laser : le couteau suisse des procédés haute résolution ...3/4 member rings (visible in raman...
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Laser : le couteau suisse des procédés haute résolution:
Micro-procédés 3D dans les matériaux transparents par laser femtoseconde
David GrojoLasers, Plasmas et Procédés Photoniques (LP3)
4/10/2017 – David GROJO
2
BC
BV
pulse energy (nJ)
Tra
nsm
issio
n
20 40 60 80 100
0.6
0.7
0.8
0.9
1.0
Experiment
“lawn mower” modeling
Fused SiO2
50fs, NA = 0.25, Imax 5x1013W/cm2
“MPI+Avalanche”
50 fs
Femtosecond laser modification of transparent materials
…3D localization of energy deposition
Microscopy non lineaire
Efield
/2n
Changement structurel
Nanostructuration
Microexplosion
Nano/micro-cavité
n
4/10/2017 – David GROJO
3
Femtosecond laser 3D nano/micro-fabrication and surgery
Hybrid systems (lab-on-chip)
Microfluidics
Nano-surgery
Memories
Waveguides Mems
…but only in transparent matter including dielectrics and some polymers ?
So
urc
e: F
em
top
rin
t
So
urc
e: N
PG
Source: SPIE
So
urc
e: F
em
top
rin
t
So
urc
e: W
iley-V
CH
So
urc
e: F
em
top
rin
t
4/10/2017 – David GROJO
4
ne(t)
Near-IR
800 nm 1300 nm
Visible
2200 nm
1.55 eV 0.95 eV 0.55 eV
- Ultrafast optical spectroscopy and imaging with visible light
- Band-Gap: D O(10 eV)
Dielectrics
- hlas < D
Ti:Saphire fs laserFund. : las = 800 nm (1.55eV) SHG: las = 400nm (3.1eV)
Optical Parametric Amp. (OPA)las > 1.2µm (hlas <1 eV)
- Band Gap: SC O(1 eV)
- Appropriate Methods ?
Semi-conductors
- hlas < D
“Similar MP processes must arise in semiconductors with focused SWIR fs pulses”
D
SC
la
s=0
.8 µ
m
la
s=1
.3 µ
m
la
s=2
.2µ
m
hlas
Mid-IR…
Non-linear Ionization inside Band gap solids
4/10/2017 – David GROJO
5
“Propagation simulation required because of coupling through the permittivity function”
3A Centrale 5
Mainly nonlinear optics in progressively ionized matter before reachingthe target (focus) !!
The space-time dependent permittivity can be simply derived using a Drude model but ne(t) must account for all the contributions in ionization (NL)
3D-fs = Complex interplay between NL phenomena
Non-Paraxial case (strong focusing) requires « exact » vectorial Maxwell solversleading to unrealistic computational ressources in most cases
