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Quantum Electronics, IEEE Journal of

Issue 2 • Date Feb 1998

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Displaying Results 1 - 23 of 23
  • Generation of high-order rotational lines in hydrogen by four-wave Raman mixing in the femtosecond regime

    Page(s): 260 - 268
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    More than 40 rotational Raman lines are generated using an 800-fs Ti:sapphire laser. The spectral region extends from the near-infrared to the far-ultraviolet with a considerably flat intensity distribution. The effects of laser polarization, pulsewidth, hydrogen pressure, and focusing conditions on the efficiencies of stimulated Raman scattering, four-wave Raman mixing, self-phase modulation, self-focusing, and harmonic generation are investigated. A white light continuum, generated by self-phase modulation, acts as a seed beam for the generation of high-order rotational lines through four-wave Raman mixing. Strong self-phase modulation, however, suppresses the generation of the Raman emission, due to a line broadening of the pump beam. Thus, optimization of experimental conditions is necessary for the efficient generation of high-order rotational lines View full abstract»

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  • Excited-state absorption studies of Cr4+ ions in several garnet host crystals

    Page(s): 292 - 299
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    An experimental study of saturable absorption and excited-state absorption (ESA) in several inorganic saturable absorbers, Cr4+ :YAG, Cr4+:GGG, and Cr4+:YSGG, is presented. We provide the theoretical background of absorption characteristics in saturable absorbers that exhibit ESA, with some new results: approximate analytical solutions are proposed for the optical transmission in the case of a slow absorber, and for various light intensity conditions of spatially or temporally Gaussian beams in fast and slow absorbers. Experimentally, partial bleaching of the first excited state itself could be observed in Cr4+:YAG at λ=1064 nm, yielding the higher excited-state lifetime as τ*=(0.55±0.1) ns. The regular transmission bleaching curve was measured in Cr4+:GGG, for the first time in this material, yielding σga=(58±5)×10-1 cm2, and σes=(13±2)×10-19 cm2 at λ=1064 nm, ESA spectra were measured for the three materials between ~700 and 900 nm. All three exhibit crossing between saturable absorption at longer wavelengths and inverse saturable absorption at shorter wavelengths View full abstract»

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  • CW submillimeter laser action in ethyl chloride

    Page(s): 238 - 240
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    We present ten new far-infrared (FIR) laser lines obtained by optically pumping ethyl chloride by means of a CW waveguide CO2 laser with a tunability range of 300 MHz. By means of a heterodyne technique and using, as mixing element, a metal-insulator-metal (MIM) point contact diode or a new home built metal-semiconductor diode, we measured the frequency of all these new lines, as well as that of another line, previously reported in literature. With our new lines, the total number of FIR laser lines emitted by ethyl chloride rises to 14; for each of them we give the offset relative to the center frequency of the pumping radiation, the polarization relative to that of the pumping CO2 laser, the relative intensity, and the optimum operation pressure. Seven of the new lines have frequencies in the 300-512-GHz range and four of them are strong enough to be used in high-field EPR spectroscopy View full abstract»

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  • Tilted mirror for lateral mode discrimination and higher kink-free power in fiber pump lasers

    Page(s): 353 - 365
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    Beam steering arising from interference between the fundamental lateral mode and higher order lateral modes limits the performance of 980-nm power lasers. In this paper, we analyze the feasibility of using a tilted mirror to discriminate against higher order modes. We calculate the reflectivity seen by different modes as a function of the thickness and tilt angle of the coating. Our results suggest that careful engineering of tilted coated mirrors represents a viable technique for improving the performance of power lasers View full abstract»

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  • Low-drive-voltage MQW electroabsorption modulator for optical short-pulse generation

    Page(s): 277 - 281
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    This paper reports on InGaAsP-InGaAsP tensile strained MQW electroabsorption (EA) modulators with a high modulation efficiency of 35 GHz/V that generate optical short pulses. We studied and optimized the multiple-quantum-well (MQW) structural parameters, barrier height, and well number, thickness, and strain in the absorption layer to ensure high attenuation efficiency and generate low duty cycle pulses. Low TE/TM polarization sensitivity was obtained by controlling strain. Stable, nearly transform-limited optical pulse trains with a narrow pulsewidth of 3.6 ps are generated by applying a 20-GHz sinusoidal modulation voltage (6 Vpp) to the EA modulator. This achieves a very small pulse duty cycle of 7.2% View full abstract»

