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Quantum Electronics, IEEE Journal of

Issue 12 • Date Dec. 1997

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Displaying Results 1 - 25 of 25
  • Investigation of efficient self-frequency-doubling Nd:YAB lasers

    Page(s): 2295 - 2300
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    We report on the investigation of efficient self-frequency doubling Nd:YAl/sub 3/(BO/sub 3/)/sub 4/ (Nd:YAB) lasers. Pumped by 1.6 W of 807 nm diode laser radiation, the Nd:YAB laser generates a green 531-nm output of 225 mW which corresponds to a conversion of pump to visible output power of 14%. Conversion efficiencies as high as 20% could be achieved by using the diffraction-limited beam of a Ti:sapphire laser as pump source. In this case, 2.2 W of 807-nm Ti:sapphire radiation produced a 531-nm output of 450 mW. The experimental performance of these Nd:YAB lasers is in good agreement with the predictions of a numerical analysis based on rate equations adequate for lasers with self-frequency doubling. View full abstract»

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  • 1997 Index

    Page(s): 0_5 - 0_46
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    Freely Available from IEEE
  • Photocurrents in a metal-semiconductor-metal photodetector

    Page(s): 2188 - 2194
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    Photocurrents in a metal-semiconductor-metal (MSM) photodetector have been analyzed in a one-dimensional structure using both time-dependent and steady-state continuity equations. Analytical solutions are presented for the carrier concentrations as well as for the currents, which form a valuable tool for the investigation of the detector behavior under various bias conditions. Applying these expressions to a GaAs device, we have studied the influence of carrier diffusion, recombination, and drift on the photocurrents as a function of the applied bias voltage. We also show that the switching time at low bias voltage is dominated by a voltage-independent diffusion time constant which is of particular interest when using the device as an optoelectronic sampling gate. On the other hand, carrier recombination is found to have minimal influence on DC characteristics and pulse response View full abstract»

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  • Isotype heterojunctions with flat valence or conduction band

    Page(s): 2195 - 2198
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    We show that isotype heterojunctions with a perfectly flat majority or minority carrier band edge can be realized by modulation doping of arbitrary continuous alloy grading. The required impurity distribution is obtained analytically from the knowledge of the compositional grading and band structure parameters in the grading. This analytic relationship is exact for heterojunctions in which the grading fields are negligible in comparison with the atomic fields. We illustrate the design of flat valence-band heterojunctions for application in high-reflectivity low-resistance distributed Bragg reflectors for vertical-cavity lasers. The presented formalism enables the design of isotype heterojunctions with arbitrary band-edge profiles View full abstract»

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  • Hot carrier internal thermionic photoemission in pulsed CO2 -laser-excited n+-p silicon junctions

    Page(s): 2203 - 2208
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    Experimental and theoretical studies were carried out on the electrical response of a forward biased n+-p silicon junction under photoexcitation with high-intensity 60-ns laser pulses at λ=10.6 μm. The observed strong bias-dependent electrical pulses are associated to changes in the junction forward current due to the carriers of the high energy tail within the photoexcited hot-electron distribution. A thermionic emission model of hot electrons over the junction barrier account for the experimental results. According to this model and the measured electrical response, the temperature of the carriers is nearly 100 K higher than the lattice temperature, which essentially remains constant at room temperature View full abstract»

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  • Effects of carrier heating on laser dynamics-a Monte Carlo study

    Page(s): 2209 - 2220
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    The static and dynamic properties of semiconductor quantum-well (QW) lasers have traditionally been analyzed by using rate equations that couple cold carriers to photons in the lasing cavity. This assumption of cold carriers, however, has often been disputed because it does not account for heating due to carrier relaxation, hot phonon effects, and spectral hole burning. All these processes affect laser performance significantly by modifying the gain because gain depends on carrier temperature as well as spectral broadening. In this paper, we study the carrier dynamics of QW lasers using a Monte Carlo method and conclude that hot carrier effects in semiconductor lasers are important and need to be considered for the analysis and design of semiconductor lasers View full abstract»

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  • Flashlamp-pumped Cr:LiSAF laser amplifier

