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We report on an in-band pumped SESAM mode-locked Ho:CALGO bulk laser with a record-high average power of 8.7 W and an optical-to-optical efficiency of 38.2% at a central wavelength of 2.1 um. At this power level, the bulk laser generates pulses with a duration of 369 fs at 84.4-MHz repetition rate, corresponding to a pulse energy of 103 nJ and a peak power of 246 kW. To the best of our knowledge, this is the highest average power and pulse energy directly generated from a mode-locked bulk laser in the 2-3 um wavelength region. Our current results indicate that Ho:CALGO is a competitive candidate for average power scaling of 2 um femtosecond lasers., 9 pages, 5 figures

Radiation-balanced lasing and thermal profiling is reported in two Yb-doped laser crystals at room temperature. In 3% Yb3+:YAG a record efficiency of 30.5% was achieved by frequency-locking the laser cavity to the input light. Both the average excursion and axial temperature gradient of the gain medium were maintained within 0.1 K of room temperature at the radiation balance point. By including saturation of background impurity absorption in the analysis, quantitative agreement was obtained between theory and the experimentally measured laser threshold, radiation balance condition, output wavelength, and laser efficiency with only one free parameter. Radiation-balanced lasing was also achieved in 2% Yb3+:KYW with an efficiency of 2.2% despite high background impurity absorption, losses from Brewster end faces that were not parallel, and non-optimal output coupling. Our results confirm that relatively impure gain media can be operated as radiation-balanced lasers, contrary to earlier predictions which ignored background impurity properties.

We report on high-power mode-locked femtosecond Ho:CALGO laser at 2.1 µm. The laser generates a record-high average output power of 8.7 W (369 fs) with SESAM mode-locking and 1.2 W (152 fs) with Kerr-lens mode-locking.

Glow-in-the-dark materials have been around for a long time. While formerly materials had to be mixed with radioactive elements to achieve a sufficiently long and bright afterglow, these have now been replaced by much safer alternatives. Notably strontium aluminate, SrAl2O4, doped with europium and dysprosium, has been discovered over two decades ago and since then the phosphor has transcended its popular use in watch dials, safety signage, or toys with more niche applications such as stress sensing, photocatalysis, medical imaging, or flicker-free light-emitting diodes. A lot of research efforts are focused on further improving the storage capacity of SrAl2O4:Eu2+,Dy3+, including in nanosized particles, and on finding the underlying physical mechanism to fully explain the afterglow in this material and related compounds. Here an overview of the most important results from the research on SrAl2O4:Eu2+,Dy3+ is presented and different models and the underlying physics are discussed to explain the trapping mechanism at play in these materials.

Despite the incredible capabilities of persistent luminescence materials for indoor applications in dark conditions, their performance for outdoor purposes is still limited by the relatively short duration of the afterglow overnight and the difficulty to excite these materials. To overcome these obstacles new materials with different shapes and forms are needed.

We report on a semiconductor saturable absorber mirror mode-locked thin-disk oscillator based on Yb:YAB delivering pulses with a duration of 462 fs at an average output power of 19.2 W and a pulse energy of 0.38 µJ.

We report the first observation of laser cooling in Yb

Luminescent single crystals are widely used as laser gain media, scintillators, and recently even as radiation converters in some inorganic LEDs. The present work concerns the use of single crystalline Y3Al5O12:Ce3+ as a reference material for photoluminescence spectroscopy and quantum efficiency determination. Garnet crystals are cubic and thus show isotropic optical properties, which is in contrast to monoclinic materials, such as KEu(WO4)2 with anisotropic optical properties. They are also known for their high stability and thus are in line with the aim to use a single crystalline material with consistent optical properties, both for everyday routine control of a given spectrometer setup and for better comparability between different spectrometer setups. Garnet crystals are particularly stable over a long period and rather easy to handle, with implications for improved reproducibility and repeatability of optical measurements. The advantages and disadvantages of this approach as well as the requirements on the quality and preparation of the Y3Al5O12:Ce3+ crystalline samples are presented. Application examples are shown as well, together with comparisons with conventional reference materials based on powders and solutions.