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  • Insulator passivation of In0.2Ga0.8As-GaAs surface quantum wells

    Page(s): 307 - 310
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    The electronic passivation of (100) In0.2Ga0.8 As-GaAs surface quantum wells (QWs) using in situ deposition of an amorphous, insulating Ga2O3 film has been investigated and compared to standard Al0.45Ga0.55As passivation. Nonradiative lifetimes τr=1.1±0.2 and 1.2±0.2 ns have been inferred from the dependence of the internal quantum efficiency η on optical excitation density P0' for the Ga2O3 and Al0.45Ga0.55As passivated In0.02 Ga0.8As-GaAs surface QW, respectively. Beyond identical internal quantum efficiency, the amorphous Ga2O3 insulator passivation simplifies device processing, eludes problems arising from lattice-mismatched interfaces, and virtually eliminates band bending in electronic and optoelectronic devices based on a low dimensional system such as quantum wells, wires, and dots View full abstract»

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  • The effects of surface acoustic waves on the optical properties of AlGaAs-GaAs quantum-well structures

    Page(s): 300 - 306
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    The effects of a propagating surface acoustic wave (SAW) on the transitions in single- and multiple-quantum-well structures and the change in their absorption and refractive index are presented here. The fundamental difference between the effects of an applied electric field and a propagating SAW are those due to a linear and a nonlinear induced field, respectively. The electron and hole energy eigenvalues and envelope functions of the unperturbed structure are determined. The effect of the SAW-induced strain and electric fields on the confining potential of the quantum-well (QW) structure is then calculated and the energy eigenvalues and envelope functions for this perturbed case are determined. The complex refractive index of the structure is then determined for both the perturbed and unperturbed cases, to give the change in refractive index and the absorption coefficient as a function of SAW wavelength, amplitude, barrier composition, well width, and number of wells. The wavelength (λac) and power of the SAW were found to be important in setting the induced changes in the refractive index View full abstract»

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  • Transient behaviors of output power in fast-axial flow-type CO laser

    Page(s): 241 - 249
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    Transient behaviors of output power were experimentally investigated with the parameters of discharge current Idis, discharge length l, gas-flow velocity ν, and O2 concentration for a compact dc discharged fast-axial flow (FAF) CO laser, and were theoretically explained, together with some empirical equations. Introducing the discharge time (t) dependence into the gas temperature and the concentration of O2 and CO2 molecules, based on the experimental data and the mass-spectrum analysis, respectively, the overall population density of CO molecule n ν' toward an arbitrary vibrational level has been expressed as a function of t. Then, since the gain parameter can also be given as a function of t, together with the measured laser parameters such as the saturation intensity Is, a measure of partial homogeneity m, and the Voigt function ψ, the transient behaviors of the output power as a function of t were well explained, being in good agreement with the experimental results and the calculations. From these analyses, it was found that control of the gas temperature rise and suppression of both the decrease of O2 and the increase of CO 2 concentrations are required to relax this unnecessary power reduction due to the transient behaviors View full abstract»

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  • Configuration Q-switching in a diode-pumped multirod variable-configuration resonator

    Page(s): 366 - 371
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    We report on a novel technique for Q-switching at high repetition rates, where the change in the Q of the cavity is due to the capability of a variable-configuration multirod resonator (VCR) to switch between an unstable Fabry-Perot configuration and a stable ring configuration. The switching between the configurations is accomplished simply by the means of a Pockels cell. Using the new Q-switching technique, 35-ns-long pulses with a peak power of 17 kW at a repetition rate of 4 kHz, giving an average power of 2.4 W, were obtained View full abstract»

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  • High-power continuous-wave quantum cascade lasers

