Revealing modes from controlling an off-optical axis conical diffraction laser

International audienceThanks to controlling the off-optical axis propagation in the monoclinic KGd(WO4)2:Nd biaxial crystal used as a laser gain medium, we exhibited remarkable crescent laser modes and mode switching, demonstrating the preservation of the conical diffraction. We revealed an optical singularity in addition to the optical axis: the directions of polarization abrupt change of the highest emission cross-section mode, which leads to un-polarized lasing. The key explanation is a severe mode selection due to the threshold behavior of lasing. This is confirmed by a theoretical model taking into account a two-axes crystal rotation and including the conical diffraction behavior. The rotation around the twofold b crystallographic axis of the frame which makes diagonal the imaginary part of the dielectric susceptibility tensor is exhibited

Thermal and Optical Characterization of Undoped and Neodymium-Doped Y3ScAl4O12 Ceramics

Y3–3xNd3xSc1Al4O12 (x = 0, 0.01, and 0.02) ceramics were fabricated by sintering at high temperature under vacuum. Unit cell parameter refinement and chemical analysis have been performed. The morphological characterization shows micrograins with no visible defects. The thermal analysis of these ceramics is presented, by measuring the specific heat in the temperature range from 300 to 500 K. Their values at room temperature are in the range 0.81–0.90 J g1–K–1. The thermal conductivity has been determined by two methods: by the experimental measurement of the thermal diffusivity by the photopyroelectric method, and by spectroscopy, evaluating the thermal load. The thermal conductivities are in the range 9.7–6.5 W K–1 m–1 in the temperature interval from 300 to 500 K. The thermooptic coefficients were measured at 632 nm by the dark mode method using a prism coupler, and the obtained values are in the range 12.8–13.3 × 10–6 K–1. The nonlinear refractive index values at 795 nm have been evaluated to calibrate the nonlinear optical response of these materials.This work is supported by the Spanish Government under projects MAT2011-29255-C02-01-02, MAT2013-47395-C4-4-R, and the Catalan Government under project 2014SGR1358. It was also funded by the European Commission under the Seventh Framework Programme, project Cleanspace, FP7-SPACE-2010-1-GA No. 263044

Polarization properties of lasing near an optical axis in the KGd(WO4)(2):Nd biaxial crystal

International audienceFluorescence and stimulated emission were obtained for propagation directions in the vicinity of the optical axis from the biaxial Nd-doped KGd(WO4)2 crystal. We visualized the peculiar role of the optical axis by fluorescence conoscopy. A fourth spectroscopic parameter due to the monoclinic symmetry was exhibited. Intra-laser-cavity conoscopy was performed in conjunction with the lasing in order to indicate the role of the elliptical modes. The lasing efficiency was found to be in agreement with the relative intensity of the left and right circular polarized components of the fluorescence near the optical axis

Lasing with conical diffraction feature in the KGd(WO4)(2):Nd biaxial crystal

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Cristallogenese, caracterisation et proprietes de fluorescence des monocristaux de type grenat Gd_3Ga_5O_1_2 dopes Cr"3"+-Tm"3"+-Ho"3"+ ou Mn"4"+

SIGLEAvailable from INIST (FR), Document Supply Service, under shelf-number : T 81746 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Chirality versus dichroism: Competition and role in conical diffraction displayed from the Nd:Bi2ZnOB2O6 acentric biaxial laser crystal

International audienceWe have grown acentric chiral Nd-doped BZBO single crystals by the Kyropoulos method, cut perpendicular to the optical axis. With a focused beam at wavelengths in the spectral domain of transparency with various polarizations, the conoscopy patterns revealed the specific role of chirality: disappearance of the optical axis replaced by two C-directions, linear polarization rotation and spiral patterns. The specific rotatory power was measured. The output near field exhibits the influence of chirality on the conical diffraction. Going to wavelengths in the spectral domain of absorption corresponding to the 4I9/2 → 4F5/2 Nd3+ transition, we first studied the chirality/dichroism competition from propagation along the C-directions, characterizing the circular and elliptic eigen-modes. We exhibited the wavelengths at which the ellipse degenerates linearly, signature of the chirality/dichroism balancing. The second aspect is the existence of the optical axis which can be restored if the dichroism is high enough. In this case a singular Voigt wave can propagate. From the experimental determination of the optical parameters, a theoretical description has been proposed, leading to quite well agreement in the far field (conoscopy) and in the near field (conical diffraction)

Light propagation properties of the Bi2ZnOB2O6 acentric biaxial crystal: angular orbital momentum from conical diffraction

International audienceWe have studied a slab of an acentric biaxial Bi2ZnOB2O6 single crystal grown by the Kyropoulos method under conditions of low temperature gradients, oriented perpendicular to the optical axis. We focused slightly behind the sample the Gaussian beam from a He-Ne laser at 632.8 nm and we made magnified images of the near field intensity on a CCD camera. A reference beam was taken from the entrance and redirected on the CCD screen to obtain a controlled wedge fringe pattern visualising the phase of the wave. The specific rotatory power was measured to be 2.74 rad/cm. We present results of conoscopy patterns obtained launching through the crystal slab a left-circular polarized beam and projecting the output beam on a right-circular polarization state or on a linearly polarization state at-45° from the horizontal axis. All the experimental results (optical activity, intensity and phase of the output wave and vortices) are well described by a theoretical model based on the bi-anisotropy of the BZBO crystal. The orbital angular momentum is calculated to be 0.996 ℏ/photon for the output circular projection and 0.456 ℏ/photon for the linear projection

Luminescence studies of Nd3+ and Yb3+ -doped α-Y(IO3)3 and β-Y(IO3)3, transparent host matrix in the mid and beginning of the far-infrared.

International audiencea-Y(IO3)3 and b-Y(IO3)3 are transparent until 12.8 and 13.4 mm, respectively; thus they are interesting as a potential laser matrix in the mid- and beginning of the far-infrared. So, in order to investigate the properties of lanthanides- doped anhydrous yttrium iodate, polycrystalline samples of a-Y1 xNdx(IO3)3 (0.01pxp0.05), b-Y1 xNdx(IO3)3 (0.001pxp0.1), a-Y1 xYbx(IO3)3 (0.01pxp0.33) and b-Y1 xYbx(IO3)3 (0.01pxp0.25) were synthesized. For Nd3+ ions, fluorescent emissions from the 4F3/2 multiplet were observed at 300 K under pulsed laser excitations at 750nm and for Yb3+, fluorescent emissions from the 2F5/2 multiplet were observed at 300 K under pulsed laser excitations at 980 nm. The decays of all these emissions were measured. They are exponential and the fluorescence lifetimes are in the range 0.093-0.193ms for Nd3+ and 0.370-0.541ms for Yb3+, depending on the nature of the host and the concentration of doping