Laser : le couteau suisse des procédés haute résolution ...3/4 member rings (visible in Raman...

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


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

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


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


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


7

Controlling extreme space-time localization of light in matter


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


9

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


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


11

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


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)


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


14

Dispersion compensations strategies

« One must be also careful with higher order dispersion for the shortest pulses »

Materials

“>0

“<0

“>0

Added

Materials


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


16

“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


17

Nonlinear propagation and intensity clamping


18

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


19

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


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


21

Energy distributions (J/cm-3)

100 nJ

250 nJ

1000 nJ

Ith=1.5 1013 W/cm2

Intensity clamping by high-order NL absorption


“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


Fused SiO2

43fs, NA = 0.25, Imax 5x1013W/cm2 (vacuum intensity)

MPI+Avalanche


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


23

Important: Attempts to deliver more intensity than the clamping level in the bulk degrade the spatial resolution rather than enhance the deposited energy density.


24

24

Effects of fs laser induced low-density plasma and applications


25

Types of applications with low density plasmas

25

3D nano/microfabrication

+ etching

« … which are not direct micromachining or surgery above breakdown threshold… »


26

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


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


28

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


29

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


30

30

Optical Breakdown and microfabrication applications


31

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


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”


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

≤


34

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


35

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


36

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


37

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


38

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


39

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


40

The challenge of 3D processing inside silicon


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]”


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


43

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


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


45

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


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


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)


48

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


49

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


50

Merci !Questions: [email protected]

Laser : le couteau suisse des procédés haute résolution ...3/4 member rings (visible in Raman...

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