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  • 1
    Electronic Resource
    Electronic Resource
    Low temperature epitaxial growth of Ge using electron-cyclotron-resonance plasma-assisted chemical vapor deposition (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 1949-1954 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Epitaxial Ge films have been deposited on Si and Ge substrates at 300 °C using electron-cyclotron-resonance plasma-assisted chemical vapor deposition. Helium was fed into the resonance chamber, and a mixture of helium and germane were fed downstream at a location above the substrate. Surface roughness increased with energetic ion bombardment as quantified by the number of ions striking the surface per Ge atom deposited. Surface roughness also increased with increasing substrate temperature. Films with very rough surface morphology were found to be polycrystalline. The large hydrogen content of the films, particularly those deposited on Si, appeared to prevent the reduction of the epitaxial temperature below 300 °C. In the temperature range between 300 and 325 °C, hydrogen bubbles formed at the Ge/Si interface and caused the films to pucker from the surface. Increasing the substrate temperature above 325 °C eliminated this problem by decreasing the surface coverage of hydrogen during deposition.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351189
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  • 2
    Electronic Resource
    Electronic Resource
    Absolute measurements of elastic-wave phase and group velocities in lossy materials (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 3477-3486 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Traditional methods of determining phase and group velocities are often inadequate for many thick-section materials that exhibit greater than 30 dB, frequency-dependent propagation losses across the passband of the transducer. This article describes a measurement method that addresses this problem. Our method is mechanized as a pulsed, swept-frequency interferometer. The method's accuracy and reliability are enhanced by a combination of circuit-design improvements, which increase the signal-to-noise ratio and linearity, and signal-processing methods, which remove circuit-related measurement errors and compensate for diffraction. First we describe the foundations of our measurement method and its mechanization. Then we describe the signal-processing procedures, used to calibrate the instrumentation and to determine the absolute phase and group velocities. To illustrate the method, we determine the phase velocities in a very lossy, 50-mm-thick, glass/epoxy specimen in the 0.3–1.2-MHz region.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143752
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  • 3
    Electronic Resource
    Electronic Resource
    Watt-range, coherent, uniphase powers from phase-locked arrays of antiguided diode lasers (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 58 (1991), S. 2070-2072 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Twenty-element near-resonant AlGaAs/GaAs arrays of antiguides have been optimized for maximum intermodal discrimination and large Strehl ratio. It is found that 1000-μm-long devices with two intracavity Talbot-type spatial filters, and a 3 to 1 ratio between element core and interelement spacing provide the best results. The intermodal discrimination is discussed for both Talbot and uniform devices. For devices with two Talbot-type spatial filters, diffraction-limited-beam operation is obtained to 1 W pulsed power, and operation in a beam with lobewidth 1.5× diffraction limit is obtained to 2 W and 19× threshold. cw diffraction-limited-beam operation is obtained to 0.5 W, limited by thermal considerations. Uniform devices operate in beams with lobewidth ≈3× diffraction limit to 5 W and 45× threshold. At 5 W total output the coherent uniphase power is 1.6 W, and the coherent power in the main lobe is 0.94 W.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.105013
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  • 4
    Electronic Resource
    Electronic Resource
    cw high-power diffraction-limited-beam operation from resonant optical waveguide arrays of diode lasers (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 58 (1991), S. 22-24 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Monolithic phase-locked resonant arrays of antiguides, resonant optical-waveguide (ROW) arrays, have been optimized for efficient in-phase-mode operation. Diffraction-limited, in-phase-mode continuous-wave (cw) operation is obtained from 20-element uniform arrays to 250 mW output power, with (front facet) external differential quantum efficiencies of 41%. Single longitudinal mode operation is observed below 100 mW cw. In-phase-operating devices with and without Talbot-type spatial filters are compared, and it is found that for ROW arrays Talbot-type spatial filters are not required.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.104425
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  • 5
    Electronic Resource
    Electronic Resource
    High-power, narrow single-lobe operation from 20-element phase-locked arrays of antiguides (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 55 (1989), S. 2060-2062 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Pure in-phase-mode operation is obtained from 20/21-element AlGaAs/GaAs antiguided arrays grown by two-step metalorganic chemical vapor deposition. Oscillation of out-of-phase modes is substantially suppressed by a built-in spatial filter: two sets of noncollinear antiguides separated by a 50-μm-long laterally unguided region, corresponding to the half-Talbot distance. Design considerations for 20- vs 10-element arrays are discussed. Diffraction-limited-beam operation (i.e., 0.8° lobewidth) is obtained to 1.5×threshold (90 mW, both facets). Beams with 1.3° lobewidth (1.6×diffraction limit) are obtained at 3×threshold and 300 mW (both facets). Devices with optimized facet coatings operate in a single, 1.5°-wide lobe (i.e., 1.8×diffraction limit) at 330 mW front-facet emitted power. The main lobe contains 80–87% of the total power.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.102105
