Showing papers in "Journal of The Optical Society of America B-optical Physics in 1997"
TL;DR: In this paper, the authors studied the ablation of metal targets by Ti:sapphire laser radiation and showed that the intensity depends logarithmically on the laser fluence.
Abstract: Ablation of metal targets by Ti:sapphire laser radiation is studied. The ablation depth per pulse is measured for laser pulse durations between 150 fs and 30 ps and fluences ranging from the ablation threshold ∼0.1 J/cm2 up to 10 J/cm2. Two different ablation regimes are observed for the first time. In both cases the ablation depth per pulse depends logarithmically on the laser fluence. A simple theoretical model for a qualitative description of the experimental results is presented.
914 citations
TL;DR: In this article, the second-order nonlinear-optical coefficients of several important nonlinearoptical materials have been obtained with improved accuracy, including congruent LiNbO3, 1%MgO:LiNbOn3, 5%MglO:LNb On3 at pump wavelengths of 0.532 and 0.488 µm.
Abstract: The absolute scale of the second-order nonlinear-optical coefficients of several important nonlinear-optical materials has been obtained with improved accuracy. Second-harmonic generation, parametric fluorescence, and difference-frequency generation measurements have been made at several wavelengths in the near-infrared region. The second-harmonic generation measurement was performed at the fundamental wavelengths of 1.548, 1.533, 1.313, 1.064, and 0.852 µm. The materials measured included congruent LiNbO3,1%MgO:LiNbO3,5%MgO:LiNbO3,LiTaO3,KNbO3,KTiOPO4,KH2PO4, quartz, GaAs, GaP, α-ZnS, CdS, ZnSe, and CdTe. We made the parametric fluorescence measurement to determine the nonlinear-optical coefficients of congruent LiNbO3 and 5%MgO:LiNbO3 at pump wavelengths of 0.532 and 0.488 µm. We made the difference-frequency generation measurement for congruent LiNbO3 at a pump wavelength of 0.532 µm. The second-harmonic generation, parametric fluorescence, and difference-frequency generation measurements yielded consistent data on the nonlinear-optical coefficients of the materials. We found that many of the currently accepted standard values are overestimated because of neglect of the multiple-reflection effect in (nearly) plane-parallel-plate samples. The dispersion of the nonlinear-optical coefficients showed that Miller’s Δ is barely constant over the wavelength range measured and thus that Miller’s rule is not so good as other methods for wavelength scaling of the nonlinear-optical coefficients.
724 citations
TL;DR: In this article, the electronic structure of spherical PbS and PbSe quantum dots is calculated with a four-band envelope-function formalism, accounting for both exciton energies and wave functions with the correct symmetry of materials.
Abstract: The electronic structure of spherical PbS and PbSe quantum dots is calculated with a four-band envelope-function formalism. This calculation accounts for both exciton energies and wave functions with the correct symmetry of the materials. The selection rules and the strength of the dipole transitions of lead-salt quantum dots are derived accounting for the symmetry of the band-edge Bloch functions of the lead salts. The calculated energies of the optically allowed exciton states are found to be in good agreement with experimental data. The effects of many-body perturbations, such as Coulomb interactions and intervalley scattering, are also discussed.
692 citations
TL;DR: In this article, the authors report measurements of the refractive indices of congruently grown lithium niobate and lithium nibate doped with 5 mol. % magnesium oxide and use these results to predict the tuning curve of a room-temperature multigrating optical parametric oscillator.
Abstract: The growth in the uses of lithium niobate for infrared applications has created a need for knowledge of its optical characteristics in the infrared spectral region for the purpose of designing phase-matched or quasi-phase-matched devices. We report measurements of the refractive indices of congruently grown lithium niobate and lithium niobate doped with 5 mol. % magnesium oxide. We use these results to predict the tuning curve of a room-temperature multigrating optical parametric oscillator in each material.
587 citations
TL;DR: In this paper, optical vortices that have quasi-point core functions, such as optical vortex solitons, may orbit one another at rates that are orders of magnitude larger than those with nonlocalized cores.
Abstract: Optical vortices in linear and nonlinear media may exhibit propagation dynamics similar to hydrodynamic vortex phenomena. Analytical and numerical methods are used to describe and investigate the interaction between vortices and the background field. We demonstrate that optical vortices that have quasi-point core functions, such as optical vortex solitons, may orbit one another at rates that are orders of magnitude larger than those with nonlocalized cores.
