Periodically domain−structured KTiOPO4 crystals grown from high temperature solution

International audiencePeriodically-poled ferroelectric crystals proved to be the most promising technique for exploiting at the best nonlinear optical frequency conversion properties of materials using quasi-phase matching (QPM). Until now the common method for obtaining periodically-poled ferroelectric crystals is by electric-field poling. In this technique local inversion of the spontaneous polarization is produced in a single-domain crystal by applying an electric field on a periodic electrode deposited on the crystal surface. The poling technology for nonlinear crystals like KTiOPO4, LiNbO3 and LiTaO3 is by now reliable to produce QPM gratings with periods down to about 8 µm. But the thickness of the periodically poled slabs is restricted to 1 mm for these gratings periods, which limits their use to low- and medium- power applications

Bulk PPKTP by crystal growth from high temperature solution

International audiencePeriodically-poled ferroelectric crystals show unprecedented efficiency and properties otherwise impossible to obtain. Unfortunately, the sample thickness obtainable today limits their use to low and moderate power application. With the aim of increasing the size of periodically domain-structured crystals with a controlled and regular grating period, we proposed an epitaxial growth process using seeds made of thin plates domain engineered by electric field poling. We demonstrated this process with the ferroelectric crystal KTiOPO4 (KTP) which is one of the most promising candidate materials for that purpose. The poling step requires a sample exhibiting (001) and (00 (1) over bar) faces, so that the growth step has to be performed onto these faces. This constraint is a difficulty to circumvent as these faces are not present in the standard equilibrium morphology. It is then necessary to find the growth conditions enabling to work below the roughening temperature of these faces. By using a high temperature solution method, the so-called "flux method", and by choosing an appropriate chemical composition of the flux solution, we obtained periodically domain-structured KTP layers with thicknesses up to 800 mu m and regular periodicity onto (001) and (00 (1) over bar) faces of the initial PPKTP seeds

Template-growth of periodically domain-structured KTiOPO4

International audienceWe performed the first growth, from a high temperature solution, of a 38.86 μm-periodicity PPKTP crystal of good optical quality over a thickness of more than 800 μm onto each of the two faces perpendicular to the c direction of a PPKTP substrate previously obtained by electric field poling. The quasi-phase matched second harmonic generation properties in the grown layer and substrate are similar and in accordance with calculation

Solution growths of remarkable phosphate crystals: From lab researches to industrial applications

International audienceWe will present the growth of several families of phosphates crystals, which exhibit remarkable properties such as high nonlinear optical efficiencies and piezoelectricity. As phosphate materials do not melt congruently due generally to partial decompositions at high temperatures, their crystal growth are performed by involving solvents. Thus, by taking several examples of phosphate crystal growths, we will introduce first different types of solution growth methods at low (close to room temperature) and high temperatures, (up to 1000°C), such as slow cooling, temperature gradient and flux methods. Indeed, we will illustrate all these techniques with examples taken from our studies at CNRS-Grenoble which include growth of hybrid organic inorganic salts, potassium dihydrogen phosphate (KDP) and crystals of the potassium titanyl phosphate family (KTP). Their crystal growths are motivated by the efficient properties for nonlinear optics to develop optical frequency conversion devices like optical parametric oscillators based on their non-centrosymmetric structures. In addition to these standard solution growth techniques, some more particular ones will be presented. Indeed, solution crystal growths, carried out under typical conditions at low supersaturations of the solutions (relative supersaturations σ of around 1%), exhibit low growth rates, less than 1mm/day. By applying an overheating and/or an ultrasonic treatment of the solution, it is possible to inhibit the spurious nucleation that take place at higher supersaturations. Thus, through this type of treatment of the solution during the crystal growth process, higher supersaturations can be applied, σ around 10-20%, and thus increase significantly the growth rates, over 1cm/day. These rapid crystal growths will be illustrated in the cases of potassium dihydrogen phosphate and hybrid organic-inorganic salts. Finally, hydrothermal techniques will be presented in the case of aluminum and gallium orthophosphate crystals, which are isomorphous to α-quartz. These crystals, exhibit promising piezoelectric properties for the development of resonators and physical sensors. Moreover, for all of these phosphate crystal growths, we will give examples of industrial processes, particularly for the growths of KDP, KTP and GaPO4 crystals

Growth conditions to stabilize both non-equivalent polar faces, c+ and c-, of KTiOPO4 crystals

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Conditions for stable growth of the non-equivalent polar faces c+ and c- of KTiOPO4

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Hemisphere m-line spectroscopy and its application to birefringent KTiOPO4 planar waveguides.

International audienceA modified m-line technique, based on the use of a high index hemisphere instead of a coupling prism is presented. It allows fast characterization of the optical properties as a function of the propagation direction inside a planar waveguide. Results of an ionimplanted KTP waveguide are presented and compared to prismmeasurements. It is shown that this techniques enhances the precision of the waveguide parameters determination and allows to study advanced features such as strong mode hybridization

Bulk cylinders and spheres: from shaping to the use for linear and nonlinear optics

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Shaping and use of crystals as spheres and cylinders for linear and nonlinear optics

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Temperature dependence of single-crystal elastic constants of flux-grown alpha-GaPO4

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