L'optique non-linéaire étudie des phénomènes capables de modifier la fréquence de la lumière incidente en s'appuyant sur la symétrie intrinsèque de certains matériaux. Le défi actuel de la miniaturisation des composants va de paire avec une perte d'efficacité à l'échelle sub-micrométrique. Pour résoudre ce problème, l'idée explorée au cours de cette thèse consiste à utiliser un phénomène d'oscillation collective des électrons libres d'une nanostructure en métal, appelé résonance plasmon de surface localisé. Cet effet est associé à une exaltation du champ au voisinage immédiat d'une structure plasmonique, une propriété adaptée pour augmenter l'efficacité non-linéaire d'un matériau placé non loin. Les objectifs principaux de ma thèse consistaient à fabriquer ces objets hybrides, à développer une plate-forme expérimentale polyvalente capable de réaliser différents types d'observation à l'échelle de la particule unique, puis à analyser leur génération de second harmonique (SHG). Ces travaux ont abouti à l'obtention de structures hybrides non-linéaires efficaces, dont l'intensité SHG atteint jusqu'à 100 fois celle d'une antenne plasmonique isolée et jusqu'à plus de 1000 fois celle d'un nanocristal non-linéaire unique, confirmant l'intérêt de ces structures. Nous avons aussi tenté d'observer de la fluorescence paramétrique (SPDC) dans une nanostructure individuelle, une prouesse encore inachevée dans le monde; si nos études n'ont pas davantage abouti, elles esquissent des pistes d'amélioration pour y parvenir, et un modèle numérique innovant développé dans l'équipe annonce un rendement compatible avec des observations. Enfin, une source de photons intriqués a été développée dans le cadre d'une collaboration sur l'intelligence artificielle dans des systèmes physiques et constitue une perspective envisageable d'application pour les travaux précédents. Ces résultats ouvrent potentiellement la voie à l'amélioration de l'éfficacité et de la fiabilité des algorithmes IA actuels. / Nonlinear optics study phenomena able to modify the frequency of incoming light by using intrinsic symmetry properties of some materials. The current challenge of component miniaturization goes with an efficiency drop at the sub-micrometer scale. To solve this issue, the idea we have explored during my PhD consists in using a collective oscillation phenomenon from free electrons in a metal structure called localized surface plasmon resonance. This effect is indeed linked to an enhancement of the electromagnetic field near a plasmonic structure, a property well suited to increase the nonlinear efficiency of a material placed beside. The main objectives of my PhD consisted in fabricating these hybrid objects, developing a versatile experimental platform able to make different kinds of observations at the single particle level, and finally analyzing their second harmonic generation (SHG). This work has managed to produce efficient nonlinear hybrid structures, whose SHG intensity is up to 100 times that of an isolated plasmonic antenna and up to 1000 times that of a single nonlinear nanocrystal, confirming the potential of this type of structures. We have also tried to detect spontaneous parametric down conversion (SPDC) in a single nanostructure, a never-achieved feat that has yet to be done; although our study wasn't successful, it gives hints to improve experiments, even more since a cutting edge numerical model developed in our team has predicted intensities compatible with observations. Finally, an entangled photon source has been developed in the framework of a collaboration on artificial intelligence in physical systems and is a reachable perspective for potential applications of our work. These results pave the way to improving efficiency and liability of current AI algorithms.

