From organic molecules to optical devicesAlain Fort

Institut de Physique et Chimie des Matériaux de Strasbourg (IPCMS) CNRS UMR 7504Département d’Optique ultrarapide et Nanophotonique (DON),

23 rue du Lœss, BP 43, 67034 Strasbourg Cedex 2, Francee-mail :alain.fort@ipcms.u-strasbg.fr

Thanks to

IPCMS researchers

K. D. Dorkenoo (Optical circuits, data storage, multiphoton microscopy)

L. Mager (LISW, quadratic NLO structures)

A. Barsella (NLO molecular properties)

B. Boeglin (Semi empirical calculations on molecular compounds)

Current collaborations

C. Andraud (ENS, Lyon)

A.-J. Attias (LCP, Paris)

H. Chaumeil (LCOB, Mulhouse)

P. Deplano (DCIA, Cagliari)

V. Rodriguez (ISM, Bordeaux)

In the field of lasers there are no boundaries, only horizons (Gérard Mourou, 2010).

The business is now at about 7 billion dollars and expanding.

“an invention in search of an application“ (1960) or

“a solution in search of a problem“ (1964).

First demonstration of a working laser:

Theodore Maiman (1960)

In fact, Gordon Gould probably made the first laser (he finally received his first patent for the laser in 1977).

Theodore Maiman

1961: Real start of Non Linear Optics (NLO)

Second harmonic generation (or frequency doubling) : process in which a

nonlinear optical medium produces light at double the frequency of the input beam

Ew, l E2w, l / 2

Quartz crystal

P.A. Franken et al. (1961)

P. A. Franken, A. E. Hill, C. W. Peters, and G. Weinreich,

"Generation of Optical Harmonics“, Phys. Rev. Lett. 7, 118 (1961).

P. A. Franken

Second Harmonic Generation (SHG)

OUTLINE

I. Introduction

II. Basic considerations

- NLO molecular response

- Push-pull molecules for quadratic optics

- Quadratic hyperpolarizability optimization

- Quadratic processes (SHG,TPA) in polymeric materials

III. Examples of applications

- photopolymerization

- optical circuits

- artificial muscles

-optical data storage

IV. Concluding remarks

Molecular response to a weak E.M. field

excitation

E

molecule

pa

responseWeak field linear response:

Induced dipole

jijgiiep a

Permanent dipole

Microscopic polarization

a linear polarizability tensor

e local electric field related to external field for a spherical cavity through field factors:

Lorentz expression (”The theory of electrons,” B.G. Teubner ed., Leipzig, 1909)

Onsager expression (JACS, 58, 1486, 1936)

3

2)?)(

ww

nf

)2²(

)2²()0(

n

nf

Molecular response to a strong E.M. field

excitation

E

molecule

response

p

jijgiiep a

... lkjijkkjijk

eeeee

Linear response

Non linear response

i, j, k, … refer to components expressed in a molecular frame

: 2nd order polarizability tensor or

1st order hyperpolarizability tensor or

quadratic hyperpolarizability tensor

: 3rd order polarizability tensor or

2nd order hyperpolarizability tensor or

cubic hyperpolarizability tensor

Macroscopic response

I, J, K.. components expressed in the laboratory frame

LKJIJKLKJIJKJIJII EEEEEEPEP )3()2(1

Dipoles oscillating at 2w: Second Harmonic Generation (SHG)

E2 = E20cos2wt = ½ (E2

0 + E2

0 cos2wt)

)(i ith order susceptibility

P = molecules

p je

ijgi a ...

le

ke

je

ijkke

je

ijk=

E = E0coswt ,

Requirement in the dipolar approximation for quadratic optics:

non-centrosymmetric structures (molecules, functionalized polymers, crystals)

P(-E) = - P(E)For centrosymmetric systems:

Even order polarizabilities , , …and

even susceptibilities )2( n = 0

....)3()2()1( EEEEEEP

Fluorescence induced

by 2-photon absorptionOne-photon absorption

EP

E

E

P

E

1 EE

2 EEE

3

EEn

...

