


2020-01-27
DANIEL SÁNCHEZ PEACHAM
DANIEL SÁNCHEZ PEACHAM

2020-01-31
CHRISTOS CHARALAMBOUS
CHRISTOS CHARALAMBOUS

2020-02-06
SERGIO LUCIO DE BONIS
SERGIO LUCIO DE BONIS

2020-02-10
JULIO SANZ SÁNCHEZ
JULIO SANZ SÁNCHEZ

2020-02-17
SANDRA DE VEGA
SANDRA DE VEGA

2020-02-21
ESTHER GELLINGS
ESTHER GELLINGS

2020-03-26
NICOLA DI PALO
NICOLA DI PALO

2020-03-30
ANGELO PIGA
ANGELO PIGA

2020-04-24
PABLO GOMEZ GARCIA
PABLO GOMEZ GARCIA

2020-06-04
ANUJA ARUN PADHEY
ANUJA ARUN PADHEY

2020-06-08
VIKAS REMESH
VIKAS REMESH

2020-06-23
DAVID ALCARAZ
DAVID ALCARAZ

2020-06-30
GERARD PLANES
GERARD PLANES

2020-07-09
IRENE ALDA
IRENE ALDA

2020-07-13
EMANUELE TIRRITO
EMANUELE TIRRITO

2020-07-16
ALBERT ALOY
ALBERT ALOY

2020-07-27
MARIA SANZ-PAZ
MARIA SANZ-PAZ

2020-07-28
JUAN MIGUEL PÉREZ ROSAS
JUAN MIGUEL PÉREZ ROSAS

2020-10-08
ZAHRA RAISSI
ZAHRA RAISSI

2020-10-30
IVAN BORDACCHINI
IVAN BORDACCHINI

2020-11-09
GORKA MUÑOZ GIL
GORKA MUÑOZ GIL

2020-11-17
ZAHRA KHANIAN
ZAHRA KHANIAN

2020-11-27
PAMINA WINKLER
PAMINA WINKLER
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2020-12-02
BIPLOB NANDY
BIPLOB NANDY
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2020-12-11
DANIEL GONZÁLEZ CUADRA
DANIEL GONZÁLEZ CUADRA
Study of Graphene Hybrid Heterostructures for Linear and Nonlinear Optics


Dr David Alcaraz
June 23rd, 2020
DAVID ALCARAZ
Quantum Nano-Optoelectronics
ICFO-The Institute of Photonic Sciences
Graphene is the first of the 2D-material family. It is formed by carbon atoms arranged in a honeycomb lattice, which confers it intriguing physical properties that are still being discovered nowadays. A fundamental advantage found in graphene is the ability to gate tune “in-situ“ its optical response from reflective (metallic) to absorptive (lossy dielectric). It is in the reflective conditions when it becomes more interesting since it supports surface plasmon polaritons in the mid-infrared, similar to metals in the near-infrared and visible spectral regions. Surface plasmons in metals are known to be more confined than free space propagating light. But graphene naturally excels in this aspect by offering a confinement factor around 100, which causes light to couple in inefficiently.
Several studies on metal plasmonics have shown the possibilities of confining light into tiny spatial dimensions with applications in molecular sensing as an example. Often, metal plasmons are used in the visible and IR regions with moderate confinement. However, Landau damping limits the optical field confinement due to penetration in the material and the consequent losses. In this thesis, it is shown that graphene-insulator-metal hybrid heterostructures can overcome that limitation by efficiently exciting plasmons in unpatterned graphene with vertical confinement down to the ultimate one-atom insulator thickness. It is accomplished by encapsulating graphene with a single layer of h-BN (or thicker oxide layers for the systematic study) and fabricating metallic nano/micro-ribbons on top. The transmission extinction of the samples was measured and compared with theoretical models accounting for material nonlocal permittivity. The ultimate confinement and the validity of the excitation method are confirmed enabling a path towards ultrastrong light-matter interaction.
An example application of the aforementioned method to graphene nonlinear optics is also presented. The large intrinsic graphene third-order nonlinear optical response has been of great interest and it has been studied both theoretically and experimentally. However, there were not experiments covering all the expected features from the theory in the mid-infrared.
This thesis expands the measurement range to cover the mentioned gap in planar graphene. Additionally, field enhancement and confinement provided by the hybrid heterostructure was exploited to increase the nonlinear third-harmonic generation signal in more than three orders of magnitude. Intriguingly, it was found that some structures presented further modulation of the nonlinear signal which is attributed to the oscillatory nature of graphene plasmons. This opened an extra channel for extreme nonlinear gate tunability for the optimized parameters. To summarize, this thesis presented means to achieve the regime of ultrastrong light-matter interaction, it fully characterizes it down to the one-atom spacer limit, and provides an example while demonstrating its applicability in graphene nonlinear optics.
Tuesday, June 23, 2020, 11:00. Semi-Presencial & MsTeams
Thesis Advisor: Prof Dr Frank Koppens
ICFO-The Institute of Photonic Sciences
Graphene is the first of the 2D-material family. It is formed by carbon atoms arranged in a honeycomb lattice, which confers it intriguing physical properties that are still being discovered nowadays. A fundamental advantage found in graphene is the ability to gate tune “in-situ“ its optical response from reflective (metallic) to absorptive (lossy dielectric). It is in the reflective conditions when it becomes more interesting since it supports surface plasmon polaritons in the mid-infrared, similar to metals in the near-infrared and visible spectral regions. Surface plasmons in metals are known to be more confined than free space propagating light. But graphene naturally excels in this aspect by offering a confinement factor around 100, which causes light to couple in inefficiently.
Several studies on metal plasmonics have shown the possibilities of confining light into tiny spatial dimensions with applications in molecular sensing as an example. Often, metal plasmons are used in the visible and IR regions with moderate confinement. However, Landau damping limits the optical field confinement due to penetration in the material and the consequent losses. In this thesis, it is shown that graphene-insulator-metal hybrid heterostructures can overcome that limitation by efficiently exciting plasmons in unpatterned graphene with vertical confinement down to the ultimate one-atom insulator thickness. It is accomplished by encapsulating graphene with a single layer of h-BN (or thicker oxide layers for the systematic study) and fabricating metallic nano/micro-ribbons on top. The transmission extinction of the samples was measured and compared with theoretical models accounting for material nonlocal permittivity. The ultimate confinement and the validity of the excitation method are confirmed enabling a path towards ultrastrong light-matter interaction.
An example application of the aforementioned method to graphene nonlinear optics is also presented. The large intrinsic graphene third-order nonlinear optical response has been of great interest and it has been studied both theoretically and experimentally. However, there were not experiments covering all the expected features from the theory in the mid-infrared.
This thesis expands the measurement range to cover the mentioned gap in planar graphene. Additionally, field enhancement and confinement provided by the hybrid heterostructure was exploited to increase the nonlinear third-harmonic generation signal in more than three orders of magnitude. Intriguingly, it was found that some structures presented further modulation of the nonlinear signal which is attributed to the oscillatory nature of graphene plasmons. This opened an extra channel for extreme nonlinear gate tunability for the optimized parameters. To summarize, this thesis presented means to achieve the regime of ultrastrong light-matter interaction, it fully characterizes it down to the one-atom spacer limit, and provides an example while demonstrating its applicability in graphene nonlinear optics.
Tuesday, June 23, 2020, 11:00. Semi-Presencial & MsTeams
Thesis Advisor: Prof Dr Frank Koppens