    Page(s): 2282 - 2285
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    A flashlamp-pumped Cr:LiSAF laser amplifier has been developed that is capable of producing ultrashort pulses with a peak power of ~TW. A systematic experimental study of laser oscillation, its small-signal gain, and chirped-pulse amplification has been performed under the same pumping conditions. The characteristic properties and performance of the Cr:LiSAF laser amplifier are reported View full abstract»

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  • Ortho-deuterium Raman laser using the S0(2) rotational transition in the mid-infrared region

    Page(s): 2174 - 2177
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    Based on a calculation for the Raman gain coefficient of the S0(2) transition in ortho-D2, we have demonstrated the generation of first Stokes waves in the 15-16-μm spectral region. Use of ortho-D enriched by a catalytic converter enabled us to realize efficient conversion at room temperature. Stokes energies as high as 400 mJ were obtained View full abstract»

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  • Numerical modeling of undercut ridge VCSELs designed for CW operation at 1.3 μm: design optimization

    Page(s): 2221 - 2230
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    Optimized undercut ridge long-wavelength vertical-cavity surface-emitting semiconductor lasers (LW-VCSEL's) are investigated and the influence of thermal effects on the light versus current characteristics is analyzed by thermal-electric, optical, and electronic modeling. The model includes nonuniform current injection, carrier diffusion, stimulated emission, distributed heat sources, and active material band structure calculations. Device parameters such as thermal resistance, threshold current, and external quantum efficiency are evaluated, in an attempt to provide an understanding of the current-funneling mechanism and the thermal limitations of such devices. Simulated power versus current characteristics exhibit the typical thermal roll-over in CW operation View full abstract»

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  • Quasi-periodic complex-coupled distributed-feedback structures with an exponential-like gradient of coupling

    Page(s): 2137 - 2145
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    We investigate theoretically the linear properties of quasi-periodic complex-coupled distributed-feedback (DFB) structures in which the coupling constants experience a longitudinal variation along the propagation axis according to an exponential-like relationship (exp, sh, ch, ···). The results of the simulations are in good accordance with what could be expected at first sight from the particular form taken in this case by the coupled-wave equations. In particular, the gradient of coupling can provide a shift, either of the apparent average absorption (respectively, gain) or of the detuning from Bragg resonance, depending upon its exact form, Moreover, we show that this shift is asymmetric with respect to the direction of propagation, leading to a nonreciprocal behavior in reflection. We extend our analysis up to the laser modes at threshold View full abstract»

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  • Parameters evolution of laser beams with quite general transverse intensity profile

    Page(s): 2178 - 2187
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    A plane-parallel cavity with a Gaussian reflectivity mirror has been applied to a XeCl laser medium having a spatially variable gain distribution. The evolution of the beam parameters has been experimentally analyzed as a function of the number of round trips. It is shown that in this case of intensity profiles affected by the spatial and temporal properties of the active medium gain, a theory formerly developed for the beam-parameter evolution of Gaussian Schell-model beams provides a satisfactory description of experimental measurements for the first few round trips View full abstract»

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  • Self-consistent calculation of the lasing eigenmode of the dielectrically apertured Fabry-Perot microcavity with idealized or distributed Bragg reflectors

    Page(s): 2319 - 2326
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    Optical confinement in the dielectrically apertured Fabry-Perot microcavity is investigated theoretically. The apertured region is first treated as embedded in an idealized planar waveguide to show that the confined eigenmode's resonant frequency can cut off parasitic waveguide modes existing outside the aperture, and lead to three-dimensional optical confinement. For more realistic cavities with nonunity mirror reflectivities, self-consistent calculations of the eigenmode characteristics are performed for the limit of an optically thin aperture to derive the lowest order confined eigenmode frequency, threshold susceptibility, and mode profile. The analysis is then extended to treat dielectric cavities based on Bragg reflectors View full abstract»

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  • Diagnostics of nonradiative defects in the bulk and surface of Brewster-cut Ti:sapphire laser materials using photothermal radiometry