This work deals with the spectroscopic properties of praseodymium doped single crystalline lutetium aluminum garnet (LuAG:Pr3+). A special focus was set on temperature- and time-dependent spectroscopy. Beyond the well-known down-conversion luminescence of LuAG:Pr3+, also UV-A/B up-conversion luminescence under excitation with a 488 nm laser was thoroughly investigated. Furthermore, the results of the spectroscopic investigations on the single crystalline material were supplemented and compared with measurements on a microscale powder sample. In addition, to the spectroscopic investigations, mechanistic considerations are presented to obtain a closer look at the up-conversion process in LuAG:Pr3+. We promote the thesis of a temperature-dependent energy transfer up-conversion mechanism.

We report on a watt-level highly efficient europium laser operating at the 5 D 0 → 7 F 4 transition. It is based on the stoichiometric K E u ( W O 4 ) 2 crystal. Under pumping by a green laser at 532.1 nm, the K E u ( W O 4 ) 2 laser generated a maximum peak output power of 1.11 W at ∼ 703 n m with a slope efficiency of 43.2% and a linear polarization ( E ‖ N m ). A laser threshold as low as 64 mW was achieved. True continuous-wave operation was demonstrated. The polarized emission properties of monoclinic K E u ( W O 4 ) 2 were determined.

Many borate crystals feature nonlinear optical properties that allow for efficient frequency conversion of common lasers down into the ultraviolet spectrum. Twinning may degrade crystal quality and affect nonlinear optical properties, in particular if crystals are composed of twin domains with opposing polarities. Here, we use measurements of optical activity to demonstrate the existence of inversion twins within single crystals of YAl 3 (BO 3 ) 4 (YAB) and K 2 Al 2 B 2 O 7 (KABO). We determine the optical rotatory dispersion of YAB and KABO throughout the visible spectrum using a spectrophotometer with rotatable polarizers. Space-resolved measurements of the optical rotation can be related to the twin structure and give estimates on the extent of twinning. The reported dispersion relations for the rotatory power of YAB and KABO may be used to assess crystal quality and to select twin-free specimens.

International audience; We report the growth of BaZrO3 single crystals by the optical floating zone technique and the investigation on its flux growth using BaB2O4 as a solvent. 6 mm long colorless and transparent single crystals were obtained with a mirror furnace without the need for post-treatment annealing. Its properties are determined and compared with those of two commercial crystals grown by the tri-arc Czochralski method. The chemical composition was investigated using glow discharge mass spectrometry (GDMS) and secondary ion mass spectrometry (SIMS), which indicate minor impurities of Sr, Hf, Ca and Ti, with maximal concentrations for Sr and Hf in the range of 0.3–0.5% at. The optical band gap determined by UV-visible spectroscopy is found to be ∼4.8 eV and indicates the high quality of the BaZrO3 crystals grown by the optical floating zone technique. Raman spectroscopy at ambient conditions and at low temperatures down to 4.2 K reveals a relatively sharp second-order spectrum and does not reveal any structural phase transition. Prospective high-temperature solution growth using BaB2O4 self-flux was investigated and led to 150–200 μm BaZrO3 crystals. This solvent opens the way to grow BaZrO3 at half its melting point by the flux method.

This work deals with the spectroscopic properties of single crystalline samples of KTb3F10. Green luminescing KTb3F10 is an efficient UV radiation converter with a quantum yield of about 40% upon UV-A excitation, while it is also an efficient scintillator upon excitation by 20–50 kV X-ray photons. The temperature dependence of the integral photoluminescence as well as the decay time of KTb3F10 monitored for the Tb3+ emission show that the internal quantum yield between 100 and 800 K is almost constant, while the external quantum yield is modulated, likely due to a change in reabsorption at elevated temperatures. In contrast, the low temperature range between 3 and 63 K reveals a change of the local Tb3+ environment in KTb3F10, which is indicated by an anomaly in the heat capacity and by a strong change of the decay time as well as by a distinct shift of the photoluminescence spectra at low temperatures. In addition, temperature dependent magnetic susceptibility measurements and a structure refinement based on single crystal X-ray diffraction data were performed.

