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Fabrication and characterization of periodically poled KTB and RB-doped KTB for applications in the visible and UV
KTH, School of Engineering Sciences (SCI), Physics.
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.

Place, publisher, year, edition, pages
2005.
Series
Trita-FYS, ISSN 0280-316X ; 2005:50
Keyword [en]
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: urn:nbn:se:kth:diva-483ISBN: 91-7178-153-6 (print)OAI: oai:DiVA.org:kth-483DiVA: diva2:14170
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
List of papers
1. Efficient Nd: YAG laser frequency doubling with periodically poled KTP
Open this publication in new window or tab >>Efficient Nd: YAG laser frequency doubling with periodically poled KTP
Show others...
1998 (English)In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 37, no 30, 7116-7119 p.Article in journal (Refereed) Published
Abstract [en]

Periodically poled flux-grown KTiOPO4 was used for efficient extracavity 1064-nm Nd:YAG laser frequency doubling. A conversion efficiency exceeding 65% was obtained in Q-switched operation, and 1.34 W of average frequency-doubled power was generated with 2.2 W of mode-locked laser output. The conversion efficiency is approximately two times higher for periodically poled KTP than for conventional type II phase-matched KTP. The measurements indicate that periodically poled KTP is less susceptible to optical damage than type II KTP.

Place, publisher, year, edition, pages
Optical Society of America, 1998
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-8753 (URN)10.1364/AO.37.007116 (DOI)
Note
QC 20111007Available from: 2005-11-09 Created: 2005-11-09 Last updated: 2017-12-14Bibliographically approved
2. Ultraviolet generation by first-order frequency doubling in periodically poled KTiOPO4
Open this publication in new window or tab >>Ultraviolet generation by first-order frequency doubling in periodically poled KTiOPO4
1998 (English)In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 23, no 24, 1883-1885 p.Article in journal (Refereed) Published
Abstract [en]

First-order quasi-phase-matched frequency doubling at 780 nm in a 1-mm-thick periodically poled KTiOPO4 crystal with an inverted-domain period of 2.95 mu m has been demonstrated for the first time to the authors' knowledge. A normalized conversion efficiency of 1.1% W-1 cm(-1) has been obtained in cw mode. Experiments show that group-velocity walk-off prevents efficient frequency doubling of femtosecond pulses in KTiOPO4 in the UV spectral range. However, because of the large optical nonlinearity, periodically poled structures can be efficiently used for frequency doubling of cw and pulsed lasers with pulse lengths as short as similar to 1 ps.

National Category
Other Physics Topics
Identifiers
urn:nbn:se:kth:diva-8754 (URN)10.1364/OL.23.001883 (DOI)000077500600005 ()2-s2.0-0002024930 (Scopus ID)
Note

QC 20140219

Available from: 2005-11-09 Created: 2005-11-09 Last updated: 2017-12-14Bibliographically approved
3. First-order type II quasi-phase-matched UV generation in periodically poled KTP
Open this publication in new window or tab >>First-order type II quasi-phase-matched UV generation in periodically poled KTP
1999 In: Optic letters, Vol. 24, no 14, 978- p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:kth:diva-8755 (URN)
Available from: 2005-11-09 Created: 2005-11-09Bibliographically approved
4. Three-dimensional characterization of the effective second-order nonlinearity in periodically poled crystals
Open this publication in new window or tab >>Three-dimensional characterization of the effective second-order nonlinearity in periodically poled crystals
2003 (English)In: Optic letters, ISSN 0146-9592, Vol. 28, no 17, 1555-1557 p.Article in journal (Refereed) Published
Abstract [en]

A novel technique for characterization of the second-order nonlinearity in nonlinear crystals is presented. It utilizes group-velocity walk-off between femtosecond pulses in type II SHG to achieve three-dimensional resolution of the nonlinearity. The longitudinal and transversal spatial resolution can be set independently. The technique is especially useful for characterizing quasi-phase-matched nonlinear crystals, and it is demonstrated in potassium titanyl phosphate.

National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-8756 (URN)10.1364/OL.28.001555 (DOI)000184836900019 ()
Note
QC 20100830Available from: 2005-11-09 Created: 2005-11-09 Last updated: 2015-03-30Bibliographically approved
5. Dynamics of green light-induced infrared absorption in KTiOPO4 and periodically poled KTiOPO4
Open this publication in new window or tab >>Dynamics of green light-induced infrared absorption in KTiOPO4 and periodically poled KTiOPO4
2004 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 96, no 4, 2023-2028 p.Article in journal (Refereed) Published
Abstract [en]

Induced thermal-lens spectroscopy with a common-path interferometer has been used for high-sensitivity measurements of green-light induced absorption dynamics in single-domain and periodically poled KTiOPO4. Although the linear infrared absorption in both materials is the same, the saturated green-light induced absorption is consistently higher in periodically poled crystals. Initial relaxation of the induced absorption is also different in these materials where periodically poled KTP does not exhibit as fast initial relaxation characteristic as the single domain KTP. These differences in the absorption are explained by higher concentration of native defects associated with weakly bonded K+ ions, which stabilize electron and hole traps forming color centers in the material. Unannealed as-poled crystals also exhibit characteristic overshoot dynamics in the induced thermal lens signal, which signifies remnant stress in the domain walls. Investigations showed that the lattice vibration energy generated by the dissociation of induced color centers is sufficient for complete relaxation of this remaining stress. The sensitivity of the measurement technique is demonstrated by the measurement of small signal absorption in the blue spectral region arising during continuous wave quasi-phase-matched second harmonic generation in periodically poled KTP.

Keyword
flux-grown ktiopo4, gray tracks, high-power, ktp, laser, generation, radiation, crystals, nm
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-8757 (URN)10.1063/1.1738528 (DOI)000223055100038 ()2-s2.0-4344717095 (Scopus ID)
Note
QC 20110211Available from: 2005-11-09 Created: 2005-11-09 Last updated: 2017-12-14Bibliographically approved
6. Nucleation and growth of periodic domains during electric field poling in flux-grown KTiOPO4 observed by atomic force microscopy
Open this publication in new window or tab >>Nucleation and growth of periodic domains during electric field poling in flux-grown KTiOPO4 observed by atomic force microscopy
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.

Keyword
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:nbn:se:kth:diva-8758 (URN)10.1063/1.2166678 (DOI)000234757100049 ()2-s2.0-31144438683 (Scopus ID)
Note
QC 20100930. Uppdaterad från submitted till published (20100930).Available from: 2005-11-09 Created: 2005-11-09 Last updated: 2017-12-14Bibliographically approved
7. High efficiency periodically poled Rd-doped KTiOPO4 using in-situ monitoring
Open this publication in new window or tab >>High efficiency periodically poled Rd-doped KTiOPO4 using in-situ monitoring
2005 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550Article in journal (Other academic) Submitted
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-8759 (URN)
Note
QS 20120316Available from: 2005-11-09 Created: 2005-11-09 Last updated: 2017-12-14Bibliographically approved

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