High-repetition-rate ultrashort-pulse optical parametric oscillator continuously tunable from 2.8 to 6.8 mum

We describe a synchronously pumped femtosecond optical parametric oscillator based on periodically poled LiNbO(3) that is broadly tunable in the mid infrared. A transmission window of periodically poled lithium niobate beyond the conventionally accepted infrared absorption edge of 5.4 mum has been exploited to produce idler pulses that are tunable across a wavelength range of 4 mum , with milliwatt-level output powers at wavelengths as long as 6.8 mum . We also present experimental tuning results that are in good agreement with the theoretical phase matching predicted from published infrared-corrected Sellmeier equations for LiNbO(3) .     

1.6-micrometer emission from Ho3+-doped fluoride glasses

We have investigated the spectroscopic properties of the 1.6-micrometer emission from the 5I(5) --> 5I(7) transition of Ho3+ ions in fluoride glasses for use in U-band fiber amplifiers. The intensity profile of the emission peaks at approximately 1660 nm, with a full width at half-maximum of approximately 60 nm. The measured lifetime and emission cross section are approximately 230 micros and approximately 5.4 x 10(-21) cm2, respectively. Frequency upconversion to the 5F(1) state occurs simultaneously with excitation of the 1.6-micrometer emission, so the shorter-wavelength side of the 5I(8) --> 5I(5) absorption spectrum is favorable for population of the 5I(5) state. Codoping with rare earths such as Tb3+, Dy3+, Eu3+, and Nd3+ decreases the lifetimes of the lower-lying 5I(6) and 5I(7) levels and as a result would be of benefit in achieving population inversion between the fluorescing level and the lower-lying levels.     

Watt-level Er-doped and Er-Pr-codoped ZBLAN fiber amplifiers at the 2.7-2.8 microm wavelength range

Characteristics of diode-pumped Er-doped and Er-Pr-codoped ZBLAN fiber amplifiers were investigated at the 2.7-2.8 microm wavelength range. An amplified signal of 4.6 W was obtained from the singly Er-doped amplifier for an input signal of 110 mW, corresponding to a net gain of 16.2 dB. An amplified signal of 2.65 W was obtained from the Er-Pr-codoped amplifier for an input signal of 70 mW, corresponding to a net gain of 15.8 dB. It is found that the gain bandwidth of the singly Er-doped amplifier is much narrower than that of the Er-Pr-codoped amplifier. Small gain, no gain, or even a loss for shorter-wavelength signals propagating through the singly Er-doped amplifier should attribute for the large number residual populations in the lower laser level caused by the inefficient depopulation of the energy transfer upconversion processes.     

The continuous emission of argon in the visible spectral range

The continuous emission of a cascade arc operated in argon at atmospheric pressure was investigated using side-on intensity measurements in the spectral range 3,700–7,000 å. Agreement to within the accuracy of the measurement was found between the present experimental continuum data and Schlüter's theoretical values. Recently published experimental results forλ≦4,000 å andλ≈ 6,500 å were confirmed.     

γ辐照对掺Er硅酸盐玻璃吸收和发光特性的影响

用传统的高温熔融法熔制了一系列掺Er硅酸盐玻璃, 并测试了这些样品经5 kGy γ 射线辐照前后紫外至近红外的吸收和荧光光谱. 实验结果表明, 辐致暗化效应使得玻璃材料中形成了大量色心, 导致在400 nm附近出现强吸收带, 其尾端延伸至近红外区. 辐照产生的新能带增加了基质与Er³⁺ 特定能级(如²H_11/2, ⁴S_3/2及⁴F_9/2等) 之间的能量传递, 从而使辐照后的样品荧光寿命减小, 且在相同激发条件下荧光强度下降. 室温下辐照样品在荧光测试过程中出现了漂白现象.     

Laser beam induced optical aberrations in phosphate and fluoride phosphate glasses

Designing pulsed laser amplifiers requires detailed knowledge about beam distortions at the amplifying medium. Time resolved experiments have been performed on fluoride phosphate and pure phosphate glass in order to study optical aberrations induced by pump beam irradiation. By means of a probe beam tunable in wavelength, it was possible to discriminate between thermally induced variations of the optical path and beam narrowing effects due to the radial gain distribution. The experimental results were analyzed theoretically regarding Fresnel diffraction. A quite different response was found for the two types of glass despite their similar nominative properties. PACS 42.60.Jf; 42.60.By; 42.15.Fr     

Study of polarized luminescence in erbium-doped laser glasses

A partial polarization of luminescence in laser phosphate and silicate erbium-doped glasses was found to take place for the fundamental laser transition ⁴ I _13/2→⁴ I _15/2 (λ=1.55 μm) under excitation by linearly polarized laser radiation (532 and 790–990 nm). The shape of the luminescence spectrum depends on the wavelength of the exciting light and on the composition of the glass matrix. The degree of polarization of the luminescence depends on the spectral range of both the excitation and the detection, attaining a maximum of ～1%. The concentration dependence of the degree of polarization is studied.     

