This thesis explores the use of engineered nonlinear crystals from the KTiOPO4 (KTP) family as the gain material in optical parametric amplifiers (OPAs), with the aim to achieve more knowledge about the benefits and limitations of these devices. The work aims further at extending the possible applications of OPAs by constructing and investigating several efficient and well performing amplifiers. An OPA consists of a strong pump source, which transfers its energy to a weak seed beam while propagating through a nonlinear crystal. The crystals employed in this work are members of the KTP family, which are attractive due to their large nonlinear coefficients, high resistance to damage and wide transparency range. The flexibility of OPAs with respect to different wavelength regions and pulse regimes was examined by employing various dissimilar seed and pump sources. The possibility to adapt an OPA to a specific pump and seed wavelength and achieve efficient energy conversion between the beams, originates from quasi-phasematching, which is achieved in periodically poled (PP) nonlinear crystals. Quasi-phasematched samples can be obtained by changing the position of certain atoms in a ferroelectric crystal and thereby reversing the spontaneous polarisation. In this thesis several material properties of PP crystals from the KTP family were examined. The wavelength and temperature dispersion of the refractive index were determined for PP RbTiOPO4, which is essential for future use of this material. Another experiment helped to increase the insight into the volumes close to domain walls in PP crystals Further, several OPAs were built and their ability to efficiently amplify the seed beam without changing its spectral or spatial properties was studied. Small signal gains of up to 55 dB and conversion efficiencies of more than 35 % were achieved for single pass arrangements employing 8 mm long PPKTP crystals. Apart from constructing three setups, which generated powerful nanosecond, picosecond and femtosecond pulses, the possibility to amplify broadband signals was investigated. An increase of the OPA bandwidth by a factor of approximately three was achieved in a noncollinear configuration. / QC 20101013

<p>This thesis explores the use of engineered nonlinear crystals from the KTiOPO4 (KTP) family as the gain material in optical parametric amplifiers (OPAs), with the aim to achieve more knowledge about the benefits and limitations of these devices. The work aims further at extending the possible applications of OPAs by constructing and investigating several efficient and well performing amplifiers.</p><p>An OPA consists of a strong pump source, which transfers its energy to a weak seed beam while propagating through a nonlinear crystal. The crystals employed in this work are members of the KTP family, which are attractive due to their large nonlinear coefficients, high resistance to damage and wide transparency range. The flexibility of OPAs with respect to different wavelength regions and pulse regimes was examined by employing various dissimilar seed and pump sources.</p><p>The possibility to adapt an OPA to a specific pump and seed wavelength and achieve efficient energy conversion between the beams, originates from quasi-phasematching, which is achieved in periodically poled (PP) nonlinear crystals. Quasi-phasematched samples can be obtained by changing the position of certain atoms in a ferroelectric crystal and thereby reversing the spontaneous polarisation.</p><p>In this thesis several material properties of PP crystals from the KTP family were examined. The wavelength and temperature dispersion of the refractive index were determined for PP RbTiOPO4, which is essential for future use of this material. Another experiment helped to increase the insight into the volumes close to domain walls in PP crystals</p><p>Further, several OPAs were built and their ability to efficiently amplify the seed beam without changing its spectral or spatial properties was studied. Small signal gains of up to 55 dB and conversion efficiencies of more than 35 % were achieved for single pass arrangements employing 8 mm long PPKTP crystals. Apart from constructing three setups, which generated powerful nanosecond, picosecond and femtosecond pulses, the possibility to amplify broadband signals was investigated. An increase of the OPA bandwidth by a factor of approximately three was achieved in a noncollinear configuration.</p>

Terahertz (THz) heterodyne receiver systems are required by NASA to monitor gas concentrations related to the Earth's ozone depletion. To this end, NASA needs compact, solid state, tunable THz local oscillators. THz LOs have been developed using three means: 1) All-electronic LOs using mixers in combination with Gunn oscillators, 2) Hybrid Photo-electronic LOs using a cw analog of the Auston switch, and 3) All-photonic THz LOs using coherent sources, such as vapor lasers or solid-state Quantum Cascade Lasers, and down converting lasers using nonlinear crystals. In this dissertation, we began with two frequency stabilized Nd:YAG lasers, locked to a common reference cavity, as a starting point to having a stable input into a nonlinear optical frequency conversion system. Following this, we explored the nonlinear crystals useful for THz generation, and the phasematching schemes that could be employed by each. We concluded by settling on highly insulating III-V semiconductor crystals as the proper choice of nonlinear element, and put together a new phasematching method that is most useful for them.

