caltech
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Prof. Chao, National Tsing Hua
Univ., Taiwan
2010/8/13 at Caltech
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Prof. Chao, National Tsing Hua
Univ., Taiwan
2010/8/13 at Caltech
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Prof. Chao, National Tsing Hua
Univ., Taiwan
Substrate roughness
=>
(1) GOOD POLISHING=> REDUCE SUBSTRATE ROUGHNESS
(2) RAISE UP THE CRYSTALLIZATION TEMPERATURE OF THE FILM
Single TiO2-SiO2 mixed film
Characteristics of ion-beam-sputtered high refractiveindex TiO2-SiO2 mixed films
Shiuh Chao and Wen-Hsiang Wang
Department of Electrical Engineering, National Tsing Hua University,
Hsin-Chu, Taiwan
Min-Yu Hsu and Liang-Chu Wang
Chung-Shan Institute of Science and Technology, Tao-Yuan, Taiwan
Vol. 16, No. 6/June 1999/J. Opt. Soc. Am. A 1477
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Prof. Chao, National Tsing Hua
Univ., Taiwan
5% SiO2
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Prof. Chao, National Tsing Hua
Univ., Taiwan
- 65-
9% SiO2
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Prof. Chao, National Tsing Hua
Univ., Taiwan
- 66-
17% SiO2
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Prof. Chao, National Tsing Hua
Univ., Taiwan
- 67-
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Prof. Chao, National Tsing Hua
Univ., Taiwan
2010/8/13 at Caltech
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Prof. Chao, National Tsing Hua
Univ., Taiwan
(A) SiO2: 0% annealed 300oC
(B) SiO2: 17% annealed 300oC
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Prof. Chao, National Tsing Hua
Univ., Taiwan
2010/8/13 at Caltech
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Prof. Chao, National Tsing Hua
Univ., Taiwan
“phase diagram” of the mixed film
2010/8/13 at Caltech
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Prof. Chao, National Tsing Hua
Taiwan
圖(二十八) TiOUniv.,
2-SiO2光學混合膜的退火相圖
-84-
Multi-layer dielectric mirror
with the mixed film
Low-loss dielectric mirror with
ion-beam-sputtered TiO2–SiO2 mixed films
Shiuh Chao, Wen-Hsiang Wang, and Cheng-Chung Lee
1 May 2001 y Vol. 40, No. 13 y APPLIED OPTICS 2177
2010/8/13 at Caltech
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Prof. Chao, National Tsing Hua
Univ., Taiwan
TiO2+ SiO2
17%
SiO2
TiO2+ SiO2
nd = 1/4 λ
17%
SiO2
TiO2+ SiO2 17%
Zerodur
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Prof. Chao, National Tsing Hua
Univ., Taiwan
nd = 1/4 λ
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Prof. Chao, National Tsing Hua
Univ., Taiwan
SiO2 : 0%
● SiO2 : 17 %
▲
- 34%
0
- 50
- 50
-100
deposition temp.(820C)
-100
0
50
100 150 200 250 300 350 400 450
Annealing Temperature (0C)
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Prof. Chao, National Tsing Hua
Univ., Taiwan
Total Loss Change (%)
Total Loss Change (%)
0
Laser Induced Damage
(A)
(B)
3 mm
1.5 mm
SiO2:0% as-deposited
damage threshold: 2.8 KJ/cm2
(A) (B): damaged spot under optical microscope
2010/8/13 at Caltech
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Prof. Chao, National Tsing Hua
Univ., Taiwan
(C)
(D)
SiO2:0% as-deposited
damage threshold: 2.8 KJ/cm2
(C) )(D) damaged spot under AFM
2010/8/13 at Caltech
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Prof. Chao, National Tsing Hua
Univ., Taiwan
(A)
(B)
3 mm
SiO2: 17% annealed 200oC
Damage threshold: >6.37 KJ/cm2
(A) Optical microscope (B) AFM of the exposed spot => no damage
2010/8/13 at Caltech
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Prof. Chao, National Tsing Hua
Univ., Taiwan
Depth profile for the mirrors (A) as-deposited(B) after
400oC annealing (17% mixing)
(Tracing the Ti2p Si2p and O1s by ESCA)
100
Ti(%)
80
(A)
60
40
20
Si(%)
O(%)
Atom Fraction (%)
Atom Fraction (%)
100
0
Ti(%)
80
Si(%)
O(%)
60
40
20
0
0
1000 2000 3000 4000 5000 6000 7000
0
1000 2000 3000 4000 5000 6000 7000
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Prof. Chao, National Tsing Hua
(B)
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Univ., Taiwan
Etching Depth (Å)
Etching Depth (Å)
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Prof. Chao, National Tsing Hua
Univ., Taiwan
(A)
80
as-deposited
2000C
3000C
4000C
60
40
20
(B)
0
500
550
600
650
700
Wavelength (nm)
750
100
800
Transmittance (%)
Transmittance (%)
100
80
60
well-defined
as-deposited
4000C
40
20
0
500
550
600
650
700
Wavelength (nm)
圖(三十五)以TiO2-SiO2(17%)混合膜為高折射係數層的雷射反射鏡退
火後
的穿透光譜(A)為從光譜儀得到的量測值(B)為從ESCA對鏡
片膜層原子分佈的偵測，以薄膜矩陣電腦模擬分析穿透率的結果
2010/8/13 at Caltech
Prof. Chao, National Tsing Hua
LIGO
Univ.,
Taiwan
-107-
750
800
Other methods for depositing mixed films
fast alternating sputter
TiO 2-S102 mixed films prepared by the
method
Shiuh Chao, Cheng-Kuel Chang, and Jyh-Shin Chen
We introduced the fast alternating sputter method and its application on deposition of TiO2-SiO2 mixed
films. By using fast alternating sputter, the TiO2 and SiO2 were completely mixed in the film, and no thinpair
structure could be found by x-ray diffraction. The structure of the mixed films was amorphous in a wide
composition range. The optical properties of the mixed films in the visible and near infrared changed from
SiO2-dominant to TiO 2 -dominant as TiO2 content in the film increased.
1 August 1991 / Vol. 30, No. 22 / APPLIED OPTICS 3233
Slow alternating sputter for “nano-film” ?
2010/8/13 at Caltech
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Prof. Chao, National Tsing Hua
Univ., Taiwan
Mixed films of TiO2–SiO2 deposited
by double electron-beam coevaporation
Jyh-Shin Chen, Shiuh Chao, Jiann-Shiun Kao, Huan Niu, and Chih-Hsin Chen
We used double electron-beam coevaporation to fabricate TiO2–SiO2 mixed films. The deposition
process included oxygen partial pressure, substrate temperature, and deposition rate, all of whichwere
real-time computer controlled. The optical properties of the mixed films varied from pure SiO2 to pure
TiO2 as the composition of the films varied accordingly. X-ray diffraction showed that the mixed films
all have amorphous structure with a SiO2 content of as low as 11%. Atomic force microscopy showed
that the mixed film has a smoother surface than pure TiO2 film because of its amorphous structure.
Linear and Bruggeman’s effective medium approximation models fit the experimental data better
than other models.
APPLIED OPTICS Vol. 35, No. 1, 90, 1 January 1996
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Prof. Chao, National Tsing Hua
Univ., Taiwan
Mixed film for LIGO application
• One more factor ---- mechanical loss ---- should be
added for investigation
• Near future: systematically characterizing the
mechanical loss of the films
• Current effort: recovering the old coating conditions for
the films
2010/8/13 at Caltech
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Prof. Chao, National Tsing Hua
Univ., Taiwan