    Page(s): 336 - 343
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    High-power continuous-wave (CW) laser action is reported for a GaInAs-AlInAs quantum cascade structure operating in the mid-infrared (λ≃5 μm). Gain optimization and reduced heating effects have been achieved by employing a modulation-doped funnel injector with a three-well vertical-transition active region and by adopting InP as the waveguide cladding material to improve thermal dissipation and lateral conductance. A CW optical power as high as 0.7 W per facet has been obtained at 20 K with a slope efficiency of 582 mW/A, which corresponds to a value of the differential quantum efficiency ηd=4.78 much larger than unity, proving that each electron injected above threshold contributes to the optical field a number of photons equal to the number of periods in the structure. The lasers have been operated CW up to 110 K and more than 200 mW per facet have still been measured at liquid nitrogen temperature. The high overall performance of the lasers is also attested by the large “wall plug” efficiency, which, for the best device, has been computed to be more than 8.5% at 20 K. The spectral analysis has shown finally that the emission is single-mode for some devices up to more than 300 mW at low temperature View full abstract»

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  • Er3+-doped Al2O3 thin films by plasma-enhanced chemical vapor deposition (PECVD) exhibiting a 55-nm optical bandwidth

    Page(s): 282 - 285
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    We report the first deposition of Er3+-doped aluminum oxide thin-film optical waveguides by plasma-enhanced chemical vapor deposition (PECVD). The aluminum and erbium precursors used for the deposition of the thin films were trimethyl-aluminum and Er tri-chelate of 2,2,6,6-tetramethylheptane-3,5 dione respectively. The samples show broad, room-temperature photoluminescence at λ=1.533 μm. The Er3+ concentration ranged from 0.01-0.2 at%. The full width half maximum (FWHM) of the Er3+ emission spectrum is 55 nm, considerably broader than in silica glass. The radiative lifetime has been measured at 50-mW pump power View full abstract»

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  • The influence of Coulomb enhancement on the modulation properties of quantum-well lasers

    Page(s): 318 - 324
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    The phenomenon of Coulomb enhancement, resulting from the consideration of many-body effects, is included in a detailed calculation of the gain of a quantum-well (QW) laser, which is then used to predict the laser's modulation response. Carrier transport in the separate-confinement heterostructure is taken into account. The modulation response is compared to experimental data and to predictions from calculations using only the free-carrier gain. The comparison shows that the inclusion of Coulomb enhancement in the theoretical calculations leads to better agreement between simulated and experimental data View full abstract»

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  • The effects of longitudinal gain distributions on the static and the dynamic properties in a λ/4 phase-shifted DFB laser

    Page(s): 225 - 232
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    The static and dynamic behaviors of the index-coupled DFB lasers are analyzed. In previous models, spatially dependent values were used for the refractive index distribution, but an averaged value was used for the gain distribution. The key feature of our model is that the “refractive index” and “gain” distributions are spatially dependent. The results of our model show a better agreement with an accurate model such as experimental data compared to those of the previous models. It was known that in the index-coupled DFB-lasers the gain profile as well as the refractive index profile plays an important role in determining the lasing characteristics, such as mode instability, chirping, linearity in the GRIN curve, and output power View full abstract»

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  • Calculation of Δn2 and κ for an acoustically induced distributed Bragg reflector (ADBR)

    Page(s): 213 - 224
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    The preliminary feasibility analysis and theoretical design of an acoustically induced distributed Bragg reflector (ADBR) suitable for possible integration with a III-V semiconductor laser is presented. The proposed ADBR structure consists of a simple unapodized interdigitated transducer (IDT) patterned by e-beam lithography atop a III-V compound semiconductor optical waveguide structure. It is proposed that a gigahertz-range surface acoustic wave (SAW) could present a tunable distributed Bragg reflector (DBR) index grating to a colinearly propagating guided optical wave. Both the change in the impermeabiility tensor, Δn2, and the resulting distributed feedback (DFB) coupling coefficient, κ, in the ADBR section are calculated due to only the classic photoelastic effect by employing a Laguerre polynomial SAW analysis technique. The SAW fields are normalized using the normal mode IDT equivalent circuit model and a power balance technique to provide realistic κ values in order to assess the feasibility of this device while driven at its center frequency. The analysis of the ADBR κ is limited to the coupling between counterpropagating TE optical modes and is calculated using general overlap integral expression. For an example λ0=1.55 μm In1-xGaxAsyP1-y-InP multiple-quantum-well (MQW) laser structure coated with a 0.1-μm ZnO piezoelectric layer, the maximum ADBR κ was calculated to be 4.9 cm-1 when using a series-inductor-tuned submicron electrode IDT-SAW reflector configuration driven by a RF source operating at approximately 2.9 GHz. It is shown that exceeding the maximum strain on the substrate or the occurrence of dielectric breakdown fan put an upper limit on the realizable value of κ. The potential optical tunability of an ADBR section is estimated for the case when an unapodized LDT is used for SAW generation. Finally, various fabrication and design techniques are listed which may enhance the ADBR κ value, along with a list of other physical effects which may need to be considered in future analyses View full abstract»

