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Tailored fiber lasers and their use in nonlinear optics
KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.ORCID iD: 0000-0001-7231-5181
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: urn:nbn:se:kth:diva-172976ISBN: 978-91-7595-668-8 (print)OAI: oai:DiVA.org:kth-172976DiVA: diva2:851279
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
List of papers
1. On the tunability of a narrow-linewidth Yb-fiber laser from three- to four-level lasing behaviour
Open this publication in new window or tab >>On the tunability of a narrow-linewidth Yb-fiber laser from three- to four-level lasing behaviour
2011 (English)In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 19, no 15, 13940-13948 p.Article in journal (Refereed) Published
Abstract [en]

We report on a tunable multi-watt ytterbium-doped fiber laser bridging the gap from three-level lasing around 980 nm to true four-level lasing at 1100 nm. Wavelength-locking and -tuning was achieved by using an external volume-Bragg grating(VBG) as the cavity end mirror. The results are compared with detailed numerical calculations based on a spectrally resolved rate equation analysis, taking competing emission at other wavelengths into account.

Keyword
OPTICAL PARAMETRIC OSCILLATOR
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-37262 (URN)10.1364/OE.19.013940 (DOI)000292877600023 ()2-s2.0-79960542076 (Scopus ID)
Funder
Swedish Research Council
Note
QC 20110810Available from: 2011-08-10 Created: 2011-08-08 Last updated: 2017-12-08Bibliographically approved
2. Efficient spectral control and tuning of a high-power narrow-linewidth Yb-doped fiber laser using a transversely chirped volume Bragg grating
Open this publication in new window or tab >>Efficient spectral control and tuning of a high-power narrow-linewidth Yb-doped fiber laser using a transversely chirped volume Bragg grating
2013 (English)In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 21, no 4, 4027-4035 p.Article in journal (Refereed) Published
Abstract [en]

A transversely chirped volume Bragg grating (TCVBG) is used for flexible wavelength-tuning of a high-power (>100 W) tunable Yb-fiber laser oscillator. Continuous tuning over 2.5 THz of the narrow-band (13 GHz) signal was achieved by transversely translating the TCVBG during high-power operation without cavity realignment. The laser operated in a single polarization with a beam propagation factor (M-2) of 1.2. Since the cavity losses remained constant, the high gain fiber laser exhibited excellent power stability (<0.6% relative deviation) over the investigated tuning range. The possibility of considerably increasing the output power and extending the tuning range while maintaining the power stability is discussed.

Keyword
Operation
National Category
Other Physics Topics
Identifiers
urn:nbn:se:kth:diva-120554 (URN)10.1364/OE.21.004027 (DOI)000315992600010 ()2-s2.0-84874518025 (Scopus ID)
Funder
Swedish Research Council
Note

QC 20130415

Available from: 2013-04-15 Created: 2013-04-11 Last updated: 2017-12-06Bibliographically approved
3. Tunable, high-power, continuous-wave dual-polarization Yb-fiber oscillator
Open this publication in new window or tab >>Tunable, high-power, continuous-wave dual-polarization Yb-fiber oscillator
2015 (English)In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 23, no 13, 17450-17455 p.Article in journal (Refereed) Published
Abstract [en]

We demonstrate a high-power, dual-polarization Yb-fiber oscillator, by separately locking the two linear polarization states defined by slow and fast axis of a polarization-maintaining gain fiber with volume Bragg gratings. Dual-line lasing is achieved with a tunable wavelength separation from 0.03 to 2 THz, while exceeding output powers of 78 W over the entire tuning range, maintaining a high beam-quality with M-2<1.2. With this laser configuration we achieve a peak-to-peak power variation of <1% for the dual-line signal and <3% for the individual signals.

National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-172727 (URN)10.1364/OE.23.017450 (DOI)000358543300094 ()26191754 (PubMedID)
Funder
Swedish Research Council
Note

QC 20150828

Available from: 2015-08-28 Created: 2015-08-27 Last updated: 2017-12-04Bibliographically approved
4. High-power continuous-wave frequency-doubling in KTiOAsO4
Open this publication in new window or tab >>High-power continuous-wave frequency-doubling in KTiOAsO4
Show others...
2013 (English)In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 21, no 25, 30453-30459 p.Article in journal (Refereed) Published
Abstract [en]

High-power continuous-wave generation at 533 nm is demonstrated in bulk periodically poled KTiOAsO4 (KTA) by single-pass frequency doubling of a VBG-locked Yb-doped fiber laser. Absorption characteristic and second harmonic generation (SHG) performance of different KTA samples are studied and compared. The best performing sample catered for 25%-efficient SHG of 13.6 W green light with high spatial beam quality M2 &lt;1.2.

Keyword
Absorption characteristics, Continuous wave generation, Continuous waves, Frequency-doubling, Green light, Periodically poled, Spatial beam quality, Yb-doped fiber lasers
National Category
Other Physics Topics
Identifiers
urn:nbn:se:kth:diva-139426 (URN)10.1364/OE.21.030453 (DOI)000328575700031 ()2-s2.0-84890474072 (Scopus ID)
Funder
Swedish Research CouncilSwedish Foundation for Strategic Research
Note

QC 20140114

Available from: 2014-01-14 Created: 2014-01-13 Last updated: 2017-12-06Bibliographically approved
5. High-power, single-frequency, continuous-waveoptical parametric oscillator employing avariable reflectivity volume Bragg grating
Open this publication in new window or tab >>High-power, single-frequency, continuous-waveoptical parametric oscillator employing avariable reflectivity volume Bragg grating
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.

Keyword
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:nbn:se:kth:diva-156407 (URN)10.1364/OE.22.029907 (DOI)000345770500058 ()2-s2.0-84914691669 (Scopus ID)
Funder
Swedish Research Council
Note

QC 20141203

Available from: 2014-11-27 Created: 2014-11-27 Last updated: 2017-12-05Bibliographically approved

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