Differences and Similarities between Lanthanum and Rare-Earth Iodate Anhydrous Polymorphs: Structures, Thermal Behaviors, and Luminescent Properties.

The Ln(IO3)3(HIO3)y (y = 1 or 1.33) compounds are isostructural with the La(IO3)3(HIO3)y phases, but thermal studies reveal different behaviors. On the one hand, the partial thermal decompositions of these lanthanide compounds lead to the Ln(IO3)3 formulation, with a room temperature structure different from the ß-La(IO3)3 obtained from La(IO3)3(HIO3)y. On the other hand, the partial thermal decompositions of the La1-xLnx(IO3)3(HIO3)y compounds prepared with lanthanides ions (Ce, Pr, Nd, Sm, Eu, Gd, and Yb) lead to acentric ß-La1-xLnx(IO3)3. As for ß-La(IO3)3, reversible structural transitions from ß-La1-xLnx(IO3)3 to centrosymmetric γ-La1-xLnx(IO3)3 are observed. Differential scanning calorimetry analyses of La1-xLnx(IO3)3 solid solutions show that the transition temperatures vary with the lanthanide concentration in the solid solution. A transition is observed only up to a certain fraction of lanthanide-ion substitution; this substitution limit decreases with the cationic radius of the lanthanide ion. Finally, the ß-La1-xNdx(IO3)3 and ß-La1-xYbx(IO3)3 phases are investigated by luminescence spectroscopy.

Two-frequency pulsed YLiF4:Nd lasing out of the principal axes and THz generation.

Thanks to a propagation direction at 50.3° from the c axis in a LiYF4:Nd crystal, we have equalized the emission cross-sections at 1047 and 1053 nm, respectively, for extraordinary and ordinary waves. The double refraction is used to balance the "o" and "e" pumping. Actively Q-switching the laser cavity leads to simultaneous pulses with duration less than 10 ns. Frequency conversion to THz radiation was performed through difference frequency mixing in two nonlinear crystals: GaSe and OH1. In the first case, we obtained 132 nW and in the second case we obtained 51 nW THz power at 6.67 kHz repetition rate.

Structures, thermal behaviors, and luminescent properties of anhydrous lanthanum iodate polymorphs.

The structural and thermal studies of six anhydrous lanthanum iodate polymorphs are presented. The variation of the [IO3(-)]:[La(3+)] molar ratio in the starting solution and the evaporation rate of the solution leads to either the centric La(IO3)3(HIO3) or the acentric La(IO3)3(HIO3)1.33 phases. The crystal structure of La(IO3)3(HIO3)1.33 was determined. The thermal treatments of these two phases up to 490 °C lead to ß-La(IO3)3, observed at room temperature. To better understand the similar thermal behaviors of La(IO3)3(HIO3)1.33 and La(IO3)3(HIO3) compounds and their structural evolution, thermogravimetry-differential thermal analysis (TG-DTA), differential scanning calorimetry (DSC) analyses and in situ temperature-dependent powder X-ray diffraction (XRD) experiments were carried out. These experiments allowed us to highlight the successive formation of δ-La(IO3)3 and γ-La(IO3)3. δ-La(IO3)3 is observed from the beginning of thermal decomposition of La(IO3)3(HIO3)1.33 (at 340 °C) or La(IO3)3(HIO3) (at 300 °C) up to 440 °C. A phase transition from δ-La(IO3)3 to γ-La(IO3)3 then occurs at 440 °C. Finally, the phase transition from γ-La(IO3)3 to ß-La(IO3)3 occurs at 140 °C. A cycle of heating and cooling shows the reversible phase transition at 185 and 140 °C, respectively. ß-, γ-, and δ-La(IO3)3 are three polymorph phases of the first α-La(IO3)3 already characterized. The structure of ß-La(IO3)3 and γ-La(IO3)3 were determined on powder XRD analyses. The iodate compounds present a very broad domain of transparency from the visible range to the beginning of the far-infrared range. The intensities of SHG light generated by α-La(IO3)3, ß-La(IO3)3, La(IO3)3(HIO3)1.33, and α-LiIO3 compounds with acentric structures were compared: ß-La(IO3)3 < La(IO3)3(HIO3)1.33 < α-La(IO3)3 ≈ α-LiIO3. Finally, the luminescence spectroscopy of La(IO3)3(HIO3)1.33:Nd(3+), α-La(IO3)3:Nd(3+), and α-La(IO3)3:Yb(3+) is studied.

Gain structuration in dual-wavelength Nd:YSAG ceramic lasers.

We demonstrate a dual-wavelength Nd:YSAG ceramic laser in which the gain volume is structurated into two different regions providing gain at the wavelength of 1061 nm and 1064 nm respectively. We discuss the role of the nonuniform distribution of the temperature in structurating the gain region via the Boltzmann effect. We show that the two laser wavelengths can be switched by adjusting the size of the pump beam or by slightly modifying the geometrical parameters of the laser cavity, either the length of the cavity or the orientation of a mirror. Additionally, we demonstrate that the transverse modes at the two wavelengths are shaped according to the effect of gain filtering caused by the structuration of the gain region.

