A study of symmetrical LLL X-Ray polylithic interferometers on the basis of the Takagi equations

The Takagi approach to the dynamical theory of x-ray diffraction has been used to study LLL x-ray polylithic interferometers. A computational tool has been implemented to solve the Takagi equations with boundary conditions of the Cauchy type. The mean intensity, visibility and initial phase of the x-ray fringes generated by displacing the analyzer have been calculated for any wavefront, absorption of the incident radiation and for the most common geometric arrangements. Geometric aberrations of different kinds, introduced during interferometer preparation, are considered. The curve relevant to the calculated difference between the reflected and transmitted x-ray fringes as a function of analyzer rotation is in agreement with the experimental curve.     

In situ observation of dynamics of plasma self-channeling and bulk modification in silica glasses induced by a high-intensity femtosecond laser

The time-resolved dynamics of plasma self-channeling and refractive index bulk modification in silica glasses were first observed in situ using a high-intensity femtosecond (110 fs) Ti:sapphire laser (λ_p=790 nm). Plasma channeling is induced in silica glass at an irradiation higher than an input intensity of 1.5×10¹² W/cm² and photoinduces either the refractive-index modification or optical crack modification. In the domain of refractive-index modification, the lifetime of induced plasma self-channeling was 20 ps and the structural transition time for forming the refractive-index change was 10 ps. In the domain of optical cracks, however, the lifetime of induced plasma formation was 30 ps and the structural transition time for forming the optical cracks was 40 ps. According to electron spin resonance spectroscopic (ESP) measurement, it was found that the defect concentration of the SiE^′ center increased significantly in the refractive index modification region. A maximum value of the refractive-index change Δn was measured to be 1.6×10^-2. The intensity profile of the output beam transmitted through the refractive-index modification showed that the bulk modification produced a permanent optical waveguide. Received: 8 April 2002 / Accepted: 12 April 2002 / Published online: 22 November 2002 RID="*" ID="*"Corresponding author. Fax: +81-48/462-4682, E-mail: shcho@riken.go.jp     

Single Mode Er-Doped π-Phase-Shifted Distributed Feedback Fibre Grating Laser

A novel method incorporating the shielded method and the post-processing method has been proposed to fabricate the π-phase-shifted fibre grating. Then an Er-doped π-phase-shifted distributed feedback fibre grating laser has been fabricated using the grating. The laser threshold is 20mW. When pumped with 90mW light at 980nm, the laser gives an output of 1.1mW. Its signal-to-noise ratio is better than 60dB. It is demonstrated that the laser is single mode operation by means of a Fabry--Perot scanning interferometer.     

Experimental Investigation of High Power Erbium-Ytterbium Co-doped Double Clad Fibre Laser

All-fibre high power erbium-ytterbium co-doped double clad fibre lasers are proposed and demonstrated. By using different back-cavity mirrors, the different double clad fibre lasers are constructed. It is experimentally found that the output behaviour of laser can be controlled by a back-cavity mirror. The lower the reflectivity of the back-cavity mirror, the higher the output power and the high the slop efficiency. The maximum output power is about 1.6 W and the slop efficiency is 27.6%.     

Production, isolation, and characterization of group-2 metal-containing endohedral metallofullerenes

80 , Ca/Sr/Ba@C₈₂, Ca/Sr/Ba@C₈₄) are investigated for the first time by UV-Vis-NIR absorption spectroscopy and high-resolution ¹³C NMR. Direct evidence of the endohedral nature and cage structures are revealed by these measurements. Furthermore, we have found that each metallofullerene has 2–4 structural isomers, which have been isolated by multistage high-performance liquid chromatography. These isomers have different cage structures and give characteristic UV-Vis-NIR absorption spectra. Received: 22 September 1997/Accepted: 16 October 1997     

PIV Measurements and Mechanisms of Adjacent Synthetic Jets Interactions

Interactions of adjacent synthetic jet actuators with varying relative amplitude and the relative phase of driving voltage are measured using a particle image velocimetry （PIV）. Varying relative amplitude or relative phase of driving voltage of the adjacent actuators vectors the direction of the ensuing merged jet of the adjacent synthetic jets. The vectoring mechanism of the adjacent vortex pairs, attract-impact causing deflection （AICD）, is provided to explain why the merged jet is generally vectored to the side of the phase-leading synthetic jet or the synthetic jet with higher driving voltage.     