We report the first observation of laser cooling in Yb3+:KYW and validate the results by comparison with experiments in the well-studied material Yb3+:YAG. Radiation from a single-mode Ti:Al2O3 laser was used to achieve cooling of 1.5 K/W in 1% Yb:KYW at 1025 nm, comparing well with the reference material 3% Yb:YAG which cooled by 3.5 K/W at 1030 nm under open lab conditions. Experimental results for KYW crystals mounted on aerogels and doped with 1-20% Yb were in excellent agreement with the theoretical dependence of cooling power on the Yb absorption spectrum. Elimination of thermal conduction through the sample support structure was found to permit the attainment of lower temperatures and to simplify modeling of radiation balance conditions in self-cooled lasers with longitudinal thermal gradients. Contrary to the notion that more coolant ions yield higher cooling power, concentrations of Yb over 1% caused re-absorption of luminescence in KYW crystals, leading to a progressive red shift in the optimal cooling wavelength and the prevention of laser cooling altogether in a 20% sample at room temperature. The prospect of attaining radiation-balanced lasing in commercially-available tungstate crystals is evaluated.

International audience; (K,Na)NbO 3 -based ferroelectric single crystals have recently undergone a substantial development, resulting in improved crystal quality and large piezoelectric coefficients, exceeding 700 pC/N, over a broad temperature range. However, further development necessitates a detailed understanding of the mechanisms defining the domain structure and its temperature evolution. This paper presents the investigation into the crystallographic structure and domain configurations of a (K,Na,Li)(Ta,Nb)O 3 single crystal over a broad temperature range. The crystal was grown by the submerged-seed solution growth technique and investigated using in situ transmission electron microscopy, X-ray diffraction, dielectric measurements, and polarized light microscopy. The lattice distortion, structural phase transitions, and domain configurations are reported. A transition from the lamellar orthorhombic to the rectangular tetragonal domain structure is observed upon heating. Moreover, the milky optical appearance of the crystal was investigated and found to result from the presence of regions with different domain configurations and domain sizes. The formation of these regions is related to the growth defects, which govern the domain formation when cooling below the Curie temperature.

This work describes the growth of crack-free single crystals of KEu(WO4)2 and their characterization with respect to spectroscopic properties. The crystal structure of KEu(WO4)2 was refined from single crystal X-ray diffractometer data at 293 (KY(WO4)2 type, C2/c, a = 1069.88(7), b = 1046.87(5), c = 760.47(5) pm, β = 130.774(4)°, wR2 = 0.0513, 1247 F2 values and 57 variables) and 90 K (a = 1067.69(4), b = 1048.45(4), c = 757.87(3) pm, β = 130.784(2)°, wR2 = 0.1078, 1237 F2 values and 57 variables). It turns out that KEu(WO4)2 is a promising material for some demanding application areas due to its excellent thermal stability. Temperature dependent spectroscopy revealed that the thermal quenching temperature T1/2 of the crystalline material is 699 K (426 °C). From time dependent emission spectra the fluorescence lifetime τr was determined to be 498 ± 2 μs at 3 K. The decay time moderately declines down to 480 μs at room temperature pointing to the presence of very little thermal quenching at ambient conditions. A strong decline of the emission integral and decay time is not observed before reaching almost 600 K. Finally, the quantum efficiency was determined to be about 64% at room temperature and the asymmetry ratio for the 5D0 -7F2 to 5D0 -7F1 emission multiplets is about 10.8, which means that the Eu3+ spectrum is dominated by the 5D0 – 7F2 transition. 151Eu Mossbauer spectroscopic and temperature dependent magnetic susceptibility data confirm stable trivalent europium.

International audience; Ferroelectric single crystals exhibit the largest known piezoelectric constants and therefore show high potential for application in electronic devices, including sensors, actuators, and transducers. Their large properties, however, can only be fully exploited if the behavior is not influenced by lattice defects, formed during high-temperature processing. Such defects can inhibit domain-wall movement, increase leakage currents, and are predominantly responsible for the poor performance of the emerging ferroelectric crystals. Here, an approach to considerably enhance the piezoelectric and ferroelectric properties of (K,Na,Li)(Nb,Ta,Sb)O3 crystals by oxygen annealing is investigated. As compared to the non-annealed crystals, polarization, strain, and piezoelectric constant of the annealed sample were enhanced by a factor of two, resulting in an outstanding room-temperature value of piezoelectric constant d33 = 732 pC/N and a peak value of d33 = 1431 pm/V at the orthorhombic-tetragonal transition. The behavior was analyzed using electromechanical measurements, Mössbauer spectroscopy, and impedance spectroscopy, revealing decreased concentrations of both oxygen vacancies and Sb3+ ions after annealing. The findings indicate that the control of the defect chemistry enables these ferroelectric (K,Na)NbO3-based single crystals to outperform their polycrystalline counterparts and reach the values of lead-containing compositions. Moreover, the present strategy enables further detailed studies of the inherent crystal anisotropy and the possibilities for domain engineering.

