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24th COOC 단기강좌
극초단 레이저 기반 투명 재료 가공기술
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극초단• 레이저 가공의 특징극초단• 레이저 가공의 역사
투명• 재료 내 광자 흡수의 원리
극초단• 레이저 투명 취성 재료 가공 기술Stealth• dicing of sapphire
Glass cutting•
Glass welding via heat accumulation•
Hybrid process•
Laser assisted selective etching•
Microfluidics•
Micro• -moulding
Laser• -assisted morphing
What is an “ultrashort” pulse?
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time
Δx = 3μm10 fs light pulse:
1fs = 10-15sec
time
ns pulsefs pulse
Wavelength
fs pulsens pulse
Femtosecond laser pulses are usually Fourier transform-limited pulses
Dw·Dt ≈ 2p Dw ≈ 2p/Dt Large spectral bandwidth for short pulses
Why ultrashort pulse?
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Femtosecond pulse (τ = 10-15 s)
nanosecond pulse (τ = 10-9 s)
Continuous Wave
Inte
nsi
ty (
W/c
m2)
Time (sec)
• 10mJ pulse with 10fs pulse width = 1TW
• Intensity at tightly focused beam spot (10µm)
= 1018 W/cm2
Power of an ultrashort laser pulse
1018 W/cm2
= Earth’s solar flux
on a pinhead
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Ultrashort pulse regime for micromachining
The evolution of pulse duration
Milestones in the evolution of pulse duration
Era of ultrashort pulsed lasers (USPLs)
Era of ultrashort pulsed laser micromachining
Commercialization of
USPL machining platforms
Commercialization of
high power USPLs 6
Copyrightⓒ Jiyeon Choi, Do not copy or distribute
Milestones in the ultrashort pulse laser micromachining
Chirped Pulse Amplification
1985• : D. Strickland & G. Mourou, Chirped pulse amplification
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Milestones in the ultrashort pulse laser micromachining
Late 80s :
first comparative study & empirical understanding
Küper, S and Stuke, M., Appl. Phys. B, 44, pp. 199-204 (1987). 8
Milestones in the ultrashort pulsed laser micromachining
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90s : quantitative investigation
80fs, 5J, 20mm/s
200ps, 20J, 15mm/s
200ps, 150J, 20mm/s
80fs, 5J, 8mm/s
deterministic
statistic
B. C. Stuart et al., Phys. Rev. Lett., vol. 74, pp. 2248-2251, 1995.
X. Liu et al., Quant. Electron., IEEE Journal of, vol. 33, pp. 1706-1716, 1997.
Damage threshold vs. pulse width
For short pulse (< 10ps)Obeys different interaction -
mechanism
Deterministic feature of USPL
Theoretical understanding
Photo-ionization vs avalanche ionization
B. C. Stuart et al., Phys. Rev. Lett., vol. 74, pp. 2248-2251, 1995 10
THG readout
Milestones in the ultrashort pulsed laser micromachining
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2000 - : efforts on industrialization
MicromachiningDrilling-Cutting-Welding-LASE-
3D photonic structuresWaveguides-Couplers-Gratings -DOEs-Optical storages-
R. Gattass and E. Mazur, Nature Photonics (2008)
J. Choi et al., Opt. Lett 37(16) 3375 (2012)
R. Berlich, J. Choi et al., Opt Lett 37 (14) 3003 (2012)
L. Canioni et al., Opt Lett 33 (4) 360 (2008)
Milestones in the ultrashort pulse laser micromachining
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2010- : Successful Industrialization and more
Biomedical
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Laser dicing of sapphire
Saw dicing vs. laser dicing
http://www.disco.co.jp/eg/solution/library/stealth.html
Chemically strengthened glass for display
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Immersed in KNO3 solution for 8 Hr@ 410 C̊
~ 30 µm
Compressive stress > 650 MPa
www.corning.com
How to cut/machine the sophisticated glass flawlessly ?
http://informationdisplay.org/
Glass goes thinner
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Glass for wearable devices
Garner, S., et al. "Ultra-slim flexible glass for electronic application." Proceedings of the MRS Fall Meeting. 2012.
Toerker, M., et al. "Transparent OLEDs for signage and decorative lighting applications." LOPE-C, June (2012): 19-21.
www.corning.com
http://www.wirelessefficiency.com/?p=2755
Glass goes into body
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Glass for implantable devices
15 mm x 3.2 mm x 2 mm
Fused silica
16 mm x 4 mm x 0.5 mm
Quartz
10 mm x 1.1 mmSilicon
Various strategies for laser cutting of glass
CO2 based thermal cleaving
NL absorption
Full body cleaving
Ablation
Thin glass?
