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Femtosecond laser direct writing of

circular optical properties in silica glass Thèse de doctorat de l'université Paris-Saclay

École doctorale n°571 : 2MIB

(Sciences chimiques : molécules, matériaux, instrumentation et biosystèmes)

Spécialité de doctorat: Chimie

Unité de recherche : Universitéé Paris-Saclay, CNRS, Institut de chimie moléculaire et des matériaux d'Orsay, 91405, Orsay, France.

Référent

Thèse présentée et soutenue à Orsay, le 17 décembre

2020, par

Jing TIAN

Composition du Jury

Fabian ZOMER

Professeur des universités

Université Paris Saclay

Président

François COURVOISIER

Directeur de recherche

CNRS - Université de Franche-Comté

Rapporteur & Examinateur

Razvan STOIAN

Directeur de recherche

CNRS - Université Jean MONNET

Rapporteur & Examinateur

Enrique GARCIA-CAUREL

Ingénieur de recherche

Ecole polytechnique

Examinateur

Direction de la thèse

Matthieu LANCRY

Enseignant-Chercheur

ICMMO,Université Paris-Saclay

Directeur de thèse

Thèse de doctorat

NNT : 2020UPASA001

Université Paris-Saclay, CNRS

Institut de chimie molculaire et des matriaux d'Orsay, 91405, Orsay, France.

OUTLINE

Acknowledgement ................................................................................................. 9

Introduction ........................................................................................................... 11

Chapter1 State of the art of Femtosecond Laser Direct Writing in

Glasses ..................................................................................................................... 20

1.1 Introduction .................................................................................................................. 21

1.2 Silica Glass ..................................................................................................................... 21

1.3 Propagation of ultrashort laser pulses in a vitreous material .................. 23

1.3.1 Basic principles ......................................................................................................................... 23

1.3.2 Self-focusing by Kerr effect .................................................................................................. 25

1.3.3 Filamentation............................................................................................................................. 26

1.3.4 Self-phase modulation........................................................................................................... 26

1.3.5 Spectral dispersion and temporal broadening ............................................................. 26

1.4 Femtosecond laser interactions in glasses ...................................................... 28

1.4.1 Ionization and relaxation in intense field ........................................................................ 28

1.4.2 Relaxation mechanisms ......................................................................................................... 30

1.4.3 Material changes induced by femtosecond laser irradiation .................................. 31

1.4.4 Heat accumulation effects .................................................................................................... 32

1.5 Damage thresholds and different type of permanent modifications ... 34

1.5.1 Isotropic index changes based modifications (Type I) ............................................... 36

1.5.2 Anisotropic refractive index changes based modifications (Type II)..................... 38

1.5.3 Voids (Type III) .......................................................................................................................... 40

1.6 Focus on Type II modifications and nanogratings formation .................. 40

1.6.1 From LIPSS to self-organized nanogratings in silica ................................................... 40

1.6.2 Physical and optical properties of nanogratings in silica glass ............................... 42

1.6.3 Tentative mechanisms for nanogratings formation .................................................... 43

1.6.4 Nanogratings parameters dependence ........................................................................... 48

1.7 Towards 3D imprinted optical chirality in inorganic glasses .................... 54

1.8 Conclusions ................................................................................................................... 57

1.9 References ..................................................................................................................... 59

Chapter2 Experimental details ........................................................................ 71

4

2.1 Introduction .................................................................................................................. 72

2.2 Femtosecond laser direct writing (FLDW) system......................................... 72

2.3 Fundamentals of polarization of light ............................................................... 76

2.3.1 Stokes vector and the Poincaré sphere ........................................................................... 76

2.3.2 Mueller matrix formalism ...................................................................................................... 78

2.4 Basic polarimetric properties ................................................................................. 78

2.4.1 Dichroism and diattenuation ............................................................................................... 79

2.4.2 Retardation and linear birefringence ................................................................................ 81

2.4.3 Depolarization ........................................................................................................................... 84

2.4.4 Polarizance ................................................................................................................................. 87

2.5 Extraction of polarimetric properties ................................................................. 88

2.5.1 Product decomposition ......................................................................................................... 88

2.5.2 Sum decomposition ................................................................................................................ 89

2.5.3 Logarithmic decomposition ................................................................................................. 90

2.6 Polarimetric instrumentation ................................................................................. 93

............................................................................................. 94

