Luyi Zhu

Thermal and laser properties of Nd:YVO4 crystal

Nd:YVO 4 crystal has been grown by Czochralski method. The data of thermal expansion and specific heat have been measured. The thermal expansion coefficients along a- and c-axis are α 1 = 2.2 × 10 -6 /K, and α 3 = 8.4 × 10 -6 /K respectively. The specific heat is 24.6 cal/mol K at 330 K. The large anisotropy along c- and a-axis of thermal expansion coefficients is explained by the structure of YVO 4 crystal. 921 mW output laser at 1.06 μm has been obtained with a 3 mm × 3 mm × 1 mm crystal sample when pumped by 1840 mW cw laser diode, and the slope efficiency is 55.5%.

Investigations on the Growth and Laser Properties of Nd:GdVO4 Single Crystal

In this paper, we report the growth of laser crystal Nd:GdVO 4 by the Czochralski method, and discuss the morphology of the crystal. The polarization absorption and emission spectra of Nd:GdVO 4 were measured. The lifetime of the Nd:GdVO 4 at 1064 nm is 100 μs. An output power up to 1 W at 1064 mn has been achieved with a 3 mm × 3 mm × 1 mm crystal sample when pumped by a 1.9 W cw laser diode.

Raman spectra and laser properties of Yb-doped yttrium orthovanadate crystals

Yb-doped yttrium orthovanadate YbxY1−xVO4 (YYV), with x=0.02, crystallizes with a zircon-type structure in the tetragonal system, conforming to the space group I41/amd. The lattice constants are a=0.7122(5) and c=0.6291(3) nm at room temperature. The primitive cell contains four formula units. The Raman spectra and crystallography show no distortion of the VO4 and Y/YbO8 groups. The crystal field is similar to that of the YVO4 crystal and is suitable for the dopant Yb3+ ions. A strong absorption at 975 nm arises from the 2F7/2 to 2F5/2 transition; with a bandwidth of 70 nm it may provide a useful pump band for InGaAs diode lasers. This band is about seven times broader than that of Nd-doped yttrium aluminum garnet and more than three times as broad as that of Nd-doped yttrium orthovanadate. The measured absorption of the YYV is compared to Judd–Ofelt (JO) theory. When applied, the JO theory of parity-forbidden electric-dipole transitions of rare earth ions on noncentrosymmetric sites demonstrates good agr...

Growth and laser properties of Nd:Ca4YO(BO3)3 crystal

Abstract Nd:Ca 4 YO(BO 3 ) 3 (Nd:YCOB) crystal was grown by the Czochralski method, and its structure was measured by using a four circle X-ray diffractometer. The transparent spectrum from 200 to 2600 nm was measured at room temperature. The fluorescence spectrum near 1.06 μm showed that the main emission wavelength of Nd:YCOB crystal was centered at 1060.8 nm. Laser output at 1.06 μm has been demonstrated when it was pumped by a Ti:sapphire laser at the wavelength of 794 nm, the highest output power was 68 mW under pumping power of 311 mW, the pumping threshold was 163 mW and slope efficiency was 46.9%. The self-frequency doubled green light has been observed when it was pumped by a Ti:sapphire or a laser diode (LD). A 14.5 mm Nd:YCOB crystal sample cut at ( θ , φ )=(90°, 33°) was used for type I second-frequency generation (SHG) of the 1.06 μm laser pulse. The SHG conversion efficiency was 22%.

Spectral parameters of Nd-doped yttrium orthovanadate crystals

Nd-doped yttrium orthovanadate (Nd:YVO4, abbreviated as NYV) crystal has been grown using a modified Czochralski method. Its main structural parameters and optical and laser properties are all presented. The absorption spectrum of Nd3+ ions doped in NYV in a wavelength range from 190 to 900 nm and that of free Nd3+ ions in HCl solution of 0.2 mol in the range of 190–900 nm have both been measured. The width of the absorption band around 808 nm to match the laser diode pumping is about 28 nm, which is approximately three times broader than that of Nd-doped yttrium aluminum garnet crystal. The line intensity of the absorption spectrum of NYV has been calculated. The calculated luminescence parameters of NYV are also listed.

