Characteristics of GaInNAsSb VCSELs operating near 1.55µm

A detailed study of the high-power pulsed operation of C-band optically-pumped GaInNAsSb vertical cavity surface emitting lasers is reported. The devices employ a resonant periodic gain structure grown by molecular beam epitaxy on a GaAs substrate with a 31-pair GaAs/AlAs bottom distributed Bragg reflector and a 4-λ, GaAs-based resonant cavity containing 10 GaInNAsSb quantum wells distributed among the 7 antinodes of the electric field. A dual-pump-band SiO2/TiO2 dielectric top mirror allows efficient optical pumping via low reflectivities at 808nm and 1064nm while providing very high reflectivity at the 1.55μm target emission wavelength. The laser characteristics were evaluated using both a Q-switched Nd:YAG 1064nm pump and a 20W-peak 180ns-pulsed 850nm diode laser. The importance of the gain-cavity detuning was evident from time-dependent spectral measurements of laser material subjected to post-growth annealing at different temperatures between 725 and 775°C. The highest annealing temperature produces the largest blue shift of the gain peak relative to the cavity resonance, resulting in the best power transfer characteristics as well as reduced temperature sensitivity

What Is Charity? William Langland’s Answers with Some Diachronic Questions

Charity turns out to be the virtue which is both the root and the fruit of salvation in Langland’s Piers Plowman, a late fourteenth-century poem, the greatest theological poem in English. It takes time, suffering and error upon error for Wille, the central protagonist in Piers Plowman, to grasp Charity. Wille is both a figure of the poet and a power of the soul, voluntas, the subject of charity. Langland’s poem offers a profound and beautiful exploration of Charity and the impediments to Charity, one in which individual and collective life is inextricably bound together. This exploration is characteristic of late medieval Christianity. As such it is also an illuminating work in helping one identify and understand what happened to this virtue in the Reformation. Only through diachronic studies which engage seriously with medieval writing and culture can we hope to develop an adequate grasp of the outcomes of the Reformation in theology, ethics and politics, and, I should add, the remakings of what we understand by “person” in these outcomes. Although this essay concentrates on one long and extremely complex medieval work, it actually belongs to a diachronic inquiry. This will only be explicit in some observations on Calvin when I consider Langland’s treatment of Christ’s crucifixion and in some concluding suggestions about the history of this virtue

Intersubband Raman laser

An intersubband Raman laser has been realized in an artificial GaAs/AlGaAs three-level quantum-well structure. A CO2 laser in resonance with the one-to-three level transition is used as the pump, while the lasing emission occurs via the three-to-two level transition. The one-to-two level spacing is designed to be in resonance with the AlAs-like longitudinal optical phonon mode, favoring the Raman process. This work presents an alternative mechanism for realizing intersubband lasers and opens up new possibilities in reaching the far infrared region and achieving room-temperature operation.NRC publication: Ye

Far-infrared Raman laser based on resonant intersubband transitions

NRC publication: Ye

Physics of Semiconductors 2002

NRC publication: Ye