Showing papers in "Applied Physics B in 2006"
TL;DR: An overview of fundamental experimental and theoretical aspects of soot measurements by laser-induced incandescence (LII) is provided in this paper. But despite the widespread application of LII for soot-concentration and particle-size measurements, there is still a significant lack in fundamental understanding for many of the underlying physical processes.
Abstract: This paper provides an overview of a workshop focused on fundamental experimental and theoretical aspects of soot measurements by laser-induced incandescence (LII). This workshop was held in Duisburg, Germany in September 2005. The goal of the workshop was to review the current understanding of the technique and identify gaps in this understanding associated with experimental implementation, model descriptions, and signal interpretation. The results of this workshop suggest that uncertainties in the understanding of this technique are sufficient to lead to large variability among model predictions from different LII models, among measurements using different experimental approaches, and between modeled and measured signals, even under well-defined conditions. This article summarizes the content and conclusions of the workshop, discusses controversial topics and areas of disagreement identified during the workshop, and highlights recent important references related to these topics. It clearly demonstrates that despite the widespread application of LII for soot-concentration and particle-size measurements there is still a significant lack in fundamental understanding for many of the underlying physical processes.
473 citations
TL;DR: The present status of clinical breath analysis is discussed and reasons why breath analysis has not received similar widespread clinical use are suggested and the availability of real-time, portable monitors will represent a breakthrough for clinical diagnosis.
Abstract: Clinical breath analysis remains in its infancy, despite the fact that its potential has been recognized for centuries and that blood, urine, and other bodily fluids and tissues are routinely analyzed to diagnose disease or to monitor therapy. This review discusses the present status of clinical breath analysis and suggests reasons why breath analysis has not received similar widespread clinical use. Currently, a number of marker molecules have been identified in breath that could be used to identify disease, disease progression, or to monitor therapeutic intervention and this list is expected increase dramatically since the analysis of breath is ideally suited for population-based studies in the developed and underdeveloped world. Recent advances in analytical instrumentation have suggested that the use of exhaled breath in medicine should now be re-examined. In particular, the availability of real-time, portable monitors will represent a breakthrough for clinical diagnosis. Progress in clinical breath analysis will require collaboration amongst device makers, experts in breath analysis, and clinicians.
344 citations
TL;DR: In this paper, the spectral response of optical metamaterials consisting of gold split-ring resonators was studied using reflection spectroscopy in the near infrared region at normal incidence in the experiments.
Abstract: We study the spectral response of optical metamaterials consisting of gold split-ring resonators. We utilize reflection spectroscopy in the near infrared region at normal incidence in the experiments. Our theoretical modeling is based on rigorous diffraction theory. We perform a comprehensive analysis of the dependence of the features of both the electric and the oscillating-circuit resonance on the geometry of the metamaterial. We show that theory and experiment are in good agreement.
172 citations
TL;DR: In this article, the authors provide a comprehensive review of the heat conduction modeling practice in the LII literature and an overview of the physics of particle conduction loss from a single spherical particle in the entire range of Knudsen number with emphasis on the transition regime.
Abstract: Laser-induced incandescence (LII) of nano-second pulsed laser heated nano-particles has been developed into a popular technique for characterizing concentration and size of particles suspended in a gas and continues to draw increased research attention. Heat conduction is in general the dominant particle cooling mechanism after the laser pulse. Accurate calculation of the particle cooling rate is essential for accurate analysis of LII experimental data. Modelling of particle conduction heat loss has often been flawed. This paper attempts to provide a comprehensive review of the heat conduction modelling practice in the LII literature and an overview of the physics of heat conduction loss from a single spherical particle in the entire range of Knudsen number with emphasis on the transition regime. Various transition regime models developed in the literature are discussed with their accuracy evaluated against direct simulation Monte Carlo results under different particle-to-gas temperature ratios. The importance of accounting for the variation of the thermal properties of the surrounding gas between the gas temperature and the particle temperature is demonstrated. Effects of using these heat conduction models on the inferred particle diameter or the thermal accommodation coefficient are also evaluated. The popular McCoy and Cha model is extensively discussed and evaluated. Based on its superior accuracy in the entire transition regime and even under large particle-to-gas temperature ratios, the Fuchs boundary-sphere model is recommended for modeling particle heat conduction cooling in LII applications.
170 citations
TL;DR: In this article, photochromism in single nitrogen-vacancy optical centers in diamond is demonstrated, and it is shown that the defect state relaxes back to the neutral form under dark conditions.