High two-photon absorption (2PA) cross-section materials have been frequently studied during the latest years due to the wide variety of technological applications, such as two-photon absorption microscopy (2PM) and microfabrication. The characterization of new materials with high nonlinearities is, therefore, indispensable to develop new applications and improve previously existing ones. Here, three different groups of novel organic compounds had their nonlinearities characterized through two-photon absorption measurements: fluorenone based compounds, which are usually used in two-photon absorption microscopy; BF2-naphthyridine (BODIPY) complexes, which have a wide range of applications, from solar cells to photodynamic therapy; and binaphthalene-based polymers, with structures built to generate large nonlinearities through inherent chirality. All compounds had their two-photon absorption spectra studied through absorptive Z-Scan, with density functional theory (DFT) calculations made to interpret the results for the first two groups of compounds, and polarization controlled measurements made for the polymers. The highest 2PA cross-section presented by the fluorenone-based compounds was of 224 GM at 710 nm, large and within the wavelength range for 2PM applications; for the BODIPYs, the largest observed cross-section was of 268 GM at 990 nm, of the same order of magnitude of more complex compounds; and 680 GM at 1100 nm for the polymer, showing a high cross-section as expected from its structure. The desired applications for the studied molecules were shown valid, and their characterization gave a better understanding of how to increase their nonlinearities depending on the compound manufacture. / Materiais com grande seção de choque de absorção de dois fótons (2PA) tem sido estudados com frequência nos últimos anos graças a ampla variedade de aplicações tecnológicas, tais como microscopia por absorção de dois fótons (2PM) e microfabricação. A caracterização de materiais com altas não-linearidades é, portanto, indispensável para o desenvolvimento de novas aplicações e para o aprimoramento das técnicas já existentes. Aqui, três diferentes grupos de novos compostos orgânicos tiveram suas não-linearidades caracterizadas através de medidas de 2PA: compostos baseados em fluorenona, geralmente utilizados em 2PM; compostos baseados em BF2-naftiridina (BODIPY), que possuem grande variedade de aplicações, desde células solares até terapia fotodinâmica; e polímeros baseados em binaftaleno, com estruturas sintetizadas para gerar altas não-linearidades através de sua quiralidade inerente. Para caracterizar o espectro de 2PA de todos os compostos a técnica de Z-Scan absortiva foi utilizada, com cálculos de funcional densidade (DFT) realizados para corroborar os resultados obtidos para os dois primeiros grupos de compostos, e medidas com controle de polarização foram realizados para o estudo dos polímeros. A maior seção de choque obtida para as fluorenonas foi de 224 GM em 710 nm, alta e dentro do comprimento de onda necessário para as aplicações de 2PM; para os BODIPYs, a maior seção de choque observada foi de 268 GM em 990 nm, da mesma ordem de magnitude que compostos mais complexos que os estudados; e 680 GM em 1100 nm para o polímero, mostrando um valor alto como esperado por sua estrutura. Com isso, demonstramos que as moléculas estudadas possuem as aplicações desejadas, e sua caracterização permitiu uma melhor compreensão de como aumentar suas não-linearidades dependendo da engenharia dos compostos.

Adsorption layers of soluble surfactants enable and govern a variety of phenomena in surface and colloidal sciences, such as foams. The ability of a surfactant solution to form wet foam lamellae is governed by the surface dilatational rheology. Only systems having a non-vanishing imaginary part in their surface dilatational modulus, E, are able to form wet foams. The aim of this thesis is to illuminate the dissipative processes that give rise to the imaginary part of the modulus. <br><br> There are two controversial models discussed in the literature. The reorientation model assumes that the surfactants adsorb in two distinct states, differing in their orientation. This model is able to describe the frequency dependence of the modulus E. However, it assumes reorientation dynamics in the millisecond time regime. In order to assess this model, we designed a SHG pump-probe experiment that addresses the orientation dynamics. Results obtained reveal that the orientation dynamics occur in the picosecond time regime, being in strong contradiction with the two states model. <br><br> The second model regards the interface as an interphase. The adsorption layer consists of a topmost monolayer and an adjacent sublayer. The dissipative process is due to the molecular exchange between both layers. The assessment of this model required the design of an experiment that discriminates between the surface compositional term and the sublayer contribution. Such an experiment has been successfully designed and results on elastic and viscoelastic surfactant provided evidence for the correctness of the model. <br><br> Because of its inherent surface specificity, surface SHG is a powerful analytical tool that can be used to gain information on molecular dynamics and reorganization of soluble surfactants. They are central elements of both experiments. However, they impose several structural elements of the model system. During the course of this thesis, a proper model system has been identified and characterized. The combination of several linear and nonlinear optical techniques, allowed for a detailed picture of the interfacial architecture of these surfactants. / Amphiphile vereinen zwei gegensätzliche Strukturelemente in einem Molekül, eine hydrophile Kopfgruppe und ein hydrophobe, meist aliphatische Kette. Aufgrund der molekularen Asymmetrie erfolgt eine spontane Adsorption an der Wasser-Luft Grenzfläche. Die Adsorptionsschicht verändert die makroskopischen Eigenschaften des Materials, z.B. die Grenzflächenspannung wird erniedrigt. Amphiphile sind zentrale Bauelemente der Kolloid- und Grenzflächenforschung, die Phänomene, wie Schäume ermöglichen. <br><br> Eine Schaumlamelle besteht aus einem dünnen Wasserfilm, der durch zwei Adsorptionsschichten stabilisiert wird. Die Stabilität der Lamelle wird durch die Grenzflächenrheologie entscheidend geprägt. Die wesentliche makroskopische Größe in diesem Zusammenhang ist das so genannte Grenzflächendilatationsmodul E. Es beschreibt die Fähigkeit des Systems die Gleichgewichtsgrenzflächenspannung nach einer Expansion oder Dilatation der Adsorptionschicht wieder herzustellen. Das Modul E ist eine komplexe Größe, in dem der Imaginärteil direkt mit der Schaumstabilität korreliert. <br><br> Diese Arbeit widmet sich der Grenzflächenrheologie. In der Literatur werden zwei kontroverse Modelle zur Interpretation dieser Größe diskutiert. Diese Modelle werden experimentell in dieser Arbeit überprüft. Dies erfordert die Entwicklung neuer experimenteller Aufbauten basierend auf nichtlinearen, optischen Techniken. Mit diesen Experimenten konnte eines der Modelle bestätigt werden.

