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Highly efficient optical parametric oscillators in the mid-IR
KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.ORCID iD: 0000-0001-8764-3372
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: urn:nbn:se:kth:diva-156714ISBN: 978-91-7595-366-3 (print)OAI: oai:DiVA.org:kth-156714DiVA: diva2:767811
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
List of papers
1. 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
2. Periodically poled KTiOAsO4 for highly efficient midinfrared optical parametric devices
Open this publication in new window or tab >>Periodically poled KTiOAsO4 for highly efficient midinfrared optical parametric devices
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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%.

Keyword
aperture, ktiopo4, crystals, energy, oscillation, generation, ktp
National Category
Other Physics Topics
Identifiers
urn:nbn:se:kth:diva-19047 (URN)10.1063/1.3258001 (DOI)000272756600088 ()2-s2.0-70449725114 (Scopus ID)
Note

QC 20100525

Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2015-03-30Bibliographically approved
3. 5 mm thick periodically poled Rb-doped KTP for high energy optical parametric frequency conversion
Open this publication in new window or tab >>5 mm thick periodically poled Rb-doped KTP for high energy optical parametric frequency conversion
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2011 (English)In: Optical Materials Express, ISSN 2159-3930, Vol. 1, no 2, 201-206 p.Article in journal (Refereed) Published
Abstract [en]

A 5 mm thick periodically poled bulk Rb-doped KTiOPO4 (KTP) crystal with a period of 38.86 μm was fabricated by electric field poling. Chemical etching and optical evaluation show a high quality of the periodic ferroelectric domain structure through the whole crystal aperture. The fabricated quasi-phase matching (QPM) device was used in an optical parametric oscillator pumped at 1064 nm with 12 ns pulses at 100 Hz repetition rate to generate 60 mJ parametric radiation with a conversion efficiency of 50%.

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-51075 (URN)10.1364/OME.1.000201 (DOI)000299046900010 ()2-s2.0-84855248482 (Scopus ID)
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation
Note

QC 20111209

Available from: 2011-12-09 Created: 2011-12-09 Last updated: 2015-03-30Bibliographically approved
4. A narrowband optical parametric oscillator tunable over 6.8 THz through degeneracy with a transversely-chirped volume Bragg grating
Open this publication in new window or tab >>A narrowband optical parametric oscillator tunable over 6.8 THz through degeneracy with a transversely-chirped volume Bragg grating
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2011 (English)In: Applied physics. B, Lasers and optics (Print), ISSN 0946-2171, E-ISSN 1432-0649, Vol. 105, no 2, 239-244 p.Article in journal (Refereed) Published
Abstract [en]

An efficient nanosecond optical parametric oscillator (OPO) with output energies of 0.75 mJ using a periodically poled KTiOPO(4) crystal pumped at 532 nm and generating narrowband output continuously tunable over the range of 6.8 THz, between 1053 nm and 1075 nm, is demonstrated by employing a transversely-chirped volume Bragg grating. The tunable reflectivity spectrum of the chirped volume Bragg grating allowed a smooth transition between singly-resonant and doubly-resonant operation of the OPO without cavity rearrangement. This gave a unique possibility to experimentally verify theoretical predictions regarding the efficiency of type-I and type-0 phase matched degenerate OPOs pumped by multimode Q-switched lasers.

National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-46841 (URN)10.1007/s00340-011-4686-x (DOI)000295938100010 ()2-s2.0-84855566884 (Scopus ID)
Funder
Knut and Alice Wallenberg FoundationSwedish Research CouncilEU, FP7, Seventh Framework Programme, FP7/2007-2011 224042
Note
QC 20111107Available from: 2011-11-07 Created: 2011-11-07 Last updated: 2017-12-08Bibliographically approved
5. Tunable Mid-infrared ZnGeP2 RISTRA OPO pumped by periodically-poled Rb:KTP optical parametric master-oscillator power amplifier
Open this publication in new window or tab >>Tunable Mid-infrared ZnGeP2 RISTRA OPO pumped by periodically-poled Rb:KTP optical parametric master-oscillator power amplifier
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2012 (English)In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 20, no 4, 4509-4517 p.Article in journal (Refereed) Published
Abstract [en]

A laser-diode pumped Q-switched single-frequency Nd:YAG MOPA operating at 100 Hz was used to generate tunable mid-infrared radiation between 6.27 µm and 8.12 µm by employing a cascaded parametric arrangement consisting of degenerate parametric master-oscillator power amplifier using a large aperture periodically-poled Rb:KTiOPO4 which in turn pumped a ZnGeP2 (ZGP) nonplanar RISTRA OPO. The noncollinear ZGP RISTRA tuning behavior is elucidated. The device is aimed for minimally invasive surgery applications at 6.45 µm where the peak power of 193 kW in 5 ns pulses is demonstrated.

National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-79485 (URN)10.1364/OE.20.004509 (DOI)000301041900116 ()2-s2.0-84857319219 (Scopus ID)
Projects
MIRSURG
Note
QC 20120507Available from: 2012-02-09 Created: 2012-02-09 Last updated: 2017-12-07Bibliographically approved
6. 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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