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Polarization switching characteristics of flux grown KTiOPO4 and RbTiOPO4 at room temperature
KTH, School of Engineering Sciences (SCI), Physics.ORCID iD: 0000-0003-2070-9167
KTH, School of Engineering Sciences (SCI), Physics.
KTH, School of Engineering Sciences (SCI), Physics.ORCID iD: 0000-0002-2508-391X
KTH, School of Engineering Sciences (SCI), Physics.ORCID iD: 0000-0001-7688-1367
2005 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 97, no 12, 124105- p.Article in journal (Refereed) Published
Abstract [en]

A study of polarization-switching characteristics under an applied electrical field at room temperature is presented for flux-grown KTiOPO4 and RbTiOPO4. By optimizing the experimental conditions, we determined the coercive field and the domain-switching time quantitatively by direct observation of the switching current. For both isomorphs, the inverse of the polarization-switching time, 1/t(s), follows an exponential dependence on the applied field E in low-field regime, and a linear dependence on E in the high-field regime. Domain morphology of KTiOPO4 based on selective etching reveals laminar structures elongated in the b crystallographic direction. An estimation of the domain-wall velocity shows that the domain speed in the polar direction is, at least, two orders of magnitude larger than in the a-b plane. The velocity along the b direction is similar to 30 times larger than along the a axis.

Place, publisher, year, edition, pages
2005. Vol. 97, no 12, 124105- p.
Keyword [en]
electrooptic imaging microscopy, potassium titanyl phosphate, periodically poled ktiopo4, lithium tantalite, ionic-conductivity, internal field, electric-field, blue-light, ferroelectric domains, single-crystals
National Category
Atom and Molecular Physics and Optics
Identifiers
URN: urn:nbn:se:kth:diva-7992DOI: 10.1063/1.1940135ISI: 000230278100083Scopus ID: 2-s2.0-21644435070OAI: oai:DiVA.org:kth-7992DiVA: diva2:13193
Note
QC 20100830Available from: 2005-10-25 Created: 2005-10-25 Last updated: 2015-03-30Bibliographically approved
In thesis
1. Characterization of domain switching and optical damage properties in ferroelectrics
Open this publication in new window or tab >>Characterization of domain switching and optical damage properties in ferroelectrics
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Nonlinear optical frequency conversion is one of the most important key techniques in order to obtain lasers with wavelengths targeted for specific applications. In order to realize efficient and tailored lasers, the quasi-phase-matching (QPM) approach using periodically-poled ferroelectric crystals is getting increasingly important. Also understanding of damage mechanisms in nonlinear materials is necessary to be able to design reliable and well working lasers. This is especially true for high power application lasers, which is a rapidly growing field, where the damage problem normally is the ultimate limiting factor.

In this thesis work, several promising novel ferroelectric materials have been investigated for nonlinear optical applications and the emphasis has been put on QPM devices consisting of periodically-poled structures. The materials were selected from three different types of ferroelectric materials: 1) MgO-doped stoichiometric LiNbO3 (MgO:SLN) and LiTaO3 (MgO:SLT), and non-doped stoichiometric LiTaO3 (SLT), 2) KTiOPO4 (KTP) and its isomorphs RbTiOPO4 (RTP), and 3) KNbO3 (KN). The focus in our investigations have been put on the spontaneous polarization switching phenomena, optimization of the periodic poling conditions, and the photochromic optical damage properties which were characterized by the help of blue light-induced infrared absorption (BLIIRA) measurements.

With electrical studies of the spontaneous polarization switching, we were able to determine quantitatively, and compare, the coercive field values of different materials by applying triangularly shaped electric fields. We found that the values of the coercive fields depended on the increase rate of the applied electric field. The coercive field of KN was the lowest (less than 0.5 kV/mm) followed by the ones of KTP, SLT, and MgO:SLT (1.5 to 2.5 kV/mm). MgO:SLN, and RTP had relatively high coercive fields, approximately 5.0 to 6.0 kV/mm, respectively. Based on the domain switching characteristics we found, we successfully fabricated periodically-poled devices in all of the investigated materials with 30 μm periodicities and sample thickness of 1 mm.

Blue light-induced infrared absorption (BLIIRA) has been characterized for unpoled bulk and periodically-poled samples using a high-sensitivity, thermal-lens spectroscopy technique. SLT showed a large photorefraction effect and the BLIIRA signal could not be properly measured because of the large distortion of the probe beam. The rise and relaxation time of BLIIRA, after switching the blue light on and off was in a time span of 10 to 30 sec except for KTP and its isomorphs, which needed minutes to hours in order to saturate at a fixed value. KN and MgO:SLN showed the lowest susceptibility to the induced absorption. Periodic poling slightly increased the susceptibility of KTP, MgO:SLT, and KN. Relatively high thresholds were observed in MgO:SLT and KN. By increasing the peak-power intensity of the blue light, the induced absorption for MgO:SLN, KTP and KN saturated at a constant value while that of MgO:SLT increase in a constant fashion. This trend is critical issue for the device reliability at high-power applications.

Place, publisher, year, edition, pages
Stockholm: KTH, 2006. 100 p.
Series
Trita-FYS, ISSN 0280-316X ; 2006:59
Keyword
quasi-phase matching, ferroelectric domains, stoichiometric LiNbO3, stoichiometric LiTaO3, KTiOPO4, KNbO3, polarization switching, periodic electric field poling, optical damages
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-4100 (URN)91-7178-443-8 (ISBN)
Public defence
2006-09-26, Sal FB54, AobaNova univ. centrum, Roslagstullsbacken 21, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20100830Available from: 2006-09-14 Created: 2006-09-14 Last updated: 2015-03-30Bibliographically approved
2. 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

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