Material and structure engineering are increasingly employed in active optical media,in this context defined as media capable of providing laser or/and optical parametric gain. For laser materials, the main aim of the engineering is to tailor the absorption and emission cross sections in order to optimise the laser performance. At the same time, the engineering also results in a collateral modification of the material’s nonlinear response. In the first part of this work, the nonlinear index of refraction is characterised for two crystallographic forms of laser-ion doped and undoped double-tungstate crystals. These laser crystals have broad gain bandwidths, in particular when doped with Yb3+. As shown in this work, the crystals also have large Kerr nonlinearities, where the values vary significantly for different chemical compositions of the crystals. The combination of a broad gain bandwidthand a high Kerr nonlinearity makes the laser-ion doped double tungstates excellent candidates to employ for the generation of ultrashort laser pulses by Kerr-lens modelocking. The second part of the work relates to the applications of engineered second-order nonlinear media, which here in particular are periodically-poled KTiOPO4 crystals. Periodic structure engineering of second-order nonlinear crystals on a submicrometre scale opens up for the realisation of novel nonlinear devices. By the use of quasi-phase matching in these structures, it is possible to efficiently downconvert a pump wave into two counterpropagating parametric waves, which leads to a device called a mirrorless optical parametric oscillator. The nonlinear response in these engineered submicrometre structures is such that the parametric wave that propagates in the opposite direction of the pump automatically has a narrow bandwidth, whereas the parametric wave that propagates with the pump essentially is a frequency-shifted replica of the pump wave. The unusual spectral properties andthe tunabilities of mirrorless optical parametric oscillators are investigated. / QC 20120330

Los solitones ópticos son paquetes de luz (haces y/o pulsos) que no se dispersan gracias al balance entre difracción/dispersión y no linealidad. Al propagarse e interactuar los unos con los otros muestran propiedades que normalmente se asocian a partículas. Las propiedades de los solitones ópticos en fibras ópticas y cristales han sido investigadas en profundidad durante las últimas dos décadas. Sin embargo, los solitones en mallas, o redes, ópticas, que podrían ser usados para procesado y direccionamiento totalmente óptico de señales, se han convertido en una nueva área de investigación. El principal objetivo de esta tesis es el estudio de nuevas técnicas para controlar solitotes en medios no lineales en mallas ópticas.El capítulo 2 se centra en ciertas propiedades de los solitones ópticos en medios no lineales cuadráticos. La primera sección presenta en detalle la existencia y estabilidad de tres familias representativas de solitones espacio temporales en dos dimensiones en series de frentes de onda cuadráticos no lineales. Se asume, además de la dispersión temporal del pulso, la combinación de difracción discreta que surge debido al acoplamiento débil entre frentes de onda vecinos. La otra sección da cuenta de la existencia y estabilidad de vórtices de solitones multicolores en retículo, consistentes en cuatro jorobas principales dispuestas en una configuración cuadrada. También se investiga la posibilidad de generarlos dinámicamente a partir de haces de entrada Gaussianos con vórtices anidados. La técnica de inducción de mallas ópticas ofrece un sinfín de posibilidades para la creación de configuraciones de guía de ondas con varios haces de luz no difractantes. El capítulo 3 presenta el concepto de estructuras reconfigurables ópticamente inducidas por haces no difractantes de Bessel mutuamente incoherentes en medios no lineales de tipo Kerr. Los acopladores de dos nucleos son introducidos y se muestra cómo calibrar las propiedades de conmutación de estas estructuras variando la intensidad de los haces de Bessel. El capítulo también discute varios escenarios de conmutación para solitones lanzados al interior de acopladores direccionales multinucleares ópticamente inducidos por apropiadas series de haces de Bessel. Es más, la propagación de solitones es investigada en redes reconfigurables bidimensionales inducidas ópticamente por series de haces de Bessel no difractantes. Se muestra que los haces anchos de solitones pueden moverse a través de redes con diferentes topologías casi sin pérdidas por radiación. Finalmente, se estudian las propiedades de las uniones X, que se crean a partir de dos haces de Bessel intersectantes. La respuesta no local de los medios no lineales puede jugar un papel importante en las propiedades de los solitones. El capítulo 4 trata el impacto de la no localidad en las características físicas exhibidas por los solitones que permiten los medios no lineales de tipo Kerr con una retícula óptica integrada. El capítulo investiga propiedades de diferentes familias de solitones en mallas en medios no lineales no locales. Se muestra