Curvy Line?
Size effect?
Proper Laser?
Microcrack?
Chipping?
NLO Control?
Speed?
Urs Eppelt et al., Proc. ICALEO 2012, #M504
Proc. of SPIE 688007-1 (2008)US PTO 5,609,284
J. Choi et al., ICALEO (2013)
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New breakthrough
Full body cleavage using ultrafast lasers
Proc. of SPIE 688007-1 (2008)
~99% Abs. < 5 µm
Proper laserCO2 laser
(10.6 µm)
YAG laser
(1.06 µm)
Excessive
absorption
Proper
absorption
No
absorption
Glass substrate
Linear absorption by doping
No active triggeringNonlinear absorption
triggered by laser intensity
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𝛼 = 𝛼𝑜 + 𝛽𝐼 + ⋯
Microscopic investigation
Laser-cut surface of Gorilla glass
1
2
21
Considerations
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Nonlinear-optical effect
@ Ep = 6μJ (P.P 20 MW)
~35μm𝑃𝑐𝑟 =
𝜋0.612𝜆2
8𝑛𝑜𝑛2
Critical power•
for fused silica, ~ 2.2 MW requiredto initiate self-focusing
Self• -focusing distance
0.3
0.5
0.7
1
3
5
10
Laser incidence
ps
~56μm
~152μm
11 μJ (37 MW)
R. Boyd, Nonlinear optics, 3rd ed. Academic press
Elongation of laser focus
21/43J. Lopez et al., SPIE LASE 2016
Various techniques in spatial & temporal beam shaping
axicon
DOE
Spatio-temporal beam shaping
Airy beam
F. Courvoisier et al., Appl.phys. A 112:pp29 (2013)
www.holoor.il
Mindaugas Gecevičius et al., Opt. Lett 39(24) (2014)
Conventional vs. USPL Glass welding
http://spie.org/x8508.xml
microcracks
Glass frit sealing No adhesives•
No • microcracksDirect bonding of glass •
Direct glass welding
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I. Miyamoto, “Welding of glass by ultrafast laser pulses”, 3rd UKP workshop
Heat accumulation at high rep. rate
Heat accumulation
S. M. Eaton et al., Opt. Express 16(13) 9443 (2008)
Hybrid process
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FLDW + LASE (laser assisted selective etching)
Optofluidics
Koji Sugioka and Ya Cheng Lab Chip, 2012,12, 3576-3589Koji Sugioka and Ya Cheng Light: Science & Applications (2014) 3, e149; doi:10.1038/lsa.2014.30
Hybrid process
28Y. Bellourd, JLMN 7(1), pp1-10, 2012
FLDW + LASE (laser assisted selective etching) 3D microstructures
• Applications: Micro-optics, MEMS, biomedical, active platforms…
Start-up companies for LASE
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Various applications of LASE
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Micro-moulding
Micro-flexure
MEMS
Passive alignment system
Micro gear (watch component)
Laser assisted morphing
31J. Drs et al., Opt. Express 23 (13) 17355 (2015)
Ultrafast laser processing of glass•Full body cutting with mirror– -like cut surface
Direct – glass welding for hermetic sealing
LASE for MEMS device fabrication–
Conclusion
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Syringe Pump
Flow : 500 nL / min
Experiment setup (Laminar flow)
outlet
YellowBlue
Redwelding Non welding
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Questions?
LASE process to fabricate a microfluidic device
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Fused silica (base)
Laser direct writing (fs)
Fluidic channel Inlet & outlet
Laser drilling
Interface Laser welding (ps) without direct bonding
Pristine fused silica(cover)
Total fabrication time within two hours !
HF(hydrofluoric acid) etching
Sonication bath
Laminar flow test w/ microfluidics via LASE
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Syringe Pump
Flow : 500 nL / min
Experiment setup (Laminar flow)
outlet
YellowBlue
Redwelding Non welding
75mm x 25mm
Ferrules
Non welding area Interference pattern
Flow result
100 μm
Injection (red)
Glass to glass bonding
Various microchannels via LASE
3 trench structure
Stereoscopic microscope image Multi channel fabrication
Transparency as a key of femtosecond laser direct writing (High aspect ratio channel)
Number of Passes 10 + HF Etching(30min)Width= 79 μm depth= 377 μm
Aspect ratio 4.77