Hybrid optical resonator type laser proposed for direct coupling into optical fiber

Combining one stable resonator with a concave mirror and a coupling-hole plane mirror, and another unstable resonator having a concave mirror and a convex mirror, a new hybrid optical resonator type laser has been proposed by overlapping the concave mirror as a common one and fitting the convex mirror exactly to the coupling-hole. Using theABCD law, the so-called g-parameters are first found for beam confinement. Then, based on the eigen-equation, the field distribution on the plano-convex mirror is obtained with the g-parameters above. Knowing this field distribution results in an effective transmittanceG _{e e}. Finally, the ratio of the inner convex to outer plane mirror radii can be determined for an optimum coupling in both the limiting cases of homogeneously and inhomogeneously broadened gain media. Some numerical examples will also be given for a CO₂ laser having the proposed hybrid resonator.     

Laser diode integrated with a low radiation loss thickness-tapered beam expander for highly efficient fiber coupling

The optimal structure of a laser diode monolithically integrated with a thickness-tapered beam expander waveguide is demonstrated by analyzing the relationship between fiber coupling efficiencies and radiation losses. It is also found that mode conversion loss is lowered in a ridge waveguide structure than in a buried hetero structure under equivalent fiber coupling. A fabricated ridge waveguide device based on this design shows threshold current as low as 16 mA and narrow beam divergences of 13° and 12°.     

Effect of shear stiffness and concrete wedge cone failure on fracture of a fiber-reinforced plastic rod at an intersection with a concrete crack

Experimental results of model speciments in which FRP rods fractured due to local deformation at a crack intersection in a concrete member were analyzed by a 3D nonlinear finite element method in which orthogonal anisotropy of the FRP rod was considered. The analytical results indicated that accurate prediction of shear modulus of the FRP rod and size of concrete wedge cone failure around the FRP rod was significant to predict deformation and fracture of the FRP rod. FRP rods as reinforcement in concrete members, the small shear modulus, because of the orthogonal anisotropy and the wedge cone failure, may prevent the FRP rod from fracturing at a very low tensile stress due to the local deformation at the crack intersection.Presented at the Ninth International Conference on the Mechanics of Composite Materials, Riga, October, 1995.Published in Mekhanika Kompozitnykh Materialov, Vol. 21, No. 2, pp. 158–166, March–April, 1996.     

Hollow-fiber delivery of high-power pulsed Nd:YAG laser light

We propose hollow fibers for delivery of high-peak-power pulsed Nd:YAG laser light. Hollow fibers with an internal polymer layer were fabricated by a liquid-phase coating technique. We reduced the losses of the fibers in the near-infrared region by producing a silver film that was very smooth owing to use of an ultrasonic wave for mixing of the silver and the reducer solutions in the silver-plating process. The straight losses of the 1-m-long polymer-coated fibers were 0.3 dB for the 700-mum bore size and 0.1 dB for the 1000-mum bore fiber.     

Photoemission study of Ag nanofilm grown on pseudomorphic fcc Fe(1 0 0)

An angle-resolved photoemission study for Ag nanofilm grown on pseudomorphic metastable-fcc-phase Fe(1 0 0) has been done in order to investigate in detail the quantized electronic structures. From the low-energy electron-diffraction and angle-resolved photoemission spectra, it is found that the present Ag nanofilms were grown in the direction of [1 1 1] on pseudomorphic fcc Fe(1 0 0) substrates. The angle-resolved photoemission spectra of Ag nanofilms grown on pseudomorphic fcc Fe(1 0 0) exhibit the features derived from Shockley-type surface state and additional fine-structures derived from the quantized state of Ag sp valence electron. The experimental nanofilm-thickness dependence of binding energies of these quantized states is compared with the theoretical calculation based on the phase accumulation model, taking into account the phase shifts of electron reflection at both interfaces of the Ag nanofilm. From these results, we discuss the quantized electronic structure in Ag nanofilm grown on pseudomorphic fcc Fe(1 0 0).     

Mössbauer spectroscopic studies of ferrocene adsorbed on silica gel

Mössbauer spectra of ferrocene adsorbed on silica gel were measured in order to study the state of adsorption. Ferrocene adsorbed on silica gel tended to oxidize in air and form ferricenium ion. It is assumed that the oxidation of adsorbed ferrocene was caused by surface hydroxyls on the silica gel and O₂ in air. It was observed that ferrocene adsorbed weakly at 293 K, although the ferricenium ion adsorbed strongly at 293 K. Thus the adsorption states of ferrocene depend on the experimental condition.     

Continuous-wave diode-pumped laser action of Nd³⁺-doped photo-thermo-refractive glass

Laser action of the photo-thermo-refractive (PTR) glass, which is the photosensitive material for holographic recording of volume Bragg gratings (VBGs), was demonstrated for the first time by introducing Nd3?. Nd:PTR glass has a bandwidth of 27.8 nm and 16.0 nm for luminescence and absorption, respectively. An uncoated 2 mm thick Nd:PTR element generated cw laser output of 124 mW, with a slope efficiency of 25%, by laser diode pumping. This Nd:PTR glass also performed wide bandwidth laser action at 1053.9-1063.3 nm, where the decrease of the pump-absorption efficiency was held off below 30%, even under a 3.5 nm shift of pump wavelength from its absorption center.