que la no localidad de la respuesta no lineal puede afectar profundamente la movilidad de los solitones. Las propiedades de los solitones de gap también se discuten en el caso de cristales fotorefractivos con una respuesta de difusión no local asimétrica y en presencia de una malla inducida.El capítulo 5 trata del impacto de la no localidad en la estabilidad de complejos de solitones en medios no lineales de tipo Kerr uniformes. En primer lugar, se muestra que la diferente respuesta no local de los materiales tiene distinta influencia en la estabilidad de los complejos de solitones en el caso escalar. En segundo lugar, se da cuenta de una serie de resultados experimentales sobre solitones multipolares escalares en medios no lineales fuertemente no locales en 2D, incluyendo solitones dipolares, tripolares y de tipo pajarita, organizados en series de puntos brillantes fuera de fase. Finalmente, el capítulo estudia la interacción entre la no linealidad no local y el acoplamiento vectorial, enfatizando especialmente la estabilización de efectos vectoriales en complejos de solitones en medios no lineales no locales.Por último, el capítulo 6 resume los principales resultados obtenidos en la tesis y discute algunas cuestiones abiertas. / Optical solitons are light packets (beams and/or pulses) that do not broaden because of the proper balance between diffraction/dispersion and nonlinearity. They propagate and interact with one another while displaying properties that are normally associated with real particles. The properties of optical solitons in optical fibers and crystals have been investigated comprehensively during the last two decades. However, solitons in optical lattices, which might be used for all-optical signal processing and routing have recently emerged a new area of research. The main objective of this thesis is the investigation of new techniques for soliton control in nonlinear media with/without an imprinted optical lattice. Chapter 2 focuses on properties of optical solitons in quadratic nonlinear media. The first section presents in detail the existence and stability of three representative families of two-dimensional spatiotemporal solitons in quadratic nonlinear waveguide arrays. It is assumed in addition to the temporal dispersion of the pulse, the combination of discrete diffraction that arises because of the weak coupling between neighboring waveguides. The other section reports on the existence and stability of multicolor lattice vortex solitons, which comprise four main humps arranged in a square configuration. It is also investigated the possibility of their dynamical generation from Gaussian-type input beams with nested vortices. The technique of optical lattice induction opens a wealth of opportunities for creation of waveguiding configurations with various nondiffracting light beams. Chapter 3 puts forward the concept of reconfigurable structures optically induced by mutually incoherent nondiffracting Bessel beams in Kerr-type nonlinear media. Two-core couplers are introduced and it is shown how to tune the switching properties of such structures by varying the intensity of the Bessel beams. The chapter also discusses various switching scenarios for solitons launched into the multi core directional couplers optically-induced by suitable arrays of Bessel beams. Furthermore, propagation of solitons is investigated in reconfigurable two-dimensional networks induced optically by arrays of nondiffracting Bessel beams. It is shown that broad soliton beams can move across networks with different topologies almost without radiation losses. Finally, properties of X-junctions are studied, which are created with two intersecting Bessel beams.Nonlocal response of nonlinear media can play an important role in properties of solitons. Chapter 4 treats the impact of nonlocality in the physical features exhibited by solitons supported by Kerr-type nonlinear media with an imprinted optical lattice. The chapter investigates properties of different families of lattice solitons in nonlocal nonlinear media. It is shown that the nonlocality of the nonlinear response can profoundly affect the soliton mobility. The properties of gap solitons are also discussed for photorefractive crystals with an asymmetric nonlocal diffusion response and in the presence of an imprinted optical lattice.Chapter 5 is devoted to the impact of nonlocality on the stability of soliton complexes in uniform nonlocal Kerr-type nonlinear media. First, it is shown that the different nonlocal response of materials has different influence on the stability of soliton complexes in scalar case. Second, experimental work is reported on scalar multi-pole solitons in 2D highly nonlocal nonlinear media, including dipole, tripole, and necklace-type solitons, organized as arrays of out-of-phase bright spots. Finally, the chapter addresses the interplay between nonlocal nonlinearity and vectoral coupling, specially emphasizing the stabilization of vector effects on soliton complexes in nonlocal nonlinear media.Finally, Chapter 6 summarizes the main results obtained in the thesis and discusses some open prospects.

