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- Balliu, Enkeleda, PhD student, et al.
(author)
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Compact single-frequency mopa using a silica fiber highly doped with yb3
- 2021
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In: Applied Sciences. - : MDPI AG. - 2076-3417. ; 11:21
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Journal article (peer-reviewed)abstract
- We report on a single-frequency fiber master oscillator power amplifier utilizing a polarization-maintaining step-index fiber with an Al/Ce/F core-glass composition doped with a very high Yb concentration (0.25 at.%). This design made it possible to use a very short fiber (~1 m) and to coil it in a tight radius (4 cm in the amplifier, while 2 cm gave similarly negligible bending loss) so that the packaged system is one of the most compact reported to date (~0.6 L). The use of a short fiber increased the threshold for stimulated Brillouin scattering well above 100 W while maintaining near-ideal beam quality. The fiber was pumped with a diode-pumped solid-state laser and cooled passively by spooling it on a grooved aluminum mandrel. The amplifier produced a strongly linearly polarized output at 1064 nm in the fundamental mode (M2 ≤ 1.2) with a 150 kHz linewidth and a power of 81.5 W for 107 W of launched pump power. No deleterious effects from the elevated thermal load were observed. The residual photodarkening loss resulting from the high Yb concentration, found to be small (~0.7 dB/m inferred at 1064 nm) with accelerated aging, reduced the output power by only ~20% after 150 h of operation.
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- Coetzee, Riaan Stuart, et al.
(author)
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An efficient, 2 µm optical parametric amplifier based on large-aperture periodically poled Rb:KTP
- 2017
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In: PROCEEDINGS VOLUME 10562 INTERNATIONAL CONFERENCE ON SPACE OPTICS — ICSO 2016 | 18-21 OCTOBER 2016 International Conference on Space Optics — ICSO 2016. - : SPIE - International Society for Optical Engineering. - 9781510616134
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Conference paper (peer-reviewed)abstract
- High-energy mid-infrared nanosecond sources are required in a number of applications including biomedicine, remote sensing, and standoff countermeasures, to name just a few. Sources which serve these applications include mid-infrared fiber and solid-state lasers, quantum cascade lasers, as well as optical parametric oscillators (OPO).
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- Coetzee, Riaan Stuart, et al.
(author)
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Efficient Backward-Wave Optical Parametric Oscillator with 500 nm-periodicity PPRKTP
- 2018
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In: 2018 conference on lasers and electro-optics (CLEO). - : IEEE. - 9781943580422
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Conference paper (peer-reviewed)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
(author)
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Energy scaling of infrared nanosecond optical parametric oscillators and amplifiers based on Rb:KTiOPO4
- 2018
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Doctoral thesis (other academic/artistic)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, 1987-, et al.
(author)
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Gamma irradiation-induced absorption in single-domain and periodically-poled KTiOPO4 and Rb:KTiOPO4
- 2017
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In: Optical Materials Express. - 2159-3930 .- 2159-3930. ; 7:11, s. 4138-4146
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Journal article (peer-reviewed)abstract
- We investigate the effect of gamma radiation on flux grown KTiOPO4 and Rb:KTiOPO4 samples, as well as their periodically poled variants. Specifically, we study the altered transmission due to color-center formation via gamma irradiation. We measured the transmission of our samples for varying radiation doses and demonstrate effective temperature annealing of gamma radiation induced color centers. We measured a maximum transmission difference of 2% in our samples, which was easily corrected with temperature annealing. No long term and permanent changes were found to be induced in our samples.
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