Fibre Optical Parametric Amplification in Defect Bragg Fibres with Zero Dispersion Slow Light Effect

Nonlinearity enhancement by slow light effect and strong light confinement in defect Bragg fibres is demonstrated and anMysed in applications of fibre optical parametric amplifiers. Broadband low group velocity and zero dispersion as well as the strong light confinement by band gap enhances the nonlinear coefficient up to more than one order than the conventional high nonlinear fibres. Moreover, the zero dispersion wavelength of coupled core mode can be designed arbitrarily, under which the phase-matching bandwidth of the nonlinear process can be extended.     

Gain characteristics of 980 nm-pumped Er<Superscript>3+</Superscript>–Tm<Superscript>3+</Superscript>–Pr<Superscript>3+</Superscript>-co-doped fiber

We present a numerical model of Er³⁺–Tm³⁺–Pr³⁺-co-doped fiber amplifier pumped with 980 nm laser for the first time, to the best of our knowledge. The rate and power propagation equations are solved numerically to analyze the effects of the pump power and active ion concentrations on the gains at 1310, 1470, 1530, 1600, 1650 nm windows. The results show that with pump power of 200 mW and when Pr³⁺, Tm³⁺, Er³⁺ concentrations are around 2.0×10²⁴, 3.0×10²⁴, 1.5×10²⁴ (ions/m³), respectively, the signals at 1470, 1530, 1600 nm may be nearly equally amplified with gain of 11–12.0 dB in the active fiber with length of 11.0 m, and the signals at 1310, 1470 and 1600 nm windows may be nearly equally amplified with gain of 12.0 dB in the active gain medium with length of 15.0 m. With pump power of 300 mW, the signals at 1470, 1530, 1600 nm may be nearly equally amplified with a gain of 16.0 dB in the active medium with a length of 15.0 m.     

Modeling erbium–thulium-co-doped fiber amplifier for 1400–1650 nm band

We present numerical models of tri-valence erbium ion and thulium ion-co-doped fiber amplifiers pumped by 800-nm and 980-nm lasers. The rate and power propagation equations of the models are numerically solved to analyze the gain as a function of co-doping concentrations, fiber length and signal wavelength. The results reveal that with 800-nm or 980-nm pump, gain competition exists between 1470- and 1530-nm bands, which may arise from the pump absorption competition and complicated energy transfer between the two types of active ions, and the results further show that the gain spectra may cover 305 nm (1375–1680 nm) for 800-nm pump and 160 nm (1400–1560 nm) for 980-nm pump. The doping concentrations and fiber length may be tuned to reduce the ripple of the gain spectra.     

Femtosecond laser embedded grating micromachining of flexible PDMS plates

We report on the femtosecond laser micromachining of photo-induced embedded diffraction grating in flexible Poly (Dimethly Siloxane) (PDMS) plates using a high-intensity femtosecond (130 fs) Ti: sapphire laser (λ_p = 800 nm). The refractive index modifications with diameters ranging from 2 μm to 5 μm were photo-induced after the irradiation with peak intensities of more than 1 × 10¹¹ W/cm². The graded refractive index profile was fabricated to be a symmetric around from the center of the point at which femtosecond laser was focused. The maximum refractive index change (Δn) was estimated to be 2 × 10⁻³. By the X-Y-Z scanning of sample, the embedded diffraction grating in PDMS plate was fabricated successfully using a femtosecond laser.