In the field of second harmonic (SH) generation most studies have been concerned with maximizing conversion efficiencies, generally achievable at the phase matching (PM) condition. Outside of the PM the conversion efficiency drastically decreases. This has caused that the possible working conditions out of PM to remain largely unexplored. In this thesis work we initiated a systematic study of the SH behavior in under conditions of large phase mismatch. When a pump pulse crosses an interface between a linear and a nonlinear medium there are always two generated SH components. These components may be understood on the basis of the mathematical solution of the inhomogeneous wave equations at the SH frequency. The homogeneous (HOM) solution is a component with wave-vector k(2¿) as expected from the dispersion relation and exchanges energy with the pump until the inevitable walk-off. The inhomogeneous (INH) solution is a component with a wave-vector 2k(¿), twice the pump wave-vector, and travels locked to the pump pulse. We divide our work in two parts, one for each generated component. Inhomogeneous component. We start a systematic study of the behavior of the generated INH component, phase locked to the pump. The consequences of phase locking (PL) can guide us towards new scenarios by allowing working conditions hitherto assumed inaccessible for absorbing materials. We show that while the HOM component travels with the group velocity given by material dispersion, the IHN component is captured by the pump pulse and experiences the same effective dispersion of the pump. It does not follow the PM condition. It naturally follows that the suppression of absorption at the SH wavelengths will occur if the pump is tuned to a region of transparency. We extended the same theory for the generated third harmonic (TH). We then studied the surprising behavior of SH and TH INH components with frequencies above the absorption edge when the material is placed inside a cavity resonant only at the fundamental frequency. We have shown that the PL mechanism not only inhibits absorption but also fosters the enhancement of harmonic generation by several orders of magnitude compared to the no-cavity case. Finally, we tested the INH SH and TH behaviors in metallic frequency regime of material. Homogeneous component. The techniques used to PM the nonlinear interaction enable efficient nonlinear interactions but drastically limit the spectral bandwidth of the nonlinear optical process, making the designed frequency converter only suitable for a fixed input wavelength and single interaction only. It has been shown that the use of disordered nonlinear media relaxes the PM condition thus allowing one to achieve relatively efficient broad bandwidth regime of the frequency conversion. An example of a quadratic nonlinear medium with a disordered domain structure is an un-poled Strontium Barium Niobate (SBN) crystal. It is composed of a system of random size anti parallel ferroelectric domains that allow to phase-match any second-order parametric process over a broad range of wavelengths without any poling. We have initiated an experimental and theoretical investigation of the properties of the SH waves generated in SBN crystals, with an extension to the generated TH. This study covers the coherence and polarization properties of the generated signal, as well as its spatial distribution. In addition, we have made an experimental study of the noncollinear interaction of short optical pulses in a SBN crystal by using two fundamental waves intersecting inside the crystal. We have shown that this effect may be employed as a simple tool for monitoring both the pulse duration and initial chirp. This method offers a simple and economic alternative to the existing methods for pulse characterization.

The objective of this research is to present a set of powerful simulation, design, and characterization tools suitable for studying novel nanophotonic devices. The simulation tools include a three-dimensional finite-difference time-domain code adapted for parallel computing that allows for a wide range of simulation conditions and material properties to be studied, as well as a semi-analytical Green's function-based complex mode technique for studying loss in photonic crystal waveguides. The design tools consist of multifunctional photonic crystal-based template that has been simulated with nonlinear effects and measured experimentally, and planar slab waveguide structure that provides highly efficient second harmonic generation is a chip-scale device suitable for photonic integrated circuit applications. The characterization tool is composed of a phase-sensitive measurement system using a lock-in amplifier and high-precision optical stages, suitable for probing the optical characteristics of nanoscale devices. The high signal-to-noise ratio and phase shift data provided by the lock-in amplifier allow for accurate transmission measurements as well as a phase spectrum that contains information about the propagation behavior of the device beyond what is provided by the amplitude spectrum alone.

