Modification of magnetic anisotropy in metallic glasses using high-energy ion beam irradiation

Heavy ion irradiation in the electronic stopping power region induces macroscopic dimensional change in metallic glasses and introduces magnetic anisotropy in some magnetic materials. The present work is on the irradiation study of ferromagnetic metallic glasses, where both dimensional change and modification of magnetic anisotropy are expected. Magnetic anisotropy was measured using Mössbauer spectroscopy of virgin and irradiated Fe₄₀Ni₄₀B₂₀ and Fe₄₀Ni₃₈Mo₄B₁₈ metallic glass ribbons. 90 MeV ¹²⁷I beam was used for the irradiations. Irradiation doses were 5×10¹³ and 7.5×10¹³ ions/cm². The relative intensity ratios D ₂₃ of the second and third lines of the Mössbauer spectra were measured to determine the magnetic anisotropy. The virgin samples of both the materials display in-plane magnetic anisotropy, i.e., the spins are oriented parallel to the ribbon plane. Irradiation is found to cause reduction in magnetic anisotropy. Near-complete randomization of magnetic moments is observed at high irradiation doses. Correlation is found between the residual stresses introduced by ion irradiation and the change in magnetic anisotropy.     

Yb3+-doped YVO4 crystal for efficient Kerr-lens mode locking in solid-state lasers

We report the first demonstration, to our knowledge, of soft-aperture Kerr-lens mode locking in a diode-pumped femtosecond Yb3+:YVO4 laser. Near-transform-limited pulses as short as 61 fs are generated around a center wavelength of 1050 nm with an output power of 54 mW and a pulse repetition frequency of 104.5 MHz. This is, to our knowledge, the shortest pulse generated directly from an Yb laser having a crystalline host material. The femtosecond operation has a mode-locking threshold at an absorbed pump power of 190 mW. The nonlinear refractive indexes of the Yb3+:YVO4 crystal have been measured to be 19 x 10(-16) cm2/W and 15 x 10(-16) cm2/W for the sigma and pi polarizations, respectively, at 1080 nm.     

Anisotropy of nonlinear absorption in Co<Superscript>2+</Superscript>:MgAl<Subscript>2</Subscript>O<Subscript>4</Subscript> crystal

Anisotropy of the nonlinear absorption of Co²⁺ ions in MgAl₂O₄ single crystal at the wavelengths of 1.35 and 1.54 μm has been experimentally demonstrated. The experimental data are analyzed in the framework of a phenomenological model when the Co²⁺ ions are described as three sets of linear dipoles oriented along the crystallographic axes. Ground-state and excited state absorption cross-sections at 1.35 and 1.54 μm are evaluated to be σ_gsa=(4.0±0.3)×10^-19, σ_esa=(3.6±0.4)×10^-20 cm² and σ_gsa=(5.1±0.3)×10^-19, σ_esa=(4.6±0.4)×10^-20 cm², respectively. PACS 42.55.Rz; 71.20.Be     

Study of nanostructures on a solar cell surface exposed on the <Emphasis Type="Italic">Mir</Emphasis> orbital station

It is shown that atomic-force microscopy under normal conditions makes it possible to obtain important information on the topography and features of nanostructures formed on the surface of cover glasses of solar cells exposed on the Mir orbital station for more than ten years. It is found that the nanostructures are multiscale; they are present on all vertical visualization scales from ∼1000 to ∼17 nm and on horizontal scales from ∼1000 to ∼100 nm. The nanoindentation study of mechanical properties of the exposed surface layer shows that the exposed surface at nanodepths is characterized by higher plastic deformation, but lower hardness and effective modulus, in comparison with unexposed surface.     

Luminescence of transparent glass ceramics containing Er<Superscript>3+</Superscript> and Yb<Superscript>3+</Superscript> zirconate-titanate nanocrystals

Luminescence regularities have been studied in new erbium/ytterbium materials based on glasses and glass ceramics of a magnesium-aluminosilicate system containing nanoscale erbium/ytterbium zirconate titanate crystals with the pyrochlore structure. Lifetimes of Yb³⁺ and Er³⁺ ions in the ² F_5/2 state and in the ⁴I_11/2 and ⁴I_13/2 states, respectively, and the efficiency of Yb³⁺ → Er³⁺ energy transfer have been evaluated. The identified spectral-luminescent characteristics of the studied glasses and glass ceramics co-doped with erbium and ytterbium ions show that these materials are promising media for producing laser generation in the spectral range around 1.5 μm.     

Nonlinear optical properties of Cu x S and CuInS2 semiconductor nanoparticles in sol-gel glass

Quartz glasses containing ultradisperse particles (with a mean radius of 5 ± 3 nm) of semiconductor compounds Cu_xS and CuInS₂ were synthesized using the sol-gel technology. The line and differential absorption spectra of such glasses were investigated. In the range 600–700 nm, the samples demonstrate absorption bands that are assigned to the lowest-lying energy transition in quantum-size particles. Excitation by laser pulses with a wavelength of 540 nm causes the effect of induced absorption in the range of 500–950 nm. The induced absorption in the samples containing Cu_xS nanoparticles undergoes relaxation which has a characteristic time of ∼500 psec, and in the samples with CuInS₂ nanoparticles it has a two-exponential form with τ₁ ≈ 30 psec and τ₂>1 nsec. Translated from Zhurnal Prikladnoi Spektroskopii, vol. 67, No. 4, pp. 507–511, July–August, 2000.     

Saturable absorbers based on tetrahedrally coordinated transition-metal ions in crystals (Review)

Published data on spectroscopic characteristics of saturable absorbers based on crystals doped with tetrahedrally coordinated transition-metal ions (Cr²⁺, Cr⁴⁺, Cr⁵⁺, V³⁺, Cr²⁺, Fe²⁺) in addition to their use as passive Q-switches for solid-state lasers emitting in the visible and near-infrared regions are reviewed. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 1, pp. 5–50, January–February, 2009.