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  • 1
    Electronic Resource
    Electronic Resource
    Raman effect in AlGaAs waveguides for subpicosecond pulses (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 2198-2203 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Raman effect in semiconductor waveguides below half-gap is studied both experimentally and numerically. We report the depolarized Raman gain spectra up to 300 cm−1 in Al0.24Ga0.76As at pump wavelengths of 0.515 and 1.55 μm from the measurement of the absolute Raman scattering cross sections using GaAs as a reference scatterer. In addition, the coupled propagation equations for the AlGaAs waveguides are modified to include the Raman effect. By solving the coupled propagation equations numerically, we verify that the energy transfer between two orthogonally polarized pulses demonstrated in previous pump-probe experiments [M. N. Islam et al., J. Appl. Phys. 71, 1927 (1992)] is caused by Raman effect. We also show numerically that the Raman effect induces spectral distortions on the pulses, and the energy transfer is inversely proportional to the pulse widths. The energy transfer results in a severe cross-talk problem for sub-picosecond pulses in AlGaAs waveguides. For example, the energy exchange is about 30% for 300 fs pulses under π phase shift conditions. Therefore, the Raman effect limits the performance of semiconductor waveguides in optical switching applications for sub-picosecond pulses. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.360135
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  • 2
    Electronic Resource
    Electronic Resource
    Comparison of surface spin wave modes at Fe/MnF2 and Fe/Mn interfaces (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 5293-5295 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have studied the thermal demagnetization in semi-infinite ferromagnets in Fe/MnF2 and Fe/Mn bilayers using Mössbauer spectroscopy. We find that the hyperfine field at the Fe/MnF2 interface follows a quasilinear temperature dependence, which reverts to a T3/2 dependence further into the bulk. The region in which linear temperature dependence was observed also showed significantly higher spin canting than in the film's bulk layers. The interface in the Fe/Mn system immediately showed a T3/2 dependence which persisted deeper into the bulk. We attribute the linear temperature behavior to surface spin wave modes created by a perpendicular surface anisotropy at the interface. This behavior diminishes farther away from the interface, until the hyperfine field goes like T3/2 as expected for bulk, 3D spin waves. We conclude that the perpendicular surface anisotropy is much stronger at the Fe/MnF2 than the Fe/Mn interface. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1314871
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  • 3
    Electronic Resource
    Electronic Resource
    Limitations on ultrafast optical switching in a semiconductor laser amplifier operating at transparency current (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 4740-4747 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.371438
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  • 4
    Electronic Resource
    Electronic Resource
    Temperature dependence of magnetization at Fe/MnFe2 interface (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 4625-4626 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Mössbauer spectroscopy is used to extract depth sensitive information near the surface of an Fe film in Fe/MnF2 bilayers. We find that the hyperfine field at the surface has a quasilinear temperature dependence. For layers deeper into the film, the quasilinear temperature dependence diminishes and deep enough into the films, the hyperfine field goes like T3/2 as expected for bulk. We interpret this behavior as evidence of surface spin wave modes created by a perpendicular surface anisotropy, as previously predicted. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.370428
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  • 5
    Electronic Resource
    Electronic Resource
    Nonlinear spectroscopy near half-gap in bulk and quantum well GaAs/AlGaAs waveguides (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 1927-1935 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We study the nonlinear properties of bulk AlGaAs and GaAs/AlGaAs multiple quantum wells (MQW) below the half-band-gap energy using subpicosecond pulses between 1.65 and 1.7 μm. In the bulk material we find a value for the nonlinear index n2 = +3.6× 10−14 cm2/W and a two-photon absorption coefficient β = 0.26 × 10−4 cm/MW. In the MQW we measure an n2 up to 2.4 times larger, and we attribute this enhancement to a stronger 1S-exciton intermediate state. The β value is up to 25 times larger in the MQW. This larger value may result from midgap states that resonantly enhance the virtual intermediate state in two-photon absorption and act as a real transition in a two-step absorption process. The resulting figure of merit (2n2/βλ) for the bulk (MQW) material is 17 (1.6), which means that these semiconductors below half band gap are appropriate for all-optical switching and quantum optics applications. We confirm that n2 is instantaneous on the 300 fs time scale of our pulses from self-phase-modulation spectra as well as time-resolved pump-probe measurements. However, we find an intriguing exchange of energy between the two orthogonal axes as evidenced by the signal along the probe axis following the negative derivative of the pump intensity. This result may be explained by self-phase modulation of the pump combined with a low-frequency Raman process that couples the modes along orthogonal axes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351182