De nos jours, la génération paramétrique optique (OPG) avec la plus grande largeur spectrale possible, est une bonne alternative pour couvrir les bandes II (2–5 µm) ou band III (8–12 µm) de transmission de l’atmosphère. Une telle émission à partir de processus non linéaires quadratiques en conditions d’accord de phase par biréfringence (BPM), nous a intéressés. Elle est réalisée sur le domaine de transparence de cristaux non linéaires déjà identifiés, mais ils ne sont pas satisfaisants. C’est pourquoi ce travail de thèse est consacré d’abord à l’étude du cristal biaxe GdCa4O(BO3)3 (GdCOB), et des cristaux uniaxes La3Ga5.5Nb0.5O14 (LGN) et NaI3O8. Nous avons enregistré leurs courbes d’accord de phase et les rendements de conversion associés en conditions de BPM. Nous avons sélectionné la génération de second harmonique et la différence de fréquence dans des lames, des sphères ou cylindres. Nous avons affiné les équations de Sellmeier. Nous avons déterminé la valeur absolue des coefficients non linéaires des cristaux uniaxes. Nous avons aussi déterminé la valeur absolue et le signe de tous les coefficients du cristal biaxe BaGa4Se7. Tous ces résultats constituent une base fiable pour les évaluations expérimentales à venir de la plus grande largeur spectrale des OPG qui utilisent ces cristaux.Key words: optique non linéaire, génération paramétrique, accord de phase, cristaux non linéaires / Nowadays, the optical parametric generators (OPG) with the broadest spectral bandwidth is a good alternative cover band II (2–5 µm) or band III (8–12 µm) of transmission range of the atmosphere. We were interested in such an emission from quadratic nonlinear processes under birefringence phase-matching conditions (BPM). It is performed in the transparency range of already identified nonlinear crystals, but they are not satisfying. Then this PhD work is devoted first to the study of GdCa4O(BO3)3 (GdCOB) biaxial crystal, and La3Ga5.5Nb0.5O14 (LGN) and NaI3O8 uniaxial crystals. We recorded their tuning curves and conversion efficiencies for BPM. We selected second harmonic generation and difference frequency generation in slabs, spheres or cylinders. We refined the Sellmeier equations. We determined the magnitude of the nonlinear coefficients, spectral and angular acceptances in uniaxial crystals. We also determined the magnitude and sign of all the nonlinear coefficients of BaGa4Se7 biaxial crystal. All these results provide reliable data for further experimental evaluations of OPG broadest spectral bandwidth covering band II or III using these crystals.Key words: nonlinear optics, parametric generation, phase-matching, nonlinear crystals

1 Title: High-average power picosecond mid-IR source Author: Michal Vyvlečka Department: Department of Chemical Physics and Optics Supervisor: Ing. Ondřej Novák, Ph.D., Hilase centre, Institute of Physics of CAS Abstract: High average power wavelength tunable picosecond mid-IR source based on optical parametric generation (OPG) and optical parametric amplification (OPA) is being developed. The conversion system is pumped by an Yb:YAG thin-disk laser delivering 100 W of average power at 100 kHz repetition rate, 1030 nm wavelength, and 2-3 ps pulse width. Part of this fundamental beam pumps an OPG process in a PPLN crystal. The generated wavelength is determined by PPLN's poling period and temperature. Tunability of the signal wavelength between 1.46 µm and 1.95 µm was achieved, the signal beam of 20 mW was generated at 2 W of pump power, when double pass of the beams through PPLN crystal was used. The corresponding idler wavelengths were in range 2.18-3.50 μm. The signal beam was further amplified by OPA process in two KTP crystals, which was pumped by the fundamental beam. The signal beam was amplified up to 2 W at pumping of 38 W. Tuning of the output wavelength was realized by change of the phase-matching angle in KTP crystals. Tunability between 1.70-1.95 µm for signal and 2.18-2.62 µm for idler was...

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