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Nonlinear response in engineered optical materials
KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Material and structure engineering are increasingly employed in active optical media,in this context defined as media capable of providing laser or/and optical parametric gain. For laser materials, the main aim of the engineering is to tailor the absorption and emission cross sections in order to optimise the laser performance. At the same time, the engineering also results in a collateral modification of the material’s nonlinear response. In the first part of this work, the nonlinear index of refraction is characterised for two crystallographic forms of laser-ion doped and undoped double-tungstate crystals. These laser crystals have broad gain bandwidths, in particular when doped with Yb3+. As shown in this work, the crystals also have large Kerr nonlinearities, where the values vary significantly for different chemical compositions of the crystals. The combination of a broad gain bandwidthand a high Kerr nonlinearity makes the laser-ion doped double tungstates excellent candidates to employ for the generation of ultrashort laser pulses by Kerr-lens modelocking. The second part of the work relates to the applications of engineered second-order nonlinear media, which here in particular are periodically-poled KTiOPO4 crystals. Periodic structure engineering of second-order nonlinear crystals on a submicrometre scale opens up for the realisation of novel nonlinear devices. By the use of quasi-phase matching in these structures, it is possible to efficiently downconvert a pump wave into two counterpropagating parametric waves, which leads to a device called a mirrorless optical parametric oscillator. The nonlinear response in these engineered submicrometre structures is such that the parametric wave that propagates in the opposite direction of the pump automatically has a narrow bandwidth, whereas the parametric wave that propagates with the pump essentially is a frequency-shifted replica of the pump wave. The unusual spectral properties andthe tunabilities of mirrorless optical parametric oscillators are investigated.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. , xii, 98 p.
Series
Trita-FYS, ISSN 0280-316X ; 2012:13
Keyword [en]
nonlinear optics, nonlinear index of refraction, double tungstates, periodic poling, KTiOPO4, quasi-phase matching, parametric down-conversion, mirrorless optical parametric oscillators
National Category
Atom and Molecular Physics and Optics
Identifiers
URN: urn:nbn:se:kth:diva-92221ISBN: 978-91-7501-295-7 (print)OAI: oai:DiVA.org:kth-92221DiVA: diva2:512774
Public defence
2012-04-27, FD5, Albanova, Roslagstullsbacke 21, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20120330Available from: 2012-03-30 Created: 2012-03-29 Last updated: 2012-03-30Bibliographically approved
List of papers
1. Nonlinear refractive indices of disordered NaT(XO4)(2) T=Y, La, Gd, Lu and Bi, X=Mo, W femtosecond laser crystals
Open this publication in new window or tab >>Nonlinear refractive indices of disordered NaT(XO4)(2) T=Y, La, Gd, Lu and Bi, X=Mo, W femtosecond laser crystals
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2008 (English)In: Applied physics. B, Lasers and optics (Print), ISSN 0946-2171, E-ISSN 1432-0649, Vol. 91, no 3-4, 507-510 p.Article in journal (Refereed) Published
Abstract [en]

The nonlinear refractive index (n(2)) of several NaT(WO4)(2) (T = Y, La, Gd, Lu and Bi) and NaY(MoO4)(2) femtosecond laser crystals has been measured using the z-scan technique. These tetragonal crystals with structural local disorder present significant n(2) values, which should allow their efficient laser pulsed operation by Kerr-lens mode locking, especially NaBi(WO4)(2), 68x10(-16) cm(2)/W (for sigma light), which is about twice than for the others. This difference is attributed to the high polarizability associated with the lone electron pair of Bi3+.

Keyword
z-scan measurements, ti-sapphire laser, lens mode-locking, raman-scattering, local disorder, operation, spectroscopy, efficient, hosts, power
Identifiers
urn:nbn:se:kth:diva-17568 (URN)10.1007/s00340-008-3041-3 (DOI)000256251400019 ()2-s2.0-44449098647 (Scopus ID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2012-03-30Bibliographically approved
2. Nonlinear refractive indices in Yb3+-doped and undoped monoclinic double tungstates KRE(WO4)(2) where RE=Gd, Y, Yb, Lu
Open this publication in new window or tab >>Nonlinear refractive indices in Yb3+-doped and undoped monoclinic double tungstates KRE(WO4)(2) where RE=Gd, Y, Yb, Lu
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2009 (English)In: Applied physics. B, Lasers and optics (Print), ISSN 0946-2171, E-ISSN 1432-0649, Vol. 96, no 2-3, 385-392 p.Article in journal (Refereed) Published
Abstract [en]

The linear absorption bandgap in the ultraviolet and the nonlinear index n (2) in near infrared were systematically measured in undoped and Yb3+-doped top-seeded solution-grown monoclinic double-tungstate KRE(WO4)(2) (RE=Gd, Y, Yb, Lu) crystals. Anisotropic n (2) nonlinear indices have been determined for EaEuro-N (m) and EaEuro-N (p) polarizations with the maximum nonlinear index n (2) observed for the light polarized EaEuro-N (m). Moreover, the value of the nonlinear response of particular crystals in this family is proportional to the ionic radius of the RE3+ ion.