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  • 6
    Electronic Resource
    Electronic Resource
    Dependence of external differential efficiency on laser length and reflectivities in multiple quantum well lasers (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 55 (1989), S. 825-827 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The external efficiency ηd of quantum well (QW) lasers is maximum at some characteristic laser length, which is dependent upon mirror reflectivities and the number of QWs in the active layer. The observed decrease in ηd in short lasers is caused by increased optical absorption associated with a high concentration of free carriers in the QW and the surrounding waveguide layer. The carriers spill into the waveguide because of QW subband filling in short cavity lasers with high threshold gains.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.101771
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  • 7
    Electronic Resource
    Electronic Resource
    Resonant optical transmission and coupling in phase-locked diode laser arrays of antiguides: The resonant optical waveguide array (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 54 (1989), S. 2183-2185 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Uniform linear arrays of antiguides have 100% optical transmission between elements when the interelement spacing is an integer number of leaky wave half-wavelengths in the lateral direction. Resonant in-phase-mode and out-of-phase-mode coupling occurs when the number of half-wavelengths is odd and even, respectively. Such devices are called resonant optical waveguide (ROW) arrays. The discrimination between the resonant array mode and adjacent array modes reaches a maximum in close proximity to the resonance. An AlGaAs/GaAs ROW diode laser array operating close to resonance is demonstrated. Devices with virtually uniform near-field intensity profiles operate in stable, diffraction-limited in-phase modes to drive levels in excess of three times threshold.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.101159
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  • 8
    Electronic Resource
    Electronic Resource
    Design considerations for diffraction coupled arrays with monolithically integrated self-imaging cavities (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 54 (1989), S. 1848-1850 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Conditions for stabilization of in-phase or out-of-phase array eigenmodes in diffraction coupled diode laser arrays are derived and applied to several array architectures. The analysis predicts that the discrimination between these two eigenmodes is strongest in arrays with half Talbot distance long free-propagation region. In this geometry, the out-of-phase and in-phase near fields are, respectively, reproduced and channeled halfway between the original channel locations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.101255
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  • 9
    Electronic Resource
    Electronic Resource
    High-power, diffraction-limited-beam operation from phase-locked diode-laser arrays of closely spaced "leaky'' waveguides (antiguides) (1988)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 53 (1988), S. 464-466 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A novel type of phase-locked diode-laser array is demonstrated: an array of closely spaced index depressions (antiguides). The arrays are ten-element AlGaAs/GaAs devices fabricated by metalorganic chemical vapor deposition and liquid phase epitaxy over a patterned substrate. The fundamental and highest-order modes of the array of antiguides have negligible radiation loss: 20–30 times less than that for a single antiguide. The modal-gain differentials between adjacent array modes are at least an order of magnitude larger than those for evanescently coupled arrays of positive-index guides. Fundamental-array-mode operation in a virtually diffraction-limited-beam (1.4°) pattern is obtained to 200 mW. Out-of-phase-mode operation in a virtually diffraction-limited-beam (1.2°) pattern is achieved to 110 mW/uncoated facet. The inherent array-mode stability of antiguided arrays is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.99885
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  • 10
    Electronic Resource
    Electronic Resource
    Gain dependence of the threshold characteristic temperature in multiple quantum well lasers (1988)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 53 (1988), S. 2272-2274 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An analytical formula that determines dependence of the threshold characteristic temperature T0 on gain in multiple quantum well lasers is derived by approximately evaluating the gain integrals. Because the threshold gain depends on lasing cavity and quantum well structures, the formula determines dependence of T0 on laser length, reflectivities, optical loss, and number of quantum wells. A very good agreement is obtained between theory and experiment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.100251
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