Monoclinic KY Research Articles

All-space existence and dispersion of athermal directions in monoclinic KY(WO4)2

The analytical expressions for thermo-optic coefficients, dn/dT, for “fast” and “slow” light waves propagating along the arbitrary direction in a biaxial crystal are derived. On the basis of these expressions, the all-space analysis of existence of athermal directions is performed for monoclinic and biaxial KY(WO4)2 at 1.03μm. The calculations are performed for an arbitrary light propagation direction and polarization (not restricted to the principal planes). The appearance of directions that can be athermal for both “fast” and “slow” waves is predicted. The dispersion of athermal directions is analyzed for visible and near-IR. The existence of upper and lower dispersion limits for athermal behavior of KY(WO4)2 is shown. It is shown that the optical indicatrix axes can be athermal itself at some light wavelengths. Wavelength- and temperature-dependent position of the optical axes of KY(WO4)2 is also determined.

Thermo-optical properties of pure and Yb-doped monoclinic KY(WO4)2 crystals

The thermo-optic coefficients, dn/dT, were determined for pure and Yb(20 at.%)-doped monoclinic KY(WO4)2 crystals for light polarized along the optical indicatrix axes (Np,Nm and Ng) in the wavelength range of 0.36–1.06 μm by a laser beam deviation method. The absolute values of thermo-optic coefficients satisfy the relation |dnp/dT|>|dng/dT|>|dnm/dT| and increase with the wavelength increasing. In the long-wavelength range, all the dn/dT values are negative: dnp/dT=−14.6, dnm/dT=−8.9, dng/dT=−12.4 [10−6 K−1] for pure KY(WO4)2 at 1.06 μm. The dependency of thermo-optic coefficients on the wavelength was modeled using an approach that takes into account contribution of volumetric thermal expansion and change of electronic bandgap with temperature. Large volumetric expansion of KY(WO4)2 plays a key role in the observed negative dn/dT values. Electronic bandgap and its temperature coefficient were determined for KY(WO4)2 crystals from thermo-optic dispersion curves as Eg=4.8–5.0 eV and −dEg/dT=0.7–1.1×10−4 eV/K. Athermal propagation directions were calculated for KY(WO4)2 crystals at the wavelength of 1.06 μm for light polarizations E∥Nm and Np.

Elastic properties of KY(WO4)2 single crystals studied by Brillouin spectroscopy

Abstract We present a Brillouin spectroscopy study of the acoustic phonons propagating in monoclinic KY(WO 4 ) 2 single crystals. The acoustic phonons were analyzed in relation to the orientation of the optical indicatrics. The velocities of the acoustic phonons propagating in the [1 0 0], [0 1 0], [0 0 1], [1 0 1], [ 1 0 1 ¯ ] and [1 1 0] directions have been determined from Brillouin experiment. Moreover, the values of elastic constants C 22 , C 44 , C 66 and C 46 of KY(WO 4 ) 2 single crystals have been calculated. The results are discussed in terms of low symmetry, high monoclinic angle and strong birefringence of the KY(WO 4 ) 2 crystal investigated.

The EPR of monoclinic KY(WO4)2 single crystal doped with Sm3+ ion

AbstractThe electron paramagnetic resonance (EPR) of Sm3+ ion in KY(WO4)2 single crystal was investigated at T = 4.2 K using an X‐band spectrometer. The observed resonance absorption represents the complex superposition of three spectra corresponding to samarium isotopes with different nuclear moment. The EPR spectrum is characterised by a strong g ‐factor anisotropy. The temperature dependences of the g ‐factor were shown to be caused by strong spin–orbital and orbital–lattice coupling. The resonance lines become broader as temperature increases due to the short spin–lattice relaxation time. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The ground state and EPR spectrum in monoclinic KY(WO 4) 2:Nd 3+ single crystal

The electron paramagnetic resonance (EPR) of Nd 3+ ion in KY(WO 4) 2 single crystal was investigated at T=4.2 K using an X-band spectrometer. The observed resonance absorption represents the complex superposition of three spectra corresponding to neodymium isotopes with different nuclear momenta. The EPR spectrum is characterized by a strong g-factor anisotropy. The temperature dependences of the g-factor were caused by strong spin–orbit and orbit–lattice coupling. The resonance lines become broader as temperature increases due to the short spin–lattice relaxation time.