    Page(s): 2301 - 2310
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    The understanding of the problem of nonradiative energy conversion in solid-state laser materials is a key factor in improving the overall efficiency of solid-state lasers. Furthermore, the reduction of the heat generated in an optically pumped laser crystal can lead to several new applications of solid-state lasers, especially in the high-power region. To improve the quality of grown crystals, laser crystal growers require accurate techniques to perform the quality control that is so vital to improving the growth process. Using a time-domain approach and a time-domain theoretical treatment of the IR radiative emission signal, it was determined that one may probe nonradiative surface and bulk processes by monitoring different time ranges. Our results show that photothermal radiometry can be used as a single-ended technique to evaluate both the bulk and surface nonradiative energy conversion rates in a solid-state laser material. This technique was compared to the standard laser cavity technique and it was concluded that photothermal radiometry can provide additional information to the standard technique by identifying the sources of heat generation as either surface- or bulk-originating View full abstract»

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  • Polarization modulation dynamics of vertical-cavity surface-emitting lasers with an extended cavity

    Page(s): 2231 - 2239
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    Vertical-cavity surface-emitting lasers (VCSELs) are known to exhibit a small birefringence and dichroism whose axes are directed along the crystal axes of the quantum wells and which fix the polarization of the oscillating light. In this paper, we consider the dynamics of the polarization of light in such a laser, extended by means of a quarter-wavelength plate in an external cavity. Periodic variations are experimentally observed. A theoretical analysis and numerical results are proposed, using a recent model which includes the carriers' spin interaction. A good match is found between experimental and numerical results View full abstract»

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  • Optimization of Cr4+-doped saturable-absorber Q-switched lasers

    Page(s): 2286 - 2294
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    Cr4+-doped saturable absorbers are characterized by long excited state lifetime and appreciable excited state absorption. In the paper, we first solve the three coupled rate equations describing the operation of Cr4+-doped saturable-absorber passively Q-switched lasers to obtain the expressions of pulse characteristics such as output energy, peak power, and pulsewidth. We then determine the key parameters of an optimally coupled passively Q-switched laser as functions of two variables concerning the amplifying medium, saturable-absorber medium, and pump level, and generate several design curves. These key parameters include the optimal normalized coupling parameter and the optimal normalized saturable-absorber parameter which maximize the output energy (or maximize the peak power, or minimize the pulsewidth), and the corresponding normalized energy, normalized peak power, and normalized pulsewidth. The results are valid for not only Cr 4+-doped saturable-absorber Q-switched lasers but also any other lasers passively Q-switched by saturable absorbers with long excited state lifetime and appreciable excited state absorption. Using the expressions and design curves, with the aid of a simple hand calculator, one can predict the pulse characteristics and perform the design of an optimally coupled passively Q-switched laser View full abstract»

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  • Ultrashort pulse generation from an integrated single-chip dye laser

    Page(s): 2146 - 2149
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    In distributed-feedback (DFB) dye lasers pumped by a nanosecond-pulse laser, a train of picosecond spikes is generated by the relaxation oscillation. A single spike with a pulse duration of 50 ps is extracted in a plastic-waveguide DFB dye laser using a quenching technique. To compress this to femtosecond pulse, a new type of integrated pulse compressor is proposed, and its performances are analyzed. The compressor is composed of a plastic waveguide in which amplifier dye and saturable dye are alternatively doped. Computer simulation shows that the 50-ps pulse is compressed to 120 fs by passing through four stages of amplifier and saturable absorber pair. Using this scheme, we expect to construct a very compact and simple ultrashort pulse generator in which the whole system is integrated on a chip of a plastic waveguide View full abstract»

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  • Theoretical optimization of V-shaped GaInAsP quantum-well lasers grown on InP substrates

    Page(s): 2277 - 2281
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    Compressively strained GaInAsP quantum wells (QW's), with a square potential profile and grown on InP substrates, have demonstrated their high potential for the improvement of 1.55-μm lasers. Recently, we have proposed another approach which consists of creating a linear variation of the bandgap inside the well, by means of a linear variation in the As concentration. Calculations show that, in such a V-shaped structure: (1) the effective density of states related to the heavy hole bands is reduced compared to that of a large abrupt-shaped QW and (2) the overlap between the electron and the hole wavefunctions is expected to be greater than in a narrow abrupt-shaped QW. The consequences of these effects are described View full abstract»

