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Studies on Domain Dynamics in Nonlinear Optical Ferroelectric Oxide Crystals
KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Nonlinear optical frequency conversion is the key technology for modifying laser output radiation, in order to target specific applications. The most powerful technique to obtain tailored second-order nonlinear interactions is the quasi-phasematching (QPM) approach. QPM is based on periodic modulation of the medium’s nonlinearity and allows versatile and efficient frequency conversion in the whole transparency region of the material. QPM is commonly implemented in ferroelectric oxide crystals by periodically inverting the spontaneous polarization, so-called, periodic poling. However, in order to achieve QPM structures of practical relevance, both the optical properties of the material and the domain engineering techniques have to be suitable for the targeted nonlinear interaction.

Rb-doped KTiOPO4 (RKTP) and vapor-transport-equilibrated stoichiometric LiTaO3 (VTE-SLT) are two of the most promising ferroelectric oxides used for nonlinear optics. The former is suitable for high peak-power applications and for engineering of QPM devices with sub-µm periodicity. The latter shows a short cut-off wavelength with low linear absorption, which makes it very attractive for UV-light generation. However, in order to fully exploit the potential of these two materials, it is of utmost importance to understand the domain dynamics and stability from a fundamental point of view, as well as to investigate ways to overcome their limitations.

This thesis presents studies on domain dynamics and stability in these two materials. A novel method for periodic poling of RKTP has been investigated. The method, based on using a micro-structured silicon chip as the contact electrode, has been used to fabricate periodically poled RKTP crystals with 9.01 µm period. The samples became well-poled and showed high conversion efficiency for second harmonic generation. The domain dynamics, when the silicon stamp was used as an electrode were studied, showing potential for short-pitch poling and complex patterning.

Furthermore, the domain stability in RKTP during thermal annealing at high temperatures was investigated. The results show anisotropic domain wall motion, with severe domain contraction along the crystallographic b-axis when the periodicity was reduced. A technique to suppress this domain contraction was developed based on dicing away the edges of the QPM grating so that the domain b-faces terminate in air. This gave excellent results for a broad range of periodicities.

Studies of the domain stability of periodically poled VTE-SLT during chemical etching were performed by on-line second harmonic generation, and optical microscopy. The results show that wet etching directly after poling leads to domain-wall motion, resulting in back-switching or domain merging. 

Furthermore, the domain wall motion induced by electron beam irradiation was investigated using a scanning electron microscope. It was found that domain switching strongly depends on the ratio of secondary electrons to incident electrons. These results are discussed in terms of electron beam and screening charges interaction.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2019. , p. 79
Series
TRITA-SCI-FOU ; 2019:17
National Category
Physical Sciences
Research subject
Physics
Identifiers
URN: urn:nbn:se:kth:diva-249387ISBN: 978-91-7873-165-7 (print)OAI: oai:DiVA.org:kth-249387DiVA, id: diva2:1304266
Public defence
2019-05-10, FA-31, Roslagstullsbacken 21, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20190412

Available from: 2019-04-12 Created: 2019-04-11 Last updated: 2019-04-12Bibliographically approved
List of papers
1. Contact poling of Rb:KTiOPO4 using a micro-structured silicon electrode
Open this publication in new window or tab >>Contact poling of Rb:KTiOPO4 using a micro-structured silicon electrode
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2015 (English)In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 23, no 2, p. 636-641Article in journal (Refereed) Published
Abstract [en]

A contact poling technique for domain engineering of ferroelectrics using a micro-structured silicon electrode is demonstrated on Rb:KTiOPO4. High quality QPM gratings were reproducibly fabricated. The silicon electrode is reusable and the technique potentially suitable when complex structures with sub-mu m features are to be domain engineered, which otherwise is incompatible with conventional photolithography. A non-negligible domain broadening was seen and attributed to a low nucleation rate using this type of electrode. However, under the appropriate poling conditions, this could be exploited to obtain a QPM grating with a short pitch (2 mu m), equal to half of the electrode period.

Keywords
Photolithography, Rubidium, Silicon, Complex structure, Contact poling, Conventional photolithography, Domain broadening, Domain engineering, Nucleation rate, Poling conditions, Silicon electrode
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-157684 (URN)10.1364/OE.23.000636 (DOI)000349166100003 ()2-s2.0-84921748073 (Scopus ID)
Funder
Swedish Research CouncilCarl Tryggers foundation
Note

QC 20150312. Updated from accepted to published.

Available from: 2014-12-12 Created: 2014-12-12 Last updated: 2019-04-11Bibliographically approved
2. Domain dynamics in stoichiometric lithium tantalate revealed by wet etching and on-line second harmonic generation
Open this publication in new window or tab >>Domain dynamics in stoichiometric lithium tantalate revealed by wet etching and on-line second harmonic generation
2017 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 121, no 18, article id 184103Article in journal (Refereed) Published
Abstract [en]

The effect of chemical etching on the stability of domains in periodically poled stoichiometric lithium tantalate is studied by on-line second harmonic generation and microscopy. It is found that wet etching directly after poling leads to domain-wall movement, resulting in back-switching or domain merging. Head-to-head domains tend to backswitch, while tail-to-tail domains merge. For samples where the domain structure stabilized for longer time, no domain motion is observed when etched.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2017
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-208816 (URN)10.1063/1.4982907 (DOI)000401364700008 ()2-s2.0-85018931797 (Scopus ID)
Note

QC 20170613

Available from: 2017-06-13 Created: 2017-06-13 Last updated: 2019-09-18Bibliographically approved
3. Stabilization of domain structures in Rb-doped KTiOPO 4 for high-temperature processes
Open this publication in new window or tab >>Stabilization of domain structures in Rb-doped KTiOPO 4 for high-temperature processes
Show others...
2019 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 114, no 5, article id 052904Article in journal (Refereed) Published
Abstract [en]

A way to stabilize the domain structure in periodically poled Rb-doped KTiOPO 4 samples at high-temperatures is presented. The domain contraction along the b-crystallographic axis that is observed when crystals are annealed at high temperatures is suppressed when the ends of the domains along the b-axis are diced away. Additionally, the thermal stability of self-assembled domain gratings with a sub-μm average periodicity of 650 ± 200 nm and a domain-width of 225 ± 75 nm in mm-thick samples is investigated, and it is shown that the key factor for the domain stability is the domain width rather than the interdomain distance.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2019
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-244202 (URN)10.1063/1.5082246 (DOI)000458202800023 ()2-s2.0-85061337178 (Scopus ID)
Note

QC 20190218

Available from: 2019-02-18 Created: 2019-02-18 Last updated: 2019-04-11Bibliographically approved
4. Domain wall motion in stoichiometric LiTaO3 induced by low-energy electron beam
Open this publication in new window or tab >>Domain wall motion in stoichiometric LiTaO3 induced by low-energy electron beam
2019 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118Article in journal, Letter (Refereed) Submitted
Abstract [en]

Scanning electron microscopy was used to study the mobility of domain walls in vapor-transport equilibrated stoichiometric LiTaO3. By using low-acceleration voltage, switching occurs solely for polarization pointing-up domains, resulting in fast domain-wall motion. When the incoming electron beam was more energetic with larger penetration depth, the switching instead occurred for polarization pointing down domains. Our results are discussed in terms of the interaction of the scanning electron beam with the polarization-screening charges at the crystal surface.

Keywords
ferroelectrics, domain wall
National Category
Other Physics Topics
Identifiers
urn:nbn:se:kth:diva-249385 (URN)
Note

QC 20190412

Available from: 2019-04-11 Created: 2019-04-11 Last updated: 2019-04-12Bibliographically approved

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