2.6.2 Circular Dichroism spectro-polarimeter - JASCO- J-810 ........................................... 97

2.6.3 Vis-Near IR (400-1000nm) Mueller Ellipsometry MM-16 .................................... 101

2.6.4 UV-Vis-Near-IR Mueller ellipsometry MM-12 ......................................................... 102

2.7 Conclusions ................................................................................................................ 105

2.8 References .................................................................................................................. 106

Chapter3 Study of laser induced circular dichroism using a CD

spectro-polarimeter .......................................................................................... 110

3.1 Introduction ............................................................................................................... 112

3.2 Samples and Methodology ................................................................................. 113

3.3 Preliminary experiments to identify the modifications thresholds of

linear optical properties ............................................................................................... 116

3.3.1 Study of writing kinetics at various repetition rates ................................................. 116

3.3.2 Study of writing kinetics according to the numerical aperture ............................ 118

3.3.3 Study of writing kinetics according to the laser polarization ................................ 119

3.3.4 Spectral measurements of the retardance and linear extinction difference .... 120

3.4 Study of femtosecond laser irradiated silica using a CD spectro-

polarimeter ........................................................................................................................ 121

5

3.4.1 Preliminary observations ..................................................................................................... 121

3.4.2 Study of circular diattenuation CD according to the pulse energy ..................... 122

3.4.3 Study of circular diattenuation CD according to the line-to-line spacing ........ 123

3.4.4 Study of circular diattenuation according to the angle between polarization

orientation and the laser scanning direction ......................................................................... 126

3.4.5 Study of circular diattenuation according to the pulse-to-pulse overlapping

rate and the laser repetition rate ................................................................................................ 129

3.4.6 Study of circular diattenuation according to the focusing depth ........................ 131

3.5 Analysis of CD measurements artifacts and asymmetric transmission of

circularly polarized light ............................................................................................... 132

3.5.1 Study of CD artifacts due to the spectro-polarimeter .............................................. 132

3.5.2 Investigations of Asymmetric transmission of circularly polarized light ........... 135

3.6 Discussion on the origin of fs laser-induced chiral optical property . 137

3.6.1 An introduction to chirality and chiral optical properties in molecules ............. 137

3.6.2 Qualitative interpretation.................................................................................................... 138

3.7 Conclusions ................................................................................................................ 140

3.8 References .................................................................................................................. 144

Chapter4 Mueller matrix spectro-polarimetry in femtosecond

irradiated silica glass ........................................................................................ 151

4.1 Introduction ............................................................................................................... 152

4.2 Materials and methods ......................................................................................... 153

4.3 Typical results using MM-16 spectro-polarimetry .................................... 155

4.3.1 Raw Mueller matrix measurements ................................................................................. 155

4.3.2 Extraction of polarimetric properties .............................................................................. 157

4.3.3 Investigation of asymmetric transmission .................................................................... 160

4.4 Study of laser parameters dependence: pulse energy, pulse-to-pulse

overlap and focusing depth ....................................................................................... 163

4.5 Influence of the laser writing configuration ................................................. 172

4.5.1 Influence of the writing polarization direction for a fixed scanning direction

and orientation i.e. along +X ....................................................................................................... 175

4.5.2 Influence of the laser scanning direction with respect to the writing laser

polarization ......................................................................................................................................... 178

6

4.6 Dependence of the stress-induced birefringence with the laser writing

polarization ....................................................................................................................... 180

4.7 Thermal stability of fs-induced anisotropic optical properties ............ 184

4.8 Conclusions ................................................................................................................ 193

4.9 References .................................................................................................................. 196

Chapter5 Investigations of the UV-Vis-NIR spectral properties: comparison between nanogratings and stress-induced birefringence

silica glass ............................................................................................................. 202

5.1 Introduction ............................................................................................................... 203

5.2 Spectral dependence of femtosecond laser induced circular optical

properties in silica .......................................................................................................... 204

5.3 A Comparison between Nanogratings-Based and Stress-Engineered

Waveplates Written by Femtosecond Laser in Silica ....................................... 205 Chapter6 Discussion on the origin of the anisotropic linear and circular optical properties created within Type II regime ................... 207

6.1 Introduction ............................................................................................................... 208

6.2 On the origin of the anisotropic linear optical properties within Type II

regime in fs-irradiated silica glass ........................................................................... 209

6.2.1 Form birefringence within Type II regime..................................................................... 209

6.2.2 Stress-induced birefringence within Type II regime ................................................. 215

6.2.3 Point defects formation and annealing within Type II regime .............................. 219

6.2.4 Conclusion on anisotropic linear properties thermal stability .............................. 222

6.3 Modeling anisotropic circular optical properties using Mueller matrix

formalism using a two linear retarders model ................................................... 223

