ultrafast laser microwelding for transparent and ...€¦ · ultrafast laser microwelding for...
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SPIE Commercial and Biomedical Applications of Ultrafast Lasers VIII, Conference 6881, 20 - 23 January 2008San Jose Convention Center, San Jose, CA
Ultrafast laser microwelding for transparent and
heterogeneous materials
Kazuyoshi ITOH1and Takayuki TAMAKI2
Osaka University1, Nara National College of Technology 2
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Outline
- Introduction to filamentation
- Ultra-fast laser micro-welding of glass
with filaments
- Ultra-fast laser micro-welding of
heterogeneous materials
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Filamentation
Normal Focusing
Nonlinear MediumLens
Filamentation
Filament
Plasma Formation
Self Focusing(Optical Kerr Effect)
High-Intensity Pulse
・・
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Filamentation- balancing between self-focusing and defocusing by plasma -
Scattering or luminescence from filament
Micrograph of the resultant index change
Magnifiedmicrograph
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NA of focusing lens : 0.1
Exposure time:5 min.
( 300,000 pulses )
× Scattering damages
× Multiple filaments
Core diameter : ~ 2 µm
100 µm
100 µm
Formation of single filament
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Applications of filamentation
- Waveguide writingWaveguides*1, WG Couplers*2
- Writing optical elementsMirrors, Lenses*3, Optical devices*4
- Welding transparent materials
*1K. Yamada, W. Watanabe, T. Toma, K. Itoh, J. Nishii, Opt. Lett. 26, 19 (2001).*2W. Watanabe, T. Asano, K. Yamada, K. Itoh, J. Nishii, Opt. Lett. 28, 2491 (2003).*3K. Yamada, W. Watanabe, Y. Li, K. Itoh, and J. Nishii,” Opt. Lett,. 29, 1846 (2004) .*4Y. Li, W. Watanabe, T. TamakiI, J. Nishii, and K. Itoh, . J. Appl. Phys., . 44, 5014 (2005).
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- Ultra-fast laser micro-welding
of glass with filaments
Takayuki Tamaki, Wataru Watanabe, Junji Nishii, and Kazuyoshi Itoh, Jpn. J. Appl. Phys.,Vol. 44, No. 22, L687-L689 (2005).
Takayuki Tamaki, Wataru Watanabe, and Kazuyoshi Itoh, Optics Express, Vol. 14, Issue 22,10460-10468 (2006).
W. Watanabe, S. Onda, T. Tamaki, and K. Itoh, Appl. Phys. B, Vol. 87, pp. 85-89 (2007).
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Scanning the filamentLow repetition sourceFast scanning
~ Gap
Low repetitionSlow scanning
~ No gap
High repetition source
~ Accumulation of heat
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Optical setup
· Wavelength: 800 nm· Pulse duration: 130 fs· Repetition: 1 kHz· Incidence energy: 1.0 µJ/pulse
· Numerical aperture: 0.30· Irradiation area: 100 µm x 100 µm· Translation speed: 5.0 µm/s
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Welding flat samples
Jig for welding
Samples
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Micrographs
Top view
Side view
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Fused silica glass
Borosilicate glass
15 MPa ~ 150 kgf/cm2
Usual adhesive ~ 50 kgf/cm2
(kgf: kilogram force)
Joining strength (Same material)
Scanning Speed [mm/s]
Puls
e En
ergy
[µJ/
puls
e]
0.1 1
15.4MPa 14.9
MPa 14.9 MPa
14.9MPa
15.1MPa
15.2MPa
15.3MPa
14.9MPa 0.0
1
10
5
15.2MPa
15.0MPa
14.9MPa
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Optical transmittance
87.1 % 88.2%
87.3 %
87.1%
87.0 %
86.0 %
85.9 %
89.0 %
81 ~ 87 %
Fused silica glass
87 ~ 89 %
Scanning Speed [mm/s]
Puls
e En
ergy
[µJ/
puls
e]
0.1 10.01
10
5
81.4 %
Theoretical limit: 92 %86.7 %
86. 8%
Borosilicate glass
Theoretical limit: 93 %
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Annealing makes welded part invisible.(Implication of disappearance of defects or stress.)