Abstract: Photochromism in single nitrogen-vacancy optical centers in diamond is demonstrated. Time-resolved optical spectroscopy shows that intense irradiation at 514 nm switches the nitrogen-vacancy defects to the negative form. This defect state relaxes back to the neutral form under dark conditions. Temporal anticorrelation of photons emitted by the different charge states of the optical center unambiguously indicates that the nitrogen-vacancy defect accounts for both 575 nm and 638 nm emission bands. Possible mechanism of photochromism involving nitrogen donors is discussed.
152 citations
TL;DR: In this paper, second harmonic generation and optical parametric amplification in negative-index metamaterials (NIMs) were studied, and the feasibility of the generation of entangled pairs of left and right-handed counter-propagating photons was discussed.
Abstract: Second harmonic generation and optical parametric amplification in negative-index metamaterials (NIMs) are studied. The opposite directions of the wave vector and the Poynting vector in NIMs results in a “backward” phase-matching condition, causing significant changes in the Manley–Rowe relations and spatial distributions of the coupled field intensities. It is shown that absorption in NIMs can be compensated by backward optical parametric amplification. The possibility of distributed-feedback parametric oscillation with no cavity has been demonstrated. The feasibility of the generation of entangled pairs of left- and right-handed counter-propagating photons is discussed.
141 citations
TL;DR: In this article, a thermoelectrically cooled, continuous-wave, distributed feedback quantum cascade laser operating at 5.45 μm (1835 cm-1) and off-axis integrated cavity output spectroscopy combined with a wavelength-modulation technique was developed to determine NO concentrations at the sub-ppbv levels that are essential for a number of applications, such as medical diagnostics, environmental monitoring, and industrial process control.
Abstract: A nitric oxide (NO) gas sensor based on a thermoelectrically cooled, continuous-wave, distributed feedback quantum cascade laser operating at 5.45 μm (1835 cm-1) and off-axis integrated cavity output spectroscopy combined with a wavelength-modulation technique was developed to determine NO concentrations at the sub-ppbv levels that are essential for a number of applications, such as medical diagnostics, environmental monitoring, and industrial process control. The sensor employs a 50-cm-long high-finesse optical cavity that provides an effective path length of ∼700 m. A noise equivalent (SNR=1) minimum detection limit of 0.7 ppbv with a 1-s observation time was achieved.
132 citations
TL;DR: In this article, the reference cavity is mounted on four support points in the horizontal symmetry plane of the optical frequency standard and the positions of the points are optimized by finite-element analysis.
Abstract: We report a novel mounting of the reference cavity used for stabilization of the clock laser in an optical frequency standard. The cavity axis is oriented horizontally and the cavity is supported in its horizontal symmetry plane on four support points. The positions of the points were optimized by finite-element analysis. A sensitivity to accelerations of 1.5 kHz/(m/s2) in the vertical and 14 kHz/(m/s2) in the horizontal direction was measured, which is a reduction in the vertical sensitivity by two orders of magnitude compared to the usual support from below.
129 citations
TL;DR: In this paper, the authors investigated the quantum noise limits for optical phase noise and carrier-envelope offset (CEO) noise of passively mode-locked lasers and showed that a feedback timing stabilization via cavity length control can, depending on the situation, reduce or greatly increase the phase noise while not affecting the CEO noise.
Abstract: The timing jitter, optical phase noise, and carrier-envelope offset (CEO) noise of passively mode-locked lasers are closely related. New key results concern analytical calculations of the quantum noise limits for optical phase noise and CEO noise. Earlier results for the optical phase noise of actively mode-locked lasers are generalized, particularly for application to passively mode-locked lasers. It is found, for example, that mode locking with slow absorbers can lead to optical linewidths far above the Schawlow–Townes limit. Furthermore, mode-locked lasers can at the same time have nearly quantum-limited timing jitter and a strong optical excess phase noise. A feedback timing stabilization via cavity length control can, depending on the situation, reduce or greatly increase the optical phase noise, while not affecting the CEO noise. Besides presenting such findings, the paper also tries to clarify some basic aspects of phase noise in mode-locked lasers.
127 citations
TL;DR: In this paper, a quantum gravity gradiometer for satellite-based global gravity field mapping is presented, which is based on cold atom interferometer techniques, and the performance enhancement is anticipated when operated in microgravity environment in space.