For intense fields

For weak fields

Macroscopic response

Frequency Frequency of the

polarisation

Processes

wp, wq w wp + wq Sum of frequencies

wp, wq w wp - wq Difference of

frequencies

wp, wp w 2 wp Second Harmonic

Generation (SHG)

wp, 0 w wp Pockels effect

wp, wp w 0 Optical correction

Molecular compounds for quadratic optics

P = molecules

p je

ijgi a ...

le

ke

je

ijkke

je

ijk=

Need of efficient molecules (with high ) for quadratic optics:

Dipolar chromophores with asymmetric electronic density distribution of

a p-electron-conjugated bridge obtained with appropriate donor and

acceptor moities

Dalton, Chem. Rev. 2010,110, 25-55

H2N NO2

p AD

N

H3C

CH3

ON

H3CNO2

ONH13C6

H3CO

H3C

CN

O

O C N

F

F

O

CNCN

N

Charge transfer molecules:anharmonic oscillators

Asymmetric polarizability of the conjugation path leading

to quadratic hyperpolarizability

+D A-

A-D+

E

E

tem

ps

Induced dipole

Linear response

Non linear response

Molecular origin of the optical properties of organics

Hyperpolarizability

E

Donnor

Acceptor

Anisotropy of the linear polarizability

2DaRefractive index modulation through (1)

Refractive polymers

Quadratic hyperpolarizability

Refractive index modulation through (2)

E.O. materials

E

Orientation

Determination of the quadratic hyperpolarizability

Methods

Finite-Field (FF) method: calculates the ground state dipole in the presence of a static

electric field (M. J. S. Dewar and J. P. P. Stewart , Chem. Phys. Lett., 11, 416, 1984)

Sum-Over-States (SOS) method: determines the frequency – dependent polarizabilities

from perturbation theory (J. F. Ward, Rev. Mod. Phys., 37, 1, 1965 ); Mol. Phys., 20, 513, 1971).

0

ej

gi

ije

a

0

²

!2

1

eki

gi

ikjijkee

µ01 transition dipole between states S0 and S1,

D01 difference between the permanent dipolar moment of S0 and S1,

G01 damping factor of S0

GOAL: Guides for the synthesis of very efficient molecules

with giant quadratic hyperpolarizabilities

S1

S0

E01

01

Evaluation of the quadratic hyperpolarizability

of push-pull molecules

Semi-empirical approaches:

-A.Two-level approximation (rod-like molecules)(J.L. Oudar, D.S. Chemla, J. Chem. Phys., 66, 2664,1977).

(0))F( ) , ;2( wwww -zzz

2

2

2222

4

)(23

))(4( ) , ;2(

eg

eg

egeg

eg

zzzw

wwww

wwww

D

---

egw w

w2w

e

v

g

e

g2

2

)(23 )0(

eg

eg

w

D

eg

D = e-g

-B. Bond Length Alternation (polyenes) (S. Marder, et al., JACS, (1994) 116, 23,10708 )

D+

A-D

AAD

Neutral form Zwitterionic form

BLA = average length difference between adjacent carbon carbon bonds

C. B. Gormann and S. R. Marder, Chem. Mater.,7, 1, (1995)

2 forms D+

A-A

D

N Z

V t

N

Z+D

A-

D

A

coupling

ZcosNsine22

-

ZsinNcosg22

egw

2 levels

V

t2tan

-C. Two-level two-form approximation (push-pull molecules)

(A. Fort et al., Chem. Phys. Lett., 257 (1996) 531).

-1,0 -1/√5 0,0 1/√5 1,0

a

MIX

22 4cos

tV

VMIX

--

Experimental determination of the quadratic hyperpolarizability

EFISH (Electric Field Induced Second Harmonic) technique:(J.-L. Oudar, J. Chem. Phys., 67, 446, 1977).

Determination of both sign and magnitude of scalar product g(2w)

with respect to a quartz crystal by SHG detection

- Polar molecules in solution

- Strong static electric field applied to break the centrosymmetry

- Need to be away from resonances at w and 2w usual operating wavelength at 1.907 nm)

EOAM (Electro Optical Absorption Measurements)(W. Baumann, Ber. Bunsenges. Phys. Chem., 80, 231,1976;

F. Würtner, F. Effenberger, R. Wormann, P. Krämer, Chem. Phys. 73, 305, 1993)

Measurement of the electric-field-induced shift of the absorption spectra

- Polar molecules

- Well suited for elongated chromophores

- Determination of Dµ more reliable than solvatochromism

HRS (Hyper Rayleigh Scattering) technique(P.D. Maker, Phys Rev. A, (1970) 1, 923; K. Clays and A. Pesoons, Phys. Rev. Lett., (1991) 66, 2980).

