dc.contributor.author
Winta, Christopher J.
dc.date.accessioned
2021-02-10T12:06:31Z
dc.date.available
2021-02-10T12:06:31Z
dc.identifier.uri
https://refubium.fu-berlin.de/handle/fub188/29124
dc.identifier.uri
http://dx.doi.org/10.17169/refubium-28873
dc.description.abstract
Nonlinear optical spectroscopy has emerged as a powerful tool for the investigation of crystalline solids. Compared to linear approaches, it offers additional experimental degrees of freedom which grant access to the sample's symmetry properties and can provide unique insight into its crystallographic and electronic structure. Moreover, owing to their higher-order field dependence, nonlinear techniques often feature improved contrast and sensitivity. These qualities are particularly useful in the infrared (IR) spectral region as it contains optical phonon resonances which carry symmetry information themselves and play a key role in determining a material's thermal, IR optical, and phase transition properties.
Among nonlinear optical techniques, second-harmonic generation (SHG) takes on a prominent role as the simplest even-order process and, while widely employed in the visible, has so far not been fully exploited in the IR—mainly due to the scarcity of suitable laser sources. With access to an IR free-electron laser (FEL), however, it becomes feasible to employ IR SHG as a phonon spectroscopy.
This work explores the potential of second-harmonic phonon spectroscopy as an alternative to more established even-order techniques. To this end, a comprehensive IR SHG study of the well-known model system α-quartz is performed, presenting the technique as a highly sensitive tool to study optical phonons in noncentrosymmetric polar crystals. Through these vibrational resonances, IR SHG can also aptly probe and characterize symmetry changes in a material which is demonstrated in a temperature-dependent study of quartz's α–β phase transition. The implementation of a cryogenic IR SHG setup extends the temperature range of second-harmonic phonon spectroscopy and enables phase transition studies at low temperatures where it also benefits from decreased phonon damping rates.
Further, second-harmonic phonon spectroscopy was successfully employed in the characterization of the unique phonon modes emerging in atomic-scale superlattices which cause a distinct dielectric response, highly suitable for nanophotonic device applications.
An attempt to exploit the technique's sensitivity to structural phase transitions in multiferroic thin films, revealed fundamental limitations of IR SHG posed by the relatively large IR FEL spot sizes and low sensitivity of available IR detectors. A proof-of-principle FEL-based IR-visible sum-frequency generation experiment shows how these limitations can be lifted while maintaining nonlinear optical and IR-resonant capabilities.
Overall, this work comprehensively explores the potential of IR SHG as a phonon spectroscopy, showcasing its unique capabilities and identifying its limitations.
Perspectives are presented on how to further develop FEL-based nonlinear optical approaches to which the present work constitutes important groundwork.
en
dc.format.extent
X, 147 Seiten
dc.rights.uri
http://www.fu-berlin.de/sites/refubium/rechtliches/Nutzungsbedingungen
dc.subject
Nonlinear optical spectroscopy
en
dc.subject
Vibrational spectroscopy
en
dc.subject
Infrared spectroscopy
en
dc.subject
Free-electron laser
en
dc.subject
Materials science
en
dc.subject
Metamaterials
en
dc.subject
Second-harmonic generation
en
dc.subject.ddc
500 Natural sciences and mathematics::530 Physics::535 Light and paraphotic phenomena
dc.title
Second-Harmonic Phonon Spectroscopy Using an Infrared Free-Electron Laser
dc.contributor.gender
male
dc.contributor.firstReferee
Wolf, Martin
dc.contributor.furtherReferee
Kuch, Wolfgang
dc.date.accepted
2020-12-17
dc.identifier.urn
urn:nbn:de:kobv:188-refubium-29124-0
refubium.affiliation
Physik
dcterms.accessRights.dnb
free
dcterms.accessRights.openaire
open access