Alternative transformation optics solution: PRL 117 (2016) 043902
4/10/2017 – David GROJO
6
Introduction
1. Maitrise des impulsions femtosecondes fortement focalisées dans la
matière
2. Propagation non-lineaire et « clamping » des conditions d’interactions
3. Microplasmas de faible densité et applications
4. Claquage optique et applications de structuration 3D
5. Le défi de la microfabrication 3D dans le silicium.
Conclusions et perspectives
Micro-procédés 3D dans les matériaux transparents par laser femtoseconde
4/10/2017 – David GROJO
7
Controlling extreme space-time localization of light in matter
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8
45° (NA=0.7)
From textbook Principle of Optics (7th ed.) p484-494
Numerical
Plane wave Truncated spherical wave
« Easier to turn to numerical simulations for non ideal cases (non-ideal plane wave at the entrance, focusing in medium which is not air, etc…) »
Using [M. J. Nasse and J. C. Woehl, J. Opt. Soc. Am. A 27, 295-302 (2010)] and the corresponding “PSFLab” MATLAB operated code
NA=0.7; =0.8µm
Airy function
Parameters:NA
1959 Born and Wolf
Ideal focusing with an objective
The Fraunhofer diffraction solution
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Filling parameter:
T=R/0
Parameters:NA
Tµ
m
T=0
T=1
T=2
NA=0.7; =0.8µm
Designed case
Gaussian Approximation (NA=0.35)
[M. J. Nasse and J. C. Woehl, J. Opt. Soc. Am. A 27, 295-302 (2010)]
« With a decreasing filling factor, the apparent NA decreases and solution tends toward Gaussian beam optics »
Gaussian optics
Focusing a Gaussian Beam with an objective
4/10/2017 – David GROJO
10
Filling parameter:
T=R/0
Parameters:NA
T
n, depth
Co
rrec
tio
n c
olla
r
Co
rrection
thickn
ess
=1.3µm; n=3.5(Si); T=1 =0.8µm; n=1.5(Glass); T=1
Air
Non-corrected
Corrected
Air
Non-corrected
Corrected
« The focus shifts and spreads along the optical axis by about a factor n and spherical aberrations must be a concern »
Focus is 350µm inside materials
n.d=350µm
[M. J. Nasse and J. C. Woehl, J. Opt. Soc. Am. A 27, 295-302 (2010)]
Focusing inside a material: spherical aberration
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Parameters:NA, , T , nmat, depth
FWHM/2NA
b n.2
Shape affected by aberrations
«In practice, not only on the spatial characteristics but also the temporal characteristics and non-linear effects acting on the beam used for writing»
nmat
0R
d
n.d
Focus shiftFr
aun
ho
fer
dif
frac
tio
n
d
0beam >>R (T<<1)
[JOSA A 16, 2658(1999)] Para
xial
Gau
ssia
nO
pti
cs
0beam<<R (T>>1)
20
Main geometrical characteristics
4/10/2017 – David GROJO
12
Higher order dispersive effectsLinear Phase shiftPulse is delayed but undistorted
Quadratic phase shiftPulse is stretched/linear chirp
Group velocity dispersion
n()
+ϕ()
«Not the shortest possible pulse duration at the focus unless GVD is precompensated»
𝐸0 𝑡 = න𝐸 𝜔 𝑒−𝑖𝜔𝑡 𝐸0 𝑡 = න𝐸 𝜔 𝑒−𝑖𝜔𝑡+𝜑(𝜔)
4/10/2017 – David GROJO
13
- 100 fs pulses are not strecthed with <1000 fs2 (about 2-3cm in glass)
For instance- 10 fs pulses at 800nm will increase its duration by 40% after only ∼ 2.5m in air (GVD=0.2fs2/cm) or 1.4mm in glass (GVD=360 fs2/cm).
For unchirped transform limited Gaussian pulses:
Initial pulse duration FWHM
Pulse stretching estimations
GVD in fs2
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14
Dispersion compensations strategies
« One must be also careful with higher order dispersion for the shortest pulses »
Materials
“>0
“<0
“>0
Added
Materials
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15
Practical solution with CPA systems
«Adjust compressor gratings (CPA systems) to look for maximum NL absorption »
PD
Compressor (CPA)
Source: PRL 102, 083001 (2009)
NA=0.25=800 nmSi02
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“Technical solutions exist for compensations for linear interactions… nonlinear space-time-spectrum distorsions are expected”
Space-time confinement of laser light inside matter
Sources: www.microscopyu.com and CVI Technical notes
4/10/2017 – David GROJO
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Nonlinear propagation and intensity clamping
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Intensity dependent index = positive and negative lensing on Gaussian beams
Filamentation
“Self-trapping of intense light at equilibrium conditions”
Ke
rr e
ffe
ct
Near critical power :
Assuming n2 >0
𝑛(𝑟, 𝑡) = 𝑛0 + 𝑛2𝐼(𝑟, 𝑡)
𝑃𝑐𝑟 =𝜋(0.61)2𝜆2
8𝑛0𝑛2
𝑃 3 (𝑡) = 𝜀0𝜒3 𝐸 𝑡 3
|||
Third order nonlinearity
Self-fo
cusin
gIo
niz
atio
n
Above ionization threshold nearcritical plasma density:
Plasm
a-d
efocu
sing
𝑛 𝑟, 𝑡 = 𝑛0 − Δ𝜂𝑝𝑙𝑎𝑠. 𝑁𝑒 𝑟, 𝑡 +
+𝑖Δ𝜅𝑝𝑙𝑎𝑠.(𝑁𝑒 𝑟, 𝑡 )
𝑁𝑐𝑟 =𝜀0𝑚𝑒𝜔
2
𝑒2Courtesy S. Tzortzakis
4/10/2017 – David GROJO
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P=700PcrP=120PcrEx
per
imen
t Simu
lation
Exp
erim
ent Sim
ulatio
n
“Built from modulational instabilities or growing up from small fluctuations in the beam intensity profile.”
