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In situ visualization of domain kinetics in flux grown KTiOPO4 by digital holography
KTH, School of Engineering Sciences (SCI), Applied Physics.ORCID iD: 0000-0003-2070-9167
KTH, School of Engineering Sciences (SCI), Applied Physics.ORCID iD: 0000-0002-2508-391X
KTH, School of Engineering Sciences (SCI), Applied Physics.ORCID iD: 0000-0001-7688-1367
KTH, School of Engineering Sciences (SCI), Applied Physics.
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2007 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 102, no 6, 064105- p.Article in journal (Refereed) Published
Abstract [en]

The fast dynamic evolution of ferroelectric domains during electric field poling in flux grown KTiOPO4 crystals was investigated online by a digital holography based technique. The dependence of the ferroelectric domain kinetics on the electric field temporal wave form and poling history was studied. High-speed imaging by means of a complementary metal-oxide-semiconductor image sensor camera allowed in situ measurement of the domain wall propagation speed under different poling conditions. The results also give evidence of the strong influence of the dielectric surface layer in this material.

Place, publisher, year, edition, pages
2007. Vol. 102, no 6, 064105- p.
Keyword [en]
Ferroelectric Domains; Resolution; Field; Generation; Microscopy; Reversal
National Category
Atom and Molecular Physics and Optics
Identifiers
URN: urn:nbn:se:kth:diva-7993DOI: 10.1063/1.2781567ISI: 000249787200085Scopus ID: 2-s2.0-34848867821OAI: oai:DiVA.org:kth-7993DiVA: diva2:13194
Note
QC 20100824Available from: 2005-10-25 Created: 2005-10-25 Last updated: 2015-03-30Bibliographically approved
In thesis
1. Domain engineering in KTiOPO4
Open this publication in new window or tab >>Domain engineering in KTiOPO4
2005 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Ferroelectric crystals are commonly used in nonlinear optics for frequency conversion of laser radiation. The quasi-phase matching (QPM) approach uses a periodically modulated nonlinearity that can be achieved by periodically inverting domains in ferroelectric crystals and allows versatile and efficient frequency conversion in the whole transparency region of the material.

KTiOPO4 (KTP) is one of the most attractive ferroelectric non-linear optical material for periodic domain-inversion engineering due to its excellent non-linearity, high resistance for photorefractive damage, and its relatively low coercive field. A periodic structure of reversed domains can be created in the crystal by lithographic patterning with subsequent electric field poling. The performance of the periodically poled KTP crystals (PPKTP) as frequency converters rely directly upon the poling quality. Therefore, characterization methods that lead to a deeper understanding of the polarization switching process are of utmost importance.

In this work, several techniques have been used and developed to study domain structure in KTP, both in-situ and ex-situ. The results obtained have been utilized to characterize different aspects of the polarization switching processes in KTP, both for patterned and unpatterned samples.

It has also been demonstrated that it is possible to fabricate sub-micrometer (sub-μm) PPKTP for novel optical devices. Lithographic processes based on e-beam lithography and deep UV-laser lithography have been developed and proven useful to pattern sub- μm pitches, where the later has been the most convenient method. A poling method based on a periodical modulation of the K-stoichiometry has been developed, and it has resulted in a sub-μm domain grating with a period of 720 nm for a 1 mm thick KTP crystal. To the best of our knowledge, this is the largest domain aspect-ratio achieved for a bulk ferroelectric crystal. The sub-micrometer PPKTP samples have been used for demonstration of 6:th and 7:th QPM order backward second-harmonic generation with continuous wave laser excitation, as well as a demonstration of narrow wavelength electrically-adjustable Bragg reflectivity.

Place, publisher, year, edition, pages
Stockholm: KTH, 2005. 108 p.
Series
Trita-FYS, ISSN 0280-316X ; 2005:49
Keyword
quasi-phase matching, KTiOPO4, ferroelectric domains, atomic force microscopy, periodic electric field poling, polarization switching, second harmonic generation
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-464 (URN)91-7178-152-8 (ISBN)
Public defence
2005-10-28, sal FA32, AlbaNova, Roslagstullsbacken 21, Stockholm, 13:00
Opponent
Supervisors
Note
QC 20100930Available from: 2005-10-25 Created: 2005-10-25 Last updated: 2010-09-30Bibliographically approved
2. Ferroelectric domain engineering and characterization for photonic applications
Open this publication in new window or tab >>Ferroelectric domain engineering and characterization for photonic applications
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Lithium niobate (LiNbO3) and KTiOPO4 (KTP) are ferroelectric crystals of considerable interest in different fields of optics and optoelectronics. Due to its large values of the nonlinear optical, electro-optic (EO), piezoelectric and acousto-optical coefficients, LiNbO3 is widely used for laser frequency conversion using the quasiphase matching (QPM) approach where the sign of nonlinearity has been periodically modulated by electric field poling (EFP). In the microwave and telecommunication field LiNbO3 is used for surface acoustic devices and integrated optical modulators. KTP and its isomorphs, on the other hand, exhibit slightly lower nonlinear coefficients but have much higher photorefractive damage thresholds, so that it is mainly used in the fabrication of QPM devices for both UV, IR and visible light generation and in high power applications.

This thesis focus on different key issues: (1) accurate characterization of specific optical properties of LiNbO3, which are of interest in nonlinear and EO applications; (2) in-situ visualization and characterization of domain reversal by EFP in LiNbO3 and KTP crystals for a through understanding of the ferroelectric domain switching; (3) fabrication of periodic surface structures at sub-micron scale in LiNbO for photonic applications. An interferometric method is used for accurate measurement of ordinary and extraordinary refractive indices in uniaxial crystals, which is of great interest in the proper design of QPM crystals. A digital holography (DH) based method is presented here for 2D characterization of the EO properties of LiNbO , which is considerably interesting in the applications where the proper design of the EO device requires a spatially resolved information about the EO behaviour and the existing pointwise techniques are not sufficient. A DH method for novel in-situ monitoring of domain reversal by EFP in both LiNbO3 and KTP, is also presented here. The technqiue could be used as a tool for high fidelity periodic domain engineering but also provides information about domain kinetics, internal field and crystals defects. 3 3 3 Finally this thesis presents novel results concerning nanoscale periodic surface structuring of congruent LiNbO3. Holographic lithography (HL) is used for sub-micron period resist patterning and electric overpoling for surface domain reversal. Surface structures are obtained by selective etching. Moiré effect is also used in the HL to fabricate complicated structures with multiple periods. The depth compatibility with waveguide implementation allows foreseeing possible applications of these structures for Bragg gratings or innovative photonic crystal devices, exploiting the additional nonlinear and EO properties typical of LiNbO3.

Place, publisher, year, edition, pages
Stockholm: KTH, 2006. x, 118 p.
Series
Trita-FYS, ISSN 0280-316X ; 2006:40
Keyword
LiNbO, KTiOPO, interferometry, digital holography, electric field poling, electro-optic materials, holographic lithography, ferroelectric domains, nanostructures, microstructures
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-4001 (URN)91-7178-382-2 (ISBN)
Public defence
2006-06-08, Sal FD5, AlbaNova univ centrum, Roslagstullsbacken 21, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100824Available from: 2006-05-30 Created: 2006-05-30 Last updated: 2015-03-30Bibliographically approved

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