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Nucleation and growth of periodic domains during electric field poling in flux-grown KTiOPO4 observed by atomic force microscopy
KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.ORCID iD: 0000-0003-2070-9167
KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.ORCID iD: 0000-0002-2508-391X
KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.ORCID iD: 0000-0001-7688-1367
2006 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 88, no 3, 032905-1-032905-3 p.Article in journal (Refereed) Published
Abstract [en]

The domain structure of periodically poled KTiOPO4 crystals were studied on both the polar and nonpolar faces utilizing a voltage-modulated atomic force microscope. The measurements give information of domain nucleation, growth, and merging. Two different kind of overpoling behaviors have been observed depending on the magnitude of the applied field.

Place, publisher, year, edition, pages
2006. Vol. 88, no 3, 032905-1-032905-3 p.
Keyword [en]
Atomic force microscopy, Crystals, Electric fields, Magnetic flux, Nucleation, Time varying systems, Electric field poling, Periodic domains
National Category
Atom and Molecular Physics and Optics
Identifiers
URN: urn:nbn:se:kth:diva-8758DOI: 10.1063/1.2166678ISI: 000234757100049Scopus ID: 2-s2.0-31144438683OAI: oai:DiVA.org:kth-8758DiVA: diva2:14168
Note
QC 20100930. Uppdaterad från submitted till published (20100930).Available from: 2005-11-09 Created: 2005-11-09 Last updated: 2015-03-30Bibliographically approved
In thesis
1. Fabrication and characterization of periodically poled KTB and RB-doped KTB for applications in the visible and UV
Open this publication in new window or tab >>Fabrication and characterization of periodically poled KTB and RB-doped KTB for applications in the visible and UV
2005 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

This thesis deals with the fabrication and the characterization of periodically-poled crystals for use in lasers to generate visible and UV radiation by second-harmonic generation (SHG) through quasi-phasematching (QPM). Such lasers are of practical importance in many applications like high-density optical storage, biomedical instrumentation, colour printing, and for laser displays.

The main goals of this work were: (1) to develop effective monitoring methods for poling of crystals from the KTiOPO4 (KTP) family, (2) to develop useful non-destructive domain characterization techniques, (3) to try to find alternative crystals to KTP for easier, periodic poling, (4) to investigate the physical mechanisms responsible for optical damage in KTP. The work shows that the in-situ SHG technique used together with electro-optic monitoring, makes it possible to obtain reliable, real-time information regarding the poling quality over the whole crystal aperture during the electric-field poling process. Using this combined monitoring method, both KTP and Rb-doped KTP (RKTP) crystals were successfully poled. By comparing these two crystals, we found that a low-doped KTP has a substantially reduced ionic conductivity and, thus, a high-quality periodic poling can be obtained without otherwise affecting the properties of the crystal. RKTP is a good alternative candidate to KTP for poling purpose. We have also shown that Atomic Force Microscopy (AFM) is an informative tool for investigating domain nucleation, growth, and merging. Furthermore, we have demonstrated a simple technique for 3D characterization of QPM samples. It utilizes a group-velocity mismatched, type-II SHG of femtosecond pulses for layer-by-layer monitoring of the effective nonlinearity along the propagation direction of the beam. The quality of these crystals was finally reflected in a number of SHG experiments with a variety of laser sources. High energies and high efficiencies were thus demonstrated using CW, mode-locked and Q-switched lasers. Gratings with pitches smaller than 3 µm, were demonstrated for first-order UV generation. Type-II QPM SHG was demonstrated as a technique for reducing the fabrication constraints.

High intensity light in the visible and the UV leads to modification of the material properties and, eventually, to optical damage. In KTP and its isomorphs, the first sign of material change is an optically-induced absorption. We have used thermal-lens spectroscopy with a common-path interferometer for high-sensitivity measurements of green light-induced infrared absorption dynamics in single-domain and periodically-poled KTP (PPKTP). The saturated, green light-induced absorption has been shown to be consistently higher in periodically-poled crystals, and is attributed to the creation of stoichiometric and interstitial defects in the crystals during the poling process. Finally, irreversible bulk damage thresholds in PPKTP have been determined for pulsed frequency converters. As the characteristics of optical damage are closely related to the material quality, this investigation can provide useful information for crystal manufactures and will help to optimise the crystal growth conditions.

Series
Trita-FYS, ISSN 0280-316X ; 2005:50
Keyword
Nonlinear optics, second-harmonic generation, quasi-phasematching, type-I QPM SHG, type-II QPM SHG, KTP, RKTP, periodic electric-field poling
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-483 (URN)91-7178-153-6 (ISBN)
Public defence
2005-11-25, Sal FB53, AlbaNova, Roslagstullsbacken 21, Stockholm, 10:00
Opponent
Supervisors
Available from: 2005-11-09 Created: 2005-11-09 Last updated: 2012-03-22
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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