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  • The optimization of the multi-atmospheric Ar-Xe laser

    Page(s): 250 - 259
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    The quasi-steady-state conditions of the multi-atmospheric e-beam sustained Ar-Xe laser are investigated. It is observed that the duration of the stationary period depends on the e-beam current, discharge power deposition, and gas pressure. The laser efficiency can be as high as 8%. Beyond the stationary period the efficiency drops. The pulse energy with optimum efficiency depends strongly on the gas pressure. The maximum discharge efficiency of 5%-6% is at high pressure not sensitive to the input power. The best results are obtained for 4 bar with a discharge input power of 8 MW/l. The pulse duration with corresponding output energies is 12 μs with 10 J/l and 16 μs with 16 J/l for e-beam currents of 0.4 and 0.9 A/cm2, respectively. An analysis of the quasi-steady-state conditions that include the effects of electron collision mixing and atomic quenching is presented. The effects of output power saturation by the fractional ionization and atomic collisions are in agreement with the observations. The analysis clarifies the optimum performance conditions View full abstract»

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  • Laser-pumped rubidium frequency standards: new analysis and progress

    Page(s): 233 - 237
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    We have achieved a stability of 3·10-13 τ -1/2 for 3<τ<30 s with a laser-pumped rubidium gas-cell frequency standard by reducing the effects due to noise in the microwave and laser sources. This result is one order of magnitude better than the best present performance of lamp-pumped devices View full abstract»

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  • Theory of non-Markovian gain in strained-layer quantum-well lasers with many-body effects

    Page(s): 344 - 352
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    A non-Markovian model for the optical gain of strained-layer quantum-well lasers is developed taking into account the valence-band mixing, strain effects, many-body effects, and the non-Markovian relaxation using the time-convolutionless reduced-density operator formalism given in previous papers for an arbitrary driven system coupled to a stochastic reservoir. Many-body effects are taken into account within the time-dependent Hartree-Fock approximation and the valence-band structure is calculated from the 6×6 Luttinger-Kohn Hamiltonian. The optical gain with Coulomb (or excitonic) enhancement is derived by integrating the equation of motion for the interband polarization. It is shown that the vertex function for the interband polarization can be obtained exactly without relying on the Pade approximation. As a numerical example, an InxGa1-xAs-InP quantum well (QW) is chosen for its wide application in optical communication systems. It is predicted that the Coulomb enhancement of gain is pronounced in the cases of compressive and unstrained QWs while it is negligible in the case of tensile strained QW View full abstract»

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  • LD optical switch with polarization insensitivity over a wide wavelength range

    Page(s): 269 - 276
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    A double-heterostructure (DH) laser with TM mode lasing has been achieved with a narrow active-layer width, and a laser-diode optical switch (LDSW) module with less than a 0.35-dB gain difference between the TE and TM modes over a wide wavelength range has been constructed by introducing a square bulk active layer formed by dry etching and regrowth. The polarization-insensitive width of a 0.3-μm-thick DH laser is clarified to be between 0.30 and 0.35 μm, since the 0.30- and 0.35-μm-wide DH lasers lase in the TM mode and TE mode, respectively. The polarization-insensitive width of the fabricated 0.3-μm-thick LDSW is estimated to be about 0.32 μm for the fabricated LDSW with a trapezoidal active layer by measuring the single-pass gain and the gain difference between the TE and TM modes. This must be to within 0.01 μm. A 0.35-μm-wide, 300-μm-long LDSW module has lossless gain in the wavelength range of 1.31 to 1.36 μm at 20 mA. The gain difference between the TE and TM modes is as low as 0.35 dB, The rise and fall times are 1.0 and 0.55 ns, respectively. The bulk active-layer LDSW module is promising for use as a polarization-insensitive optical-gate switch in optical information systems View full abstract»

