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Quantum Electronics, IEEE Journal of

Issue 4 • Date Apr 1999

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Displaying Results 1 - 25 of 28
  • Generation of high-average-power ultrabroad-band infrared pulses

    Page(s): 565 - 576
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    This paper summarizes the results of analytical and numerical studies on a novel technique that is capable of providing high average power ultra broadband radiation that extends from approximately 2 to 16 μm. Such a spectrum has several potential applications, including telecommunications and remote sensing. Additional attractive features of the new source are its anticipated compact size, light weight, ruggedness, and affordable cost. The technique is based on the interaction of a beat wave with a nonlinear medium. The beat wave is formed from the mixing of two CO2 laser beams with closely spaced wavelengths, such as 9.5 and 9.6 μm. The discrete ultrabroad-band spectrum is generated in a nonlinear optical medium by the self-phase modulation process, a third-order nonlinearity. The long-wavelength portion of the spectrum, i.e., from 5 to 16 μm is produced directly from the interaction of the beat wave with a GaAs crystal. The short-wavelength portion of the spectrum is produced from the interaction of a frequency-doubled beat wave with a GaAs crystal following the chirping of the pulse by a different GaAs crystal and its subsequent optimal compression by a thin sapphire slab View full abstract»

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  • Experimental stability diagram of a diode laser subject to weak phase-conjugate feedback from a rubidium vapor cell

    Page(s): 577 - 582
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    We report on a systematic experimental investigation of the dynamical behavior of a diode laser subject to delayed feedback from a phase-conjugating mirror based on nearly-degenerate four-wave mixing in rubidium vapor. We present the first experimental stability diagram for this system. In the weak feedback regime, with feedback levels up to -30 dB, me demonstrate locking to the pump frequency with a reduced linewidth smaller than 8 MHz. In contrast to a laser with external injection, and contrary to predictions made for phase-conjugate feedback, the extent of this locking region is found to be limited. For increased feedback rates, the laser leaves the locking region and enters an unstable region through a series of multiple sidebands spectra. This is associated with self-excitation of the relaxation oscillation, and the observed scenario suggests a series of period-doublings after an initial Hopf bifurcation View full abstract»

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  • Guiding effects in Nd:YVO4 microchip lasers operating well above threshold

    Page(s): 675 - 681
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    Guiding of the transverse mode in Nd:YVO4 microchip lasers is examined both experimentally and theoretically at pump powers well above threshold. It is found that thermal changes in the cavity geometry induced by intense diode pumping can be well understood using a simple model. However, an understanding of these effects is not sufficient to explain the nature of the transverse mode. Gain-related guiding effects are found to play an important role even at pump powers well above threshold. For a 0.5-mm-thick microchip laser, a difference of around 30% is observed between the minimum beam waist expected due to thermal guiding and the measured beam waist. The gain-related effects are described theoretically and their importance is demonstrated experimentally View full abstract»

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  • Characterization of excitons in wurtzite GaN quantum wells under valence band mixing, strain, and piezoelectric field

    Page(s): 590 - 602
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    Low-dimensional excitons in general, and quantum-well (QW) excitons in particular, are important for linear and nonlinear semiconductor optics applications. The recent observation of the high binding energy of bulk excitons in gallium nitride samples being the main impetus, we undertake a theoretical work to characterize QW excitons in wurtzite semiconductors. In our formulation, we take into account valence band mixing, strain, and piezoelectric field effects. The in-plane behavior of excitons is treated variationally, whereas the finite-element method is used for the dependence along the growth direction. The formulation is applied to GaN-Alx Ga1-x N QW's. The presence of the piezoelectric field leads to the well-known quantum-confined Stark effect. We deduce from an oscillator strength analysis that the quantum-confined Franz-Keldysh effect is operational for QW's of width around 45 Å for an aluminum content of x=0.15. Our results further indicate that, for very clean samples, QW excitons should not ionize at room temperature even in the presence of the piezoelectric field for sufficiently narrow QW's. We determine the fractional dimensionality of the QW excitons in the absence of the piezoelectric field, which can in principle be cancelled by introducing delta-doped ionized layers on either side of the QW. The absorption spectra associated with the low-lying 1s excitons are also presented for several well widths View full abstract»

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  • Characterization of Yb3+:Sr5-xBax(PO4)3 F crystals for diode-pumped lasers

