Synthesis and laser patterning of Bi-doped Y3Fe5O12 crystals in germanosilicate glasses

New germanosilicate glasses giving the crystallization of yttrium iron garnet Y₃Fe₅O₁₂ (YIG) and Bi-doped YIG, 23Na₂O-xBi₂O₃-(12−x)Y₂O₃-25Fe₂O₃-20SiO₂-20GeO₂ (mol%), are developed, and the laser-induced crystallization technique is applied to the glasses to pattern YIG and Bi-doped YIG crystals on the glass surface. It is clarified from the Mössbauer effect measurements that iron ions in the glasses are present mainly as Fe³⁺. It is suggested from the X-ray diffraction analyses and magnetization measurements that Si⁴⁺ ions are incorporated into YIG crystals formed in the crystallization of glasses. The irradiations (laser power: 32-60 mW and laser scanning speed: 7 μm/s) of continuous wave Yb:YVO₄ fiber laser (wavelength: 1080 nm) are found to induce YIG and Bi-doped YIG crystals, indicating that Fe³⁺ ions in the glasses act as suitable transition metal ions for the laser-induced crystallization. It is suggested that YIG and Bi-doped YIG crystals in the laser irradiated part might orient. The present study will be a first step for the patterning of magnetic crystals containing iron ions in glasses.     

Synthesis and spectroscopy of sodium-gadolinium tungstate NaGd(WO4)2 crystals activated by Tm3+ ions

Single crystals of disordered double sodium-gadolinium tungstate NaGd(WO₄)₂ doped with Tm ions were grown by the Czochralski method. The polarized absorption and emission spectra of these crystals with different activator concentrations and the decay kinetics of the ³ H ₄ and ³ F ₄ excited states of Tm³⁺ ions at 300 K were investigated. The absorption and emission cross sections of the expected laser transition ³ F ₄ ? ³ H ₆ in the Tm³⁺ ion were determined and the amplification spectra of the active laser medium NaGd(WO₄)₂:Tm at different levels of inverse population of the upper laser level ³ F ₄ of the Tm³⁺ ion were constructed. The prospects for using these crystals as active media in 2-μm solid-state lasers are discussed.     

Simultaneous dual-wavelength laser operation at 1342 and 946 nm in two laser crystals and their sum-frequency mixing

A sum-frequency yellow-green laser at 554.9 nm is reported by this paper, 946 nm wavelength is obtained from ⁴F_3/2-⁴I_9/2 transition in Nd:YAG and 1342 nm wavelength is obtained from ⁴F_3/2-⁴I_13/2 transition in Nd:YVO₄. Using a doubly folded-cavity type-II critical phase matching KTP crystal intra cavity to make 946 nm laser from Nd:YAG and 1342 nm laser from Nd:YVO₄ frequency summed, with incident pumped power of 30 W in Nd:YAG and 20 W in Nd:YVO₄, TEM₀₀ mode yellow-green laser at 554.9 nm at 1.15 W is obtained and its M² factor is less than 1.22. The experimental results show that the Nd:YAG and Nd:YVO₄ crystals intra-cavity sum-frequency mixing is an effective method for yellow-green laser and it can be applied to other two laser crystals to obtain more all-solid-state lasers with different wavelengths.     

Excited state absorption and stimulated emission of Nd3+ in crystals. Part 2: YVO4, GdVO4, and Sr5(PO4)3F

3+ ion in the crystals YVO₄, GdVO₄, and Sr₅(PO₄)₃F. The measurements were performed in the spectral region of the main laser transitions ⁴F_3/2→⁴I_9/2, ⁴F_3/2→⁴I_11/2, and ⁴F_3/2→⁴I_13/2by a continuous wave pump and probe technique. The calibrated gain and ESA spectra are presented and possible implications of ESA on the laser performance are estimated. It is shown that ESA can be a small loss factor to the laser emission near 1060 nm but does considerably diminish the effective emission cross sections near 1340 nm especially in Nd:YVO₄ and Nd:GdVO₄. Received: 29 January 1998/Revised version: 8 May 1998     