Abstract: Recent progress in cold atom interferometry has lead to a new method of sensitive inertial sensing. Significant performance enhancement of cold atom interferometer-based sensors is anticipated when operated in the microgravity environment in space. Based on cold atom interferometer techniques, we are developing a quantum gravity gradiometer for satellite-based global gravity field mapping. As a first step, we have built a laboratory-based gradiometer employing component technologies suitable for a future flight instrument. This paper describes the implementation of the laboratory instrument and its initial results.
123 citations
TL;DR: In this paper, the femtosecond stimulated Raman spectrograph (FSRS) was designed for measurements in the near UV, where a 387.5-nm Raman pump pulse was used for molecular absorbing in the UV.
Abstract: The design of a femtosecond stimulated Raman spectrograph (FSRS) optimized for measurements in the near UV is presented. It features a 387.5 nm Raman pump pulse causing a (pre-)resonance enhancement for molecular absorbing in the UV. As many photoreactive molecules absorb there, the set-up is particularly suited to study photochemical reactions. The 387.5 nm pulses are generated by frequency adding two femtosecond laser pulses with linear chirps, equal in magnitude but opposite in sign. This results in intense and spectrally narrow (∼10 cm-1) Raman pump pulses which allow recording of Raman spectra with a good spectral resolution. The power of the spectrograph to trace ultrafast photoreactions is illustrated by measurements on the photochemistry of o-nitrobenzaldehyde.
TL;DR: The cold atom clock PHARAO as mentioned in this paper was designed for microgravity operation and all elements of the clock have been manufactured and delivered to CNES, the French space agency, for initial science operation.
Abstract: In this paper we describe the cold atom clock PHARAO, designed for microgravity operation. All elements of the PHARAO engineering model have been manufactured and delivered to CNES, the French space agency. We present the clock design, its main characteristics, and initial science operation. PHARAO is one of the main components of the Atomic Clock Ensemble in Space payload that is scheduled to fly on board the International Space Station in 2010.
TL;DR: An improved aggregate-based low-fluence laser-induced incandescence (LII) model has been developed in this article, where the shielding effect in heat conduction between aggregated soot particles and the surrounding gas was modeled using the concept of the equivalent heat transfer sphere.
Abstract: An improved aggregate-based low-fluence laser-induced incandescence (LII) model has been developed. The shielding effect in heat conduction between aggregated soot particles and the surrounding gas was modeled using the concept of the equivalent heat transfer sphere. The diameter of such an equivalent sphere was determined from direct simulation Monte Carlo calculations in the free molecular regime as functions of the aggregate size and the thermal accommodation coefficient of soot. Both the primary soot particle diameter and the aggregate size distributions are assumed to be lognormal. The effective temperature of a soot particle ensemble containing different primary particle diameters and aggregate sizes in the laser probe volume was calculated based on the ratio of the total thermal radiation intensities of soot particles at 400 and 780 nm to simulate the experimentally measured soot particle temperature using two-color optical pyrometry. The effect of primary particle diameter polydispersity is in general important and should be considered. The effect of aggregate size polydispersity is relatively unimportant when the heat conduction between the primary particles and the surrounding gas takes place in the free-molecular regime; however, it starts to become important when the heat conduction process occurs in the near transition regime. The model developed in this study was also applied to the re-determination of the thermal accommodation coefficient of soot in an atmospheric pressure laminar ethylene diffusion flame.
TL;DR: In this paper, an optical feedback cavity-enhanced spectroscopy (OF-CEAS) was used to measure the isotopic composition of water in high-altitude research aircraft.
Abstract: Measurements of the isotopic composition of water are thought to help explain stratospheric aridity and related issues in atmospheric sciences. Simultaneous in situ measurements of 2H/1H, 17O/16O, and 18O/16O at high spatial resolution are required for this purpose. We present the design and laboratory performance of a device that will be used on high-altitude research aircraft. It is based on optical feedback cavity-enhanced spectroscopy (OF-CEAS), with better sensitivity than traditional multi-pass arrangements. It utilizes a near-infrared laser source, avoiding the need for cryogens. We demonstrate an airborne precision during tropospheric flight conditions of 1 ‰, 3 ‰, and 9 ‰ for δ18O, δ17O, and δ2H, respectively, for 30-s averaged data and a water concentration of about 200 ppm. With recent improvements we expect to remain within a factor of about three of these values under true stratospheric conditions (water mixing ratio ∼10 ppmv).
TL;DR: In this paper, the authors used a distributed feedback diode laser operating at λ = 2 μm with the primary purpose of studying vibrational relaxation processes in the CO2-N2-H2O system.