    Page(s): 665 - 674
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    Ytterbium-doped Sr5(PO4)3F (S-FAP) has been shown to be a useful material for diode pumping, since it displays high gain, low loss, and a long radiative lifetime. One of the issues with S-FAP is that it has a relatively narrow absorption bandwidth (~5 nm) at 900 nm, the diode-pumping wavelength, while the diode's output bandwidth can be large (~10 nm). By changing the host slightly, the absorption feature can be broadened to better match the pump bandwidth. Four mixed crystal boules of Yb3+:Sr5-x Bax(PO4)3F were grown by the Czochralski method with x=0.25: 0.5, 1, and 2. The bandwidth of the 900-nm absorption feature was found to grow with increasing barium concentration from 4.7 nm to a maximum of 15.9 nm. Emission spectra showed a similar bandwidth increase with barium content from 4.9 nm to a maximum of 10 nm. Emission cross sections for these materials were deduced by the methods of reciprocity, the Einstein method, and small-signal gain. The absorption feature's homogeneity was probed using a tunable pump source which qualitatively showed that the barium broadened lines were at least partly inhomogeneous. Each of these materials lased with a variety of output couplers. This family of materials was found to provide suitable laser hosts where a broader absorption and/or emission bandwidth is desired View full abstract»

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  • Complete characterization of ultrashort pulse sources at 1550 nm

    Page(s): 441 - 450
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (548 KB)  

    This paper reviews the use of frequency-resolved optical gating (FROG) to characterize mode-locked lasers producing ultrashort pulses suitable for high-capacity optical communications systems at wavelengths around 1550 nm, Second harmonic generation (SHG) FROG is used to characterize pulses from a passively mode-locked erbium-doped fiber laser, and both single-mode and dual-mode gain-switched semiconductor lasers. The compression of gain-switched pulses in dispersion compensating fiber is also studied using SHG-FROG, allowing optimal compression conditions to be determined without a priori assumptions about pulse characteristics. We also describe a fiber-based FROG geometry exploiting cross-phase modulation and show that it is ideally suited to pulse characterization at optical communications wavelengths. This technique has been used to characterize picosecond pulses with energy as low as 24 pJ, giving results in excellent agreement with SHG-FROG characterization, and without any temporal ambiguity in the retrieved pulse View full abstract»

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  • Transient response of vertical-cavity surface-emitting lasers of different active-region diameters

    Page(s): 608 - 615
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    The multimode dynamics of vertical-cavity surface-emitting lasers with different active-region diameters was measured under subnanosecond electrical excitation (800-ps pulse duration, 100-ps risetime). The dynamics is characterized by the delayed onset of higher order modes which have a turn-on delay that is dependent on the active-region diameter and the excitation parameters. A simple model that can be used to estimate this turn-on delay for large-area devices is presented. Polarization-resolved measurements show that, under this fast excitation condition, both orthogonal polarization states are isomorphic. The influence of the observed dynamics on the relative intensity noise of these devices is also discussed View full abstract»

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  • Energy-transfer upconversion and thermal lensing in high-power end-pumped Nd:YLF laser crystals

    Page(s): 647 - 655
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    Thermal lensing in an end-pumped Nd:LiYF4 rod, under lasing and nonlasing conditions, has been investigated. Under lasing conditions, a weak thermal lens, with dioptric power varying linearly with pump power, was observed. Under nonlasing conditions, where higher inversion densities were involved, hence relevant to Q-switched operation or operation as an amplifier, a much stronger thermal lens was measured, whose power increased nonlinearly with pump power. This difference has been attributed to the increased heat deposition due to the subsequent multiphonon decay following various interionic upconversion processes, which increase strongly under nonlasing conditions, and is further exacerbated by the unfavorable temperature dependencies of heat conductivity and the rate of change of the refractive index with temperature. A strategy for reducing upconversion and its associated thermal loading, without degrading laser performance, is discussed View full abstract»

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  • Frequency-resolved optical gating measurement of ultrashort pulses passing through a high numerical aperture objective

    Page(s): 479 - 486
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    We investigate using collinear type II second harmonic generation frequency-resolved optical gating (SHG FROG) to measure the pulse intensity and phase at the focus of high numerical aperture (NA) oil objectives. Because of the strong focusing for such objectives, it is not clear theoretically that such a measurement should work. Such objectives can produce severe distortions of the pulse as a function of radius in the objective. In addition, the standard SHG FROG algorithms are based on the assumption that the fundamental and second harmonic fields are plane waves that can be described by the paraxial approximation, and for high NA objectives, such assumptions are suspect. We show that such measurements work remarkably well. The tight focus, while a theoretical difficulty, eliminates many of the problems traditionally associated with SHG FROG including the difficulty of phase matching and walkoff of different polarizations in the crystal. Specifically, we use collinear type II SHG FROG to measure the intensity and phase at the focus of a Zeiss CP-Achromat 100x, 1.25 NA, infinity-corrected oil objective, and accurately retrieve 20 fs pulses View full abstract»

