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Mode spectrum of multi-longitudinal mode pumped near-degenerate OPOs with volume Bragg grating output couplers
KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
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
2009 (English)In: Optics Express, ISSN 1094-4087, Vol. 17, no 20, 17582-17589 p.Article in journal (Refereed) Published
Abstract [en]

Spectral requirements for the first stage OPO used to pump a tandem ZGP mid-infrared OPO are theoretically investigated. Based on these requirements we demonstrate a singly-resonant type-I OPO including periodically poled KTiOPO4 and volume-Bragg gratings as output couplers. Singly resonant oscillation is demonstrated very close to degeneracy, where signal and idler spectra are not well separated. Investigations of the longitudinal mode spectrum and the idler spectrum with high resolution using a scanning Fabry-Perot interferometer show the essential role played by the phase correlations of the multi-longitudinal mode Q-switched pump laser in formation of the nonresonant idler spectrum.

Place, publisher, year, edition, pages
2009. Vol. 17, no 20, 17582-17589 p.
Keyword [en]
Volume gratings ; Parametric oscillators and amplifiers
URN: urn:nbn:se:kth:diva-12861ISI: 000270295300036ScopusID: 2-s2.0-70349679288OAI: diva2:319372
EU, FP7, Seventh Framework Programme, 224042
QC 100517Available from: 2010-05-17 Created: 2010-05-17 Last updated: 2015-03-30Bibliographically approved
In thesis
1. Tandem optical parametric oscillators using volume Bragg grating spectral control
Open this publication in new window or tab >>Tandem optical parametric oscillators using volume Bragg grating spectral control
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis describes research on near degenerate quasi phase-matched opticalparametric oscillators (OPO) where volume Bragg gratings (VBG) are used toproduce narrow oscillation bandwidth. These OPOs are then used to pump a secondOPO to generate mid-infrared radiation.

The atmospheric transmission windows in the 3.5 to 5 μm wavelength region areused for seekers on infrared homing missiles. These missiles are available to guerrillaand terrorist groups and have been used in a number of attacks on military and civilianaircraft. Laser sources at the same wavelengths are an important component incountermeasure systems for aircraft self-protection. Similar laser sources also haveapplications in laser surgery.

At wavelengths longer than 4 μm crystal materials for multi-Watt level averagepower nonlinear devices is a problem. The best solution so far is to use ZnGeP2(ZGP). ZGP and the available alternatives all have a problem of near-infraredabsorption, and a mid-infrared OPO thus has to use a pump wavelength near 2 μm.This pump source can be a neodymium laser at 1.06 μm with a near degenerate OPO.

Nonlinear devices for low to medium pulse energies are dominated by quasi phasematchedmaterials because of their higher effective nonlinearities and lack of walkoff.In addition they allow type I interaction where signal and idler from the OPOhave the same polarization, which has the advantage that both waves can be used topump the ZGP OPO. The drawback of this is that the near-degenerate interaction hasvery wide gain bandwidth. Efficient pumping of the second OPO demands narrowbandwidth output from the first OPO.Volume Bragg gratings that are glass materials with a periodic refractive indexmodulation have emerged as high quality narrow bandwidth reflectors. By using aVBG as one cavity mirror in an OPO the feedback bandwidth and hence the OPOoscillation bandwidth can be kept very narrow. Signal and idler bandwidths of 10 and20 GHz (FWHM) at 2122 and 2135 nm, respectively, have been demonstrated. Thisshould be compared to the several hundred nanometre bandwidth from an OPO usingdielectric mirrors. Very narrow bandwidth operation has been achieved so close todegeneracy that the signal and idler are not resolvable.

The total output energy generated in the PPKTP OPO (signal and idler together)has been used to pump a ZGP OPO that produced mid-IR radiation. Tuning of thesignal from a ZGP OPO from 2.9 μm to degeneracy at 4.3 μm has been shown, with acorresponding idler wavelength tuneable up to 8 μm. The highest conversionefficiency that has been reached from 1.06 μm to the mid-IR was 12 %. This setupused a PPKTP OPO with 30 % conversion efficiency and 13 nm separation of signaland idler (2122 and 2135 nm). The pulse repetition frequency was 20 kHz and thegenerated output power in the mid-IR was 3.2 W.

Place, publisher, year, edition, pages
Stockholm: KTH, 2010. xii; 54 p.
Trita-FYS, ISSN 0280-316X ; 21
optical parametric oscillators, mid-infrared, volume Bragg gratings, PPKTP, ZGP, nonlinear optics, narrowband OPO
National Category
Physical Sciences
urn:nbn:se:kth:diva-12864 (URN)978-91-7415-626-3 (ISBN)
Public defence
2010-06-04, Sal FA32, AlbaNova, Roslagstullsbacken 21, Stockholm, 16:00 (English)
QC 20100517Available from: 2010-05-17 Created: 2010-05-17 Last updated: 2010-11-08Bibliographically approved

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