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  • High-sensitivity porous silicon photodetectors fabricated through rapid thermal oxidation and rapid thermal annealing

    Page(s): 2199 - 2202
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    The sensitivity of a porous silicon Schottky barrier photodetector is much improved through rapid thermal oxidation and rapid thermal annealing processes. Under our optimum preparation conditions, photocurrent can reach about 21 mA (under 22.4 mW/cm2 tungsten lamp illumination) and dark current is about 5.4 μA (at reverse bias of 10 V). The quantum efficiencies are about 90% at wavelengths shorter than 750 nm and 80%-70% in the wavelength range 750-1050 nm View full abstract»

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  • Simultaneous emission of the HF and N2 lines from a plasma cathode TEA laser

    Page(s): 2167 - 2173
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    Simultaneous laser action from HF and N2 is obtained, from a plasma cathode TEA laser, for the first time. The sliding discharge along the surface of a dielectric is used as a plasma cathode, for the main volumetric discharge. The laser operates at atmospheric pressure, with a gas mixture of SF6:C3H8:N2:He. For a typical flow rate ratio of 0.27:0.024:0.2:19.8 1 min-1, it produces simultaneously 160 mJ HF and 0.6 mJ N2 laser outputs at 0.43% and 1.4×10-3% efficiencies respectively, at the moderate charging voltage of 28.5 kV. These output characteristics are obtained from a small active discharge volume and length of 106 cm3 and 38 cm respectively. These values extend the performance, recently reported in the literature, of a sliding discharge HF/N2 laser with corresponding simultaneous energy outputs of 12 mJ HF and 1.1 mJ N2, to a higher energy output level, thus making the device suitable for a broader range of applications. This novel dual wavelength HF/N2 laser system presented, can be particularly convenient for medical experiments, where the IR beam can be used for tissue ablation, while the UV beam can be used as the excitation source for fluorescence spectroscopic measurements, for the evaluation of the ablation process. Details are presented on the dependence of the laser performance parameters, such as output energy, discharge voltage and current and structure of the laser output pulses on the mixture composition and the circuit parameters View full abstract»

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  • Full vector analysis of two-dimensional angled and coated optical waveguide facets

    Page(s): 2311 - 2318
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    We analyze the important problem of scattering from two-dimensional (2-D) optical waveguide facets, including the effects of both antireflection coatings and facet angle. The facet is allowed to be angled in both vertical and horizontal planes, necessitating a fully vectorial approach to model correctly the polarization coupling that occurs. To achieve this, the highly efficient Free Space Radiation Mode method has been extended to the general vector case, yielding novel expressions for both the reflectivity and the coupling coefficients which can be rapidly evaluated on a desktop PC for a wide variety of practical structures. Results are presented for both angled, coated and coated angled facets. Full field profiles, also available from the approach, are presented and provide useful design information and aids to understanding View full abstract»

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  • High-power high-efficiency 0.98-μm wavelength InGaAs-(In)GaAs(P)-InGaP broadened waveguide lasers grown by gas-source molecular beam epitaxy

    Page(s): 2266 - 2276
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    We describe the design and experimental results for high-power, high-efficiency, low threshold current, 0.98-μm wavelength, broadened waveguide (BW) aluminum-free InGaAs-(In)GaAs(P)-InGaP lasers. The decrease in the internal losses with an increase in the width of the waveguide layer for a separate-confinement heterostructure multiple-quantum-well (SCW-MQW) structure is attributed to lower free-carrier absorption due to the reduced overlap of the optical mode with the highly doped cladding regions. The BW lasers grown with both InGaAsP and GaAs waveguides show lower internal losses and similar threshold currents than those designed for an optimum optical confinement factor within the QW region. We report a record-low internal loss of 1.8±0.2 cm-2 for (In)GaAs(P)-InGaP lasers grown by gas-source molecular beam epitaxy (GSMBE). The temperature dependence of internal loss suggests that optical loss from free-carrier absorption in the waveguide dominates at T>40°C, while near room temperature, the residual loss is attributed to scattering and free-carrier absorption in the QW's. The relative insensitivity of internal loss near room temperature has enabled the use of a simplified InGaAs-GaAs-InGaP BW structure to achieve very high CW and quasi-CW (QCW) power operation. We report the highest CW output power of 6.8 W for a GaAs-InGaP laser, and the highest quasi-continuous output power of 13.3 W measured for a single 100-μm-wide aperture, 0.8-0.98-μm wavelength Al-free laser diode grown by GSMBE View full abstract»