Keyword
single-crystals, laser crystals, continuous-wave, diode bars, kyw, laser, kgw laser, z-scan, growth, polarizability, klu(wo4)(2)
Identifiers
urn:nbn:se:kth:diva-18594 (URN)10.1007/s00340-009-3487-y (DOI)000267885000023 ()2-s2.0-67650809908 (Scopus ID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2014-12-03Bibliographically approved
3. Fabrication of submicrometer quasi-phase-matched devices in KTP and RKTP [Invited]
Open this publication in new window or tab >>Fabrication of submicrometer quasi-phase-matched devices in KTP and RKTP [Invited]
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2011 (English)In: Optical Materials Express, ISSN 2159-3930, Vol. 1, no 7, 1319-1325 p.Article in journal (Refereed) Published
Abstract [en]

We review the techniques used for fabrication of bulk submicrometer ferroelectric domain gratings in KTiOPO4 (KTP) and demonstrate that bulk Rb-doped KTiOPO4 (RKTP) is an excellent candidate for implementation of dense domain gratings. Compared to KTP, RKTP presents predominant domain propagation along the polar c-direction, substantially reduced lateral domain broadening, and higher poling yield. As a result we obtain homogeneous sub-μm periodic poling of RKTP with a period of 690 nm in 1 mm thick samples.

Place, publisher, year, edition, pages
Optical Society of America, 2011
Keyword
Ferroelectrics, nonlinear optics, parametric processes
National Category
Atom and Molecular Physics and Optics Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-51093 (URN)000299049200019 ()2-s2.0-80755172823 (Scopus ID)
Funder
Swedish Research Council
Note
QC 20111209Available from: 2011-12-09 Created: 2011-12-09 Last updated: 2015-03-30Bibliographically approved
4. Self-established noncollinear oscillation and angular tuning in a quasi-phase-matched mirrorless optical parametric oscillator
Open this publication in new window or tab >>Self-established noncollinear oscillation and angular tuning in a quasi-phase-matched mirrorless optical parametric oscillator
2011 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 98, no 5, 051108- p.Article in journal (Refereed) Published
Abstract [en]

We experimentally demonstrate self-established noncollinear interactions in a quasi-phase-matched mirrorless optical parametric oscillator using a periodically-poled KTiOPO4 crystal with submicrometer periodicity. It is shown that the oscillation is established in a very specific geometric configuration where the two possible solutions of the energy and momentum conservation conditions become spatially degenerate and contribute coherently to the gain. In this configuration, the signal and the idler remain mutually counter-propagating. The tuning capabilities of a noncollinear mirrorless optical parametric oscillator are investigated. (c) 2011 American Institute of Physics.

Keyword
PERIODICALLY POLED KTIOPO4, FLUX-GROWN KTIOPO4, GENERATION
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-32033 (URN)10.1063/1.3551526 (DOI)000286988400008 ()2-s2.0-79951492432 (Scopus ID)
Note
QC 20110405Available from: 2011-04-05 Created: 2011-04-04 Last updated: 2012-03-30Bibliographically approved
5. Coherent phase-modulation transfer in counterpropagating parametric down-conversion
Open this publication in new window or tab >>Coherent phase-modulation transfer in counterpropagating parametric down-conversion
2011 (English)In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 84, no 2Article in journal (Refereed) Published
Abstract [en]

Distributed positive feedback established by a counterpropagating three-wave mixing process in a submicrometer structured second-order nonlinear medium leads to mirrorless parametric oscillation with unusual spectral properties. In this work, we demonstrate experimentally and theoretically that the phase modulation of the pump is coherently transferred to the co-propagating parametric wave, while the counterpropagating wave retains a narrow bandwidth and high coherence. The main mechanisms responsible for these properties are the maximized convective separation between the counterpropagating waves and the associated phase-locking between the pump and the co-propagating parametric wave. This suggests that mirrorless optical parametric oscillators can be pumped with incoherent light and still generate highly coherent backward-propagating radiation.

Keyword
RESONANT INTERACTIONS, WAVES, OSCILLATOR, LIGHT
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-39020 (URN)10.1103/PhysRevA.84.023825 (DOI)000293917200021 ()2-s2.0-84860389594 (Scopus ID)
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation
Available from: 2011-09-06 Created: 2011-09-06 Last updated: 2017-12-08Bibliographically approved
6. Temporal coherence in mirrorless optical parametric oscillators
Open this publication in new window or tab >>Temporal coherence in mirrorless optical parametric oscillators
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2012 (English)In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 29, no 6, 1194-1202 p.Article in journal (Refereed) Published
Abstract [en]

One of the unique features of mirrorless optical parametric oscillators based on counterpropagating three-wave interactions is the narrow spectral width of the wave generated in the backward direction. In this work, we investigate experimentally and numerically the influence that a strong phase modulation in the pump has on the spectral bandwidths of the parametric waves and on the efficiency of the nonlinear interaction. The effects of group-velocity mismatch and group-velocity dispersion are elucidated. In particular, it is shown that the substantial increase in temporal coherence of the backward-generated wave can be obtained even for pumping with a temporally incoherent pump. A configuration of a mirrorless optical parametric oscillator is proposed where this gain in spectral coherence is maximized without a penalty in conversion efficiency by employing group-velocity matching of the pump and the forward-generated parametric wave.

Keyword
Counterpropagating, Group velocities, Group-velocity mismatch, Incoherent pump, Nonlinear interactions, Parametric waves, Spectral bandwidth, Spectral coherence, Spectral widths, Temporal coherence, Three-wave interactions, Unique features, Conversion efficiency, Phase modulation
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-92274 (URN)10.1364/JOSAB.29.001194 (DOI)000305029900008 ()2-s2.0-84861809132 (Scopus ID)
Funder
Swedish Research Council
Note

QC 20120702

Available from: 2012-03-30 Created: 2012-03-30 Last updated: 2017-12-07Bibliographically approved

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