Fe-B-Y-Nb bulk metallic glasses in relation to clusters

Bulk metallic glass formations in the Fe-B-Y-Nb quaternary alloy system were investigated by using the cluster line rule in combination with the minor alloying principle. The Fe-B-Y ternary system was selected as the basic system and the intersections of cluster lines were taken as the basic ternary compositions. The basic compositions were further alloyed with minor amounts of Nb. After 3–5 at.% Nb was added, the basic composition Fe_68.6B_25.7Y_5.7, which was developed from the most densely packed cluster Fe₈B₃, formed 3 mm bulk metallic glasses. These quaternary bulk metallic glasses (Fe_68.6B_25.7Y_5.7)_100−x Nb _x (x = 3–5 at.%) are expressed approximately with a unified simple composition formula: (Fe₈B₃)₁(Y, Nb)₁. The (Fe_68.6B_25.7Y_5.7)₉₇Nb₃ bulk metallic glass has the largest glass forming ability with the following characteristic parameters T _g = 907 K, T _x = 1006 K, T _g/T _l = 0.644, γ = 0.434, and longness t = 22 mm. The combination of the cluster line rule and the minor-alloying principle is a promising new route towards the quantitative composition design of multi-component metallic glasses. Supported by the National Natural Science Foundation of China (Grant Nos. 50671018, 50631010 and 50401020) and the National Basic Research Program of China (Grant No. 2007CB613902)     

Laser emission efficiency of semiconductor target of gas diode in the picosecond range

Laser radiation excited in a cadmiumsulfide semiconductor target (ST) (λ = 522 nm) by a high-intensity subnanosecond electron beam (EB) with an energy of 70–150 keV has a maximum intensity of 3 · 10⁷W/cm² at an efficiency of~10%. Lasing arose at the EB exciting pulse front. The laser radiation pulse shape reproduced the EB pulse shape.     

Instantaneous emission spectra and molecular rotation of n-dimethylaminobenzonitrile fluorescing in the long-wavelength spectral range

The kinetics of the instantaneous luminescence spectra and of the polarization of luminescence of n-dimethylaminobenzonitrile in polar solutions are studied. The luminescence is excited by radiation at 403 nm from a picosecond laser, which populates states of strongly nonequilibrium forms of the compound under consideration. The behavior of the instantaneous emission spectra and the rotation of these forms upon recording of their luminescence radiation in different spectral ranges are analyzed. As the luminescence recording wave-length increases from 470 to 530 nm, the average time of rotational relaxation in a glycerol solution decreases from 25 to 15 ns. The results obtained indicate that, upon rotation of excited luminophore molecules, the boundary conditions of sticking of solvent molecules are satisfied in this solution. The calculated effective volume of rotation corresponds to that of a solvate that, apart from luminophore, involves the first coordination sphere of glycerol molecules.     

Medium range order of bulk metallic glasses determined by variable resolution fluctuation electron microscopy

Variable resolution fluctuation electron microscopy (FEM) experiments are implemented with hollow-cone dark-field transmission electron microscopy. Medium range order lengths of zirconium and iron based bulk metallic glasses and amorphous silicon nitride are determined from the FEM results. It shows that maximum normalized intensity variances of FEM images occur when their nominal resolution approaches the correlation length Λ of the amorphous materials. Additionally, differences in the length and magnitude of medium range order are compared between metallic and covalent bond amorphous materials.     

Temperature dependence of upconversion luminescence in erbium-doped tellurite glasses

Temperature quenching characteristics of infrared-to-visible frequency upconversion in ytterbium-sensitized erbium-doped tellurite glasses under 970 nm excitation were reported. Intense upconversion emissions around 530, 545 and 657 nm corresponding to the ²H_11/2, ⁴S_3/2 and ⁴F_9/2 transitions to the ⁴I_15/2 ground state were observed. The green emission around 530 nm presents continuous increase with increase of temperature. While the emission around 545 nm increases from 20 to 80 K and reaches the largest value around 80 K, then decreases from 80 to 300 K. The dependence of intensity characteristics on temperature was systematically analyzed by rate equations and a simple three-level system. In addition, the temperature dependence on the multiphonon relaxation rates (²H_11/2, ⁴S_3/2→⁴F_9/2) fitted with 4 phonons of the 760 cm⁻¹ was presented.     