Spectroscopic properties of Yb ions in La2(WO4)3 crystal

Yb³⁺-doped La₂(WO₄)₃ single crystals were grown by the Czochralski technique. Absorption and fluorescence spectra of the crystal were recorded at the room temperature. The stimulated emission cross-sections of Yb³⁺ ions were calculated using the reciprocity method and Fuchtbauer-Ladenburg formula, respectively. The fluorescence decay curves of ²F_5/2 manifold of Yb³⁺ ions were recorded at room temperature for both crystal and powder samples. The effect of radiation trapping on the spectroscopic properties is discussed. Comparison with other Yb³⁺-doped laser crystals is made. The results show that Yb³⁺:La₂(WO₄)₃ crystal is a promising laser material.     

Quantum efficiency of Nd-doped lasers measured by pump-induced crystal heating: application to the Nd3+:Gd2(MoO4)3 crystal

In this paper we show how the quantum efficiency of Nd³⁺-doped laser crystals can be measured by means of a very simple method. This method is based on a multiwavelength study of pump-induced crystal heating, and its major advantage is the simplicity of the required experimental set-up. It has been used to determine the quantum efficiency of the main infrared laser channel (⁴ F _3/2?⁴ I _11/2) of the Nd³⁺:Gd₂(MoO₄)₃ non-linear laser crystal. The value obtained for the quantum efficiency (φ=0.97) is in good agreement with that obtained from the Judd–Ofelt formalism (φ=0.95). Received: 25 October 2000 / Revised version: 2 January 2001 / Published online: 27 April 2001     

Upconversion from the I13/2 and I11/2 levels in Er:YAG

The efficiency of erbium three-micron laser (laser transition ⁴I_11/2→⁴I_13/2) depends essentially on the ratio of the parameters of active energy transfer upconversion (ETU) from the laser levels. The parameters of both ETU processes can be obtained from the analysis of the shape of the kinetics of the ⁴I_11/2 level in concentrated Er:YAG crystals, under short pulse pumping. Mathematical modeling is used to evaluate the sensitivity of the method and to estimate the errors which can be introduced by the inhomogeneous pumping and accidental impurities. It was found that the ratio of the parameters corresponding to the ETU from the laser levels is less sensitive to the pumping inhomogeneities than that corresponding to the lower laser level. A reduction of this ratio with increasing erbium concentration is observed.     

Ultraviolet to infrared refractive indices of tetragonal double tungstate and double molybdate laser crystals

Sellmeier parameters of thirteen tetragonal (space group $I\overline{4}$ ) double tungstate and double molybdate laser crystals with M⁺T³⁺(X⁶⁺O₄)₂ composition have been calculated using the room temperature refractive indices determined from the ultraviolet band gap of the crystals to ????2 ??m. All considered crystals are uniaxial but only crystals with Bi in their composition show a significant birefringence (??n>10^?2). The refractive index value increases for the sequence T³⁺=La, Y, Gd, Lu, and Bi independently of the M⁺ and X⁶⁺ cation pair. Implications for the design of laser waveguides and laser pulse dispersion are discussed.     

Spin-spin and spin-other-orbit effects of optical spectra and the spin-Hamiltonian parameters for Cr ions in MgO crystals

An extended complete diagonalization method/microscopic spin-Hamiltonian (CDM/MSH) program has been developed, which is applicable for d³ ions at sites of tetragonal symmetry type I (C_4v, D_2d, D₄, D_4h) and trigonal symmetry type I (C_3v, D₃, D_3d). The Hamiltonian includes the spin-spin (SS) and spin-other-orbit (SOO) magnetic interactions besides the spin-orbit (SO) magnetic interaction usually taken into account. Utilizing the extended CDM/MSH program, the optical spectra, the spin-Hamiltonian (SH) parameters of the ground state ⁴B₁, and the splitting δ(²E) of the first excited ²E state for Cr³⁺ (3d³) ions at C_4v symmetry sites in MgO crystals have been successfully investigated. It is found that although the SO magnetic interaction is the most important one, the contributions to the SH parameters and the optical spectra from the SS and SOO magnetic interactions for Cr³⁺:MgO crystals are appreciable and should not be omitted, especially reaching 27.8% for the zero field splitting parameter D.     