Relative measurement of the magnitude of

- Available for ionic and non polar molecules

- Incoherent light-scattering detection

- Operating fundamental wavelength usually at 1064 nm

- Problems correlated to two-photon absorption induced fluorescence

From microscopic to macroscopic:

Need of a molecular alignment

E

Iw, l I2w, l/2E0

Iw, l Iw, lWithout poling

N

H3C

CH3

ON

H3CNO2 =

Polymer functionalized with

NLO chromophores

NO SHG

SHG with

molecular alignment

LKJIJKLKJIJKJIJII EEEEEEPEP )3()2(1

Electro-optic effect in organics

: SHG, Sum- and difference- frequency, Pockels effect,

related to molecular parameters by:

)(2 w

dipole moment of the molecular ground state

L3 third-order Langevin function

E poling field felt by the chromophores

T temperature

Gas phase approximation (non-interacting dipolar chromophores)

)(cos),()( 32 www fN

4

)2(

33

)(2)(

nr zzz w

w-

and for g <<1,

kTEg /

N number of molecules/cm3

f Lorentz factor

Dominant linear Pockels EO effect tensor

kTE

gL

5/cos

)(cos

3

3

3

average molecular orientation relative to the electric field

(in pm/V)

Strategies for the optimization of the NLO properties

of polymers with embedded push-pull molecules

1. Increase of and/or - Lot of papers to optimize the charge transfer through optimized electron donors and electron

acceptors substituents and aromatic bridges.

- Giant hyperpolarizability obtained using twisted intramolecular charge transfer chromophores

with around 500 000 10-48 esu ( nearly 103xDR1, a model compound!)

2. Increase of N- Shape engineering to reduce dipole-dipole interactions

- Use of dendrimetric structures or hyperbranched polymers

- Association of chromophores incorporated using specific chemical tools (Click chemistry,

RAFT, ATRP) with adapted matrices

3. Optimization of cos3- Increase of the poling field strength by reducing chromophore conductivity

- Laser-assisted electric field poling (using cis-trans photoisomerisation mechanisms)

- Corona poling in adapted poling cell

Corona poling cell

Corona grid

Window

Sample

Heating plate

Laser

sourcePhotomultiplier

PicoammeterVacuum

Gas input

Vacuum≈ 20 mBars

Corona tension max = 10 kV

Corona current > 100 A

Temperature Tamb.→ 200°C

SHG

H.T.

70 80 90 100 110 1200,85

0,90

0,95

1,00

1,05

I(2w

) /I

(2w

)

ma

x

Température (°C)

Tg

PMMA doped with DR1 molecules

from L. Mager, IPCMS

from H.L. Rommel , B.H. Robinson,J. Phys. Chem.C, 2007,11, 18765 from T. D. Kim et al., J. Phys. Chem.C, 2008,112, 8091

Quadratic NLO efficiencies

From K.D. Dorkenoo and A. Fort , in “Multiphoton processes in organic materials

and their applications”, I. RAU and F. KAJZAR ed., Old City Publishing, in press.

Two-photon absorption (TPA)

(a) Single photon absorption

(b) Two-photon absorption (TPA)

(c) Second harmonic generation (SHG)

Virtual state

Experimental demonstration:

W. Kaiser, C.G. Garret , Phys. Rev. Lett. , 7, 229 (1961).

Theoretical prediction of TPA:

M. Göppert-Mayer, Naturwissenschaften 1929, 17, 932 (1929),

Ann. Phys. 9,273 (1931)

M. Göppert-Mayer, Nobel prize 1961

TPA at the microscopic scale

SOS perturbative approach, 3 level contributions

Need of a high spatial density of photons during a short time

2

2

r

2photons

2photonsτ.S

P

f

σproba

: TPA cross section

: impulsion duration

P : laser power

: laser frequency2photons

σ

S : surface

fr

femtosecond laser beams

t

For theoretical considerations, see for example:

- Y.R. Shen, The principles of nonlinear optics, New York, Wiley-Interscience, 1984.