349 citations
TL;DR: In this article, the authors analyzed the spectral changes that occur when unfocused femtosecond pulses at 800 nm propagate through different atomic and molecular gases, and found that the observed red shift in the self-phase modulated spectra after propagation through N2, O2, and air is attributed to a delayed change of the nonlinear refractive index, a consequence of the molecular response to impulsive excitation of rotational coherences.
Abstract: We analyze the spectral changes that occur when unfocused intense femtosecond pulses at 800 nm propagate through different atomic and molecular gases. The observed red shift in the self-phase-modulated spectra after propagation through N2, O2, and air is attributed to a delayed change of the nonlinear refractive index, a consequence of the molecular response to impulsive excitation of rotational coherences. We compare these results on the nonlinear refractive index with those obtained from Ar, Xe, and SF6.
326 citations
TL;DR: In this article, a large and good-optical-quality crystal of gadolinium and calcium oxoborate, Ca4GdO(BO3)3 (GdCOB), has been grown from a melt by the Czochralski pulling method.
Abstract: Large and good-optical-quality crystals of gadolinium and calcium oxoborate, Ca4GdO(BO3)3 (GdCOB) have been grown from a melt by the Czochralski pulling method. The crystal is absolutely insensitive to moisture. Linear- and quadratic nonlinear-optical properties of this new monoclinic biaxial borate crystal are reported. The crystal is transparent in the visible and the near IR (from 0.32 to 2.7 µm), with favorable phase matching conditions for second-harmonic generation. Experimental phase-matching results, measured with a femtosecond broadband pulse parametric generator source tunable from 0.8 to 2.100 µm, are compared with theoretical predictions. The effective nonlinear coefficients are determined, leading to deff=1 pm/V for type I crystals in the ZX plane. The damage threshold is as high as 1 GW/cm2 at 0.532 µm. The second-harmonic generation conversion efficiency of a Q-switched Nd:YAG laser with a 15-mm long crystal is greater than 50%. These values together with the possibility of growing large crystals make GdCOB an excellent candidate for the next generation of crystals for frequency conversion and parametric processes.
325 citations
TL;DR: In this article, the authors show that low time jitter of a harmonic passively mode-locked laser can be obtained at repetition rates close to acoustic eigenfrequencies of the optical fiber.
Abstract: We show that low time jitter of a harmonic passively mode-locked laser can be obtained at repetition rates close to acoustic eigen-frequencies of the optical fibre.
238 citations
TL;DR: In this article, the structure of the first azimuthal stationary state for a nonlinear medium presenting simultaneously a cubic (focusing) and a quintic (defocusing) dependence with the light intensity in the refractive index was analyzed.
Abstract: We analyze the structure of the first azimuthal stationary state for a nonlinear medium presenting simultaneously a cubic (focusing) and a quintic (defocusing) dependence with the light intensity in the refractive index. This solution takes the form of a dark vortex of light hosted in a compact light beam. The existence of these modes is guaranteed if the flux exceeds a certain minimum threshold and if the modes are extremely stable for fluxes larger than a critical value that we calculated. We verified the robust nature of this solution inducing internal oscillations by an initial phase chirp. Using the variational method, we obtain an approximate picture for the beam internal dynamics. We also studied numerically the interactions between two near-vortex solutions, finding that for a wide combination of beam parameters they show elastic collisions.
210 citations
TL;DR: In this paper, the role of the relative thickness of the interaction region as dictated by the acousto-optic Q parameter was analyzed and it was shown that varying Q allows flexibility in choosing between diffraction efficiency and pixels of resolution.
Abstract: We focus theoretically and experimentally on the fundamental limitations of spectral pulse shaping using an acousto-optic modulator. We analyze the role of the relative thickness of the interaction region as dictated by the acousto-optic Q parameter and show that varying Q allows flexibility in choosing between diffraction efficiency and pixels of resolution. We model and experimentally demonstrate the effects of potential nonidealities such as nonlinear acoustic attenuation. In addition, we derive a simple and intuitive expression to predict the magnitude of the distortions in the spatial profile generated by an acousto-optic-modulator spectral light modulator. Finally, we demonstrate amplification of acousto-optic-modulator-generated shaped pulses for the first time.