NIR to visible upconversion emission from Dy: ZBLYAN glasses

This paper reports on the near infrared (730-783 nm) to the visible upconversion emissions at 482 nm (⁴F_9/2→⁶H_15/2), 576 nm (⁴F_9/2→⁶H_13/2) and 662 nm (⁴F_9/2→⁶H_11/2) from the Dy³⁺doped 53ZrF₄-20BaF₂-2LaF₃-2YF₃-3AlF₃-19NaF-1DyF₃ glasses. We have also carried out a systematic study on the normal emission properties of these glasses in order to understand their performance both as a NIR upconverted visible luminescent and as normal visible fluorescent optical systems of technical importance. With an increase in Dy³⁺ concentration beyond a particular value (1 mol%), activator-activator interaction becomes a significant cause of concentration quenching in the luminescence properties. The dependence of the emission spectra on the excitation wavelengths has also been examined and 451 nm was found to be the ideal excitation wavelength in the measurement of normal fluorescence spectra. In the case of NIR upconverted visible emission, we have observed that the NIR excitation at 783 nm as the suitable pump wavelength in demonstrating prominent visible emission colours from these glasses. The relevance in undertaking these optical materials lies in their potential for upconversion laser application in the visible wavelength region. The NIR upconversion phenomenon has been explained in terms of energy level schemes due to excited state absorption (ESA) and energy transfer upconversion (ETU) processes.     

Absorption and emission spectral studies of Sm and Dy doped alkali fluoroborate glasses

Absorption and photoluminescence spectra of Sm³⁺ and Dy³⁺ doped alkali fluoroborate glasses of the composition 90.5% B₂O₃+4% AlF₃+5% MF+0.5% LnF₃ (M=Li, Na, K and Ln=Sm, Dy) have been reported. On excitation, with , the Sm³⁺ glasses are found to be orange fluorescent in color and richness of that color is high in the Na+ glass, compared to Li⁺ and K⁺ glasses. Similarly, on excitation with , the Dy³⁺ glasses are fluorescent yellow in color and that color is richer in the K⁺ glass.     

Effect of the ultrasound action on the acoustic emission and mechanical properties of zirconium-based bulk metallic glasses

The effect of preliminary ultrasound action on the mechanical properties and features of the structure of zirconium-based bulk metallic glasses has been studied by the method of acoustic emission under uniaxial compression. Results of studies have been interpreted using the polycluster model of the structure of amorphous metallic alloys. Analysis of the obtained data has allowed us to substantiate the mechanism of the change in the structure and strength of metallic glasses as a result of alternating-sign mechanical loading with an ultrasound frequency of 20 kHz.     

Laser induced long-lived emission spectra of laser dyes in rigid glasses at 77 K

Phosphorescence decay of 3-(2′-N-methylbenzimidazolyl)-7-N, N-diethylaminocoumarin; 2,3,5,6-1H, 4H-tetrahydro-8-methylquinolizino-〈9, 9a, 1-gh〉 coumarin; 2,3,5,6-1H, 4H-tetrahydro-8-trifluormethylquinolizino-〈9,9a,1-gh〉 coumarin; 9(10H)-acridone; 9-aminocridine hydrochloride, 1-hydrate and 2-(4-biphenylyl)-5-(4-t-butylphenyl)-1,3, 4-oxadiazole dyes in EPA glass at 77 K have been recorded using N₂ laser. The results were used to determine lifetimes. Emission intensities from the first two dyes have been examined in relation to dye concentration and excitation intensity. The results are discussed.     

Intensities of f-f transitions in Pr3+ and Dy3+ in glasses in the near-IR spectral range

The absorption spectra of Pr³⁺ and Dy³⁺ ions in three glass matrices (SiO₂-P₂O₅-GeO₂, Al₂O₃-B₂O₃-SiO₂, and LiB₃O₅) are thoroughly studied in the near-IR spectral range (4600–14 300 cm^?1). The temperature dependences of the intensity, the width, and the location of the absorption bands observed are investigated for the first time. It is shown that the f-f transitions in the studied glasses are allowed by static odd distortions in the environment of the rare-earth ions and these distortions decrease with an increase in temperature. A comparative analysis of the absorption band parameters and their temperature behavior in different materials makes it possible to determine the differences in magnitudes, symmetries, and dispersions of the distortions in the nearest environment of rare-earth ions in different glasses.     

Charged ρ photoproduction in the energy range 2.8–4.8 GeV

Measurements of the photoproduction processes γρ→ρ⁺ n and γρ→ρ^-Δ⁺⁺ (1236) are reported in the energy range 2.8 to 4.8 GeV. The data show shrinkage of the differential cross section in this energy region for the process γρ→ρ^-Δ⁺⁺ (1236); no shrinkage is observed for the ρ⁺ n process. The energy dependences of the ρ⁺ n and ρ^-Δ⁺⁺ (1236) total cross sections are much steeper than current model prediction. The ρ spin density matrices for each process are also presented.