- P.N. Butcher, D. Cotter, The elements of nonlinear optics, Cambridge University Press, 1991.

- R. Boyd, Nonlinear optics, Academic Press, 2003.

Macroscopic approach

(3) related to two-photon absorption and to the optical Kerr effect

From K.D. Dorkenoo and A. Fort, in “Multiphoton processes in

organic materials and their applications”, I. RAU and F.

KAJZAR ed., Old City Publishing, in press.

Gaussian beam in a nonlinear media:

(a) self-focusing, (b) self-defocusing

Voxel size with TPA

Warren R. Zipfel et al. Nature biotechnology, 21, 1369 (2003)

0.3 1.30.6 0.85

Influence of the numerical aperture

( NA=nsin

N.A

N.A :

excitation

photonun

cefluorescenII - 2

excitation

photons2

cefluorescenII -

Excited volume < 1µm3

Two-photon induced fluorescence

Ar laser

(514,5 nm)

Ti:sapphire laser

(800 nm)

Applications of quadratic processes in organics

3D Micro-fabrication and lithography

Photopolymerization

Optical circuits

Organic lasers

Photodynamic therapy

Imaging

High frequency modulators

High density optical storage

…(like a “Prévert list”)

Micro- and nano-fabrication through two photon

absorption polymerization: Pioneering works

2 μm

J. Serbin et al., Opt. Lett. 28, p. 301, 2003. S. Kawata, H. B. Sun, T. Tanaka, K. Takada, Nature, 412, 698 (2001).

P. Galajda and P. Ormos, Applied Physics Letters, 78, 249, 2001

S. Marder, J. Perry et al, 296, Nature, 1106 (2002)

P. N. Prasad et al. , Applied Physics Letters, 74, 170, 1999

3D micro-structures

K. -S. Lee et al., Appl. Phys. Lett., 2005, 87, 154108-1;Polym. Adv. Technol., 2006, 17, 72-82;

M. Straub, L.H. Nguyen, A. Fazlic, M. Gu, Optical Materials, 2004, 27, 359.

Nowadays, spatial resolution around 60 nm!

Photopolymerized waveguides

Laser beam

R. Bachelot, C. Ecoffet, D. Deloeil, P. Royer, D. J. Lougnot, Appl. Optics, 32, 5860 (2001).Integration of micrometer-sized polymer elements at the end of optical fibers by free-radical

photopolymerization

Polymerized waveguide Polymerized waveguides

Optical monomode fiber

Resin

Resin

Optical fiber

S. Kewitsch, A. Yariv, Opt. Lett., 21, 24 (1996). Self-focusing and self-trapping of optical beams upon photopolymerization

Simulation Experiment

Light induced self-written (LISW) waveguides

A. Monomode guide

Chaotic behaviour

P = 16 Wresin

Monomode optical fiberCladding: 125m, Core 3 m

P = 5 W

Single waveguide

l = 514 nm

resin

Solitonic propagation

Linear process:Diffraction (dispersion)

Non-linear process : self-focusing due to photopolymerization (self-phase modulation)

linear = non-linear solitonic behaviour

022

1000

2

02

2

2

2

00 D

Enk

inEnk

y

E

x

E

z

Enik a

losses

Phys. Rev. Lett. 93, 143905, 2004.

Light induced self written waveguides (LISW)

Time [mn]0 5 10 15 20 25 30 35 40

1.48

1.485

1.49

1.495

1.5

1.505

1.51

Ref

ract

ive

ind

ex

White lamp

l=514 nm

chaotic zone

two

modes

single

mode

cladding

core

Solitonic propagation if V<2.4

2a: diameter of the core

222claddingcore nnaV -

l

p

V = 5

V = 1.5

Simulations Experiments

V = 20resin = cladding

core

Examples of applications

Long (# 10 cm) and flexible guides

Optics Letters, 27, 20 (2002)

Appl. Phys. Lett., 83, 2474 (2003)

