Photorefractive damage resistance threshold in stoichiometric LiNbO_3:Zr crystals

Abstract

Several optical methods including ultraviolet absorption, infrared absorption of the hydroxyl ions, Raman spectroscopy, and the Z-scan method have been used to determine the damage resistance threshold in 0-0.72 mol. % Zr-containing, flux-grown, nearly stoichiometric LiNbO 3 single crystals. All spectroscopical methods used indicate that samples containing at least ≈0.085 mol: % Zr in the crystal are above the threshold while Z-scan data locate the photorefractive damage threshold between 0.085 and 0.314 mol. % Zr. For LN grown from congruent melt the threshold concentration of the optical damage resistant (ODR) ions is roughly 5, 4, and 2 mol. % for di-, tri-, and tetravalent ions, respectively. For example, the threshold concentration for Zr-doped congruent LN crystals was found to be at about 2 mol. % [3,10,11]. Another factor beside the ODR ions and their valency strongly effecting the threshold concentration is stoichiometry of the crystal. The incorporation of ODR ions reduces the amount of antisite Nb Li in the lattice. In nearly stoichiometric LiNbO 3 (sLN) crystals where the Nb Li concentration is almost zero, the threshold value of the dopant concentration can be lower than 0.2 mol. % as was observed for Mg-doped sLN [12] used for instance for terahertz pulse generation [13]. Zr-doped nearly stoichiometric LN crystals prepared by the vapor transport equilibration method were found to have high resistance against optical damage when doped above 0.5 mol. % Zr [14]. The basic advantage of choosing tetravalent ODR dopants comes from their lower damage threshold concentrations; lower built-in dopant content facilitates the growth of more homogeneous crystals, resulting in high-quality samples for device applications.The aim of the present work is to characterize the damage resistance properties of tetravalent Zr-doped sLN crystals by ultraviolet (UV), infrared (IR), and Raman spectroscopies as well as by the Z-scan method. These methods proved earlier very efficient to determine the threshold concentration of the dopants.A series of stoichiometric LN crystals doped with Zr in the 0-0.45 mol. % concentration range were grown by the high-temperature top-seeded solution growth method using K 2 O flux [12]. The Zr concentration in the crystal was determined by inductively coupled plasma mass spectroscopy (ICP-MS). As shown in Fig. 1, the amount of incorporated Zr, at least in the range 0-0.715 mol. % realized in our samples, monotonously increases with increasing concentration of Zr in the starting flux. The relatively high distribution coefficient of Zr as compared to that observed in the melt-grown congruent crystals [3] may be related to the different growing technique, similarly to the case of Mg [12].For optical spectroscopical measurements 1-2 mm thick z-and y-cut samples have been prepared. The UV-visible absorption spectra of z-cut sLN:Zr crystals were measured by a Jasco V-550 spectrometer at room temperature. The spectra of the stretching vibrational bands of the hydroxyl ions (OH − ) in sLN:Zr were

Growth, defect structure, and THz application of stoichiometric lithium niobate

“…Periodically poled sLN:Mg (PPLN), in particular, received special attention in quasi-phase-matched frequency conversion devices. 15 Investigations on the critical threshold concentration of ODR ions in HTTSS grown near stoichiometric crystals have been reported for Mg, Zn, In, and Zr ions using alkali fluxed systems, [43][44][45][46] and for Sc using a Li-rich solution; 47 further references and discussion on this topic will be given in Section III C. …”

“…% range have been grown by the HTTSSG technique. 46 All methods (Z-scan, UV, IR, and Raman) used to characterize the sLN:Zr crystals indicated that the photorefractive damage threshold is at about 0.1 mol. % Zr in the crystal.…”

“…The higher the dopant concentration in the crystal, the higher the intensity ratio between the new and the 3466 cm À1 band, as it was observed, e.g., for sLN:Zr. 46 It is clearly seen that the spectra belonging to dopants of different valences form different groups in sLN crystals. The vibrational frequency for hydroxyl ions in the M Consequently, the OH À vibrational frequencies of doped crystals show a monotonous decrease as a function of the valence of the dopant which can be qualitatively understood taking into account the stronger attractive force for the pro-…”

“…%. 46 In the Li 2 O-Nb 2 O 5 binary system using Li 2 O rich solution, to suppress the photorefractive damage with Mg doping, a minimum of 1 mol. %, 48 with Sc 0.4 mol.…”

Lattice Parameters of Optical Damage Resistant In-Doped LiNbO3 Crystals

“…The approach proposed for the interpretation of Mg (Zn) doping effects, appeared to be not completely adequate for the trivalent and tetravalent ODRI, thus, a refinement of the current model is required. Certain progress is achieved owing to recent studies in ODRI-doped stoichiometric LiNbO 3 (SLN) crystals, e.g., [10,11].…”