188 citations
TL;DR: In this article, the role of SLA carrier dynamics, which permits switching rates faster than the recovery time, has been highlighted for all-optical ultrafast signal processing, and experimental results imply that switching rates of as much as ∼100 GHz should be possible.
Abstract: Recent progress in the use of semiconductor laser amplifiers (SLA's) for high-speed all-optical switching is reviewed. We show that, despite SLA's having lifetimes of ⩾100 ps, they are, to date, the most promising material system for all-optical ultrafast signal processing. We highlight the role of SLA carrier dynamics, which permits switching rates faster than the recovery time. Experimental results are presented that imply that switching rates of as much as ∼100 GHz should be possible. Recent experiments are described in which SLA-based switches were incorporated into novel all-optical architectures.
TL;DR: In this paper, the authors demonstrate the existence of Bragg grating solitons in fiber gratings at high intensities and demonstrate how trains of such solITons can be generated.
Abstract: We discuss experimental results that demonstrate the existence of Bragg grating solitons in fiber gratings at high intensities. These solitons can exist because of the balance of the nonlinearity in the glass and the group-velocity dispersion introduced by the grating. We show that Bragg grating solitons can travel at velocities substantially below that in bare fiber and also how trains of such solitons can be generated.
TL;DR: In this paper, the authors analyze self-trapping of one-dimensional optical beams in photorefractive, photovoltaic media for open-and closed-circuit realizations.
Abstract: We analyze self-trapping of one-dimensional optical beams in photorefractive, photovoltaic media for open- and closed-circuit realizations. We show that a passive load (resistor) in the external circuit can be used for switching of dark photovoltaic solitons. Dark solitons in a short-circuited crystal can be obtained for a much smaller nonlinearity than in open-circuit conditions. Shorting the crystal affects bright solitons very little.
TL;DR: In this article, the energy and angular distributions of ejected electrons at barrier-suppression and tunneling ionization of complex atoms and atomic ions by low-frequency strong electromagnetic radiation were analyzed.
Abstract: Analytical expressions are obtained for energy and angular distributions of ejected electrons at the barrier-suppression and tunneling ionization of complex atoms and atomic ions by low-frequency strong electromagnetic radiation. The results reduce to previously known expressions in the case of the ground state of the hydrogen atom. Both linear and circular polarizations of the electromagnetic field are considered. The ionization rates are found by integration over angles and energies of the ejected electron in the case of barrier-suppression ionization of complex atoms and atomic ions. The barrier-suppression results reduce correctly to the tunneling results of the Ammosov–Delone–Krainov approach in the limit of weak fields compared with the barrier-suppression fields.
TL;DR: In this paper, the characteristics of an interferometric system based on two-wave mixing at 1.06 µm in photorefractive InP:Fe under an applied field for the detection of ultrasonic motion of a scattering surface are described.
Abstract: The characteristics of an interferometric system based on two-wave mixing at 1.06 µm in photorefractive InP:Fe under an applied field for the detection of ultrasonic motion of a scattering surface are described. A theoretical analysis of possible configurations for the detection of small phase modulation in the undepleted-pump approximation is presented. Experimental assessment of the device for both cw and pulse regimes is performed: The sensitivity, the etendue, the response time, and the behavior under ambient vibrations or moving inspected samples are provided. This adaptive device presents many features appropriate for industrial inspection and compares advantageously with the passive confocal Fabry–Perot device that is now widely used.
TL;DR: In this article, an original poling technique that uses a purely optical excitation process is presented, which consists of a seeding-type process that alternates between writing and probing periods.
Abstract: We present an original poling technique that uses a purely optical excitation process. The experiment consists of a seeding-type process. Writing and probing periods are alternated. Writing periods correspond to simultaneous irradiation of the sample by the coherent superposition of the 1064-nm fundamental and the 532-nm second-harmonic light of a picosecond-pulsed Nd:YAG laser. The sample is a spin-coated film of a poly(methyl methacrylate) copolymer onto which the azo-dye molecule Disperse Red 1 is grafted. We demonstrate efficient and quasi-permanent poling of the molecules with a spatial period that satisfies the phase-matching condition for second-harmonic generation. The influence of seeding parameters such as the relative phase and the relative intensities between the writing beams is studied both theoretically and experimentally. Tensorial properties and the spatial profile of the photoinduced χ(2) are analyzed from a microscopic point of view. Dark and photostimulated relaxation processes are investigated from a chemical-physics point of view. The physical origin of the photoinduced molecular orientation process is discussed. A minimal model involving the relevant experimental parameters is developed. Numerical simulations are in agreement with the experiment.
