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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

22

Outline

- Introduction to filamentation

- Ultra-fast laser micro-welding of glass

with filaments

- Ultra-fast laser micro-welding of

heterogeneous materials

3

Filamentation

Normal Focusing

Nonlinear MediumLens

Filamentation

Filament

Plasma Formation

Self Focusing(Optical Kerr Effect)

High-Intensity Pulse

・・

44

Filamentation- balancing between self-focusing and defocusing by plasma -

Scattering or luminescence from filament

Micrograph of the resultant index change

Magnifiedmicrograph

5

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

66

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).

77

- 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).

88

Scanning the filamentLow repetition sourceFast scanning

~ Gap

Low repetitionSlow scanning

~ No gap

High repetition source

~ Accumulation of heat

9

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

1010

Welding flat samples

Jig for welding

Samples

1111

Micrographs

Top view

Side view

1212

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

1313

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 %

1414

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

1515

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

1818

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

1919

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

2121

- Ultra-fast laser micro-welding

of glass and metal

2222

Ultra-fast Laser Micro-welding of Glass andCopper

Realizing tight contact between

glass and copper

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Optical Setup

2424

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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29

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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

3232(a) Birds-eye view (b) Top view

Application of Ultra-fast Laser Micro-weldingto Metal Package (Glass & Kovar)

3333

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.