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Nonlinear refractive indices in Yb3+-doped and undoped monoclinic double tungstates KRE(WO4)(2) where RE=Gd, Y, Yb, Lu
KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.ORCID iD: 0000-0001-8764-3372
KTH, School of Engineering Sciences (SCI), Applied Physics.
KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.ORCID iD: 0000-0002-2508-391X
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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.

Place, publisher, year, edition, pages
2009. Vol. 96, no 2-3, 385-392 p.
Keyword [en]
single-crystals, laser crystals, continuous-wave, diode bars, kyw, laser, kgw laser, z-scan, growth, polarizability, klu(wo4)(2)
Identifiers
URN: urn:nbn:se:kth:diva-18594DOI: 10.1007/s00340-009-3487-yISI: 000267885000023Scopus ID: 2-s2.0-67650809908OAI: oai:DiVA.org:kth-18594DiVA: diva2:336641
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Nonlinear response in engineered optical materials
Open this publication in new window or tab >>Nonlinear response in engineered optical materials
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
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:nbn:se:kth:diva-92221 (URN)978-91-7501-295-7 (ISBN)
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
2. Highly efficient optical parametric oscillators in the mid-IR
Open this publication in new window or tab >>Highly efficient optical parametric oscillators in the mid-IR
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis shows how sources of coherent radiation in the mid-infrared (mid-IR) region can be enhanced. To achieve this, optical parametric oscillators (OPOs) employing improved novel materials, new optical elements, and novel cavity designs have been implemented. Moreover, important measurements for the development of ultrashort-pulsed lasers were conducted. In turn, such lasers are suitable pump sources for the nonlinear conversion to the mid-IR.

The mid-infrared spectral region is of interest for many applications in the areas of medicine, sensing, climate monitoring, and ranging. Here the target wavelength 6.45μm was especially interesting since it is considered particularly useful in surgical applications. Commercially available lasers perform poorly as pump sources for the generation of this wavelength. Therefore, a superior cascaded conversion scheme with large aperture crystals was implemented. In these, Rb-doped KTiOPO4(KTP) was employed since it was found that Rb-doping improves the poling properties of KTP. Moreover, for the conversion scheme to be efficient, a narrow-band out putspectrum of the OPO is required. It was shown here that this can successfully be achieved by utilizing a volume Bragg grating (VBG).

Alternatively, for the direct generation of mid-IR radiation, KTiOAsO4(KTA) crystals with an extended transmission into the mid-IR as compared to KTP have been investigated. Novel room-temperature periodic-poling of KTA was shown and the fabricated crystals were successfully employed in a highly-efficient OPO.

The newly developed pump sources based on the Rb-doped KTP crystals were successfully implemented in a cascaded OPO experiment. Here, a so-called RISTRA cavity was employed and high-energy nanosecond pulses at 6.45μm with improved beam quality were demonstrated.

Pulsed lasers emitting at around 1μm, e.g. Yb-doped host materials, are frequently employed as pump sources of nonlinear optical conversion schemes. To allow further development of ultrashort pulsed Yb-doped double tungstate lasers, the nonlinear refractive index of several materials was measured. Among these are new materials which were for the first time characterized with regard to their nonlinear refractive index.

In addition to the pulsed experiments above, a periodically poled lithium niobate crystal was employed to generate continuous-wave output. Even here, a volume Bragg grating was implemented and thereby demonstrated a novel method to control the threshold of the OPO. Thus, a stable high-energy highly-efficient OPO could be demonstrated.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. xiii, 69 p.
Series
TRITA-FYS, ISSN 0280-316X
National Category
Atom and Molecular Physics and Optics
Research subject
Physics
Identifiers
urn:nbn:se:kth:diva-156714 (URN)978-91-7595-366-3 (ISBN)
Public defence
2014-12-19, FB 53, Roslagstullsbacken, AlbaNova, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20141203

Available from: 2014-12-03 Created: 2014-12-02 Last updated: 2015-03-30Bibliographically approved

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Thilmann, NickyPasiskevicius, Valdas

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