TL;DR: In this article, a new chromophore, N, N-diphenyl-7-[2-(4-pyridinyl) ethenyl]-9,9-di-ndecyl-fluoren-2-amine (AF-50) has been experimentally studied under excitation with 10-Hz, ∼8-ns, and ∼800-nm laser pulses.
Abstract: Strong two-photon-absorption (TPA) based nonlinear optical properties of a new chromophore, N, N-diphenyl-7-[2-(4-pyridinyl) ethenyl]-9,9-di-n-decyl-fluoren-2-amine (AF-50) has been experimentally studied. Under excitation with 10-Hz, ∼8-ns, and ∼800-nm laser pulses, the TPA cross section and the TPA-induced frequency-upconverted emission spectra are measured for AF-50 solutions in various solvents. The most attractive feature of this chromophore is its remarkably high value of the molecular TPA cross section (∼78×10-20 cm2/GW in benzene solution). Based on this feature, superior optical power limiting and stabilization performance has been demonstrated in a 1-cm-long AF-50 solution sample with concentration of d0=0.045 M/L. The nonlinear transmission of the measured sample decreased from ∼0.93 to ∼0.3 when the input-beam intensity increased from ∼10 MW/cm2 to ∼360 MW/cm2; the relative intensity fluctuation of the output laser pulses was reduced to one third of that of the input laser beam.
TL;DR: In this paper, the effect of carrier heating and spectral-hole burning on the amplification of picosecond pulses in a semiconductor optical amplifier was studied, and an analytical expression for the amplifier output was derived for a given bit-width input, where the critical pulse width ranges from a few seconds to 20 ps in most cases.
Abstract: We study the amplification of picosecond pulses in a semiconductor optical amplifier, including the effect of carrier heating and spectral-hole burning. Under simplifying approximations we obtain an analytical expression for the amplifier output to a given picosecond pulse input. The effect of the intraband dynamics becomes important for pulses below a critical pulse width that is related to the K factor that characterizes the modulation properties of semiconductor lasers. The critical pulse width ranges from a few picoseconds to 20 ps in most cases.
TL;DR: In this article, the authors provided a comprehensive experimental and theoretical study of incoherently coupled photorefractive spatial-soliton pairs in all three possible realizations: bright-bright, dark-dark, and dark-bright.
Abstract: We provide a comprehensive experimental and theoretical study of incoherently coupled photorefractive spatial-soliton pairs in all three possible realizations: bright–bright, dark–dark, and dark–bright. We also show that when the total intensity of two coupled solitons is much lower than the effective dark irradiance, the coupled soliton pair is reduced to Manakov solitons. In all cases, mutual trapping of both components in the coupled soliton pair is verified by analyzing, experimentally and numerically, the beam evolution after decoupling.
TL;DR: In this paper, a Carpenter pruning-based grating pair was proposed to compensate for second-and third-order dispersion as a function of grating separation, as opposed to traditional systems, which require an additional grating angle mismatch.
Abstract: We present a grating pair based on Carpenter prisms whose third-order dispersion is opposite that of a traditional grating pair. A properly designed stretcher–compressor system with these gratings has the unique characteristic that it simultaneously compensates for second- and third-order dispersion as a function of grating separation, as opposed to traditional systems, which require an additional grating angle mismatch. The applicability of this design to 30-fs, millijoule-level chirped-pulse amplification is discussed.
TL;DR: In this paper, the optical properties of rare-earth organic complexes have been studied because of their possible application to polymer optical fibers and waveguides, and numerical simulations reveal that gains as high as and exceeding 20 dB should be realizable in rare earth-doped polymer fiber amplifiers having lengths <60 cm.