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  • Semiclassical theory of rectangular waveguide gas lasers

    Page(s): 682 - 689
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    The semiclassical theory for gas lasers is extended from one dimension into three. Self-consistency equations of a rectangular waveguide resonator and the component equations of motion for the population matrix are derived. Laser parameters related to the waveguide structure and active medium are analyzed by solving the equations. For homogeneously broadened lasers, theoretical investigation shows that single-mode operation depends on the waveguide dimensions, the most probable speed of the active medium, and the decay constants or the saturation parameter. Under some conditions, the oscillating modes can be determined by the frequency interval and the relative excitation View full abstract»

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  • 12-THz frequency difference measurements and noise analysis of an optical frequency comb in optical fibers

    Page(s): 559 - 564
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    A span up to 50 THz of optical frequency comb (OFC) has been obtained by self-phase modulation in an optical fiber. The coherent nature of the process was verified by heterodyne-detecting the sidebands offset by up to 12 THz from the carrier. The signal-to noise ratio (SNR) of the beat signal between a sideband at 12 THz offset and another single-mode laser was 32 dB in a 1-MHz bandwidth. Although the linewidth of each beat signal was maintained within a few megahertz, phase noise pedestal power increased with the offset frequency View full abstract»

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  • Heating and structural alterations in cartilage under laser radiation

    Page(s): 532 - 539
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    The authors have developed a theoretical model to calculate the temperature field and the spatial distribution of modified cartilage following laser irradiation. The model incorporates both thermal and mass transfer in a tissue with bulk absorption of laser radiation, water evaporation from the surfaces of a slab, and temperature dependence of the diffusion coefficient. The authors propose that water undergoes a bound-to-free phase transition in cartilage heated to about 70°C and the mobility of proteoglycan units in the cartilage matrix increases. Movement of the proteoglycan units takes place only when the temperature exceeds 70°C and results in tissue denaturation. Using their model, the authors show: (1) the maximal temperature is reached not on the surface irradiated but rather at some distance below; (2) surface temperature reaches its asymptotic value quicker than the maximal temperature; and (3) the depth of the denatured tissue volume strongly depends on laser fluency, wavelength, exposure time, and cartilage thickness. The model allows for the prediction and control of temperature and depth of structural alterations during the course of laser reshaping and treatment of cartilage View full abstract»

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  • Hole distribution in InGaAsP 1.3-μm multiple-quantum-well laser structures with different hole confinement energies

    Page(s): 603 - 607
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    We have investigated the hole distribution in strained InGaAsP multiple-quantum-well (MQW) structures by direct hole transport measurements with time-resolved photoluminescence spectroscopy. The results show that the hole transport time over the MQW primarily depends on the hole confinement energy in the wells and increases sharply with the well depth. A simple thermionic emission model indicates that the heavy holes escape predominantly over the light-hole barrier edge for strain-compensated MQW structures. The results are corroborated with observed laser performance data View full abstract»

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  • Diode-laser-based absorption spectroscopy diagnostics of a jet-type O2(1Δ) generator for chemical oxygen-iodine lasers

    Page(s): 540 - 547
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    Using diode-laser-based diagnostics, O2(1Δ) yield and water vapor fraction were measured at the exit of a jet-type singlet oxygen generator (JSOG) for a chemical oxygen-iodine laser (COIL). Chlorine utilization and gas temperature at the generator exit were also measured, simultaneously. For conditions corresponding to the maximum chemical efficiency of the supersonic COIL energized by the JSOG, the O2(1Δ) yield, water vapor fraction, chlorine utilization, and temperature at the generator exit are 0.65, 0.08 and 0.92, and 30°C, respectively. Increase of the basic hydrogen peroxide temperature results in an increase of the water vapor fraction caused by an increase of the saturated water vapor pressure in the generator. As the pressure in the generator rises from 18 to 60 torr, the yield decreases from 0.65 to O.48. Dependence of the yield on the generator pressure is consistent with a rate constant for the O2 (1Δ) energy pooling reaction of 2.7×10-17 cm3·S-1. The same rate constant explains the measured variation of the temperature along the flow in the diagnostic cell View full abstract»