Spectroscopic study of double sodium-yttrium fluoride crystals doped with erbium Na<Subscript>0.4</Subscript>Y<Subscript>0.6</Subscript>F<Subscript>2.2</Subscript>:Er<Superscript>3+</Superscript>: II. Luminescence self-quenching and microparameters and macrorates of energy transfer

Na_0.4Y_0.6F_2.2:Er³⁺ (NYF:Er³⁺) crystals with an Er concentration up to 15% were grown by the Bridgman-Stockbarger method. The luminescence kinetics was investigated for a series of NYF:Er³⁺ crystals (0.5–15% Er), as well as the concentration and temperature quenching of the luminescence from radiative Er levels upon selective laser excitation. It is shown that the luminescence from the ⁴S_3/2 level is quenched significantly with increasing temperature and concentration. The luminescence from the ⁴G_11/2, ²G(H)_9/2, ⁴F_9/2, and ⁴I_9/2 levels is quenched mainly due to nonradiative multiphonon transitions. The concentration quenching of the luminescence from the ⁴I_11/2 and ⁴I_13/2 levels was not observed. Possible schemes of the self-quenching of excited levels of erbium are considered and the microparameters and macrorates of self-quenching are estimated by model quantum-mechanical calculation. Based on the comparison of the calculated and experimental self-quenching rates, the most probable mechanisms and schemes of self-quenching are determined. The self-quenching of the ⁴S_3/2 level of erbium was investigated experimentally and theoretically. Good agreement is obtained between the experimental and the calculated kinetic curves and the dependences of the self-quenching rates on Er concentration. It is concluded that NYF:Er³⁺ crystals are promising as active media for tunable lasers with laser diode pumping.     

Pulsed blue-light generation by the frequency doubling of the 4F3/2 to 4I9/2 transition in Nd:YAG and Nd:YAlO3

We report on the frequency doubling of Q-switchedNd:YAG and Nd:YAlO₃ lasers emitting at 946 and 930 nm, respectively (⁴F_3/2 to ⁴I_9/2 transition). The neodymium-doped laser host crystals were excited with a flashlamp-pumped Cr:LiSAF laser operating in a free-running mode. Blue-light pulses were obtained at both 473 nm (9 mJ, 25 ns FWHM) and 465 nm (4.4 mJ, 35 ns FWHM) by using a potassium niobate crystal as an extra-cavity frequency doubler. The second-harmonic generation conversion efficiencies reached 53% and 31%, respectively. Received: 23 June 1999 / Revised version: 8 August 1999 / Published online: 3 November 1999     

Preparation of Ca(1−x)EuxGa2S4 crystals and their photoluminescence, absorption and excitation spectra

The single crystal of CaGa₂S₄:Eu is expected as a useful laser material with a high quantum efficiency of light emission. However, as far as our knowledge is concerned, the systematic study of the mixed compounds of Ca_(1−x)Eu_xGa₂S₄ as a function of x has not been reported up to now. Here, we have first constructed the phase diagram of the CaGa₂S₄ and EuGa₂S₄ pseudo binary system, and show that it forms the solid solution. Then we have grown single crystals of these compounds. The maximum photoluminescence efficiency is achieved at x=0.25. From the three peak energies observed in the photoluminescence excitation (PLE) and absorption spectra, the 5d excited states are suggested to consist of three levels arising from the multiplets of Eu²⁺ ions.     