Abstract: The optical properties of rare-earth organic complexes have been studied because of their possible application to polymer optical fibers and waveguides. Er3+, Nd3+, and Sm3+ ions are encapsulated in tetrakis(benzoyltrifluoroacetonate) and tetrakis(dibenzoylmethide) chelates, and their radiative properties are evaluated in several organic solvents. Analysis reveals that tetrakis(benzoyltrifluoroacetonate) chelates are promising dopants for use in rare-earth-doped polymer devices. These rare-earth complexes can be doped to high concentrations in polymer systems without quenching, providing the means for short-length amplification devices. Numerical simulations reveal that gains as high as and exceeding 20 dB should be realizable in rare-earth-doped polymer fiber amplifiers having lengths <60 cm. Similar calculations reveal threshold pump powers of tens of milliwatts for rare-earth-doped polymer fiber lasers.
TL;DR: In this article, an extension of the recently introduced nonlinear finite-difference time-domain technique for the study of electromagnetic wave propagation in a nonlinear Kerr medium to include absorption is presented.
Abstract: An extension of the recently introduced nonlinear finite-difference time-domain technique [Opt. Lett.21, 1138 (1996)] for the study of electromagnetic wave propagation in a non-linear Kerr medium to include absorption is presented. The optical limiting and switching of short pulses by use of a nonlinear quarter-wave reflector (a one-dimensional photonic bandgap structure) with a defect is studied. Comparison with an optical limiter and with an optical switch with a perfect nonlinear quarter-wave reflector shows that introducing a defect can improve the performance of these devices.
TL;DR: In this article, the authors compare the accuracy and computational cost of the split-step method and solution of the coupled equations for the amplitudes of the spatial frequency components of the beams (Fourier-space method), and investigate the effect of using a first-order expansion for the refractive index as a function of propagation direction.
Abstract: Two computational methods are common for simulating the evolution of three beams propagating in a birefringent medium and interacting through a second-order nonlinearity: the split-step method and solution of the coupled equations for the amplitudes of the spatial frequency components of the beams (Fourier-space method). I (i) compare the accuracy and computational cost of both methods, (ii) investigate the effect of using a first-order expansion for the refractive index as a function of propagation direction, and (iii) generalize both methods to handle arbitrary propagation directions in biaxial crystals. It turns out that the Fourier-space method with a Runge–Kutta solver gives best accuracy, but a symmetrized split-step method may be faster when low accuracy is sufficient. The first-order expansion for the refractive index gives a very small error for well-collimated beams, but the approximation is not important for computational efficiency. Modeling of parametric amplification outside the principal planes of a biaxial crystal is demonstrated, and to the author's knowledge this process has not been modeled in such detail before.
TL;DR: In this paper, a large enhancement of optical nonlinearity in one-dimensional photonic-crystal structures with a defect is considered theoretically, and it is shown that the enhancement can be obtained for absorption saturation and degenerate four-wave mixing efficiency as a result of large optical field amplitude of the localized photonic defect mode at the defect layer.
Abstract: Enhancement of optical nonlinearity in one-dimensional photonic-crystal structures with a defect is considered theoretically. It is shown that a large enhancement can be obtained for absorption saturation and degenerate four-wave mixing efficiency as a result of large optical field amplitude of the localized photonic-defect mode at the defect layer. The figure of merit of the use of the photonic-crystal structure is derived especially for systems in which the concentration of the nonlinear optical material can be arbitrarily adjusted. Optical bistability is also predicted for optically dense samples. They can be applied in real photonic devices because of their simple structure and the large enhancement obtained.
TL;DR: In this article, the authors study the properties of waveguides induced by one-dimensional steady-state photorefractive screening solitons and show that the number of possible guided modes in a waveguide induced by a bright soliton depends on the intensity ratio of the soliton, which is the ratio between the solitus peak intensity and the sum of the background illumination and the dark irradiance.
Abstract: We study theoretically and experimentally the properties of waveguides induced by one-dimensional steady-state photorefractive screening solitons. We show that the number of possible guided modes in a waveguide induced by a bright soliton depends on the intensity ratio of the soliton, which is the ratio between the soliton peak intensity and the sum of the background illumination and the dark irradiance. We find that the number of guided modes increases monotonically with increasing intensity ratio. By adjusting the intensity ratio and the applied field, one can keep a fixed soliton size and at the same time vary the number of guided modes continuously. On the other hand, waveguides induced by dark screening solitons can support only one guided mode for all intensity ratios. Our experiments show good agreement with the theoretical results for both bright- and dark-soliton-induced waveguides.