Abstract: Carbon dioxide (CO2) trace gas detection based on quartz enhanced photoacoustic spectroscopy (QEPAS) using a distributed feedback diode laser operating at λ=2 μm is performed, with a primary purpose of studying vibrational relaxation processes in the CO2-N2-H2O system. A simple model is developed and used to explain the experimentally observed dependence of amplitude and phase of the photoacoustic signal on pressure and gas humidity. A (1σ) sensitivity of 110 parts-per-million (with a 1 s lock-in time constant) was obtained for CO2 concentrations measured in humid gas samples.
TL;DR: In this article, the authors study the dependence of the simultaneous phononic and photonic band gaps on material parameters and provide design guidelines on how to create these photonic-phononic crystals.
Abstract: We study elastic and electromagnetic properties in periodic structures and present “deaf and blind” structures, i.e. materials having simultaneous complete phononic and photonic band gaps, that is, transverse electric (TE) and transverse magnetic (TM) electromagnetic waves, pure shear elastic waves, and mixed shear and dilatation elastic waves, cannot propagate within these structures. These composite materials can control the flow of light and sound at the same time. The existence of complete gaps for electromagnetic and elastic waves can lead to the simultaneous localization of light and sound, a novel phenomena that can have strong influence on photon–phonon interactions. We study the dependence of the simultaneous and complete gaps on material parameters to provide design guidelines on how to create these photonic–phononic crystals.
TL;DR: In this article, a tunable diode laser (TDL) temperature sensor is designed, constructed, tested, and demonstrated in the exhaust of an industrial gas turbine, where the sensor is determined from the ratio of the measured absorbance of two water vapor overtone transitions in the near infrared where telecommunication diode lasers are available.
Abstract: A tunable diode laser (TDL) temperature sensor is designed, constructed, tested, and demonstrated in the exhaust of an industrial gas turbine Temperature is determined from the ratio of the measured absorbance of two water vapor overtone transitions in the near infrared where telecommunication diode lasers are available Design rules are developed to select the optimal pair of transitions for direct absorption measurements using spectral simulations by systematically examining the absorption strength, spectral isolation, and temperature sensitivity to maximize temperature accuracy in the core flow and minimize sensitivity to water vapor in the cold boundary layer The contribution to temperature uncertainty from the spectroscopic database is evaluated and precise line-strength data are measured for the selected transitions Gas-temperature measurements in a heated cell are used to verify the sensor accuracy (over the temperature range of 350 to 1000 K, ΔT∼2 K for the optimal line pair and ΔT∼5 K for an alternative line pair) Field measurements of exhaust-gas temperature in an industrial gas turbine demonstrate the practical utility of TDL sensing in harsh industrial environments
TL;DR: In this article, a temperature-dependent Sellmeier equation for the extraordinary refractive index of 5 mol % MgO doped congruent lithium niobate was presented for wavelengths in the range of 1.3-5 μm and temperatures between 40 °C and 200 °C.
Abstract: We present a temperature-dependent Sellmeier equation for the extraordinary refractive index of 5 mol % MgO doped congruent lithium niobate. This equation is adapted for wavelengths in the range of 1.3–5 μm and temperatures between 40 °C and 200 °C. The calculation of the appropriate Sellmeier coefficients is based on the wavelengths of the signal and idler radiation measured for quasi-phase-matched optical parametric generators excited by 10-ns-long, 1064-nm pulses of a Q-switched Nd:YVO4 laser.
TL;DR: In this article, the authors report on the generation of high power superbroad spectrum bunched noise-like pulses from a passively mode-locked erbium-doped fiber ring laser without using the stretched-pulse technique.
Abstract: We report on the generation of high power superbroad spectrum bunched noise-like pulses from a passively mode-locked erbium-doped fiber ring laser without using the stretched-pulse technique. The maximum 3-dB spectral bandwidth of the noise-like pulses is about 93 nm with an energy of about 15 nJ. We further show numerically that the superbroad spectrum of the pulses is caused by the transform-limited feature of the pulses together with the Raman self-frequency shift effect.
TL;DR: In this paper, the optical forces acting on a nanoparticle placed into a single and two counter-propagating non-paraxial Bessel beams created behind the axicon are analyzed.