Spectroscopic characterization of Ti-doped α-ZnAl2S4 spinel-type single crystals.

The spectroscopic characteristics of the α-ZnAl(2)S(4) wide bandgap semiconductor doped with Ti ions are investigated. It is shown, that the ZnAl(2)S(4):Ti spinel-type crystals exhibit luminescence in the IR spectral range 0.8-1.4 µm. The observed spectroscopic characteristics are assigned to the emission bands arising from the ligand -Ti(4+) charge transfer for octahedral sites of titanium that is in agreement with the experimental evidence for the absence of the EPR signal from Ti ions. A qualitative explanation of the experimental data is given.

High-power laser with Nd:YAG single-crystal fiber grown by the micro-pulling-down technique.

We present optical characterization and laser results achieved with single-crystal fibers directly grown by the micro-pulling-down technique. We investigate the spectroscopic and optical quality of the fiber, and we present the first laser results. We achieved a cw laser power of 10 W at 1064 nm for an incident pump power of 60 W at 808 nm and 360 kW peak power for 12 ns pulses at 1 kHz in the Q-switched regime. It is, to the best of our knowledge, the highest laser power ever achieved with directly grown single-crystal fibers.

[Study on the growth and spectral characteristics of LiNbO3:Cr:ZnO crystal].

The LiNbO3:Cr:ZnO crystals with the size up to phi20 mm x 50 mm were grown by the Czochralski technique. The absorption spectrum shows that there are two strong absorption wideband peaks and one weak absorption peak of to Cr3+ ion in the crystal. The peak values of the two strong absorption wideband peaks are 480 and 660 nm, which correspond to 4A2-->4 T1 and 4A2-->4 T2 transitions, respectively. The weak absorption peak at 727 nm corresponds to 4A2-->2 E(R line) transition; The fluorescence spectrum shows that one emission wideband peak ranging from 802 to 988 nm coexists with one weak emission peak at 754 nm corresponding to 4T2-->2 E transition. The peak value of emission wideband is at 871 nm, which corresponds to 4T2-->4A2 transition. The crystal field and Racah parameters were calculated, and Dq/B = 2.72 indicates that it has an stronger crystal field. The result shows that the wideband tunable laser can be obtained from this crystal because it not only has the necessary spectral characteristics required for tunable laser crystal but also has good physical chemical properties. Furthermore, the UV laser at about 420 nm can also be obtained from the crystal by its self-frequency doubling because it has a higher frequency-doubling coefficient.

Passive Q-switching characteristics of Yb3+:Gd3Ga5O12 crystal.

The passively Q-switched laser characteristics of a quasi-three level Yb3+:Gd3Ga5O12 (Yb3+:GGG) crystal with Cr4+:YAG saturable absorbers are studied experimentally and theoretically. The pulse parameters under different experimental conditions are measured. Some characteristics different from those of a four-level system are found. In the theoretical aspect, taking into account the spatial distributions of the pump light and intracavity laser mode, the rate equations describing the single Q-switched pulse characteristics of a quasi-three-level system are obtained. The obtained theoretical results are in fair agreement with the experimental results. Some topics such as the influence of the pumping power, the selection of the pump beam size, the optimal combination of output coupler reflectivity and saturable absorber initial transmission, the influence of the excited absorption of the saturable absorber, are discussed.

Tunable coherent infrared generation near 2.5 microm from self-difference frequency mixing in YAl3(BO3)4:Nd3+.

Idler generation from self-difference frequency mixing of the pump wave near 750 nm and the 1062-nm Nd3+ laser emission in the bifunctional laser and nonlinear optical YAl3(BO3)4:Nd3+ crystal was shown. The efficiency was 0.37%, and the infrared wavelength was tunable in the 2430-2600-nm range. New Sellmeier formulas that predict phase-matching polar angles for frequency conversion processes involving wavelengths up to 2600 nm were established.

Self-sum- and -difference-frequency mixing in GdAl(3)(BO(3))(4):Nd(3+) for generation of tunable ultraviolet and infrared radiation.

We exploited Nd(3+) laser emission at 1061.9 nm ((4)F(3/2)?(4)I(11/2) channel) in a self-chi((2)) active GdAl(3)(BO(3))(4):Nd(3+) laser crystal. UV radiation was obtained from a 1.8% yield from self-sum-frequency mixing: 1/pump + 1/1061.9 = 1/UV, during pumping in the Nd(3+) (4)G(5/2)-(2)G(7/2) levels near 588 nm. The UV tunability had a range of 378-382 nm. We have demonstrated, for the first time to our knowledge, generation of coherent IR radiation from a self-difference-frequency mixing laser: 1/pump - 1/1061.9 = 1/IR. We got a 0.5% yield and tunability in the 1305-1365-nm range.