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  • Dynamical model of directly modulated semiconductor laser diodes

    Page(s): 624 - 634
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    We present a new dynamical model for a directly modulated semiconductor diode, applicable to systems in which the dynamical time scales of interest are longer than the round-trip time of light in the diode. Employing a multiple scales analysis to simplify the familiar phenomenological equations, we find that the dynamical response of the diode can be described by time-dependent reflection and transmission coefficients for the electric field and one ordinary differential equation for the integrated carrier density. We do not assume that the photon and carrier densities are uniform along the diode and do not need to calculate them explicitly at each point. Additionally, we need not restrict ourselves to only a small-signal response. We justify the multiple scales analysis for parameters corresponding to typical structures through a comparison of the numerical solution of our results and a direct numerical integration of the original phenomenological equations View full abstract»

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  • Postgrowth tuning of semiconductor vertical cavities for multiple-wavelength laser arrays

    Page(s): 616 - 623
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    Combined lateral-vertical oxidation of AlGaAs is investigated as a means of tuning the resonant wavelength of a semiconductor microcavity after the epitaxial growth. It is shown that this technique can provide arrays with a wavelength spread equal to the cavity's free spectral range with a single postgrowth processing step. Design issues for multiple-wavelength vertical-cavity laser arrays using this postgrowth tuning technique are discussed, comparing the performance of devices with all-semiconductor and partially or totally oxidized Bragg mirrors. Experimental results are presented on arrays with a 48-nm lasing span around 970 nm, using partially and totally oxidized mirrors View full abstract»

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  • Field distributions inside fiber gratings

    Page(s): 548 - 558
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    We have developed a technique to calculate the electric field distributions of a light wave propagating through a fiber grating (FG). The technique is based on a transfer matrix method developed for electric field calculations in multilayer thin films. We apply this method to several FG structures of practical interest in optical fiber networks based on wavelength-division multiplexing. Two-dimensional plots of the average internal power versus the distance along the grating axis and light frequency are presented. This representation allows a better understanding of the macroscopic behavior of these structures View full abstract»

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  • Ultrafast all-optical modulation of infrared radiation via metal-semiconductor waveguide structures

    Page(s): 583 - 589
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    We present a novel optical-optical semiconductor switching technique for application to infrared laser beam modulation and ultrashort infrared laser pulse switching. This method relies on the ultrafast optical excitation, with femtosecond above-bandgap laser radiation, of an air-filled metal-clad semiconductor waveguide. Guided electromagnetic wave analysis combined with time-varying dielectric properties of the semiconductor layer are used to investigate the ultrafast switching speed of the structure. The device is capable of modulation at various infrared wavelengths. In particular, we investigate intensity modulation of the quasi-TE10 mode for 10.6-μm laser radiation. At an electron-hole photoinjection density of ~1.8×1018 cm-3, an extinction ratio of 83 dB is demonstrated. This ratio is significantly higher than that exhibited by current optical-optical semiconductor switches. Potential applications to all-optical Mach-Zehnder metal-clad semiconductor modulators and self-limiting switches are also discussed View full abstract»

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  • Carrier dynamics and microwave characteristics of GaAs-based quantum-well lasers

    Page(s): 635 - 646
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    We investigate the effects of carrier capture and re-emission on the electrical impedance, equivalent circuit, and modulation response of quantum-well (QW) laser diodes. The electrical impedance is shown to be a sensitive function of the time constants associated with carrier capture/transport and carrier re-emission. We compare the theoretical results with measured values of the electrical impedance of high-speed InGaAs-GaAs multiple-quantum-well lasers fabricated using different epilayer structures with a common lateral structure. The experimental results agree well with the theoretical model, allowing us to extract the effective carrier escape time and the effective carrier lifetime in the QWs, and to estimate the effective carrier capture/transport time View full abstract»

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  • Heavy-hole and light-hole quantum beats in the polarization state of coherent emission from quantum wells

    Page(s): 523 - 531
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    Dual-channel spectral interferometry is used to measure the vectorial dynamics of the the four-wave-mixing signal from a GaAs-AlGaAs multiple quantum well when both heavy-and light-hole excitons are excited. The ellipticity, the orientation, and the sense of rotation of the polarization ellipse associated with this emission are observed to oscillate dramatically at the heavy-hole-light-hole quantum beat frequency. The qualitative nature of the beating can be described by a simple model based on the density matrix equations for two independent three-level systems without the inclusion of many body effects; however, these beats are superposed on a polarization that is dominated by many-body effects View full abstract»