6.3.1 Short description of the modeling procedure ............................................................ 224

6.3.2 Modelling a single linear retarder ................................................................................... 226

6.3.3 Modelling the formation of CB only using two linear retarders ........................... 227

6.3.4 Modeling the formation of CD with two linear retarders ....................................... 231

6.3.5 Modeling the formation of both CB and CD using two linear retarders ........... 234

6.4 Polarization dependent anisotropic optical properties: a comparison

between modeling and experimental measurements ..................................... 236 7

6.5 Interpretation of the polarization dependent anisotropic optical

properties and the creation of circular optical properties ............................. 239

6.6 Conclusions ................................................................................................................ 244

6.7 References .................................................................................................................. 246

Conclusions and perspectives ....................................................................... 252

Publications list ................................................................................................... 260

Résumé substantiel en Français ................................................................... 262

8 9

Acknowledgement

I would like to express my gratitude to the numerous individuals whose help and support assisted my professional growth during my recent years and contributed to my work presented in this thesis. Firstly, I want to thank to my PhD supervisor Matthieu LANCRY, who introduced me to the research in physics and optics and lead my doctoral project and creating good atmosphere in the laboratory. I acknowledge all the help and support from our research group members Bertrand Poumellec, Rudy Desmarchelier, Yitao Wang, Maxime Cavillon, Ruyue Que, Benjamin Sapaly. Especially I want to thank to our collaborators Enric Garcia-Caurel, Sang Hyuk Yoo, Razvigor Ossikovski from Ecole Polytechnique and Michel Stchakovsky, Celine Eypert from HORIBA, as they helped me a lot to learn new field about Mueller matrix ellipsometry techniques. I am grateful to my friends Miaobo Pan and Kuankuan Zheng who supported me a lot during my PhD. And my final appreciation is to the China scholarship council (CSC) who gave the opportunity to study in the Université Paris-Saclay by supporting my PhD financially. 10 11

Introduction

What is the common problem existing between the mastering of elaboration of all optical functions in a glass for integrated optics? It is the control of the final product structure (the atomic arrangement) and of its orientation resulting in a control of the imprinted optical properties. One current challenge is to achieve the The photosensitivity of glass (e.g. in germanosilicates and Boron-doped silica glasses) to ultraviolet (UV) laser radiation (continuous wave or nanosecond pulsed lasers) was perceived in the 1990s as a tool for functionalizing materials. Chemistry quickly took its share within this field, as it was realized that photosensitivity was a function of glass chemical composition as well as its physico-chemical environment (including material thermal history and surrounding environmental conditions). Thus, the physical properties of the material, subsequent its laser irradiation, originated from photochemistry processes. The lasers used at that time, though relatively intense (usually continuous or nanosecond UV lasers) to induce substantial structural modifications of a material, were still in linear optical domain or nonlinear through two-photon absorption. The main strategy was to use point defects, absorbing in the material optical bandgap, as an initial step to couple energy into the glass network. Typically, homogeneous Gaussian laser beams, with an axisymmetric structure, were used to deposit optical energy inside the glass material mainly by linear absorption or sometimes through a two-photon process [1]. The development of femtosecond lasers, enabling the use of pulses having extremely high powers, completely transformed this vision. Using these lasers, the peak power density is such that the research community moved to nonlinear optics with the possibility of electrons excitation across the silica optical bandgap, using six photons or even eight photons at 800 nm or 1030 nm, respectively. In fact, the femtosecond pulses make it possible, by delivering the energy in a controlled volume, to easily reach very high power densities (typically 10