Terbium-substituted KYW2O8 single crystals of high optical quality were grown by the top seeded solution growth technique. The degree of yttrium–terbium mixed occupancy was determined for two samples through structure refinements on the basis of single crystal X-ray diffractometer data. Temperature dependent magnetic susceptibility data underline the paramagnetic nature of terbium doped crystals. No magnetic ordering is evident down to 2 K. Luminescence measurements yield the typical excitation and emission spectra as expected for Tb3+ activated materials. The decay time of Tb3+ decreases linearly with the Tb3+ concentration, while the excess of thermal quenching does not change significantly. At about 405 K the decay time is reduced by roughly 50% relative to the low-temperature value, both for the powders as for the single crystals.

We report on the absorption profile of the monoclinic holmium-doped $$\hbox {KY}(\hbox {WO}_4)_2$$ crystal near the optic axis for the maximal absorption wavelength at 1960 nm. The full angular distribution of the absorption coefficient at the vicinity of such optical singularity has been experimentally and numerically investigated. Furthermore, laser experiments along the optic axis have been carried out. So-called conical refraction laser and classical Gaussian laser operation are compared near the optic axis, taking into account the complex absorption profile.

High-quality single crystals of partially europium-substituted KYW 2 O 8 (KYW) were grown by the top-seeded solution growth technique. The structures of four crystals with different europium content were refined on the basis of single crystal X-ray diffractometer data. The trivalent character of europium in these crystals was manifested through 151 Eu Mossbauer spectra and magnetic susceptibility measurements. Moreover, reflection and photoluminescence spectra were recorded and from these spectra the quantum efficiency, lumen equivalent, and CIE1931 color point were calculated. It turned out that Eu 3+ doped KYW is an efficient photoluminescent material at room temperature, while the thermal quenching temperature T 1/2 is at about 633 K (360 °C), thus making the material a potential radiation converter for light emitting diodes.

International audience; We have developed laser grade and highly Yb3+-doped cubic rare-earth sesquioxides (RE2O3, RE = Y, Gd, Lu) single crystals by means of a newly designed high-temperature solution growth method which gives them spectroscopic properties different from those obtained by high-temperature solidification methods. Absorption and emission cross sections, visible anti-Stokes emission, fluorescence decays of the new cubic Gd2O3:Yb3+ single crystals are presented and compared to those of Y2O3:Yb3+ and Lu2O3:Yb3+ crystals. The case of cubic Gd2O3:Yb3+ is particularly interesting since its basic spectroscopic properties have never been detailed and we were capable of achieving Yb-doping level as high as 20%.

Absorption, stimulated-emission and gain cross-sections are determined for 3 at.% Tm:CaGdAlO4. This crystal is employed in a microchip laser diode-pumped at 802 nm. In the continuous-wave (CW) regime, this laser generates 1.16 W at 1883-1893 nm with a slope efficiency of 32% with respect to the absorbed pump power. Using a special "bandpass" output coupler, vibronic CW laser operation up to 2043 nm is achieved. For passive Q-switching of the Tm:CaGdAlO4 laser-saturable absorbers (SAs) based on CVD-grown graphene and randomly-oriented arc-discharge single-walled carbon nanotubes (SWCNTs) in a PMMA film. The SWCNT-SA demonstrates superior performance. The laser produced a maximum average output power of 245 mW at 1844 nm with a slope efficiency of 8%. The latter corresponds to a pulse energy and duration of 6 μJ and 138 ns, respectively, at a repetition rate of 41 kHz. Using the graphene-SA, 2.8 μJ, 490 ns pulses are obtained at a repetition rate of 86 kHz.

