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- Coetzee, Riaan Stuart, et al.
(författare)
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Efficient Backward-Wave Optical Parametric Oscillator with 500 nm-periodicity PPRKTP
- 2018
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Ingår i: 2018 conference on lasers and electro-optics (CLEO). - : IEEE. - 9781943580422
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Konferensbidrag (refereegranskat)abstract
- Backward-wave OPO with forward mid-infrared idler and backward signal generation is demonstrated in 500-nm-periodicity PPRKTP. The output energy of 2.39mJ and efficiency of 46.4% is obtained. This design has potential for broad tunability in mid-infrared.
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- Coetzee, Riaan Stuart
(författare)
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Energy scaling of infrared nanosecond optical parametric oscillators and amplifiers based on Rb:KTiOPO4
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- High-energy, narrowband, nanosecond pulsed mid-infrared sources centred on 2 μm are requiredin applications in remote sensing, standoff detection and pollution monitoring using LIDARs.Currently, space-borne LIDAR missions are under development by major space agencies aroundthe world for active measurements of the atmospheric gas constituents and their dynamics. Thespectral range around 2 μm is one of the windows of operation for these instruments. Opticalparametric oscillators (OPOs) and amplifiers (OPAs) operating at 2 μm are often used as pumpsources for cascaded down-conversion schemes to enable generation of wavelengths deeper intothe mid-infrared. In order to fulfil these purposes, they are required to have high-energy outputwith good overall efficiency, while maintaining a narrowband or tailored spectrum. Moreover, forspace-based instruments, the radiation hardness of the parametric sources needs to be assessed.The central objectives of this thesis were the scaling of the energy and efficiency of 2 μm basedOPOs and OPAs, tailoring their spectral brightness and assessing their suitability for applicationsin space-borne active gas detection systems. Specifically, we investigated OPOs and OPAs basedon periodically-poled Rb:KTiOPO4 (PPRKTP), an engineered nonlinear material which can befabricated with large optical apertures and sub-μm periodicities. One of the key limitations toenergy scaling of these devices is the laser-induced damage threshold (LIDT) of the nonlinearmaterial used. In down-conversion schemes, the devices are subject to both high intensity 1 μmand 2 μm radiation. Prior to the work in this thesis, no LIDT value at 2 μm of KTP and Rb:KTPhad been reported. Furthermore, the work in this thesis provides data on effects of different dosageof gamma radiation on the optical properties of this material and the ways to mitigate the damageinduced by the ionizing radiation. To demonstrate energy scaling with narrow bandwidth andtunability, a nanosecond, master oscillator power amplifier (MOPA) system operating around 2μm and based on large-aperture PPRKTP was built. The MOPA system demonstrated dualnarrowband spectrum, tunable over 1.5 THz by means of a transversally chirped volume Bragggrating, while delivering tens of mJ in output. The output from this MOPA system will be furtherused for tunable THz generation. Even narrower spectra can be generated employing backwardwaveoptical parametric oscillators (BWOPO) based on PPRKTP with the periodicity of 509 nm.This work demonstrates for the first time an efficient, millijoule-level BWOPO with backwardpropagating signal. The device possessed narrowband spectrum with stable output, making it anexcellent seed source in MOPA arrangements.
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- Coetzee, Riaan Stuart, et al.
(författare)
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Low-threshold, mid-infrared backward-wave parametric oscillator with periodically poled Rb : KTP
- 2018
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Ingår i: APL Photonics. - : American Institute of Physics (AIP). - 2378-0967. ; 3:7
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Tidskriftsartikel (refereegranskat)abstract
- We report on the development of a nanosecond mirrorless optical parametric oscillator (OPO) pumped at 1 mu m. The gain medium of the OPO was periodically poled Rubidium-doped KTP with a grating period of Lambda = 509 nm for the first order quasi-phase matching. For grating periods of this length, we demonstrate backward propagation of the signal field and forward propagation of the idler field. To the best of our knowledge, this is the first time such a counter-propagating geometry has been demonstrated in mirrorless OPOs. Pumping with a maximum energy of 6.48 mJ, the OPO yielded an overall conversion efficiency exceeding 53% with signal and idler energies of 1.96 mJ and 1.46 mJ, respectively. The generated signal and idler field spectra were measured to show narrowband linewidths on the order of 0.5 nm. We motivate that such a MOPO is ideal for seeding applications and discuss further improvements and work.
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- Coetzee, Riaan Stuart, et al.
(författare)
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Narrowband, tunable, 2 A mu m optical parametric master-oscillator power amplifier with large-aperture periodically poled Rb:KTP
- 2018
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Ingår i: Applied physics. B, Lasers and optics (Print). - : SPRINGER. - 0946-2171 .- 1432-0649. ; 124:6
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Tidskriftsartikel (refereegranskat)abstract
- A high-energy, ns, narrow-linewidth optical parametric oscillator and amplifier system based on large-aperture periodically poled Rb:KTP is presented. The 2 A mu m seed source is a singly resonant OPO locked with a transversely chirped volume Bragg grating, allowing a wavelength tuning of 21 nm and output linewidth of 0.56 nm. A maximum output energy of 52 mJ and conversion efficiency of 36% was obtained from the amplifier for a pump energy of 140 mJ. The high-energy and the robust and narrow dual-wavelength spectra obtained make this system an ideal pump source for difference frequency generation-based THz generation schemes.
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- Pasiskevicius, Valdas, et al.
(författare)
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Spatial and Temporal Coherence in Optical Parametric Devices Pumped with Multimode Beams
- 2018
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Ingår i: Lithuanian Journal of Physics. - : Lithuanian Physical Soc. - 1648-8504 .- 2424-3647. ; 58:1, s. 62-75
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the emergence of spatial and temporal coherence for the fields in the noncritical nondegenerate parametric second-order down-conversion process pumped with low spatial and temporal coherence beams. It is shown that in this scenario, which is of considerable practical importance, the parametric gain in the near field breaks down into an ensemble of mutually incoherent beamlets containing parametric waves. The field generated in a single beamlet is fully spatially coherent. The size of such coherent parametric gain regions is governed by the near-field spatial coherence radius of the pump, which also acts as a parameter, restraining the linear diffraction of the parametric waves generated in the nonlinear interaction. Furthermore, we experimentally demonstrate how the spatial and temporal coherence can be substantially enhanced by manipulating the spatial field correlation of the multilongitudinal and multi-transversal mode pump.
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