Highly strained GaInAs-GaAs quantum-well vertical-cavitysurface-emitting laser on GaAs (311)B substrate for stable polarizationoperation

We have realized high-quality GaInAs-GaAs quantum wells (QWs) with high strain of over 2% on GaAs (311)B substrate for a polarization controlled vertical-cavity surface-emitting laser (VCSEL). By increasing the In composition in GaInAs, the optical anisotropy in photoluminescence (PL) intensity was increased. The anisotropy of 50% was obtained at 1.15 μm emission wavelength. We have demonstrated edge-emitting lasers and VCSELs emitting at over 1.1 μm on GaAs (311)B substrate for the first time. The 1.15-μm edge-emitting laser showed a characteristic temperature of 210 K and the threshold current density of 410 A/cm². The threshold current and lasing wavelength of VCSELs are 0.9 mA and 1.12 μm, respectively. The orthogonal polarization suppression ratio was 25 dB and CW operation up to 170°C without a heat sink was achieved     

High performance of 1.55-μm buried-heterostructurevertical-cavity surface-emitting lasers

We report a record low threshold current of 1.55-μm vertical-cavity surface-emitting laser (VCSEL). Thin-film wafer-fusion technology enables InP-based buried heterostructure VCSELs to be fabricated on GaAs-AlAs distributed Bragg reflectors. Threshold current density is independent of mesa size, and a 5-μm VCSEL exhibits a threshold current as low as 380 μA at 20°C and a single transverse mode up to the maximum optical output power under continuous-wave operation     

High-temperature operation up to 170°C of GaInNAs-GaAsquantum-well lasers grown by chemical beam epitaxy

High-temperature pulsed operation of GaInNAs-GaAs double-quantum-well lasers grown by chemical beam epitaxy has been demonstrated for the first time. The lasing wavelength was from 1.20 to 1.27 μm with different composition at room temperature. The highest lasing operation temperature up to 170°C and a high characteristic temperature of 270 K were obtained for 300-μm-long lasers at 1.2 μm     

Temperature-insensitive micromachined AlGaAs-GaAs vertical cavityfilter

We have demonstrated a temperature-insensitive micromachined vertical cavity filter with an AlGaAs-GaAs distributed Bragg reflector (DBR), which can be thermally tuned by differential thermal expansion. The achieved temperature dependence was as small as +0.01 nm/K, which is one-tenth of that of conventional semiconductor based optical filters     

Continuous wave operation of 1.26 μm GaInNAs/GaAsvertical-cavity surface-emitting lasers grown by metalorganic chemicalvapour deposition

Electrically pumped near 1.3 μm GaInNAs/GaAs vertical-cavity surface-emitting lasers grown by metalorganic chemical vapour deposition are demonstrated for the first time. The threshold current and voltage under continuous wave operation of a 10×10 μm² oxide aperture device were 7.6 mA and 2.8 V, respectively. The output power exceeded 0.1 mW and the slope efficiency was ~0.1 W/A     

Comparative pharmacokinetics of four cholinesterase inhibitors in rats

Pharmacokinetics of a very short-acting, a short-acting and two long-acting cholinesterase (ChE) inhibitors, edrophonium, neostigmine, pyridostigmine and ambenonium, respectively, were compared to elucidate the major determinant of their pharmacokinetics. No dose-dependency in pharmacokinetic behavior was observed within the range of 2-10 mumol/kg for edrophonium, 0.5-2 mumol/kg for pyridostigmine, 0.1-0.5 mumol/kg for neostigmine and 0.3-3 mumol/kg for ambenonium, respectively. Neostigmine has the shortest elimination half-life, and edrophonium, pyridostigmine and ambenonium follow in that. Four ChE inhibitors have similar Vdss values within the range of 0.3-0.7 l/kg, which is similar to the muscle/plasma concentration ratio of these drugs. The liver or kidney to plasma concentration ratio of all ChE inhibitors at 20min after i.v. administration ranged from 5 to 15. Small distribution volumes estimated from the plasma concentration profiles may reflect the distribution to muscle and to the extracellular space of other organs/tissues, while the rapid disappearance of ChE inhibitors from plasma may reflect the concentrative uptake to the liver and kidney.     