The development of materials showing efficient red-emitting persistent luminescence is still an ongoing challenge. As it shows red emission, around 613 nm, Pr3+ remains a good candidate for such application. Indeed, the transition from its 1D2 excited state to its 3H4 ground state is responsible of the red emission. In this paper the effect of Na substitution in NaNbO3:Pr3+ by K or Li cations in term of Metal-to-Metal Charge Transfer (MMCT) band position and its possible effect on persistent luminescence properties were investigated. MMCT energy shows increasing tendency with increasing average distance between A site (A = Li, Na, K, Pr) of perovskite. The most intense (efficient) photoluminescence was observed under MMCT excitation in Li0.03Na0.97NbO3:Pr3+. The relaxation pathways were discussed based on the configurational coordinate model.

Centimeter size LiEu(MoO4)2 bulk single crystals have been grown by top-seeded solution growth using Li2MoO4 as a flux. The resulting crystals exhibited different coloration shades from dark to bright violet. Small single crystal fragments were studied by X-ray diffraction: CaWO4 type, space group I41/a, a = 519.74(4), c = 1132.56(11) pm, wR2 = 0.0143, 270 F2 values at 300 K and a = 518.70(4), c = 1130.25(11) pm, wR2 = 0.0197, 268 F2 values at 90 K. The Li+ and Eu3+ cations statistically occupy the 4b site. Down to 90 K, the single crystal X-ray data give no hint for cation ordering. Some of the grown crystals show dark violet color. This is due to defects in the oxygen substructure accompanied by partial reduction of Mo6+ (d0) to Mo5+ (d1) which was detected by electron spin resonance. 151Eu Mossbauer spectra of the bright and also of the dark violet LiEuMo2O8 samples show the presence of trivalent europium solely. Temperature dependent magnetic susceptibility data exhibit weak van Vleck type paramagnetism as a consequence of trivalent europium ([Xe]4f6). The dark violet samples show slightly higher susceptibility due to the contribution of Mo5+. These data point to a formula LiEuMo2O8–x for the violet samples. 7Li solid state NMR spectra underline the single lithium sites in both samples. Both colored crystals show identical emission spectra, which indicate the same chemical surrounding of the trivalent europium ions. However, excitation spectra and thermal quenching and decay curves points to a higher defect density in the violet sample.

Dielectric and piezoelectric properties of K(Ta0.51Nb0.49)O3 [KTN] single crystals along [100], [001] and [011] pseudo-cubic crystallographic orientations are reported and discussed. Temperature dependences of the dielectric permittivity in tetragonal phase of monodomain and polydomain crystals of these orientations are compared. A strong dielectric anisotropy is found in the tetragonal phase, with an ϵ[100] / ϵ[001] ratio equal to 16 at 300 K. Room temperature piezoelectric coefficients for the monodomain state of KTN are reported.

International audience; Orientation and temperature dependence of dielectric and electromechanical properties of Mn-doped (Li,Na,K)(Nb,Ta)O3 single crystals were investigated. Samples exhibited very low dielectric losses, with tanδ between 0.03 and 0.05 over a broad temperature range between room temperature and 480 °C. Influences of the crystallographic structure and external electric field on polarization and strain parameters are discussed. The orientation-dependent electrical properties were ascribed to the anisotropic polarization rotation in the crystals. Higher maximum polarization, coercive field, and negative strain were achieved when the electric field was oriented along one of the spontaneous polarization directions. The highest maximum unipolar strain of 0.42% (at 3 kV/mm) and the normalized strain d 33 * of 1391 pm/V were obtained in the [001]PC-oriented sample at 100 °C, which was much higher than the values obtained for the [110]PC-oriented sample. Further insight of the phase transition behavior is given by comparing the temperature-dependence of the small- and large-signal dielectric and piezoelectric properties. The observed changes are rationalized by the different increase rates of the dielectric permittivity and piezoelectric coefficients with temperature.