Phys. Rev. Lett., 93, 143905(2004)

FIBREFIBRE

Integrated components

Fibres connections

Filamentation at a multimode optical fiber exit

Multimode waveguides

Optical multimode fiberCladding: 250 m, Core 62.5 m

l = 514 nm

Self-written waveguide created using a white light from a 500W halogen lamp

white light

Flow

direction

Photopolymerizable

mixture

Multimode

optical

waveguide

LISW

AIR

Building of a LISW guided “on the flow”

SPIE, San Diego 2010

AIR

AIR

Multimode fiber connections

0 50 100 150 200 250 300 350 400

-30

-25

-20

-15

-10

-5

0

Lo

sses (

dB

)

Distance (meters)

1.9 dBApplied Optics, 49, 2095, (2010)

LISW functionalized with dye

for laser operation

K. Yamashita et al., Journal of lightwave technology, 27, 4570, (2009)

O. Sugihara et al., Opt. Lett., 33, 294, (2008)

LISW functionalized with photochromic molecule

Functionalized LISW

-10 -8 -6 -4 -2 0 2

-0.004

-0.003

-0.002

-0.001

0.000

0.001

0.002

0.003

0.004

Mo

du

late

d In

ten

sity

Time (s)

LISW functionalized with 5CB molecule

for phase modulation

S. Kamoun, L. Mager et al, to be published and

Applied optics, 49, 2095, (2010)

Laser 120fs

PM

Caméra

Spectrograph

Spectrograph

Acquisition System

z

xy

Dichroic

mirror

Beam spliter

X400.6

HV

sample

Filters

Filters

Pin hole

TPA set-up for 3D controlled polymerization

Fiber Fiber

0.8 mm

HeNe laser beam

TPA polymerization: fibres connection

Guide created by TPA polymerization

Cell

Fiber

core = 3 μm

cladding 125 μm

Fiber

Fibres connection trough a curved guide

1.3

mm

0.15 mm

1.5 mm

Passive Mach-Zehnder

Appl. Phys. Lett.,

86, 211118 (2005)

EO polymer

optical waveguide

Traveling-wave

electrodes

Substrate

Active E.O. modulator

Electrodes

SPIE, San Diego 2010

•Artificial Muscles

Artificial Muscles

C O

O

(CH2)4

O

CO

O C

O

OC4H9OC

O

C4H9O

monomer acrylate

+

Crosslinker 1,6-hexanediol diacrylate

+

UV photoinitiator 2-benzyl-2-(dimethylamine)-4’-

morpholinobutyrophenone (Irgacure 369)

PolymerbackbonesLiquid-crystalunit

Cross-linker

Temperature

PolymerbackbonesLiquid-crystalunit

Cross-linker

PolymerbackbonesLiquid-crystalunit

Cross-linker

Temperature

h

υ

Aligned sample

Photopolymerisation and temperature induced

reversible contraction :Liquid crystal elastomer

Température (oC)A

ng

le b

etw

ee

n 0

an

d 1

st o

rde

r (d

eg

.)

Thermoactive microsystems for diffractive optics

30 µm period grating on 30 µm thick sample

T=80°C T=96°C

heating

T=99°C

a

b

T=99°CT=80°C T=96°C

cooling

Optics Express, 15, 6784 (2007)

Applied Physics A, 98, 119 (2010)

SPIE, San Diego 2010

•Optical Data Storage

CD : l = 780 nm

track spacing 1.6 m. 700 Mo

DVD : l = 650 nm

track spacing 740 nm.

5 Go

Blu-Ray : l= 405 nm

track spacing 300 nm

25 Go (1 layer) or

50 Go (2 layers)

Commercially available optical disks

Need to increase the storage capacity

D.Parthenopoulos and P. Rentzepis, Science , 843 (1989)

3D optical storage, 2 photon writing, reading and erasing of the information (fluorescence) using photochromic

molecules embedded in a polymer matrix

J. Stricker and W. Webb, Optics letters, 16, 1780 (1991)

3D optical data storage, 2 photon excitation (1012 bits/cm3) for photopolymerization