Intensity parameters for Er<Superscript>3+</Superscript> ions in calcium-niobium-gallium garnet crystals

Based on the analysis of the absorption spectra of Er-doped calcium-niobium-gallium garnet (Er:CNGG) crystals according to the Judd-Ofelt theory, the intensity parameters for these crystals are determined to be Θ₂ = 3.43 × 10^?20 cm² Θ₄ = 1.20 × 10^?20 cm², and Θ₆ = 0.58 × 10^?20 cm². The parameters found are compared with the intensity parameters for other laser oxide crystals. Using these intensity parameters, the probabilities of radiative transitions between the energy levels of Er³⁺ ions in CNGG crystals and the luminescence branching ratios β_JJ’ are calculated. From the measured lifetime of the ⁴ I _11/2 level of Er³⁺ ions (τ = 626 μs) and the probability of the radiative transition from this level (A = 192 s^?1), it is found that about 88% of the excitation energy in the Er:CNGG crystals is nonradiatively transferred from the ⁴ I _11/2 to the ⁴ I _13/2 level. It is suggested that an increase in the oscillator strength and in the line strength of the ⁴ I _15/2 → ² H _11/2 transition of Er³⁺ in CNGG crystals, as well as an increase in the intensity parameter Θ₂ with respect to the corresponding parameters for other garnet crystals are caused by the existence in CNGG crystals of Er³⁺ centers with the environment symmetry lower than D ₂.     

Growth and characterization of a new organic NLO material: Glycine nitrate

Single crystals of glycine nitrate [(C₂H₆NO₂)⁺ · (NO₃)⁻] were grown using submerged seed solution method. The crystals were characterized by using single crystal X-ray diffraction and density measurements. Spectroscopic, thermal and optical studies were carried out for analyzing the presence of the functional groups, thermal stability, decomposition and transparency of the sample. These studies showed that the crystals are thermally stable upto 145 °C and transparent for the fundamental and second harmonic generation of Nd:YAG (λ = 1064 nm) laser. Second harmonic generation (SHG) conversion efficiency was investigated to explore the NLO characteristics of this material. Microhardness and dielectric studies were also carried out.     

Optical and theoretical investigations of V ions in CdZnTe crystal

High-resistivity CdZnTe:V crystals are investigated by photoluminescence (PL) and by time-resolved PL in the infrared spectral range. A double peaked emission band is detected around 0.8 eV and it is related to vanadium doping. No-phonon lines of the internal transitions were detected. This emission is interpreted as a balance between the ⁴T₁(⁴P)→⁴T₁(⁴F) internal transition and an electronic transition from the conduction band to the ⁴T₁(⁴F) ground state of V²⁺. The corresponding decay time after laser excitation gives evidence to the contribution of two different recombination processes. These two emission bands are separated by time-resolved luminescence. Crystal-field calculations of the detected transition energies based on Tanabe-Sugano scheme are presented and the Racah parameter B and crystal-field intensity D_q were determined.In addition, a model is developed in terms of one-electron orbital, to explain the characteristics of the PL excitation processes of V²⁺. Excitations with above and below band edge energy confirm the proposed schemes.     

Influence of chemical bond length changes on the crystal field strength and “ligand-metal” charge transfer transitions in Cs2GeF6 doped with Mn and Os ions