A series of centimeter-sized lead-free piezoelectric Li+- and Ta5+-modified (Na,K)NbO3 single crystals with an ABO3 perovskite structure was successfully grown by the top-seeded solution growth method. Effective segregation of the elements was considered in order to further develop the growth of Li+- and Ta5+-modified (Na,K)NbO3 single crystals. The crystallographic structure and electrical behaviour along the [001]PC orientation were studied. X-ray diffraction, Raman spectroscopy and dielectric studies reveal that the increase in Ta5+ content reduces the orthorhombic–tetragonal phase transition. Bipolar and unipolar strain curves were investigated at 2 kV mm−1. The highest bipolar and unipolar strains associated with a large-signal piezoelectric constant of 368 pm V−1 were achieved for Li0.02Na0.626K0.354Nb0.808Ta0.192O3. The asymmetric bipolar strain curves were observed and related to the existence of internal bias fields induced by defect dipoles, which were created during the crystal growth process.

We measured the rotation of the dielectric frame and determined the orientation of the optical axes in KRE(WO4)2 (RE = Gd, Y, Lu) crystals, as a function of wavelength in the 0.4-1.6 μm range.

DOI: 10.1364/OME.6.002984 URL: https://www.osapublishing.org/ome/abstract.cfm?uri=ome-6-9-2984 Filiació URV: SI We measured a rotation of the dielectric frame as a function of wavelength of about 2° in the spectral range of 0.4-1.6 ¿m in the monoclinic double tungstate crystals, KRE(WO4)2 where RE = Gd, Y or Lu. We also refined the Sellmeier equations of their three principal refractive indices. By taking into account these data, we calculated the real orientation of the optical axes as a function of wavelength which is of key importance for the design of conical refraction lasers based on monoclinic double tungstate crystals.

(K0.5Na0.5)NbO3 (KNN) is a potential lead-free replacement for Pb(Zr, Ti)O3 (PZT) piezoceramics, but its piezoelectric properties are inferior to those of PZT. By growing single crystals of KNN, it may be possible to improve the piezoelectric properties. Recently, single crystals of KNN were grown by the solid-state crystal growth (SSCG) method, but the crystals were very porous. In this paper, a method of growing dense single crystals by SSCG in a hot press will be described. (110)-oriented single seed crystals of KTaO3 were buried in KNN powder, with 0.5 mol% of K4CuNb8O23 added as a sintering aid. After consolidation by uniaxial and isostatic pressing, the tablets were hot pressed in a two-stage treatment. During hot pressing, dense single crystals of KNN grew using the KTaO3 seed crystal as a template. The effect of hot pressing on single crystal growth will be discussed.

Single crystals of (K 0.5 Na 0.5 )NbO 3 have been grown for the first time by the solid state crystal growth process. A KTaO 3 seed crystal was embedded in a matrix of (K x Na 1− x )NbO 3 powder with a nominal composition of (K 0.5 Na 0.5 )NbO 3 . K 4 CuNb 8 O 23 was used as a liquid-phase sintering aid. During sintering a single crystal of (K 0.5 Na 0.5 )NbO 3 grew on the KTaO 3 seed. Scanning electron microscopy energy dispersive X-ray spectroscopy (SEM-EDS) showed that Ta did not migrate into the single crystal and that the single crystal had a composition very close to that of the nominal value. SEM-EDS showed that the single crystal and the matrix grains had the same composition within the limits of experimental error. Transmission electron microscopy (TEM) confirmed that the grown material was indeed single crystalline and had grown epitaxially on the seed crystal. The single crystal contained a considerable amount of porosity, which could be reduced by pre-densification of the matrix by hot pressing.

A single crystal of (Na, K, Li)(Nb, Ta)O 3 has been grown for the first time by the solid state crystal growth process. A seed crystal of 〈0 0 1〉-oriented KTaO 3 was embedded in a matrix of (Na, K, Li)(Nb, Ta)O 3 powder, which was then densified by hot-pressing. During annealing of the hot-pressed sample, a single crystal of (Na, K, Li)(Nb, Ta)O 3 of between 20 and 50 μm thickness grew on the KTaO 3 seed. The single crystal contained porosity incorporated from the matrix. Chemical analysis showed the single crystal to have the same composition as the matrix. A single crystal of constant thickness could be grown by adding a liquid phase sintering aid to the powder. The solid state crystal growth method is promising for the growth of single crystals of (Na, K, Li)(Nb, Ta)O 3 .