Source: PRL 92, 225002 (2004)
Multiple Filamentation P>>Pcr
4/10/2017 – David GROJO
20
|||
Plasma density(free carrier)
Electron-ion collision rate
Taking a simple MPI description and
Pulse durationMPI order
We find a equilibrium intensity
Si at 1300 nmK=2, cm/W2/s
cm-3
SiO2
Si
for 100-fs
Air
1300 nm
800 nm
800 nm 1013 W/cm2
1013 W/cm2
I = 1.2 1012 W/cm2
Example
“There is a limitation on the intensity that can be delivered by simply increasing the incoming pulse energy because of this intensity clamping “
Self-Limited Intensity of a Filament
NL index Plasma
4/10/2017 – David GROJO
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Energy distributions (J/cm-3)
100 nJ
250 nJ
1000 nJ
Ith=1.5 1013 W/cm2
Intensity clamping by high-order NL absorption
“lawn mower” modeling
“Tends to maintain the power below the self-focusing threshold (1.5 MW for SiO2) and lead to nearly uniform excitation in the pre-focal region“
Source: OE 13, 3208 (2005)
pulse energy (nJ)
Tra
nsm
issio
n
20 40 60 80 100
0.6
0.7
0.8
0.9
1.0
Experiment
“lawn mower” modeling
Fused SiO2
43fs, NA = 0.25, Imax 5x1013W/cm2 (vacuum intensity)
MPI+Avalanche
4/10/2017 – David GROJO
22
Simulation
10 nJ
50 nJ
350 nJ
Flu
en
ce
[a.u
.]
linear
Laser direction
« It is hard to exceed significantly the plasma critical density. Plasma effects completelyprevent modification in silicon with IR fs pulses in standard configurations »
Plasma screening and defocusing
Ne 3 1019 cm-3
(Drude model)<< Ncr = 6.6 1020 cm-3
Appl. Phys. Lett. 105, 191103 (2014)
Nature Communications 8 (2017) 773
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Important: Attempts to deliver more intensity than the clamping level in the bulk degrade the spatial resolution rather than enhance the deposited energy density.
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24
Effects of fs laser induced low-density plasma and applications
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Types of applications with low density plasmas
25
3D nano/microfabrication
+ etching
« … which are not direct micromachining or surgery above breakdown threshold… »
4/10/2017 – David GROJO
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26
Two-photon lithography (positive)
near IR fs-pulses
resin
Applications. Complex nano-electromechanical systems, active and passive integrated photonic devices, complex architecture photonic bandgap crystals, remotely controllable micromachines, microfluidic and medical devices.
Sub-100nm resolution
Radicals
(dissociation of a photoninitiator)
weakly cross-linked polymersor monomer(liquid state)
Highly cross-linked polymers
(solid state)
+
Source: Adv. Mater. 17 (2005) 541
4/10/2017 – David GROJO
27
27
3D Optical Functionalization (Fluorescence writing)
Stab
le f
luo
resc
ent
silv
er c
lust
ers
Application:High capacity optical recording
Excitation Emission
Source: Adv. Mater. 22, 5282–5286 (2010)
“… with specially designed and synthesized materials.”
Silver dopedphosphate glass
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28
3D waveguide writing
5/6 member rings
Repeated bond breaking causing a molecular rearrangement and a local uniform change of the refractive index
« Low loss weguides in various glassy materials and no need of material preparation.Flexibility meeting the requirements of challenging applications »
Densification, n+10-3
3/4 member rings (visible in Raman spectra)
e.g. Fused Silica
Source: Optics Letters 26 (2001) 1726
Apps:- Quantum Information Science (QIS)- Ultra-stable optical devices (e.g. spatial)- Specific telecomunication systems- Lab-on-chip hybrid systems
Sou
rce:
SP
IE
4/10/2017 – David GROJO
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Source: Nat. Photon. 8, 791–795 (2014)
- Low transmission losses 0.1dB/cm
- Embedded – highly stable nestedinterformeters
- Complex designs requiring true 3D capabilities
- « Cheap » flexible prototyping(growing research)
Quantum circuits requirements
“A rapidly growing field of research with the most advanced demonstration based on fs-laser writing but also other field of application as: specific telecommunication devices and spatial ultra-sable integrated optics devices applications”
3D waveguide writing for QIS
4/10/2017 – David GROJO
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30
Optical Breakdown and microfabrication applications
4/10/2017 – David GROJO
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Npulses=103
Npulses=104
Npulses=105
10 um
n
C.B.