12-14W/cm2 after focusing). These multiphoton excitations lead to photo-induced

physicochemical reactions and various structural modifications [2]: changes of the intrinsic material ordering (through a fictive temperature change), phase changes (re-crystallization, phase separation), chemical migrations. These modifications induce permanent changes of physical properties, including dielectric tensor, second order nonlinear optical properties (frequency doubling, electro-optical effects...). It is thus an attractive candidate for many applications since the photo-induced effects are by nature strongl volume of a few cubic microns (µm 3). Since the early birth of femtosecond lasers in the 1990s, Femtosecond Laser Direct Writing (FLDW) has opened a new path allowing 3D micro/nano-structuring of the linear and non-linear optical properties of transparent materials with functionalities inaccessible by other processes. From a broader standpoint, it becomes possible to imprint optical components at low cost, and/or to shape any beam into any other one, characterized by a set of parameters , and , where r is a spatial position located in the beam cross- section, is the wave vector, is the polarization vector and I is the intensity). In this sense, the research community envisions to produce new structures and new 3D optical devices 12 such as Fresnel lenses, axicons, delay plates (e.g. for the compensation of aberrations), Bragg gratings in volume (e.g. pulse compression or stabilization of fiber lasers) but also birefringent elements such as micro-wave arrays for polarimetry, radial / azimuth polarization converters, polarizing waveguides [3-7]. These devices have enormous potential for micro-optics, communications, lasers, data storage systems or imaging. The impact at the industrial level is recognized and it is clear that this technology will generate employment activities. Thus, femtosecond laser direct writing is expected to become an ubiquitous tool of choice for the realization of micro optical devices in 3D. One objective of this thesis is to control the material transformations induced through it. In this context, understanding interaction of matter with femtosecond laser pulses will enable the evaluation of the industrial potential this new direct writing method has to offer. Some aspects of the light-matter interaction are fundamentally new. The underlying physics is the behavior of electron plasma in the presence of an ionic support and of a light wave. Here, solid and plasma states coexist for a fraction of picosecond. In addition, both, matter and light are in interaction to produce a structured organization of the plasma density. The fundamental problems are to accurately describe the structuration of the plasma of free electrons produced at the end of multiphoton ionization (transition through the gap of the transparent insulator). Here the solid intervenes as a source of electrons. Its microstructure organizes the plasma in coherence with that of the light beam. Then, after the pulse, this electron density distribution is "imprinted" by trapping electrons in the solid, and, it can be solid is not destroyed; it remains below the vaporization threshold, it is restructured in the force field created by the laser. We can therefore imagine the orientation of the material, imprinted oriented nano/microstructures like directionally solidified eutectics. This is a new physics. But for chemistry too, there are new aspects because the processes involve highly excited states, which are largely off equilibrium. It is therefore necessary to question some previous ideas. For example, the knowledge on the effect of impurities, defects states, or easily ionized states, remains highly limited. In addition the use of ultrashort pulses has an original characteristic: a large spectral width (100 fs 10 nm). The phasing of the spectral components is the laser manufacturer's goal to achieve maximum compression of the pulse (minimum duration of the pulse). But these components can be separated, modified and recombined to produce pulses of various shapes that have different effects in the transparent material. In particular, force fields and not energy fields are produced. Their control opens the door to a science of material modification by laser. This is the focus of the today work carried out by Bertrand Poumellec and Matthieu Lancry. In particular, three discoveries form the basis of this PhD thesis. The first breakthrough is from our colleagues at Southampton and Kyoto Universities, namely Peter Kazansky and Y. Shimotsuma, who discovered self-organized nanogratings in SiO

2 (200-400 nm periodicity persisting on mm range, including fringes as thin as 10-30 nm),

which are in fact the smallest structures ever created by light [8]. From the authors, these nanogratings arise from modulation of the chemical composition (probably oxygen redistribution) and this would be related to stationary density waves in the plasma produced by the coupling between bulk plasmonic waves and light waves. In 2011, our group revealed 13 that nanogratings are in fact an assembly of nanoporous layers due to oxide decomposition [9, 10] likely through a tensile stress assisted nanocavitation process [11]. These structures, also called Type II modifications in the literature, are at the root of other experimental unusual phenomena like high linear birefringence response (up to -10-2), polarized gative index changes experimental observations left a number of opened questions that should be addressed to enable reliable applications. How to master such structures and the resulting properties, and consequently how to use them efficiently? The second breakthrough is the discovery of a sensitive interaction with the direction of writing (directional writing dependence), which is original [12, 13]. Thus, we observed differences in the effect between scanning the sample (centrosymmetric) with the laser beam, for a given direction, in one direction and the other; a bit like we can see a difference between writing a line of characters from right to left or from left to right with the same pen holder! But this is also different according to the scanning orientation (orientational writing dependence) . This asymmetrical behavior of the interaction is likely due to the interaction process between the laser and the material revealing some unusual behavior. It appears that the pulse is ultra-short, the latter being associated with a significant spectral width and that the beam at the focal point is probably not axisymmetric [14]. Moreover these asymmetric structures translate in an original way on several properties [15] such as the appearance of a strong linear birefringence, a linear dichroism, and the transition from nanogratings to bubbles formation...quotesdbs_dbs26.pdfusesText_32

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