Title: The influence of magnetic fields on light-matter interaction
Other Titles: De invloed van magnetische velden op licht-materie interactie
Authors: Vandendriessche, Stefaan
Issue Date: 5-May-2014
Abstract: In this dissertation we sought to improve the understanding of the influence of magnetic fields on light–matter interaction. While this influence is small, it is crucial for optical communication as well as next-generation networks. It was discovered almost two centuries ago and was initially characterized in glass by Michael Faraday, who stated "Still, I have at last succeeded in illuminating a magnetic curve or line of force, and in magnetizing a ray of light...". Since then great progress has been made in understanding Faraday rotation as well as other magneto-optical effects, and they have become an important but unseen part of everyday life. From our perspective of nonlinear optics we sought to contribute to the field of magneto-optics.We built a setup in order to magneto-optically characterize materials. This setup contains a single photoelastic modulator and simultaneously measures circular dichroism, circular birefringence, magnetic circular dichroism and Faraday rotation. Because of the importance of this setup to this dissertation, we analyzed it and verified the measurements, both in an ideal framework and taking into account photoelastic modulator non-idealities.As with other nonlinear optical effects, scientists first investigated Faraday rotation in inorganic materials. However, organic materials provide many advantages over inorganic materials, such as flexibility in processing and synthesis, leading to our initial focus on organic materials. Using both computational methods and experimental measurements, we created a model to predict the Faraday rotation of organic compounds. Our model accurately predicts the Faraday rotation of small organic compounds in a wavelength region off-resonance, and can be expanded to include larger molecules or additional chemical groups. Despite the usefulness of calculating or predicting the Faraday rotation of molecules off-resonance, we subsequently demonstrated that resonance can have an important effect on Faraday rotation. We observed giant Faraday rotation in a class of mesogenic organic molecules, and we hypothesize that it is caused by resonance with a triplet state at that energy. This hypothesis is strengthened by time-dependent density functional theory calculations revealing triplet transitions close to these wavelengths.Certain inorganic materials also warrant further investigation for magneto-optical effects. Superparamagnetic nanoparticles offer an interesting combination of relatively easy synthesis, flexibility in processing and sample preparation and a very strong magnetic response. We therefore chose to analyze their behavior in alternating current magnetic field measurements. They show a characteristic response at the uneven harmonics of the applied magnetic field strength frequency. This enables rapid identification and analysis, even in complex samples consisting of multiple types of magnetic materials. Subsequently we showed that superparamagnetic nanoparticles also hold promise for higher order nonlinear optical measurements such as magnetization-inducedsecond harmonic generation.Our results improved the understanding of the influence of magnetic fields on light–matter interaction. Progress has been made in understanding the optical response of both organic materials and superparamagnetic materials in a magnetic field. Both materials show promise for further fundamental research as well as practical applications such as magnetometers and magnetoencephalography. In addition, our results provide a solid basis that future research can build on in order to deepen the understanding of the influence of a magnetic field on light–matter interactions.
Table of Contents: Preface
Beknopte samenvatting
List of abbreviations
List of symbols
1 Introduction
1.1 Introduction to linear and nonlinear optics
1.1.1 Linear optics
1.1.2 Nonlinear optics
1.2 Faraday rotation
1.2.1 Principles
1.2.2 Measurement
1.2.3 Calculation
1.2.4 Materials
1.2.5 Applications
1.2.6 State of the art
1.3 Magnetization-induced second harmonic generation
1.3.1 Second harmonic generation
1.3.2 Magnetization-induced second harmonic generation
1.4 Research goals
2 Photoelastic modulator non-idealities in magneto-optical polarization measurements
2.1 Abstract
2.2 Introduction
2.3 Experimental details
2.4 Theoretical and experimental results
2.4.1 General theoretical derivation
2.4.2 Measuring circular birefringence and dichroism with an ideal PEM
2.4.3 Measuring circular birefringence and dichroism with a real PEM
2.5 Discussion and perspectives
3. Faraday rotation and dispersion in the visible region for saturated organic liquids
3.1 Abstract
3.2 Introduction
3.3 Experimental
3.4 Results and discussion
3.4.1 Trends for alkanes and alcohols
3.4.2 Relation to the diamagnetic susceptibility
3.4.3 Relation to the molecular polarizability
3.4.4 Modeling the Verdet constant
3.5 Conclusions
4 Giant Faraday rotation in mesogenic organic molecules
4.1 Abstract
4.2 Introduction
4.3 Experimental section
4.4 Results and discussion
4.5 Conclusion
5 Magneto-optical harmonic susceptometry of superparamagnetic materials
5.1 Abstract
5.2 Introduction
5.3 Experimental details
5.4 Theoretical derivation
5.5 Experimental results
5.6 Discussion
5.7 Conclusion
6 Characterization of magnetization-induced second harmonic generation in iron oxide polymer nanocomposites
6.1 Abstract
6.2 Introduction
6.3 Experiments
6.4 Results and discussion
6.5 Conclusions
7 Conclusions and perspectives
A Tensors
B Faraday rotation and dispersion in the visible region for saturated organic liquids: supporting information
B.1 Units
B.2 Measured and calculated Verdet constants of liquids
C Giant Faraday rotation in mesogenic organic molecules: supporting information
D Magneto-optical harmonic susceptometry of superparamagnetic materials: supporting information
D.1 First harmonic
D.2 Third harmonic
Health, safety & environment considerations
List of publications
ISBN: 978-90-8649-706-5
Publication status: published
KU Leuven publication type: TH
Appears in Collections:Molecular Imaging and Photonics

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