Optical parameters and luminescent properties of Nd:GdVO4 crystals

Based on the quantum electrodynamics and using Einstein’s coefficient and Planck’s energy density, the stimulated emission cross section was given. The measured absorption of 0.5 at. % Nd-doped Nd:GdVO4 crystal was compared to the Judd–Ofelt (JO) theory. When applied, the JO theory of parity-forbidden electric–dipole transitions of rare-earth ions on noncentrosymmetric site lacking inversion symmetry demonstrates good agreement. An absorption band around 808 nm is suitable to match laser diode pumping. The branching ratio of the fluorescence emission and stimulated emission cross section at the emissive wavelength of 1064 nm are of great advantage to produce a laser output.

Bulk growth and physical properties of diguanidinium phosphate monohydrate (G2HP) as a multi-functional crystal

Bulk single crystals of diguanidinium phosphate monohydrate (G2HP) with dimensions up to 55 × 28 × 27 mm3 have been grown by solution growth methods. Thermal properties including specific heat, thermal conductivity and thermal expansion were investigated as a function of temperature. The specific heat was measured to be 1.339 to 1.614 J g−1 K−1 over the temperature range of 293 to 347 K. The thermal conductivities are descending as the temperature increases. The average linear thermal expansion coefficients along a and c axes from 298 to 338 K are α11 = 1.878 × 10−5 K−1 and α33 = 1.930 × 10−5 K−1, respectively. The laser-induced damage threshold measurements show that the G2HP crystal possesses an excellent resistance to laser radiation with a high threshold up to 5.29 GW cm−2. The optical behaviors, including the transmission spectrum and reflective indexes, were investigated to study its linear and nonlinear optical properties. The results reveal that the crystal is a phase matchable nonlinear optical material in the visible and UV regions. A complete set of dielectric, elastic and piezoelectric constants of G2HP have also been measured, and the results display that the crystal also possesses fine piezoelectric properties with d14 = 10.00. Furthermore, the structure–property relationships are discussed on the basis of the crystal structure combined with theoretical calculations. As a multi-functional crystal, G2HP is a particularly promising candidate for a variety of potential applications in many fields.

Preparation and characterization of TiO2 fiber with a facile polyorganotitanium precursor method

TiO(2) precursor fibers were prepared with a new facile polyorganotitanium precursor by a dry-spinning method. The synthesis process, structure of the precursor, and its evolution from the precursor to polycrystalline TiO(2) fibers were studied by (1)H nuclear magnetic resonance ((1)H NMR), Fourier transformation infrared (FTIR), X-ray diffraction (XRD), and differential scanning calorimetry and thermal gravimetry analysis (DSC/TGA). The average diameter of the fibers is in the range of 10-20 microm from scanning electron microscopy (SEM) and the length can reach tens of centimeters. The BET surface area of the fibers calcined at 500 degrees C/2 h is around 160.3 m(2)/g and decreases with temperature increase.

Energy state of Nd3+ doped in barium sodium niobate crystals

Nd-doped barium sodium niobate (Ba2Na)1−xNdxNb5O15 (BNN:Nd), with x=0.025 and a Curie temperature of 537±2 °C, crystallizes with a filled tungsten bronze-type structure in the tetragonal system. The lattice constants are a=b=1.2446(1) and c=0.3991(1) nm at room temperature. There are two formulas per unit cell. The five typical deep energy levels, formed by the Nd3+ ions doped in the A1 and A2 sites, are 2.36, 2.12, 1.68, 1.55, and 1.43 eV. Investigating the green and yellow second-harmonic generation shows that the BNN:Nd crystal can be expected as a useful material for the green, especially for the yellow laser radiation at room temperature.

Spectroscopic and laser properties of Nd: Gd0.8La0.2VO4 crystal

Abstract The polarised absorption and fluorescence spectra of Nd:Gd0.8La0.2VO4 crystal are measured and compared to those of Nd:GdVO4. CW laser properties of diode-pumped Nd:Gd0.8La0.2VO4 crystal operating at fundamental wavelengths of 1.06 and 1.34 μm , as well as when intracavity frequency-doubled to 532 and 670 nm , have been studied. The maximum output powers at 1.06 μm , 1.34 μm , 532 nm and 670 nm are 1.18 W , 671 mW , 206 mW and 42 mW respectively, at a diode-launched pump power of 2.9 W . The threshold pump powers are 80, 267, 7 and 15 mW respectively.