9eV
V.B.
1.5eV
NA 0.65
Fused Quartz
Efield
/2n
Uniform index change, n +10-3
Nanoscale cracking, n -10-2
Femtosecond Laser writing inside Fused SiO2
laser = 130 fs, 350 nJ
laser = 50 fs, < 200 nJ
Etching+AFM
Etching+SEM
fs
4/10/2017 – David GROJO
32
High refractive index decrease by nanostruturing
R << = critical assumption
0
Elas
D
En=1.45
- D/0
- D/
n=1
avg <
R
“The apparent reactive index is below the average index of the structure”
4/10/2017 – David GROJO
33
Light energy preferentiallyresides in low index regions
R << = critical assumption
(Rayleigh approximation)
Scattering is kept to its minimum with small featuresR
High refractive index decrease by nanostruturing
≤
4/10/2017 – David GROJO
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Micro-Lensing
z
n=1.45
Measured HWHM
n=1.45, n/n=-1.8%
Reference
After 107 shots
n/n=-1.8±0.2%
Npulses=105
10 um
n
Beam profiles
Journal of Physics B, 43 (2010) 125401Applied Physics Letters, 93 (2008) 243118
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Behaves like an uniaxial crystal
Form Birefringence
Ewriting/2n
n=1n=1.45
1.42
1.435
(ns-np)/ n 1%
nmax/n=(n-np)/n 2%
np ns
E
E1 = D/1
t2
t1
E2 = D/2 R=t2/t1
=D/E
Details in : Born and Wolf, Principle of Optics
4/10/2017 – David GROJO
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p
Writing
p
ProbePolarization
In-situ Birefringence Diagnostic
PD
Polarization Analyzer
Half-wave plate
ASE
Probing 45deg.
s
25µm
0.01 n
Applied Physics Letters, 93 (2008) 243118
4/10/2017 – David GROJO
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Optical data storage
Source : Optics Letters 21 (1996) 2023
1996 Mazur group, Harvard
Binary
Source : Physical Review Letters 112 (2014) 033901
2014 Kazansky group, Univ. SouthamptonParallel writing
High capacity360TB per disc
5DPosition 3D+ Retardance (32 states=5bits)+ Slow axis (8states=3bits)
Long lifetime
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Confined ultrafast microexplosion
38
“… multi-TPa pressure, ultrahigh temperature (Warm Dense Matter) and ultrafast cooling”
Source: A. Rode, Autralian National University
Source: PRL 96 (2006) 166101
4/10/2017 – David GROJO
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Applications of ultrafast microexplosionDiscovery of new superdense materials
Nano/microvoid generation for bulk machining: glass cutting, Microfuidic devices
Source: Applied Physics Letters 97(8) 081102
Source: http://wophotonics.com
Stealthy cutand/orcontrols of crack extension (dash line cutting)
High Aspect Ration Channel by single pulse (Bessel beam)
Sapphire (Y = 400 GPa) -> Discovery of bcc-Al
Si -> Discovery of new tretagonal polymorphsSource: Nature Communications 6 (2015) 7555
See: Nature Communications 2 (2011) 445
4/10/2017 – David GROJO
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The challenge of 3D processing inside silicon
4/10/2017 – David GROJO
41
InfraredVIS-NIR-fs
Challenges with narrow gap semiconductorsChallenge #1: Producing and manipulating infrared ultrafast pulses and novel interaction diagnostics ( > 1.2 µm for Si)
60 fs, 1300 nm pulses focused at depth of de 1 mm inside Si (NA=0.45)
Challenge #2: Breaking the strong limit to energy space-time confinements inside Si
Focus ici !
