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Notes: Background  Much clinical evidence suggests that the nervous system, including psychological factors, can influence the course of alopecia areata (AA). However, there has been little substantial evidence of specific participation of cutaneous neurogenic factors in the disease process. Objectives  As previous studies have demonstrated that stress elicits the release of the neuropeptide substance P (SP) from peripheral nerves and that some patients with AA show prominent SP expression in nerves surrounding their hair follicles, we aimed to evaluate the role of SP in AA. Methods  We used immunohistochemistry to examine the expression of SP and SP-degrading enzymes in scalp biopsies from patients with AA and from healthy controls. Results  Affected hair follicles in the centre of the areas of hair loss of patients with AA were richly innervated by SP-staining nerve fibres. Strong expression of the SP-degrading enzyme, neutral endopeptidase (NEP), was observed in hair follicles not only in the acute progressive phase of AA but also in the chronic stable phase. Expression of NEP in hair follicles from the margins of areas of hair loss was stronger than in normal controls, but was weaker than in the centre of the areas of hair loss. In addition, endothelial immunoreactivity for angiotensin-converting enzyme (also capable of degrading SP) was not observed in the centre of the areas of hair loss, which was in significant contrast to normal controls as well as to the margins of areas of hair loss where it was expressed. Further, intense expression of endothelial leucocyte adhesion molecule-1 on vessels and many degranulating mast cells was observed adjacent to affected hair follicles in AA, in admixture with dense lymphocytic inflammation. Conclusions  These findings suggest that SP is endogenously released by dermal nerve fibres around hair follicles and that it may play an important part in epithelial–mesenchymal–neuroectodermal interactions in AA. This study reveals that SP and its degrading enzymes are involved in the pathogenesis of AA, which in turn might explain the pathological significance of neurogenic and psychogenic aspects in the disease process.

Notes: Two types of wavelength switching are observed experimentally in two-segment 1.55 μm InGaAsP/InP ridge waveguide multiquantum-well distributed-feedback (DFB) lasers. The first type occurs between the longitudinal modes on the opposite sides of the DFB stop band, while the second type occurs on the same side of the stop band. The physical mechanism is correlated to a slight difference of the effective grating period between the two inhomogeneously injected laser segments. © 1995 American Institute of Physics.

Notes: The "reservoir'' model of Kan, Vassilovski, Wu, and Lau [Appl. Phys. Lett. 61, 752 (1992)] is extended to analyze frequency chirp in separate confinement heterostructure (SCH) multiple-quantum-well lasers. Small-signal analysis is performed and compared between linear and logarithmic material gain. It is shown that there is an optimum value of SCH width at which frequency chirp becomes minimum. © 1995 American Institute of Physics.

Notes: Optical injection effects and all-optical set-reset operations in two-segment strained multiquantum-well (MQW) distributed feedback (DFB) bistable lasers were experimentally investigated. The optical bistable characteristics under detuned optical injection, of strained MQW DFB bistable lasers, show the effect of the residual Fabry–Perot side modes of the DFB structures; optimizing the input wavelength and the input power is suggested for applications. The switching properties of dynamic optical set-reset operations with pulsed optical injection were reported, which appear to be related to the optical bistable characteristics under cw optical injection; however, the switching transients are found to be essential to full understanding of these switching properties. © 1996 American Institute of Physics.

Notes: The effect of carrier transport on the small-signal dynamics of multiple-quantum-well lasers is investigated both theoretically and experimentally. The dependence of modulation bandwidth on quantum-well number is examined. Based on the phenomenological model, it is shown that there is an optimum value of the ratio between carrier quantum capture time and escape time, at which the modulation bandwidth of multiple-quantum-well lasers achieves maximum. The theoretical results agree well with experimental data. © 1995 American Institute of Physics.

Notes: An efficient phenomenological model describing the temperature dependence of the output power of multiquantum well (MQW) lasers is presented. The model can predict all the general features of the experimental results. The effect of series resistance, thermal resistance, cavity length, leakage current, and facet reflectivity on the maximum achievable power are analyzed in a systematic manner. The calculated maximum operating temperature (Tm), defined as the heat sink temperature at which the saturated output power vanishes due to heating, is in reasonable agreement with reported experimental results. © 1997 American Institute of Physics.

Notes: The effect of confinement on the exciton binding energies has been systematically investigated for two series of ZnO/ZnMgO multiquantum wells with various well widths and barrier heights. The exciton binding energies were extracted from the energy difference between the stimulated emission band induced by inelastic exciton–exciton scattering and the free exciton absorption band. The binding energies of excitons are found to be sensitively dependent on the well widths. The experimental results of the well width dependence of binding energies are in good agreement with Coli and Bajaj's theoretical calculations for these structures [G. Coli and K. K. Bajaj, Appl. Phys. Lett. 78, 2861 (2001)]. The remarkable reduction in coupling strength between excitons and longitudinal optical phonons is closely correlated with the enhancement of the exciton binding energy, indicating that the stability of excitons is greatly increased by the enhancement of exciton binding energy in quantum wells. © 2002 American Institute of Physics.

Notes: A set of ZnO/Mg0.12Zn0.88O multiple quantum wells (MQWs) with well widths, Lw, varying from 6.91 to 46.5 Å has been grown by laser molecular-beam epitaxy. We estimated the Lw dependence of the radiative and nonradiative recombination times of localized excitons at 5 K. Suppression of quantum efficiency can be avoided even in the MQWs having small Lws studied in this work. Effects of excitonic localization are discussed in order to explain the Lw dependence of radiative recombination time at 5 K. © 2001 American Institute of Physics.

Notes: We report the high temperature operation of 1.3 μm ridge waveguide Fabry–Perot lasers utilizing a double-carrier-confinement heterostructure, with an active region containing an n-type lattice-matched multiple quantum well (MQW) as well as a p-type strained MQW. All devices with a cavity length of 400–1000 μm and as-cleaved uncoated facets operated beyond 100 °C in the cw mode with an optical power in excess of 8 mW. T0 was found to be in the range of 65–75 and 72–98 K, for uncoated devices and devices with one high-reflectivity-coated facet, respectively.

Notes: The effective linewidth enhancement factor αeff and the spectral linewidth Δυ are reported for the first time for a partly gain-coupled distributed feedback laser with a gain corrugation in a strained multiple quantum-well active region emitting at 1.55 μm wavelength. The αeff value is estimated to be as low as 1 and is independent of the laser cavity length L, while a decrease in the linewidth-power product ΔυPo with L has been observed, with a measured linewidth of 2 MHz at 10 mW optical output power for 300-μm-long devices. The experimental results demonstrate that a small αeff is obtained due to the strain and the gain coupling effects, while further reduction of the spectral linewidth with L is the result of longitudinal index coupling effects.