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  • 6
    Electronic Resource
    Electronic Resource
    Picosecond study of near-band-gap nonlinearities in GaInAsP (1986)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 59 (1986), S. 2619-2628 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: From picosecond pump-probe and forward degenerate four-wave mixing (DFWM) experiments, we obtain the near-band-gap nonlinear absorption and refraction properties of GaInAsP for λ∼1.5 μm. Using a mode-locked color center laser, the nonlinear signals are studied in room-temperature samples as a function of time and wavelength for different pump energies and for materials with different band-gap energies. Nonlinear absorption cross sections σeh as large as −5.7×10−15 cm2 are obtained from the pump-probe results, while effective nonlinear cross sections σeff as large as 7.8×10−16 cm2 (corresponding to a steady state ||χ(3)||∼3.8×10−3 esu for a 20-ns relaxation time) are measured in the DFWM experiments. The spectral behavior of the data shows that above the band gap, the nonlinearity is due both to band filling and screening of excitonic effects. However, the effectiveness of the screening diminishes within one or two plasma frequencies of the band edge.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.336989
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  • 7
    Electronic Resource
    Electronic Resource
    Bulk semiconductor saturable absorber for a NaCl color center laser (1990)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 56 (1990), S. 2177-2179 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Using bulk InGaAsP as a saturable absorber we have passively mode locked a NaCl color center laser to produce transform-limited, pedestal-free pulses near 1.6 μm as short as 197 fs with up to 4.2 kW peak power. Our results simplify the saturable absorber material requirements and prove that excitons are not required for generating subpicosecond pulses. By comparing a dozen samples we find that a minimum band-edge absorbance of 40% is required to generate subpicosecond pulses, although details of the band edge are not critical. In addition, we find stable mode locking always occurs on the long-wavelength side of the laser gain peak.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.102960
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  • 8
    Electronic Resource
    Electronic Resource
    Multiple quantum well passive mode locking of a NaCl color center laser (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 54 (1989), S. 1203-1205 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Using multiple quantum well (MQW) saturable absorbers, we passively mode locked a NaCl color center laser to produce transform-limited, pedestal-free pulses with τ as short as 275 fs and peak power as high as 3.7 kW. Because of exciton ionization with a 200±30 fs time constant, the MQW shows a fast absorption recovery that is comparable to our pulse widths. This fast component plays a major role in pulse shaping and may limit the pulse width. We also show that the wavelength for the short pulses can be tuned from 1.59 to 1.7 μm by choosing MQWs with different band gaps.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.100753
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  • 9
    Electronic Resource
    Electronic Resource
    Detailed characterization of HgCdTe/CdTe multiple quantum wells (1990)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 56 (1990), S. 283-285 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present absorption measurements in HgCdTe/CdTe multiple quantum wells as a function of temperature, polarization, and well size in the 3–4 μm wavelength region. The energy levels are calculated using a model that includes band nonparabolicity. The spectra are fitted to a sum of continuous broadened steps including the two-dimensional Sommerfeld enhancement factor. Polarization measurements confirm the assignment of heavy and light holes. The ratio between heavy and light hole absorption of 2.3/1 agrees well with theory. The fit of the linewidth with temperature shows a homogeneous linewidth of 4.6 meV times the density of longitudinal optical phonons and an inhomogeneous linewidth of 6.4 meV, which is similar to the alloy broadening in the bulk material.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.102809
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  • 10
    Electronic Resource
    Electronic Resource
    Room-temperature confinement and photoluminescence near 3 μm from HgCdTe multiple quantum wells (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 54 (1989), S. 745-747 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report room-temperature confinement and photoluminescence near 3 μm in a mercury cadmium telluride multiple quantum well. The absorption spectra show transitions from the first heavy and light hole confined levels to the first conduction electron confined level. Photoluminescence is present even at room temperature. The transition energies and temperature dependence of our data can be described by a square well model provided that a temperature-independent value of approximately 400 meV is used for the HgTe-CdTe valence-band offset.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.100880
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