Ytterbium and erbium dopep rbti1-xmxopo4 (m=nb or ta) crystals. new laser and nonlinear bifunctional materials

Ytterbium and erbium doped RbTi1-xMxOPO4 (M = Nb or Ta) crystals. New laser and nonlinear bifunctional materials. Lobjectiu daquesta tesi va ser millorar la qualitat dels cristalls de RbTi1-xNbxOPO4 dopats amb Yb3+, obtinguts mitjancant la tecnica Top Seeded Solution Growth-Slow Cooling (TSSG-SC), i tambe trobar un altre codopand el qual incrementes la concentracio de Yb3+ en els cristalls de RTP, pero sense reduir la resposta no lineal dels cristalls de RTP pur. Aquest io codopand hauria de presentar les mateixes caracteristiques que el Nb5+. Un altre objectiu daquesta tesi va ser lobtencio duna manera efectiva de fluorescencia del Er3+, al voltant de 1.5 µm, la qual donara lloc a lobtencio de radiacio laser a aquesta longitud dona. Per aconseguir aquest ultim objectiu, es van dopar cristalls de Nb:RTP amb la parella de ions actius Er3+/Yb3+, actuant el Yb3+ per sensibilitzar el Er3+. Per aconseguir el primer objectiu proposat, millorar la qualitat i la mida dels cristalls de Nb:RTP dopats amb Yb3+, es van optimitzar algunes condicions de creixement, tal com la rampa de refredament aplicada durant el proces de creixement, el perfil termic axial de la solucio i la qualitat dels germens emprats en les experiencies de creixement. Amb aquestes modificacions es van obtenir cristalls de mida i qualitat suficients per tal de preparar mostres, en una de les quals sha obtingut radiacio laser al voltant de 1 µm. Amb les mostres obtingudes tambe sha pogut determinar la longitud dona fonamental per lacord de fase no critic en la qual es donaria la generacio de segon harmonic de tipus II en el pla xy, determinant que seria possible obtenir radiacio laser autodoblada en la regio espectral del verd en aquest pla a q = 90o i j ? 45o. El segon objectiu, trobar un io codopand, amb el qual es pogues obtenir aproximadament la mateixa concentracio de Yb3+ que lobtinguda en cristalls de Nb:RTP, es va assolir utilitzant el Ta5+ com a io codopand. En cristalls volumics de Ta:RTP es va aconseguir una concentracio de Yb3+ de 1.6×1020 ions/cm3 i leficiencia de generacio de segon harmonic obtinguda va ser un 80 % de la del KTiOPO4 pur. Amb aquests resultats, podem pensar que en els cristalls de Ta:RTP dopats amb Yb3+ tambe es podria aconseguir radiacio laser autodoblada en la regio espectral del verd. Pel que fa a laugment de leficiencia de la fluorescencia del Er3+, mitjancant el codopatge de cristalls de Nb:RTP amb la parella dions actius Er3+/Yb3+, al voltant de 1.5 µm, sha aconseguit, fins i tot en mostres amb poca concentracio de Er3+ (<1020ions/cm3). A mes, cal afegir que tambe sha realitzat un estudi comparatiu entre la conductivitat ionica del RTP pur, del RTP crescut en solucio de tungste, Nb:RTP i Nb:RTP dopat amb Yb3+. Totes les mesures shan realitzat en plaques polides perpendiculars a la direccio cristallogafica c, i dels resultats obtinguts shan pogut extreure algunes conclusions. Que no hi ha diferencies entre les conductivitats ioniques de cristall de RTP purs i els crescuts en flux de tungste, pero en mostres de Nb:RTP la conductivitat augmenta considerablement, tenint una conductivitat de lordre de lobtinguda pel KTP (10-7-10-5 S/cm), i que les mostres de Nb:RTP dopades amb Yb3+ presenten una conductivitat ionica lleugerament superior (10-8 S/cm) a la que presenten les mostres de RTP (10-9 S/cm). Ytterbium and erbium doped RbTi1-xMxOPO4 (M = Nb or Ta) crystals. New laser and nonlinear bifunctional materials. The aim of this thesis was not only to enhance the quality and size of Yb doped RbTi1-xNbxOPO4 (Nb:RTP) crystals obtained by the Top Seeded Solution Growth-Slow Cooling (TSSG-SC) technique, but also to find another codopand which increases the Yb3+ concentration in RTP without reducing drastically the nonlinear optical response of pure RTP; so a codopand which shows the same characteristics of niobium. Another objective of this thesis was to obtain efficient fluorescence of Er3+ at around 1.5 µm which would lead to laser action at this wavelength, by codoping Nb:RTP with the pair Er3+/Yb3+, acting Yb3+ as a sensitizing ion of Er3+. To achieve the first objective proposed, enhance the quality and size of Yb:Nb:RTP, we optimize some growth conditions, such as the cooling ramp applied during the crystal growth process, the thermal axial gradient of the solution and the quality of the crystals seeds used in the crystal growths. With those modifications we obtain crystals with size and quality enough to prepare samples from which laser action at around 1 µm has been obtained, for the first time in a crystal of the KTP family, and to determine the fundamental wavelength for non-critical type II SHG in the xy plane, determining that in this plane, at q = 90o and j ? 45o it will be possible to obtain self-frequency doubling laser action in the green spectral range. The second objective, find a codopand with which Yb3+ concentration in RTP was in the range of the one obtained in Nb:RTP, it was achieved by using tantalum. Firstly, it was determined how the RTP crystallization region changes with the Ta5+ and Yb3+ introduction, and which was the optimal solution composition to achieve a higher Yb3+ concentration. With this optimal solution composition bulk crystal of Yb doped RbTi1-xTaxOPO4, grown by TSSG-SC technique, with a Yb3+ concentration of 1.6×1020 ions/cm3 were obtained and the SHG efficiency of powdered samples was an 80 % of that of pure KTP. So, as the Yb3+ concentration obtained in Ta:RTP is of the same order of the one obtained in Nb:RTP, the SHG efficiency is not drastically decreased, and the refractive indexes measured at 632.8 nm do not differ significantly from the ones of Yb:RbTi1-xNbxOPO4, we can assume that in Yb:RbTi1-xNbxOPO4 crystals could also be possible to obtain self-frequency laser action in the green spectral range. About the enhancement of the IR fluorescence of Er3+ by codoping Nb:RTP with Yb3+, bulk crystals of codoped Er3+/Yb3+ Nb:RTP were grown from solutions containing always the same Yb2O3 mol % and by modifying the Er2O3 mol % added in the initial solution. The spectroscopic characterization of these crystals shows the Er3+ fluorescence at around 1.5 µm by pumping between 900 nm and 980 nm, even in the crystals containing low Er3+ concentration (<1020ions/cm3). Moreover to these results, a comparative study between the ionic conductivity of pure RTP grown in its self flux, RTP grown in tungsten flux, Nb:RTP and Yb:Nb:RTP had been performed, in polished plates perpendiculars to c crystallographic direction, to see how it evolves in the mentioned crystals. The results obtained showed that there are no differences between the ionic conductivity in RTP samples, grown in its self flux or in tungsten flux, but in Nb:RTP the ionic conductivity increases considerably. Nb:RTP shows an ionic conductivity of the order of the KTP one (10-7-10-5 S/cm), but in Yb:Nb:RTP the conductivity is only a little bit higher (10-8 S/cm) of the RTP one (10-9 S/cm).