Raman Scattering and Nd$^{3+}$ Laser Operation in NaLa(WO$_{4}$)$_{2}$

The continuous-wave laser operation of Nd-doped tetragonal NaLa(WO 4)2 crystal is studied at room temperature by optical pumping in the spectral region overlapping AlGaAs diode laser emission. This crystal has inhomogeneously broadened optical bands. From the room-temperature spectroscopic parameters determined it is found that the optimum Nd concentration for the 4F3/2rarr4IJ laser channels must be in the 3-5 at.% range. For J=11/2 and 13/2 channels (lambdaap1.06 and 1.3 mum) the most favourable polarization configuration is parallel to the crystallographic c axis, while for J=9/2 little polarization dependence of the laser efficiency is predicted. Laser operation was achieved with a 3.35 at.% Nd-doped sample grown by the Czochralski method. The laser operation was tested in an hemispherical optical cavity pumped by a Ti:sapphire laser. Stimulated emission at lambda=1056 nm was achieved for a wide spectral pumping range, lambda=790-820 nm. Stimulated Raman scattering was achieved in the picosecond regime with an efficiency similar to that of monoclinic KY(WO4)2 reference compound

Yb-doped KY(WO4)2 planar waveguide laser

High-quality monoclinic KY(WO4)2 optical waveguides were grown by liquid-phase epitaxy, and laser operation of an Yb-doped KY(WO4)2 waveguide was demonstrated for the first time to our knowledge. Continuous-wave laser emission near 1 microm was achieved with both surface and buried planar waveguides. An output power of 290 mW was obtained in the fundamental mode and the slope efficiency was above 80%.

Crystal growth, optical and spectroscopic characterisation of monoclinic KY(WO4)2 co-doped with Er3+ and Yb3+

Abstract We grew un-doped KY(WO 4 ) 2 (hereafter KYW), Er 3+ and Yb 3+ single-doped KYW and Er 3+ , Yb 3+ co-doped KYW single crystals at several dopant concentrations by the Top-Seeded Solution Growth slow-cooling method (TSSG). We studied several optical properties of the host (the transparency window, the orientation of the principal optical axes and the measurement of the refractive indices as a function of the wavelength). We also analysed the spectroscopy of Er 3+ and Yb 3+ ions in KYW in terms of the optical absorption at room temperature (RT) and at low temperature (6 K), and the luminescence at RT and 10 K in the 1425–1650 nm range corresponding to the 1.5 μm emission of Er 3+ ( 4 I 13/2 → 4 I 15/2 transition), after pumping at 981 nm (overlap in energy between 4 I 11/2 and 2 F 5/2 levels of Er 3+ and Yb 3+ , respectively) and at 798 nm ( 4 I 9/2 level of Er 3+ ). Luminescence was studied in terms of optical emission and lifetimes measurements.

Polarized Raman spectra of the oriented NaY(WO4)2 and KY(WO4)2 single crystals

Polarized Raman scattering spectra of the NaY(WO4)2 (NYW) single crystal have been measured. Its structure is described in the tetragonal space group isomorphic to CaWO4 scheelite. The Ag, Bg and Eg spectra were made and discussed in terms of factor group analysis. These spectra are compared to those of monoclinic KY(WO4)2 (KYW) single crystals whose structure differs from the other crystal. The NYW unit cell comprises of the isolated WO4 tetrahedra whereas the KYW structure is built from the WO6 octahedra joined by WO2W double bonds and WOW single bridges. The vibrational characteristics of the bridge bond systems are proposed. On this basis, the role of the vibronic transitions for the KYW crystal doped with Eu3+ ions is discussed.

New Crystalline Lasers on the Base of Monoclinic KR(W04)2:Ln3+ Tungstates (R=Y and Ln)

Monoclinic KY(WO4)2:Pr3+, Tm3+:KY(WO4)2:Er3+, Yb3+ single crystals are grown by low-gradient Czochralski technique. Stimulated emission at 1.0223μm wavelength in the new lasing 1D2→3F3 channel of Pr3+ ions in KY(WO4)2 at room temperature under Xe-flashlamp pumping is excited. Full sets of Stark-level energies for Pr3+ ions in KY(WO4)2 and KGd(WO4)2 crystals at 77 K are determined. 4f2-4f2 intensity-transitions for the KY(WO4)2:Pr3+ are analyzed preliminarily. All observed at present and earlier one-micron Pr3+-ion, induced transitions in the 1D2→3F3 and 1D2→3F4 channels are identified. In yttrium and gadolinium sensitized-tungstates a two-micron (3H4→3H6) low-threshold generation of Tm3+ ions at cryogenic temperatures is achieved.

New optical phenomena in laser insulating crystal hosts with third-order nonlinear susceptibilities

Besides the multiple cascade stimulated Raman scattering, new optical nonlinear phenomena in laser crystal hosts are observed, in particular, in monoclinic KY (WO4)2 and KGd(WO4)2 compounds, under high density visible nano- and picosecond laser excitation in single-pass geometry. The first one is a “laser rainbow”, a multiple co-axial ring Stokes Raman emission by four-wave mixing parametric processes, and the second one is the self-trapping (filamentation) of the propagating laser pump beam and Stokes generation.

Efficient single-mode cw lasers based on monoclinic double potassium-(rare earth) tungstenate crystals containing Nd3+ions with semiconductor-laser pumping

Efficient (~ 20%) single-mode, cw and quasi-cw laser action of Nd3+ ions (in the 4F3/2→4I11/2 channel) has been achieved with diode-laser pumping for the first time at room temperature in monoclinic KY(WO4)2, KGd(WO4)2, and KLu(WO4)2 crystals with an ordered structure.