International audience; In this work, we present the first crystal growth of cubic Tb2O3 single crystals by a controlled atmosphere flux method which uses a heavy metal free solvent working at less than half the melting temperature of this sesquioxide. Cubic millimeter-sized crystals extracted from as-grown boules are phase (powder XRD) and chemically (GDMS) pure and exhibit a Verdet constant in the visible and near-infrared spectral ranges, which is at least three times higher than that of a commercial Tb3Ga5O12 (TGG) crystal. The 1.36 mm thick crystals display a transmission coefficient higher than 77% over the 525 nm–1.38 μm spectral range. The absorption spectrum, magnetic susceptibility and specific heat measurements on the single crystals confirm the absence of detectable Tb4+ cations and other impurities.

YAl 3 (BO 3 ) 4 crystal enables the highest UV power of 1.8 MW and shortest pulse of 118 ps with power conversion efficiency of 37 % at 266 nm by using LBO crystal and Nd:YAG/Cr:YAG microchip laser.

Bismuth Ferrite (BFO) nanoparticles (BFO-NP) display interesting optical (nonlinear response) and magnetic properties which make them amenable for bio-oriented applications as intra- and extra membrane contrast agents. Due to the relatively recent availability of this material in well dispersed nanometric form, its biocompatibility was not known to date. In this study, we present a thorough assessment of the effects of in vitro exposure of human adenocarcinoma (A549), lung squamous carcinoma (NCI-H520), and acute monocytic leukemia (THP-1) cell lines to uncoated and poly(ethylene glycol)-coated BFO-NP in the form of cytotoxicity, haemolytic response and biocompatibility. Our results support the attractiveness of the functional-BFO towards biomedical applications focused on advanced diagnostic imaging., Word Count: 109 Complete Word Count (body text and figure legends) : 4886 Number of Figures: 6 Number of Tables: 0 Number of reference: 45

We demonstrate the first (to our knowledge) quasi-three-level conical refraction laser operating at 2 μm, with 1.6 W of output power at 2074 nm, using a holmium-doped KY(WO4)2 crystal. A maximum slope efficiency of 52% has been achieved, along the optic axis with respect to the absorbed pump power. Furthermore, lasing operation around the optic axis has been performed. In this case, a maximum output power of 3 W has been reached, with a slope efficiency better than 70%, which are the best performances ever reported on this material.

International audience; We demonstrate the first (to our knowledge) quasi-three-level conical refraction laser operating at 2 μm, with 1.6 W of output power at 2074 nm, using a holmium-doped KY…WO 4 † 2 crystal. A maximum slope efficiency of 52% has been achieved, along the optic axis with respect to the absorbed pump power. Furthermore, lasing operation around the optic axis has been performed. In this case, a maximum output power of 3 W has been reached, with a slope efficiency better than 70%, which are the best performances ever reported on this material. Studies of conical refraction (CR) have recently revived. When a Gaussian light beam propagates along the optic axis of a biaxial crystal, under certain conditions a two ring-shaped beam can be observed, at the exit face of the crystal. Several publications describe this effect, theo-retically and experimentally [1–4]. Recent availability of long biaxial crystals, with good optical quality, facili-tates CR studies. Therefore, several applications of this effect have recently been investigated, such as optical tweezers [5], particle trapping [6], beam shaping [7–11], and microscopy [12]. There are also some publications about laser operation along an optic axis of a biaxial crys-tal, the first publication being [13]. Using a short (3 mm long) biaxial crystal of a CR-cut ytterbium-doped KGd…WO 4 † 2 (KGW), the output polarization of their laser was modified, by translating the output coupler mirror. The researchers obtained a slope efficiency of 60% along the CR axis, which is similar to the value obtained for a classical N g -cut orientation. However, the threshold was 2× higher for CR orientation. A few years later, [14,15] presented a four-level conical refraction laser, made with neodymium-doped KGW. The researchers obtained both a Gaussian and CR output beam. They reported a slope efficiency close to the quantum defect limit [14], and no influence of any thermal effect over the measurement range (up to 3 W at 1067 nm) was observed. The thermo-optic properties of neodymium-doped KGW were studied in [16]. The researchers show the anisotropy of the thermo-optic properties, along this propagation direc-tion with a short crystal (1 mm long). However, the effect of CR inside the cavity, changing the light distribution in-side the crystal, is still not well-known. In this Letter, we report the first experimental results (to our knowledge) of a holmium-doped KY…WO 4 † 2 (KYW) CR laser, showing laser action along the CR axis. Measurements near the optic axis have also been per-formed, in order to be able to compare CR and Gaussian beam intracavity laser performance.