F. Charra, F. Kajzar, J.M. Nunzi et al, Optics letters, 18, 941 (1993)

All optical poling , orientational hole burning and trans to cis isomerization of azo-dye chromophores, SHG

detection

M. Wang, P. Rentzepis et al, Optics letters, 22, 558, (1997)

Two photon memory recording of 100 planes of 30µmx30µmx80µm

S. Marder et al, Nature, 398, 51(1999)

D-p-D molecules for 2 photon polymerization for 3D optical data storage

A. Labeyrie, J.P. Huignard and R. Loiseaux, Optics Letters , 23, 301 (1998)

3D optical data storage in microfibers of polymers, superposition of phase gratings in the microfibers

Organic optical memories: previous studies

Organic optical memories: previous studies

Gang Xu et al., Optics communication,88 (1999)

All optical poling for orientational hole burning and photoinduced reorientation of azobenzene molecules

P. N. Prasad et al., APL 74, 1338 (1999)

3D optical data storage using 2 photon up converting chromophore, series of images separated by 6µm in depth

M. Maeda, H. Ishitobi, Z. Sekkat, S. Kawata, APL, 85, 351 (2004)

TPA + Nonlinear hole burning in PMMA-DR1

J. Zyss et al. Optics Express, 13, 505, 2005

Encoding of nonlinear information by all-optical poling of photoisomerizable

NLO molecules, 2µm resolution

W. Yuan et al., Advanced Materials, 17, 156 (2005)

TPA and photochromic materials (spiropyrane) for 3D memory systems, 4µm resolution

M. Gu et al., Appl. Phys. Lett., 92, 063309 (2008).

TPA energy transfer enhanced using quantum dot and azo-dye doped polymers

P. Zijlstra, J. W. M. Chon, M. Gu, Nature Letters, 459, 409 (2009).

Five –dimensional optical recording mediated by surface plasmons in gold nanorods (Tera bits storage).

High density data storage

Photo-isomerization cis-transPMMA DR1 sample

Step 1: Obtention of an aligned sample by corona

poling

Step 2: Local disorientation of DR1 molecules by

two photon absorption (photoisomerisation cycles)

Step 3: Reading of the data by SHG

3D SHG grating. Smallest distance between two

adjacent points (column on the left hand side) is about

2 μm (writing power 23 mW, exposure time 200 ms

with objectif of NA: 0.85, reading power 1.8 mW,

scanning speed 10 μm/s). 1012 dots/cm2.

4.5 µm

Data inscription

1 2 3

Bit “1” Bit “0”

Rewritable Data Storage

(a) SHG image taken at 3 mW, 785 nm, 10

μm/s, of a grating (50 lines of 50 μm

with a pitch of 4μm) written at P = 10 mW,

800 nm (a border burned in at 105 mW serves

as a marker); (b) microscope image of the same

area; (c) SHG scan after repoling; (d)

SHG scan after rewriting 20 lines of

50 μm with a pitch of 10 μm.

Optical and AFM images of printed dots. (a) Optical

microscopy of an array of 20 lines of dots written with illumination power

increasing from 1.3 (top left) to 48.1 mW (bottom right). (b) SHG imaging

scan of the same area of the sample with a power of 2 mW. (c)–(e) AFM

scans of three areas depicted by white squares in hole depths of (c) 4, (d)

7, and (e) 20 nm. Scale bars in all pictures are 7.5 µm.

7.5 µm

7.5 µm

Optics express,14, 9896 (2006)

JOSA B, 24,532 (2007)

Gray Scale Imaging

Gra

y s

cale

(a) Initial image of M. Göppert-Mayer, (b) Optical microscopy image, (c) SHG image

25 µm

-b-

Applied physics Letters, 90, 094103 (2007)

Adv. In Opto Electronics, D967613,(2009)

“Physics would be dull and life most unfulfilling if all physical

phenomena around us were linear. Fortunately, we are living in a

nonlinear world.

While linearization beautifies physics, nonlinearity provides

excitement in physics.”

Y. R. Shen in The Principles of Nonlinear Optics, New York,

Wiley-Interscience, 1984.

As a conclusion……..

Financial supports:

CNRS, Université de Strasbourg, Région Alsace,

European Interreg Program, Agence Nationale pour la Recherche (ANR),

Frontier Research Chemistry