Abstract: We present the theoretical and experimental study of nondiffracting Bessel beams as a device for optical manipulation and confinement of nanoparticles. We express analytically the optical forces acting on a nanoparticle placed into a single and two counter-propagating non-paraxial nondiffracting beams created behind the axicon. Nanoparticle behavior in these configurations is predicted by computer simulations. Finally we demonstrate experimentally how standing waves created from two independent counter-propagating nondiffraction beams confines polystyrene beads of radii 100 nm, and organizes them into a one-dimensional chain 1 mm long. Phase shift in one beam causes the motion of the whole structure of the standing wave together with any confined objects over its extent.
TL;DR: In this article, the fluorescence spectrum of ethanol molecules induced by femtosecond laser pulses has been recorded as the fingerprint of the molecules, and it was demonstrated that if this is combined with a LIDAR-based technique, fluorescence from pollutants in the atmosphere could be detected over a long distance.
Abstract: The fluorescence spectrum of ethanol molecules induced by femtosecond laser pulses has been recorded as the fingerprint of the molecules. It was demonstrated that, if this is combined with a LIDAR technique, the fluorescence from pollutants in the atmosphere could be detected over a long distance.
TL;DR: In this paper, the plasmonic structure of a metallic nanoparticle near a metallic thin film was investigated, and it was shown that in the thin film limit, a virtual plasm resonance composed of delocalized thin film plasmons is induced.
Abstract: We investigate the plasmonic structure of a metallic nanoparticle near a metallic thin film. We show that in the thin film limit, a virtual plasmon resonance composed of delocalized thin film plasmons is induced. We investigate how the physical properties of the virtual state depend on polarization, film thickness and nanoparticle-film separation. We show that the electromagnetic field enhancements associated with the virtual plasmon resonance are large, suggesting applications of metallic nanoparticle/thin film systems as substrates for surface enhanced spectroscopies and surface enhanced scanning probe microscopies.
TL;DR: In this article, the results of a field campaign in which a portable Fourier transform infrared (FTIR) spectrometer was used to measure gas emissions from Yasur volcano, Vanuatu, in January 2005 were reported.
Abstract: We report here the results of a field campaign in which a portable Fourier transform infrared (FTIR) spectrometer was used to measure gas emissions from Yasur volcano, Vanuatu, in January 2005. By collecting FTIR spectra at a high rate (about 1 Hz), we were able to observe a marked difference in the proportions of SO2 and HCl in emissions released during Strombolian eruptions (SO2/HCl molar ratio up to ∼30 or more) compared with the intervening passive emissions discharged from the magmatic vent (SO2/HCl ∼2). This contrast can be explained by sourcing gas at different depths with respect to levels at which SO2 and HCl exsolve from the melt: deeper volatile exsolution supplies relatively SO2-rich gas responsible for the ephemeral explosions at the top of the conduit; while degassing of shallow magma, depleted in sulfur but rich in chlorine, contributes to the passive emission.
TL;DR: In this paper, high-order inertial phase shifts are calculated for time-domain atom interferometers and closed-form analytic expressions for these shifts in accelerometer, gyroscope, optical clock and photon recoil measurement configurations.
Abstract: High-order inertial phase shifts are calculated for time-domain atom interferometers. We obtain closed-form analytic expressions for these shifts in accelerometer, gyroscope, optical clock and photon recoil measurement configurations. Our analysis includes Coriolis, centrifugal, gravitational, and gravity gradient-induced forces. We identify new shifts which arise at levels relevant to current and planned experiments.
TL;DR: In this article, the optical near fields of the bowtie aperture and comparable square and rectangular apertures made in gold and chromium thin films are measured and compared under linear polarizations in two orthogonal directions.
Abstract: In this paper, the enhanced optical transmission through a special type of aperture of a bowtie shape is investigated through near-field imaging and finite-difference numerical analysis. Under linear polarizations in two orthogonal directions, the optical near fields of the bowtie aperture and comparable square and rectangular apertures made in gold and chromium thin films are measured and compared. The bowtie aperture is able to provide a nanometer-sized optical spot when the incident light is polarized across the bowtie gap and delivers a considerable amount of light. Localized surface plasmons are clearly observed in the near-field images for both bowtie and rectangular apertures in gold, but invisible in chromium. Finite-difference time-domain calculations reveal that, depending on the polarization of the incident light, the unique optical properties of the bowtie aperture are a result of either the optical waveguide and the coupled surface plasmon polariton modes existing in the bowtie gap or the coupling between the two open arms of the bowtie aperture.
TL;DR: In this article, an optical feedback cavity-enhanced absorption spectroscopy was used for real-time quantitative measurement of tropospheric methane traces from an airplane using a compact, low cost instrument based on a telecommunication-type diode laser operating close to room temperature.