100 µm 100 µm
Welded part
Effects of Annealing
Optical Micrographbefore annealing
Optical Micrograph after annealing
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Enhancement of joining strength & optical transmittance
Borosilicate glass Fused silica glassBefore annealing 15 MPa 15 Mpa
After annealing 33 MPa 33 MPa
Before annealing 88 % 87 %After annealing 92 % 91 %:
Joining strength
Optical transmittance
(Theoretical limit: 93 %) (Theoretical limit: 92 %)
( 336 kgf/cm2 )
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Enhancement of optical transmittance by annealing
Borosilicate glass Fused silica glass
Before annealing 88 % 87 %
After annealing 92 % 91 %
(Theoretical limit: 93 %) (Theoretical limit: 92 %)
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- Ultra-fast laser micro-welding
of different glass
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Heterogeneous welding:dissimilar kinds of glass
Borosilicate glass
Fused silica glass
39* [×10‐7 /℃]
5.9* [×10‐7 /℃]
GeometryLaserPulses
1
10
Scanning Speed [mm/s]0.1 1
Puls
e En
ergy
[µJ/
puls
e]
Not joinedJoined
Wataru Watanabe, Satoshi Onda, Takayuki Tamaki,Kazuyoshi Itoh, and Junji Nishii,Appl. Phys. Lett., Vol. 89, No. 2, 021106 (2006).
*Thermal expansion coefficient
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10
Scanning Speed [mm/s]0.1 1
Scanning Speed [mm/s]0.1 1
Puls
e En
ergy
[µJ/
puls
e]
15.3 MPa 14.9 MPa
14.9MPa
14.9MPa
71.5 %
72.6 %
73.2 %
73.6 %15.2MPa
88.3 %
14.9MPa
15.2MPa
15.0MPa
15.1MPa
15.0MPa 10
Puls
e En
ergy
[µJ/
puls
e]
73.0 %
73.0 %
72.1 %
73.4 %71.8 %
Joining strength and transmittance
Joining strength Optical transmittance
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○ 14.9 MPa ○ 14.9 MPa
○ 15.0 MPa ○ 15.0 MPa
PMMA700 [×10 ‐7/℃]
Silicon 28 [×10 ‐7/℃]
Cupper183 [×10 ‐7/℃]
Stainless steel175 [×10 ‐7/℃]
Fused silica glass5.9 [×10‐7/℃]
Borosilicate glass39 [×10‐7/℃]
○ 14.9 MPa ○ 14.9 MPa
○ 14.9 MPa ○ 14.9 MPa
Polymer
Semiconductor
Metal
Alloy
Material*Thermal expansion coefficient
Other material
Glass
Geometry
Heterogeneous welding: dissimilar kinds of materials
Wide range of heterogeneous welding
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2121
- Ultra-fast laser micro-welding
of glass and metal
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Ultra-fast Laser Micro-welding of Glass andCopper
Realizing tight contact between
glass and copper
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Optical Setup
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Optical microscope images
(a) Side view (b) Top view (c) Whole image
Laser source: Regenerative Ti:sapphire laser (Spectra Physics, Spitfire)Central wavelength: 800 nmPulse duration: 130 fsRepetition rate: 1 kHzPulse energy: 4 µJ/pulseScan speed: 1 mm/s
Joining strength: 23 MPa
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Joining Strength
0.38 µJ
Average:21.5 MPa
・
0.1 1 1005
10152025303540
Join
t Str
engt
h [M
Pa]
Pulse Energy [µJ]
Glass plate ( 5 × 10 × 0.7 mm3 ) Small glass plate ( 5 × 5 × 0.7 mm3)
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Copper
Glass
Electron Micrograph of an Interface
1 µm
No crack nor gap was observed.But, some bumpy irregularity presents.
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Summary
-Ultra-fast laser micro-welding of glass with filaments
-Ultra-fast laser micro-welding of
homogeneous and heterogeneous welding,
such as
silica and borosilicate glass,
silica glass and metals
average joining strength: 21.5 Mpa
( ~220 kgf/cm2 )
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Wavelength: 1558 nmPulse duration: 947 fsRepetition rate: 500 kHzInput energy: 0.8 µJ/pulseTranslation speed: 20 µm/sObjective lens: 0.40-NA (Numerical aperture)
Samples: Borosilicate glassJoint strength: 9.87 MPa @ 100 µm/s
6.81 MPa @ 200 µm/s
Welding with High Repetition Laser Pulses
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A
B
Expansion due totemperature rise
Wide heating Cooling with cracks
Femtosecond pulses
Glass
Other material
Local heating
Contraction due tocooling
Cooling without cracks
Conventional and ultra-fast laser micro-welding
Conventional
Glass
Other material
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3232(a) Birds-eye view (b) Top view
Application of Ultra-fast Laser Micro-weldingto Metal Package (Glass & Kovar)
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Coworkers:Dr. Junji NISHII National Institute of Advanced Industrial Science and TechnologyDr. Yasuyuki OZEKI and Mr. Tomoyuki INOUE Osaka UniversityMr. Satoshi ONDA Yokogawa Electric CorporationMr. Seiji SOWA Konica Minolta Opto, Inc.