Detailed study of dependence of the crystal field strength 10Dq and lowest charge transfer (CT) energies for different interionic distances in Cs₂GeF₆:Mn⁴⁺ and Cs₂GeF₆:Os⁴⁺crystals is presented. The calculations were performed using the first-principles discrete-variational Dirac-Slater (DV-DS) method. As a result, the functional dependencies of 10Dq and lowest CT energy on the metal-ligand distance R were obtained without any fitting or semiempirical parameters. It was shown that 10Dq depends on R as 1/Rⁿ, with n=4.0612 and 4.3874 for Cs₂GeF₆:Mn⁴⁺ and Cs₂GeF₆:Os⁴⁺, respectively. Two approximations (linear and quadratic) are obtained for the dependence of the lowest CT energy on R; CT energy decreases when R increases with dE(CT)/dR=−638 and −1080 cm⁻¹/pm for Cs₂GeF₆:Mn⁴⁺ and Cs₂GeF₆:Os⁴⁺, respectively, if the linear approximation is used. These values can be used for estimations of the lowest CT energies for Mn⁴⁺ and Os⁴⁺ ions in other hosts with fluorine ligands. Estimations of the electron-vibrational interaction (EVI) constants, Huang-Rhys parameters, and Stokes shifts for all the above-mentioned crystals were performed using the obtained 10Dq and E(CT) functions.     

An all-solid-state tunable 214.5-nm continuous-wave light source by using two-stage frequency doubling of a diode laser

3 and β-BaB₂O₄ crystals. The power of the generated 214.5-nm light amounts to more than 100 μW. This light source will be used for laser cooling of Cd⁺ ions. Received: 4 August 1997/Revised version: 28 October 1997     

Stimulated Raman scattering in natural crystals of SrSO4, BaSO4 and PbSO4: High-order Stokes and anti-Stokes generation with?single-wavelength UV, visible, and near-IR excitation, as?well?as cascaded up-conversion nonlinear �� (3)?�� (3) lasing effects under dual-wavelength picosecond collinear coherent pumping

Orthorhombic crystals of SrSO₄, BaSO₄, and PbSO₄, known as natural crystals celestine, barite, and anglesite, were found to be attractive ?? ⁽³⁾-active nonlinear optical materials. High-order Stokes and anti-Stokes picosecond generation that spans almost two octaves has been recorded with single-wavelength laser excitation in the UV, visible, and near-IR ranges. All recorded Raman induced lasing components were identified and attributed to the SRS-promoting vibration modes of the studied crystals (?? _SRS??999?cm^?1 for SrSO₄,?? _SRS??985?cm^?1 for BaSO₄ and ?? _SRS??977?cm^?1 for PbSO₄). Under dual-wavelength (?? _f1=1.06415???m + ?? _f2=0.53207???m) collinear coherent picosecond pumping several new manifestations of cascaded ?? ⁽³⁾??? ⁽³⁾ nonlinear up-conversion lasing effects were observed in BaSO₄ and SrSO₄ crystals. We classify all three studied sulfate crystals as promising SRS-active materials for Raman laser frequency converters and as efficient ?? ⁽³⁾-crystals that efficiently generate Stokes and anti-Stokes frequency combs, which can enable experiments of ultra-short pulse syntheses.     

Tunable room-temperature cw laser action in Cr3+: GdScGa-Garnet

We report for the first time on tunable room temperature cw laser action of a transition metal laser material. In Cr³⁺:GdScGa-garnet crystals almost the total fluorescence is channelled into the broad band⁴ T ₂→⁴ A ₂ transition. The fluorescence lifetime is τ=120 μs. Laser pumping in the blue-green and yellow-red spectral range yields pump thresholds around 250 mW and slope efficiencies up to 11%. The wavelength of the free running Cr³⁺ laser is centered at 777 nm.     

New measurements of the emission spectra of Sm2+ in KMgF3 and NaMgF3 crystals

The fluorescence of divalent samarium in KMgF₃ and NaMgF₃ crystals is investigated. The emission is observed to originate from transitions between the ⁵D_J, and ⁷F_J multiplets of the 4?⁶ configuration. More precisely, the lowest ⁵D_J level, ⁵D₀, appears to be the most efficient emitting level in the temperature range 4–300K. Contrary to what has been reported elsewhere, the Sm²⁺ fluorescence in both crystals does not exhibit any broad band emission even at room temperature. The great number of lines in the ⁵D₀→⁷F_J patterns gives evidence of the multiple-center origin of the fluorescence.