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  • A tapered graded-index lens: analysis of transmission properties and applications in fiber-optic communication systems

    Page(s): 2159 - 2166
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    Propagation properties of a linearly tapered parabolic-index dielectric cylinder are studied using a ray-optics approach. Analytical solutions for trajectories of skew rays with arbitrary initial conditions are obtained for tapers with small slope and small index variations over transverse dimensions. Conditions for an arbitrary ray to remain bound to the core of the taper are derived. Applications of these tapered lenses for coupling of light sources to fibers, for beam expanding/refocusing in microoptics devices, and for splicing two fibers of different core sizes are addressed, Power coupling efficiency for illumination from both Lambertian and narrow-beam light sources are calculated. Improvement in coupling efficiency, when taper is are used to couple power from directed-beam sources to optical fibers, is demonstrated. Radiation losses when a taper is used as a transition element between two fibers of different core radii are evaluated. Plots of skew-ray paths, illustrating the gradual concentration of power as light travels toward the smaller end of the taper, are also presented View full abstract»

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  • Numerical simulation of broad-area high-power semiconductor laser amplifiers

    Page(s): 2240 - 2254
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    A comprehensive model is presented to study the electrical, thermal, and optical behavior of broad-area traveling-wave InGaAs-AlGaAs semiconductor amplifiers. Finite-element thermal analysis and carrier transport mechanisms are integrated into the beam propagation method to include thermal lensing and optically induced nonlinearities. A self-consistent iteration is developed to simulate the beam filamentation in broad-area semiconductor amplifiers with residual facet reflectivities. The experimentally observed periodic filamentation with intensity minima close to zero is investigated numerically View full abstract»

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  • Bandwidth-limited diffraction of femtosecond pulses from photorefractive quantum wells

    Page(s): 2150 - 2158
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    The diffraction of 100-fs pulses from the static gratings of photorefractive quantum wells (QWs) produces diffracted pulses that are nearly transform-limited, despite the strong dispersion near the quantum-confined excitonic transitions. This quality makes the QW's candidates for use in femtosecond pulse shaping, although the currently limited bandwidth of the quantum-confined excitonic transitions broadens the diffracted pulses. Femtosecond electric-field cross correlation and spectral interferometry techniques completely characterize the low-intensity pulses diffracted from stand-alone photorefractive QWs, and from QWs placed inside a Fourier-domain femtosecond pulse shaper View full abstract»

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  • Fluctuations of the laser characteristics and the effect of the index-coupling component in the gain-coupled DFB laser

    Page(s): 2255 - 2265
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    The normalized oscillation frequency δL and threshold gain αL of gain-coupled distributed feedback (DFB) lasers with an AR/AR (symmetric) structure vary significantly with a variation in the corrugation phase at the facets when the facet reflectivity |r| is large, even though the spatial-hole-burning-corrected yield is 100%. For example, the standard deviation for the δL, σ(δL), increases from 0.018 to 0.40 when |r| is increased from 0.03 to 0.30. The magnitude of σ(δL) and σ(αL) are small, however, for the gain-coupled, index-coupled, and complex-coupled DFB lasers when the |r| is kept small. For the HR/AR (asymmetric) structure, these two values are more than an order of magnitude larger than those for the AR/AR structure, except for the σ(αL) for the index-coupled laser, even though yields of each of these lasers are relatively large. In the AR/AR structure, the contamination by the index-coupling and gain-coupling components always degrades the device characteristics because of the difference in the phase shifter and when the amount of contamination is small this degradation is particularly severe for the index-coupled laser. Several properties of the index-coupled laser with the HR/AR structure can be improved, however, by introducing the gain-coupling component 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