“Bulk modification impossible in the fs regime for all even the highest intensity tested… in conventional machining configuration [Appl. Phys. Lett. 105, 191103 (2014)] including Bessel [J. Appl. Phys. 117 (2015) 153105]”
4/10/2017 – David GROJO
42
Observing and controling microplasmas inside Si
From local free-carrier injection to applications in microelectronics…
BV
BC
t=2ps
electrons
laser
Chip
The conductivity can be turned on and off by ultrafast plasma formation
Source : NPG
0.2 ns 1.2 ns 2.5 ns
2 ps
1
2 3 4
…
Time-resolved IR microscopy(fs pump and probe)
Self-limited plasmas in Si: Applied Physics Letters 105 (2014) 191103Carrier dynamics in Si: Applied Physics Letters 108 (2016) 041107
Taking control of FLASH memories: Applied Physics Letters 110 (2017) 161112
4/10/2017 – David GROJO
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Experiment Simulation
10 nJ
50 nJ
350 nJ
Flu
ence [a.u
.]Z [mm]
1.00.9
linear
Laser direction
0
0.8
10
-10
X[µ
m]
Novel experimental and numerical tools for studying the complex physical mechanismstaking place in the nonlinear interactions (propagation, ionization, plasma, etc..)
Accessing extreme spatio-temporal laser energy localizations
Experimental Modeling
Full space-time IR microscopy of the beam and matter
Transformation optics enabling the use of scalar equations for non-paraxial propagation problems
Physical Review Letters 117 (2016) 043902Nature Communications (2017) Accepté DOI: 10.1038/s41467-017-00907-8
4/10/2017 – David GROJO
44
A strict clamping of the delivered intensities
“An increase of the maximum fluence with NA but also a quenching below the threshold for modification for all focusing configurations*”
*Simulations reveal a strong depletion prior to the focus region because of 2-photon absorption and plasma defocusing/absorption play essential roles at very modest densities (Nc1/) for in the long wavelength regime.
The minimal target !
Surface damage threshold (meas.)
Nature Communications (2017) Accepté DOI: 10.1038/s41467-017-00907-8
Air Liquid Si
4/10/2017 – David GROJO
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NA=2.97, 20nJ/pulse
Ultrafast optical breakdown in Si with hyper-focusing
“Toward solid-immersion lens solutions for femtosecond laser 3D processing…”Nature Communications (2017) Accepté DOI: 10.1038/s41467-017-00907-8
4/10/2017 – David GROJO
46
NA=2.97, 20nJ/pulse
Femtosecond Laser Index Modification
“The perspective of 3D Si Photonics but also an opportunity for extreme interaction experiments and potentially new types of material modifications”
n<0 amorphization
Nature Communications (2017) Accepté DOI: 10.1038/s41467-017-00907-8
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47
Toward Solid-Immersion Laser Processing ?
SIL technology:Succesfully demonstrated in in
microscopy and lithography for resolution
enhancement…
But rarely adopted due its practical
complexity and the availability of other
methods.
“Interestingly, SIL could find in laser
processing an application where it
provides super-resolution but also high-
nonparaxiality which is a requirement for 3D femtosecond laser writing inside
narrow gap materials. This may fully justify
its complexity”
Note that at NA3, the spot size shrinks down to about /6220 nm for =1.3µm…
Source: Nat. Photonics 2, 311–314 (2008)
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Guides light in bulk c-Si
n
/n
+10
-3
CW 1300nm
Writing1550nm
5ns1kHz, 10µJ
Quantitative Phase IR-imaging
PositioningIR imaging
Phase-imaging-controlled nanosecond laser writing
« Positive index change waveguides demonstrated but improved control required to decrease losses !!! »
1mm
Patent Application FR1655979 (27/06/2016); Optics Letters 41 (2016) 4875
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Summary and Conclusions
Microscopy concepts can be used for improved confinement and resolution : this has recently open the field to silicon
- 3D nonlinear propagation in progressively ionized materials addingcomplexity in comparison to surface machining studies
- There are natural limits to the spatial resolution and the deposited energy densities (and so type of modifications) that can be achieved in femtosecond bulk interactions.
A unique opportunity for the development 3D photonics
- Main advantages: Direct – Contact free/Near single stepStability of embedded devicesFlexibility – Prototyping toolPrecision – sub-wavelenght and high aspect ratio
Lithography VS
4/10/2017 – David GROJO
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Merci !Questions: grojo@lp3.univ-mrs.fr
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