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High-power, single-frequency, continuous-waveoptical parametric oscillator employing avariable reflectivity volume Bragg grating
KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.ORCID iD: 0000-0001-7231-5181
KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics. (Laser Physics)
KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
2014 (English)In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 22, no 24, 29907-29913 p.Article in journal (Refereed) Published
Abstract [en]

A continuous-wave singly-resonant optical parametric oscillator (SRO) with an optimum extraction efficiency, that can be adjusted independent of the pump power, is demonstrated. The scheme employs a variable-reflectivity volume Bragg grating (VBG) as the output coupler of a ring cavity, omitting any additional intra-cavity elements. In this configuration, we obtained a 75%-efficient SRO with a combined signal (19 W @ 1.55 mu m) and idler (11 W @ 3.4 mu m) output power of 30 W.

Place, publisher, year, edition, pages
2014. Vol. 22, no 24, 29907-29913 p.
Keyword [en]
Optical parametric oscillators, Reflection, Continuous waves, Extraction efficiencies, Intracavities, Output couplers, Single-frequency, Singly-resonant optical parametric oscillators, Volume bragg grating (VBG), Volume Bragg gratings
National Category
Atom and Molecular Physics and Optics
Research subject
Physics
Identifiers
URN: urn:nbn:se:kth:diva-156407DOI: 10.1364/OE.22.029907ISI: 000345770500058Scopus ID: 2-s2.0-84914691669OAI: oai:DiVA.org:kth-156407DiVA: diva2:766608
Funder
Swedish Research Council
Note

QC 20141203

Available from: 2014-11-27 Created: 2014-11-27 Last updated: 2017-12-05Bibliographically approved
In thesis
1. 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
2. Tailored fiber lasers and their use in nonlinear optics
Open this publication in new window or tab >>Tailored fiber lasers and their use in nonlinear optics
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The objective of this thesis work was to develop tailored fiber lasers, which meet the pump requirement for efficient continuous-wave (cw) frequency conversion to the visible and the mid-infrared wavelength regimes: a stable, high-power, wavelength-tunable, narrow-linewidth output in a single polarization. As a first step, the prospect of tuning ytterbium fiber lasers over an unprecedented wavelength range, from 980nm to 1100nm, was investigated. The results further substantiate the enormous potential of fiber lasers to act as widely tunable pump sources for nonlinear frequency conversion schemes, allowing the design of coherent light sources in large parts of the optical spectrum. Subsequently, a method of flexible wavelength-tuning and -locking for high-power fiber oscillators was demonstrated, incorporating the use of a highly reflective transversely-chirped volume Bragg grating as cavity mirror. Through a simple lateral translation of the grating, continuous wavelength-tuning over 2.5 THz was achieved without sacrificing efficiency, spectral or spatial beam quality. As the latter free-space laser architecture relied on an intra-cavity polarization filter to ensure a linearly polarized output state, the filtered orthogonal polarization state was available for a secondary laser oscillation. Following this basic design idea, a high-power dual-wavelength laser with a tunable wavelength separation of up to 2 THz was demonstrated. With both signals separated in wavelength and polarization, gain competition was effectively suppressed and the presented source possessed the necessary stability for potential use in power-demanding applications such as difference frequency generation of cw THz radiation. After establishing a flexible and reliable fiber pump source, continuous-wave, quasi-phase matched, second harmonic generation experiments were performed on several crystals from the KTiOPO4 family. The power scaling limitations of these materials, when generating high-power signals in the visible spectral range were studied. Although, a conclusive identication of the optimal KTiOPO4 isomorph for this process was hindered due to varying crystal quality from different vendors, comparative transmission studies suggest that the arsenate isomorph, KTiOAsO4, could be best suited by virtue of its low linear absorption in the visible region. Finally, a singly-resonant optical parametric oscillator, pumped by the above narrowband fiber laser source, efficiently generated 11W of mid-infrared radiation at 3.4 µm and 19W single-frequency radiation at 1.55 µm. Stable, high-power operation of this parametric source was facilitated by a novel method of controlling the intra-cavity signal power using a volume Bragg grating with variable reectivity.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. xiii, 87 p.
Series
TRITA-FYS, ISSN 0280-316X ; 2015:61
National Category
Atom and Molecular Physics and Optics
Research subject
Physics
Identifiers
urn:nbn:se:kth:diva-172976 (URN)978-91-7595-668-8 (ISBN)
Public defence
2015-09-25, Sal FB52, AlbaNova Universitetscentrum, Roslagstullsbacken 21, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20150904

Available from: 2015-09-04 Created: 2015-09-04 Last updated: 2015-09-04Bibliographically approved

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