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  • Investigating nonlinear femtosecond pulse propagation with frequency-resolved optical gating

    Page(s): 451 - 458
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    Frequency-resolved optical gating (FROG) is used to investigate nonlinear pulse propagation in normally dispersive media. We present high-dynamic-range measurements of broad-bandwidth femtosecond pulses that result from nonlinear propagation in fused silica and compare these measurements with a (3+1)-dimensional modified nonlinear Schrodinger equation. We also demonstrate the ability of FROG to provide information about a noninstantaneous nonlinearity in methanol. In this case, the instantaneous nonlinear index and the time response of the noninstantaneous nonlinearity are used as fit parameters in a (1+1)-dimensional model View full abstract»

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  • Recent progress toward real-time measurement of ultrashort laser pulses

    Page(s): 421 - 431
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (472 KB)  

    Frequency-resolved optical gating (FROG) is a technique that produces a spectrogram of an ultrashort laser pulse optically. While a great deal of information about the pulse can be gleaned from its FROG trace, often it is desirable to obtain of the pulse information immediately, in real time. Quantitative information about the guise is not readily obtainable from its spectrogram without the use of a two-dimensional phase retrieval algorithm. While current algorithms are quite robust, retrieval of all the pulse information can be slow. In this paper, I describe a recently developed FROG trace inversion algorithm called Principal Component Generalized Projects that is fast, robust, and can invert FROG traces in real time. A femtosecond oscilloscope based on second-harmonic generation FROG is also described that uses this new algorithm to rapidly (up to 2.3 Hz) and continuously display the intensity and phase of ultrashort laser pulses View full abstract»

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  • Characterization of a distortion-corrected Nd:YAG laser with a self-conjugating loop geometry

    Page(s): 656 - 664
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    A detailed experimental and theoretical characterization of a self-adaptive solid-state laser is presented. The system uses a saturable gain medium (Nd:YAG amplifier) as the adaptive element in an externally injected self-intersecting loop geometry. We demonstrate energy output >300 mJ, high energy reflectivity >104, low input energy threshold of ~5 μJ, and phase-conjugate properties of the system that compensate for both intracavity and extracavity phase distortions. The spatial output beam size is compared to a Gaussian mode analysis based on ABCD ray transfer matrices. The temporal, spectral, energy, and threshold characteristics are compared to one-dimensional analytical and transient numerical simulations View full abstract»

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  • Spectral interferometry of semiconductor nanostructures

    Page(s): 510 - 522
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    Fourier transform spectral interferometry is applied to measure both amplitude and phase of the electric field in different types of semiconductor nanostructures, thus determining the real and imaginary parts of the dielectric function. The importance of measuring the phase is shown and discussed in three studies. First, the phase measurement is used to access directly the refractive index across excitonic resonances in bulk GaAs and AlGaAs-GaAs quantum wells, with unprecedented resolution. Second, we measure the density dependence of the full dielectric function across a Fano resonance in bulk GaAs and show that this allows us to obtain some information on the collisional broadening of the usually hidden linewidth of the coupled exciton/continuum. Third, the phase is studied in a complex heterostructure, a semiconductor microcavity. We investigate and discuss the effect of the cavity detuning and of the excitation density View full abstract»

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  • Second-harmonic generation frequency-resolved optical gating in the single-cycle regime

    Page(s): 459 - 478
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (796 KB)  

    The problem of measuring broad-band femtosecond pulses by the technique of second-harmonic generation frequency-resolved optical gating (SHG FROG) is addressed. We derive the full equation for the FROG signal, which is valid even for single-optical-cycle pulses. The effect of the phase mismatch in the second-harmonic crystal, the implications of the beam geometry, and the frequency-dependent variation of the nonlinearity are discussed in detail. Our numerical simulations show that, under carefully chosen experimental conditions and with a proper spectral correction of the data, the traditional FROG inversion routines work well even in the single-cycle regime. The developed description of the SHG FROG signal was applied to measure the white-light continuum pulses in the spectral region of 500-1100 nm. The obtained spectral phase of these pulses served as a target function for the pulse compressor design. The pulses produced by compression around 800 nm were also characterized by SHG FROG. The resulting pulse duration measures 4.5 fs which corresponds to ~2.5 optical cycles 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