TL;DR: In this paper, the authors proposed a method to measure the finesse of swept Fabry-Perot cavities with a precision of 1% for intermediate finesses (F≈10 000).
Abstract: The phenomenon of ringing in swept Fabry–Perot cavities, which leads to discrepancies with respect to usual Airy peaks, exhibits three different regimes, depending on the values of the finesse, the sweep frequency, and the free spectral range of the cavity. In particular, the intermediate case in which the Fabry–Perot cavity transmission essentially oscillates is shown theoretically and experimentally to provide a new simple method to measure the finesse of the cavity. For cavities with intermediate finesses (F≈10 000) this method is experimentally shown to have a precision of the order of 1%.
TL;DR: In this paper, two stages of type II optical parametric amplification of a white-light continuum are used for efficient generation of ultrashort (30-50-fs) pulses at kilohertz repetition rates.
Abstract: Two stages of type II optical parametric amplification of a white-light continuum are used for efficient generation of ultrashort (30–50-fs) pulses at kilohertz repetition rates. Various nonlinear techniques can be used to cover the range from 12 µm to 280 nm. The amplitude and the phase of the generated UV pulses are characterized by use of frequency-resolved optical gating.
TL;DR: By applying the Maxwell Garnett model to gold nanoparticles in water, this article deduced a value of Imχi(3)=1.1×10-7 e cient for the imaginary part of the cubic susceptibility for gold corresponding to a Fermi smearing mechanism.
Abstract: By applying the Maxwell Garnett model to gold nanoparticles in water we deduce a value of Im χi(3)=1.1×10-7 esu for the imaginary part of the cubic susceptibility for gold corresponding to a Fermi smearing mechanism. We also demonstrate a sign reversal in the nonlinear absorption for gold particles in 1, 1′, 3, 3, 3′, 3′-hexamethylindotricarbocyanine iodide. Although the imaginary part of χ(3) is positive for each component by itself, remarkably the imaginary part of χ(3) is negative for the colloid as a whole. We show that the nonlinearity of the host must be considered and that the sign reversal in χ(3) is a result of the fact that at the surface plasmon resonance the local field factor has an imaginary component that arises from a phase shift between the applied field and the local field inside the particle.
TL;DR: In this paper, the authors measured and modeled parametric gain and oscillation for two-crystal ring oscillators arranged for walkoff compensation, and showed how the orientation of the crystals determined the relative sign of the nonlinear mixing coefficient in the two crystals.
Abstract: We measure and model parametric gain and oscillation for two crystals arranged for walkoff compensation. We show how the orientation of the crystals determines the relative sign of the nonlinear mixing coefficient in the two crystals. This sign dramatically influences small signal gain and oscillator performance, and we show how to determine the correct crystal orientation from parametric-gain measurements. The performance of two-crystal oscillators is examined with particular attention to beam tilts, conversion efficiency, and beam quality. We find reduced efficiency and increased oscillation threshold when the coefficients have opposite signs in a two-crystal ring oscillator. Sign reversal seems to have little influence on spectral purity or far-field beam profiles when the oscillator is seeded.
TL;DR: In this article, a phase-retrieval algorithm that retrieves both the probe and the gate pulses independently by converting the frequency-resolved optical gating (FROG) phase retrieval problem to an eigenvector problem is presented.
Abstract: Frequency-resolved optical gating (FROG) is a technique that produces a spectrogram of an ultrashort laser pulse. The intensity and phase of the ultrashort laser pulse can be determined through solving for the phase of the spectrogram with an iterative, phase-retrieval algorithm. This work presents a new phase-retrieval algorithm that retrieves both the probe and the gate pulses independently by converting the FROG phase-retrieval problem to an eigenvector problem. The new algorithm is robust and general. It is tested theoretically by use of synthetic data sets and experimentally by use of single-shot, polarization-gate FROG. We independently and simultaneously characterize the electric field amplitude and phase of a pulse (probe) that was passed though 200 mm of BK7 glass and the amplitude of an unchanged pulse (gate) from an amplified Ti:sapphire laser. When the effect of the 200 mm of BK7 glass was removed mathematically from the probe, there was good agreement between the measured gate and the calculated, prechirped probe.