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1 Nov 1999

Volume 86, Issue 9, pp. 4723-5318

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Thermodynamic studies on dissociation of metal iodides at high temperatures in metal halide lamps

Tetsuya Ozaki and Gin-ya Adachi

J. Appl. Phys. 86, 4723 (1999); http://dx.doi.org/10.1063/1.371435 (6 pages) | Cited 3 times

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Thermodynamics of dissociation of metal iodides into metal and iodine atoms in metal halide arc discharges was investigated for ScI3/NaI/Hg, DyI3/Hg, CsI/Hg, and TlI/NaI/Hg systems at the temperature range of 1000–3000 K. Densities of the metal vapors calculated in the systems with the common thermodynamic quantities of metal atoms and iodides in vapor phases were compared with those experimentally determined from spectroscopic measurements or model calculations. For CsI and TlI, the experimental and calculated density values were closed to each other. On the other hand, the experimental values were much smaller than the calculated ones for sodium and rare-earth iodides because of diffusion of the iodides by chemical transport and convection in the discharges at high temperatures. Apparent Gibb’s energy changes of the dissociation in the lamps were expressed as first-order equations of temperature containing the terms of the increments of the average enthalpy and entropy changes, which were dependent on the molecular weight of the iodides. The densities of metal vapors derived with the obtained equations were comparable to those experimentally determined for all the systems under investigation. A series of equations were applicable to estimating the vapor density distribution of the other metal iodides, whose partial pressure distribution had never been experimentally estimated. © 1999 American Institute of Physics.
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82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
33.15.Fm Bond strengths, dissociation energies
52.80.Mg Arcs; sparks; lightning; atmospheric electricity
51.30.+i Thermodynamic properties, equations of state
05.70.Ce Thermodynamic functions and equations of state
82.60.Cx Enthalpies of combustion, reaction, and formation

Type-II quantum-well “W” lasers emitting at λ = 5.4–7.3 μm

D. W. Stokes, L. J. Olafsen, W. W. Bewley, I. Vurgaftman, C. L. Felix, E. H. Aifer, J. R. Meyer, and M. J. Yang

J. Appl. Phys. 86, 4729 (1999); http://dx.doi.org/10.1063/1.371436 (5 pages) | Cited 17 times

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A series of optically pumped type-II quantum-well “W” lasers with wavelengths ranging from 5.4 to 7.3 μm operated at temperatures up to at least 220 K for pulsed operation. The peak output power at 80 K was 1.1 W/facet for a device emitting at λ = 7.0 μm. Internal losses were characterized for the temperature range between 40 and 190 K. Auger coefficients determined from an analysis of the threshold pump intensities were found to be suppressed by up to an order of magnitude compared to type-I III–V semiconductors with the same energy gaps. © 1999 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
81.05.Ea III-V semiconductors
78.66.Fd III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

High-speed spin-polarized intersubband lasers

I. Vurgaftman, J. R. Meyer, and L. R. Ram-Mohan

J. Appl. Phys. 86, 4734 (1999); http://dx.doi.org/10.1063/1.371437 (6 pages)

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Spin-polarized intersubband lasers based on optically pumped type-II antimonide quantum wells in a magnetic field are proposed. Complete discretization of the electron energy spectrum is predicted to extend the electron lifetime considerably. Continuous-wave room-temperature operation is projected for both interband and intersubband pumping configurations lasing at λ=16–24 μm. Furthermore, the parasitic capacitances associated with electrical injection are eliminated, and the large differential gain and fast intrinsic time scale should give modulation bandwidths in excess of 100 GHz. © 1999 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Limitations on ultrafast optical switching in a semiconductor laser amplifier operating at transparency current

Y.-H. Kao, T. J. Xia, M. N. Islam, and G. Raybon

J. Appl. Phys. 86, 4740 (1999); http://dx.doi.org/10.1063/1.371438 (8 pages) | Cited 9 times

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Ultrafast optical switching in a semiconductor laser amplifier (SLA) at transparency current is studied under a strong pump condition. The switch configuration is a nonlinear optical loop mirror with a SLA as the nonlinear element. We demonstrate optical switching with 2 ps recovery time and 60% nonlinear transmission at switching energy of 9 pJ. We find that the transparency current is pump power dependent and that the transparency current is different for uniform 7-bit input control pulses at 100 Gb/s. We believe these two outcomes are due to significant carrier generation via two photon absorption (TPA) at high pump intensity. To verify our hypothesis, we modify coupled propagation equations by including the carrier generation due to the TPA and solve the equations numerically. Good agreement between the experimental and simulation results is obtained. We conclude that to achieve complete pattern-independent 100 Gb/s optical switching using a SLA at transparency current, we have to avoid TPA or use the SLA with a transit time shorter than the control pulse width. © 1999 American Institute of Physics.
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42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.55.Px Semiconductor lasers; laser diodes
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.79.Sz Optical communication systems, multiplexers, and demultiplexers
42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Strain relaxation in graded composition InxGa1−xAs/GaAs buffer layers

F. Romanato, E. Napolitani, A. Carnera, A. V. Drigo, L. Lazzarini, G. Salviati, C. Ferrari, A. Bosacchi, and S. Franchi

J. Appl. Phys. 86, 4748 (1999); http://dx.doi.org/10.1063/1.371439 (8 pages) | Cited 24 times

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A model to compute the strain relaxation rate in InxGa1−xAs/GaAs single layers has been tested on several compositionally graded buffer layers. The existence of a critical elastic energy has been assumed as a criterion for the generation of new misfit dislocations. The surface strain accuracy results are within 2.5×10−4. The influence of different grading laws and growth conditions on residual strain, threading dislocation density, misfit dislocation confinement, and surface morphology has been studied. The probability of dislocation interaction and work hardening has been shown to strongly influence the mobility and the generation rate of the dislocations. Optimization of the growth conditions removes residual strain asymmetries and smoothes the surface roughness. © 1999 American Institute of Physics.
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68.35.Gy Mechanical properties; surface strains
81.05.Ea III-V semiconductors
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
68.35.Ct Interface structure and roughness
61.72.Yx Interaction between different crystal defects; gettering effect
66.30.Lw Diffusion of other defects
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Equivalent retarder approach to reflective liquid crystal displays

S. Stallinga

J. Appl. Phys. 86, 4756 (1999); http://dx.doi.org/10.1063/1.371440 (11 pages) | Cited 21 times

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Reflective liquid crystal displays (LCDs) are studied using the Jones 2×2 matrix method. The reflective LCD effectively behaves as a single retardation layer. Conditions on the retardation and optical axis orientation of this equivalent retarder in order to obtain high brightness and high contrast are derived and applied to twisted nematic layers without and with a compensating waveplate. The optimization of the display performance by numerical calculations is greatly simplified by analytical results relating the parameters of the liquid crystal, incident polarization, and compensator. © 1999 American Institute of Physics.
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42.79.Kr Display devices, liquid-crystal devices
85.60.Pg Display systems
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