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Periodically poled KTiOAsO4 for highly efficient midinfrared optical parametric devices
KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.ORCID iD: 0000-0001-8764-3372
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
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2009 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 95, no 19Article in journal (Refereed) Published
Abstract [en]

We demonstrate high pattern-fidelity periodic poling of KTiOAsO4 at room temperature. The periodically poled crystal shows a d(eff) of 10.1 pm/V and is used in an optical parametric oscillator pumped at 1064 nm to generate parametric radiation at 1538 and 3452 nm with a conversion efficiency of 45%.

Place, publisher, year, edition, pages
2009. Vol. 95, no 19
Keyword [en]
aperture, ktiopo4, crystals, energy, oscillation, generation, ktp
National Category
Other Physics Topics
Identifiers
URN: urn:nbn:se:kth:diva-19047DOI: 10.1063/1.3258001ISI: 000272756600088Scopus ID: 2-s2.0-70449725114OAI: oai:DiVA.org:kth-19047DiVA: diva2:337094
Note

QC 20100525

Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
In thesis
1. QPM Devices in KTA and RKTP
Open this publication in new window or tab >>QPM Devices in KTA and RKTP
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Even though KTiOPO4 (KTP) is considered to be one of the best nonlinear materials for quasi phase matched (QPM) frequency conversion in the visible and the near-infrared spectral regions, its use is often limited by poor material homogeneity, high ionic conductivity, a considerable linear absorption and photochromatic damage. On the other hand, the improved material homogeneity and the lower ionic conductivity of bulk Rb-doped KTP (RKTP) make this material an ideal alternative for fabrication of fine-pitch QPM gratings, while the arsenate isomorph KTiOAsO4 (KTA) promises a better performance in the green spectral region and adds the advantage of a wider transparency window in the infrared. Unfortunately, the available studies on these materials are limited and unable to answer the question whether RKTP and KTA are feasible alternatives to KTP in terms of periodic poling and optical performance. The optical performance of the QPM devices depends on the periodic poling quality, therefore, a detailed comprehension of domain-grating formation in the KTP isomorphs is highly desired. The goals of this thesis were to gain a better understanding of the periodic poling process in the KTP isomorphs, in order to study the specifics of ferroelectric domain engineering in KTA and RKTP, and to evaluate the optical performance of these isomorphs. Fine-pitch periodically poled structures were engineered both in KTA and RKTP crystals. It was demonstrated that QPM gratings with excellent quality and with periods as short as 8.49 μm can be fabricated in KTA crystals. Comparative transmission studies have shown that periodically poled KTA (PPKTA) crystals can be superior to KTP for QPM second harmonic generation in the visible spectral region due to lower linear absorption. It was also demonstrated that RKTP is a superior alternative to KTP for high-quality QPM grating fabrication. A consistent room-temperature periodic poling of 5 mm thick RKTP crystals with a period of 38.86 μm has been achieved. The obtained large aperture periodically poled RKTP (PPRKTP) crystals showed an outstanding QPM grating uniformity and excellent optical performance in optical parametric oscillator (OPO) applications. Moreover, it was shown that RKTP is less susceptible to blue-induced infrared absorption than KTP. Finally, a novel and a relatively simple method for self-assembling quasi-periodic sub-μm scale ferroelectric domain structure in RKTP crystals has been presented. It was shown that, after treatment in aqueous KOH/KNO3 solution, periodic poling of RKTP with planar electrodes resulted in one-dimensional ferroelectric domain structure with an average periodicity of 650±200 nm, extending over the whole 1 mm thick crystal. Such self-assembled structures in RKTP were used to demonstrate 5th order non-collinear QPM backward second harmonic generation.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2014. xiv, 98 p.
Series
TRITA-FYS, ISSN 0280-316X ; 2013:71
Keyword
QPM, periodic poling, KTP
National Category
Other Materials Engineering Other Physics Topics
Identifiers
urn:nbn:se:kth:diva-139475 (URN)978-91-7501-974-1 (ISBN)
Public defence
2014-01-31, sal FB52, AlbaNova Universitetscentrum, Roslagstullsbacken 21, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20140114

Available from: 2014-01-14 Created: 2014-01-13 Last updated: 2014-01-14Bibliographically 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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