This thesis investigates the generation of second harmonic bulk waves in the presence of a free boundary. Second harmonic waves have proven to be useful in the field of nondestructive evaluation to detect fatigue in a material at an early stage. Since most experimental setups include a free surface, the influence of such a boundary is of significant practical interest. As a result, the objective of this research is to develop a quantitative understanding of the complete process of second harmonic generation at a free boundary. This research shows that the interaction of primary waves (with each other) in the nonlinear framework leads to the generation of second harmonic bulk waves. We distinguish between self-interaction of a single primary wave and the cross-interaction of two different primary waves. The proposed approach uses the perturbation method to solve the nonlinear equations of motion, and shows two fundamentally different solutions. In the case of resonance, the secondary waves grow with propagation distance. This is the most important practical case, since the growing amplitudes of these waves should be easier to experimentally measure. In the second, non-resonant case, the amplitudes of the secondary waves are constant. The complete process of second harmonic generation is analyzed for an incident Pand an incident SV-wave, with the primary and secondary fields given. Finally, the degenerate case of normal incidence is presented. Normal and oblique incidence are compared with regard to their feasibility in experimental setups. The specific behavior of second harmonic waves propagating in aluminum is numerically determined. These results enable a variety of physical insights and conclusions to be drawn from the analytical and numerical investigations.

Processing of high-speed data using optical signals is a promising approach for tackling the bandwidth and speed challenges of today's electronics. Realization of complex optical signal processing functionalities seems more possible than any time before, thanks to the recent achievements in silicon photonics towards large-scale photonic integration. In this Ph.D. work, a novel thermal reconfiguration technology is proposed and experimentally demonstrated for silicon photonics that is compact, low-loss, low-power, fast, with a large tuning-range. These properties are all required for large-scale optical signal processing and had not been simultaneously achieved in a single device technology prior to this work. This device technology is applied to a new class of resonator-based devices for reconfigurable nonlinear optical signal processing. For the first time, we have demonstrated the possibility of resonance wavelength tuning of individual resonances and their coupling coefficients. Using this new device concept, we have demonstrated tunable wavelength-conversion through four-wave mixing in a resonator-based silicon device for the first time.

<p>This thesis discusses a new scheme for generating radiation in the mid infrared spectral region, especially the 3.5-5 µm range. The scheme uses established Nd³⁺-lasers at 1.06 µm and down conversion in nonlinear optical crystals. The down conversion is made by two optical parametric oscillators (OPO) in series. The second OPO is a classical OPO using a zink germanium phosphide (ZGP) crystal. ZGP is the best nonlinear material available for the 4-8 µm spectral range, but it is absorbing below 2 µm. The new development presented in this thesis is the OPO used to convert the 1.06 µm laser radiation to a suitable OPO pump near 2 µm.</p><p>The OPO uses a type I quasi phase-matched crystal, which accesses high nonlinearities and avoids walk-off. The problem with type I OPOs close to degeneracy is the broad bandwidth of the generated radiation, which reduces the efficiency of a second OPO. This has been solved with a spectrally selective cavity using a volume Bragg grating output coupler. Unlike other bandwidth limiting schemes this introduces no intracavity losses and thus efficient OPO operation is achievable.</p><p>Narrow linewidth (~0.5 nm) OPO operation has been achieved with periodically poled LiNbO₃ (PPLN) and periodically poled KTiOPO4 (PPKTP) while locking the signal wavelength at 2008 nm and simultaneously generating an idler at 2264 nm. A high average power PPLN OPO with 36 % conversion efficiency and 47 % slope efficiency is reported. Operation very close to degeneracy at 2128 nm with the narrowband signal and idler peaks separated by 0.6 nm was demonstrated in a PPKTP OPO. Both the signal at 2008 nm and the combined signal and idler around 2128 nm from the PPKTP OPOs have been used to show efficient pumping of a ZGP OPO. The maximum conversion efficiency from 1 µm to the mid-IR demonstrated is 7 % with a slope efficiency of 10 %. This is not quite as high as what has been presented by other authors, but the experiments reported here have not shown the optimum efficiency of the new scheme. Relatively simple improvements are expected to give a significant increase in conversion efficiency.</p>