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  • Modeling the temporal-pulse-shape dynamics of an actively stabilized regenerative amplifier [OMEGA Nd:YLF laser rod]

    Page(s): 286 - 291
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    We have modeled the temporal evolution of a shaped optical pulse injected into a feedback-stabilized regenerative amplifier (regen). We solve the coupled-rate and energy-transport equations including upper- and lower-laser-level lifetimes explicitly. The regen dynamics including the losses due to the feedback stabilizer are included in the model. We provide a prescription for determining the injection-pulse shape required to produce a given output-pulse shape from this regen. The model shows excellent agreement with the measured regen output View full abstract»

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  • 27-W average output power with 1.2*DL beam quality from a single-rod Nd:YAG laser with phase-conjugating SBS mirror

    Page(s): 372 - 377
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    The beam quality of a single-rod Nd:YAG laser with large mode volume was improved almost up to the diffraction limit by using a phase-conjugating mirror (PCM) based on stimulated Brillouin scattering (SBS). A new resonator design was used with sulfur hexafluoride as the SBS medium. The laser is Q-switched by the nonlinear reflectivity of the PCM. The stable fundamental mode operation and high efficiency via large mode volume was guaranteed by the combination of a highly selective aperture setup and the SBS mirror. The system exhibits a temporal burst structure of up to 50 Hz and a repetition rate of 11 kHz within the burst. The single Q-switch pulse showed a width of 42 ns. The energy, width, and repetition rate of the Q-switch pulses within the burst can be adjusted by varying the parameters of the laser system View full abstract»

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  • Spectral shift of a Gaussian Schell-model beam beyond a thin lens

    Page(s): 378 - 383
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    We give a comprehensive representation of the Wolf effect in propagation both in free space and after a lens for an outstanding class of partially coherent beams, namely Gaussian Schell-model beams. We characterize the correlation-induced spectral changes, throughout the whole space, by means of isoshift lines and transverse shift profiles. The maximum value of the frequency blueshift, occurring on the optical axis, is also calculated View full abstract»

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  • Analytical formulation of distortion and chirp in CATV DFB lasers including spatial hole burning

    Page(s): 311 - 317
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    Analytical formulas for distortions permitting the calculation of composite second order (CSO) and composite triple beat (CTB) in distributed feedback (DFB) laser diodes are given, including gain compression and longitudinal spatial hole burning (LSHB). An improved chirp expression including both effects is also proposed. Gain compression is compared to LSHB over the CATV band: LSHB effects on distortion and chirp are found to be dominant in actual CATV lasers. Nonmonotonous behavior (dips) function of frequency and bias current is verified in second- and third-order distortions in agreement with recent results View full abstract»

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  • Modeling multiple-longitudinal-mode dynamics in semiconductor lasers

    Page(s): 325 - 335
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    We present a time-dependent coupled-wave equation analysis for simulating both single- and multilongitudinal-mode dynamics in semiconductor lasers, while incorporating frequency-dependent gain in a particularly simple way. In our first application, we analyze the response of Fabry-Perot semiconductor lasers to feedback levels ranging from -60 to -30 dB. This allows us to anchor, continuously, from single-mode phenomena at weak feedback levels to multimode behavior at stronger feedback levels. To our knowledge, this is the first simulation of multilongitudinal-mode dynamics that are induced in a laser at feedback levels exceeding -30 dB, Feedback-induced phenomena provide a significant test of both the single-mode and multimode capabilities of our coupled-wave model. In our second application, we analyze a modern, large-scale device for which multiple longitudinal modes, as well as compound cavity modes, are a significant possibility. Specifically, we consider facet-coating requirements for a new class of monolithic master-oscillator power-amplifier (MOPA) devices View full abstract»

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Aims & Scope

The IEEE Journal of Quantum Electronics is dedicated to the publication of manuscripts reporting novel experimental or theoretical results in the broad field of the science and technology of quantum electronics..

Full Aims & Scope

Meet Our Editors

Editor-in-Chief
Aaron R. Hawkins
Brigham Young University