We report a study of second- and third-harmonic generation in BiB3O6 (BiBO). The effective nonlinearity, phase-matching angle, acceptance bandwidth, and walk-off are calculated and analyzed within the principal planes of the optical indicatrix. In the experiment, the phase-matched harmonic generation is investigated within the xz and yz planes. Also, the temperature dependence of the noncritical phase matching for laser radiation propagating along the z axis is measured for second-harmonic generation (SHG) at crystal temperatures of 25–265^∘C. The corresponding wavelengths of the laser radiation are in the range of 1.16 to 1.34μm. In addition, SHG of 1342-nm radiation of a q-switched Nd:YVO4 laser system is investigated for noncritical and critical phase matching. The achieved conversion efficiencies are 59% and 20%, respectively. Besides SHG, third-harmonic generation (THG) of 1064-nm, ns laser pulses is investigated. The measured conversion efficiency is as high as 34%. For THG the properties of BiBO are compared with those of BBO and LBO.

We report the phase matching of parametric frequency conversion in the nonlinear material BiB3O6 (BiBO) and on an investigation of optical parametric oscillators (OPOs) of this new crystal. Based on the calculation of collinear type I and type II phase matching within the refractive-index planes, the most favorable directions for phase matching are identified for OPOs pumped by the fundamental or the harmonics of 1064-nm Nd-doped lasers. Based on these results, pulsed 532-nm-pumped ns OPOs are realized. The pump source is either a Q-switched high repetition rate (10 kHz) Nd:YVO4 laser (with a pulse energy of 24 μJ) or a low repetition rate (10 Hz), high pulse energy (120 mJ) Nd:YAG laser system. The BiBO OPO pumped by the Nd:YVO4 laser showed a very low threshold of 0.047 J/cm2. At an average pump power of 2.4 W the total OPO output power was 630 mW. By changing the phase-matching angle Θ within the yz plane from 0 to 11.6° the signal wavelength was tuned from 735 nm to 970 nm, while the spectral width changed from 0.2 nm to 1.4 nm. By pumping the OPO with the Nd:YAG laser, the OPO had a threshold of 0.12 J/cm2, a steep slope (59%) and a high total efficiency (of up to 48%). Due to divergence broadening the spectral width changes from 8.5 nm at 800 nm to 70 nm near degeneracy. The properties of BiBO determined from the experimental results are compared with those of well-known nonlinear materials such as BBO, LBO and KTP.

The sequence of optical phase transitions is considered for a photorefractive coherent oscillator with a conventional mirror and a four-wave mixing phase conjugate mirror. Analogous to phase transitions in solids, the phase diagrams are constructed and defined qualitatively as different states of a whole system (light-induced scattering below the threshold of oscillation, single-frequency oscillation, two-frequency oscillation, and multimode mirrorless oscillation). The attempt of experimental mapping of a phase diagram is presented for a coherent oscillator with Co-doped BaTiO3.

The saturation intensity, oscillation spectrum, and temporal dynamics of oscillation are studied for a semilinear coherent oscillator with two counterpropagating pump waves and a photorefractive crystal with dominating reflection gratings. The instability of the single-frequency oscillation spectrum is revealed, similar to that known for an oscillator with dominating transmission gratings. The experimental manifestation of this transition in the output characteristics of the oscillator is favourably compared with numerical calculations.

The absorption spectrum of BaTiO 3 :Rh is measured from 400 nm to 1100 nm, there is strong absorption peak (α = 7 cm -1 at 633 nm) while at 850 nm the absorption is rather weak: α = 2 cm -1 .Then, we propose an experimental investigation of the EO coefficients, for two different wavelengths corresponding to strong and weak absorption, based on an interferometric and ellipsometric assembly using application of a static electric field and leading to the measurement of the coefficients r 13 and r 33 separately and the linear combination r c .