Spontaneous emission factor of a microcavity DBR surface emittinglaser. II. Effects of electron quantum confinements

For pt.I see ibid., vol.27, p.1347-58 (1991). A method for the theoretical analysis of the spontaneous emission factor (C factor) has been developed for microcavity distributed Bragg reflector (DBR) surface emitting lasers having various quantum-well active regions. It is shown that the C factor can be enlarged by the enhancement of mode density, the anisotropic emission, and the narrow spectral width in quantum wells. C~0.6 may be obtained with GaAs-AlAs DBRs, 0.55 μm×0.55 μm cross section of the cavity, three times vertically long cross section of quantum-wire active regions, and the spectral width of several nanometers at room temperature. This value can be further increased by utilizing a narrower spectral width expected at low temperature     

Pure effects of strain in strained-layer multiple-quantum-welllasers

The pure effects of strain in strained-layer InGaAs-InGaAsP multiple-quantum-well (MQW) Fabry-Perot (FP) lasers operating in the 1.5 μm region are measured separately from the quantum effects by using lasers whose active layer wells have the same thickness but different amounts of strain. The gain peak wavelengths of transverse electric (TE) and transverse magnetic (TM) modes and the difference between TE- and TM-mode gain peak wavelengths increase when compressive strain is introduced. The differential gain coefficient and the gain saturation coefficient of the lasers are determined by measuring relative intensity noise (RIN) spectra and are found to increase with increasing compressive strain. The K factors of the lasers are determined from the relationship between the damping constant and the resonant frequency square     

Hardening in Creep of Alumina by Zirconium Segregation at the Grain Boundary

The effect of zirconium segregation on hardening in the creep of fine-grained alumina was studied by using the tensile creep test. To avoid the effect of zirconia particle dispersion on creep, 100-ppm-zirconium-doped alumina and 1000-ppm-zirconium-doped alumina were fabricated by using a zirconium-containing precursor. The scanning transmission electron microscopy/energy-dispersive X-ray spectroscopy study revealed that the zirconium was segregated at the alumina grain boundary. Doping even as little as 100 ppm of zirconium caused the hardening effect. The creep rate was further reduced by increasing the amount of zirconium dopant. Although the stress exponent of 2 was not affected by zirconium segregation, the apparent activation energy of the creep was found to be increased, from 520 kJ/mol for undoped alumina to 670 kJ/mol for 100-ppm-zirconium-doped alumina and 760 kJ/mol for 1000-ppm-zirconium-doped alumina. It was suggested that grain-boundary sliding was accommodated by impurity-drag-controlled diffusional creep.     

Prediction of sleep disorders induced by beta-adrenergic receptor blocking agents based on receptor occupancy

beta-adrenergic receptor blocking agents (beta-blocking agents) have been widely used clinically for the treatment of various cardiovascular conditions. However, beta-blocking agents are liable to cause sleep disturbance, such as vivid dreams, nightmares, increased waking, and insomnia. The mechanisms of the sleep disorders are not known, but several may conceivably be responsible for these CNS-related side effects. In the present study, we hypothesized that the sleep disorders are induced by the blockade of central or peripheral beta 2 receptors and/or central serotonin (5-HT) receptors. To verify the hypothesis, we retrospectively analyzed the relationships between the extent of the sleep disorders and the beta 1, beta 2, or 5-HT receptor occupancies for four beta-blocking agents (atenolol, metoprolol, pindolol, and propranolol). No significant correlations were observed among pharmacokinetic/physicochemical parameters (therapeutic dose, plasma concentration, plasma unbound concentration, cerebrospinal fluid concentration, and lipid solubility) and pharmacodynamic parameters (the scores of the sleep disorders such as the number of dreams). Furthermore, no significant relationship (correlation coefficient: r < 0.3) was observed between beta 1 receptor occupancies of the drugs and the number of dreams. On the other hand, good relationships (r > 0.95) were observed between central and peripheral beta 2 or central 5-HT receptor occupancies and the number of dreams. These findings suggest that beta 2 and/or 5-HT receptor occupancy is superior to beta 1 receptor occupancy as an index for the sleep disorders.