Abstract: We report on the application of the new technique of optical–feedback cavity–enhanced absorption spectroscopy to the real–time quantitative measurement of tropospheric methane traces from an airplane using a compact, low cost instrument based on a telecommunication–type diode laser operating close to room temperature. Methane concentration is obtained by fitting the absorption line centered at 1658.96 nm (6026.23 cm-1) which belongs to the first overtone transition of the CH stretch vibration. The measurement rate is about 30 Hz, but the response time is limited to about 0.3 s by the gas flow in the measurement cell. The instrument provides the absolute ambient methane concentration accurate to ±1% (±20 ppb) without need for a periodic calibration. This is demonstrated by a hands–off comparison with a self–calibrating chromatographic setup during 10 days. The observed measurement stability can be extrapolated to much longer time periods. With respect to the short–term performance (minutes) fast concentration changes at the level of 1 ppb can be detected, and we believe this performance can be extended to the long term. Finally, a laboratory comparison with a lead–salt mid–infrared diode laser multipass spectrometer (operating close to 3028 cm-1 at liquid nitrogen temperature) demonstrates a similar performance.
TL;DR: In this article, the architecture and operation of a trace hydrogen cyanide (HCN) gas sensor based on quartz-enhanced photoacoustic spectroscopy and using a λ=1.53 μm telecommunication diode laser are described.
Abstract: The architecture and operation of a trace hydrogen cyanide (HCN) gas sensor based on quartz-enhanced photoacoustic spectroscopy and using a λ=1.53 μm telecommunication diode laser are described. The influence of humidity content in the analyzed gas on the sensor performance is investigated. A kinetic model describing the vibrational to translational (V–T) energy transfer following the laser excitation of a HCN molecule is developed. Based on this model and the experimental data, the V–T relaxation time of HCN was found to be (1.91±0.07)10-3 s Torr in collisions with N2 molecules and (2.1±0.2)10-6 s Torr in collisions with H2O molecules. The noise-equivalent concentration of HCN in air at normal indoor conditions was determined to be at the 155-ppbv level with a 1-s sensor time constant.
TL;DR: In this article, the authors investigate the generation mechanisms for ultra-wide spectra in nonlinear optical fibers and show that Soliton fission and modulation instability represent fundamental mechanisms for the generation process, and the interplay between these two effects leads to various characteristics of the resulting spectra, which are modified by the relative impact of modulation instability.
Abstract: We investigate the generation mechanisms for ultra-wide spectra in nonlinear optical fibers. Soliton fission and modulation instability represent fundamental mechanisms for the generation process. The primary origin of the spectral broadening changes with the pump-pulse duration. Soliton fission dominates for low input power and short pulses. Its efficiency for supercontinuum generation and especially the extension to the blue side can be increased by proper design of the dispersion profile. The modulation instability has a strong impact for high input powers and greatly enhances the generation process, but leads to a degradation of the coherence properties. Also for short pulses with durations of 60 fs the modulation instability is present and can hardly be suppressed. The interplay between these two effects leads to various characteristics of the resulting spectra, which are modified by the relative impact of the modulation instability.
TL;DR: In this article, the theory of chirped-pulse oscillators operating in the positive dispersion regime is presented, and it is found that the chirp pulses can be described analytically as solitary pulse solutions of the nonlinear cubic-quintic complex Ginzburg-Landau equation.
Abstract: Theory of chirped-pulse oscillators operating in the positive dispersion regime is presented. It is found that the chirped pulses can be described analytically as solitary pulse solutions of the nonlinear cubic-quintic complex Ginzburg–Landau equation. Due to the closed form of the solution, basic characteristics of the regime under consideration are easily traceable. Numerical simulations validate the analytical technique and the chirped-pulse stability. Experiments with 10 MHz Ti:Sa oscillator providing up to 150 nJ chirped pulses, which are compressible down to 30 fs, are in agreement with the theory.
TL;DR: The linear propagation properties of laser written hexagonal waveguide arrays in fused silica have been studied for the first time in this article, where the authors determine the behavior of the coupling constants for different waveguide separations and for different wavelengths.
Abstract: The linear propagation properties of laser written hexagonal waveguide arrays in fused silica have been studied for the first time. We determine the behavior of the coupling constants for different waveguide separations and for different wavelengths. The high accuracy of these arrays demonstrates the ability to fabricate complex and elongated devices based on evanescently coupled waveguide structures using the fs direct writing approach.