Showing papers on "Doppler broadening published in 2013"

Highly Nonlinear Fibers

Abstract: This chapter deals with the properties of highly non-linear fibers. It reviews the techniques used to measure the non-linear parameter ( γ ). The four kinds of fibers that are developed to enhance the non-linear effects are also reviewed. The three major non-linear effects occurring inside the optical fibers—the self-phase modulation (SPM), the cross-phase modulation (XPM), and the four-wave mixing (FWM), are governed by a single non-linear parameter γ. This parameter is fixed for each glass material. The chapter elaborates that the use of the non-silica glasses provides an alternative approach to designing non-linear fibers. The SPM technique uses the broadening of the pulse spectrum. It measures the maximum value of the non-linear phase shift. In place of deducing the SPM-induced phase shift from spectral broadening, a related technique deduces it from the spectral changes occurring when light from two lasers operating at slightly different wavelengths is transmitted through the fiber. Measurements in such an approach can be performed with CW lasers. The chapter summarizes that the combination of unusual dispersive properties and a high value of γ leads to a variety of novel non-linear effects.

Spectral broadening in Brillouin imaging

Abstract: Brillouin microscopy is an emerging imaging modality that provides fundamental information about mechanical properties of media in a non-contact manner. To date, low numerical aperture (NA) optics have been used, due to noticeable angular broadening of the Brillouin spectrum at higher NAs. In this work, we investigate theoretically and experimentally the dependence of spectral broadening effects in Brillouin imaging on system NA, for both 90° and 180° scattering geometries. Lineshape deformations and broadening are found to be minimised in a backscattering geometry, hence paving the way for high resolution in-vivo mechanical imaging.

Determination of the Boltzmann constant by means of precision measurements of H2(18)O line shapes at 1.39 μm.

Abstract: We report on a new implementation of Doppler broadening thermometry based on precision absorption spectroscopy by means of a pair of offset-frequency locked extended-cavity diode lasers at 1.39 μm. The method consists in the highly accurate observation of the shape of the 4(4,1)→4(4,0) line of the H2(18)O ν1+ν3 band, in a water vapor sample at thermodynamic equilibrium. A sophisticated and extremely refined spectral analysis procedure is adopted for the retrieval of the Doppler width as a function of the gas pressure, taking into account the Dicke narrowing effect, the speed dependence of relaxation rates, and the physical correlation between velocity-changing and dephasing collisions. A spectroscopic determination of the Boltzmann constant with a combined (type A and type B) uncertainty of 24 parts over 10(6) is reported. This is the best result obtained so far by means of an optical method. Our determination is in agreement with the recommended CODATA value.

Spectral bandwidth reduction of Thomson scattered light by pulse chirping

Abstract: Based on single particle tracking in the framework of classical Thomson scattering with incoherent superposition, we developed a relativistic, three-dimensional numerical model that calculates and quantifies the characteristics of emitted radiation when a relativistic electron beam interacts with an intense laser pulse. This model has been benchmarked against analytical expressions, based on the plane wave approximation to the laser field, derived by Esarey et al. [Phys. Rev. E 48, 3003 (1993)]. For laser pulses of sufficient duration, we find that the scattered radiation spectrum is broadened due to interferences arising from the pulsed nature of the laser. We find that by appropriately chirping the scattering laser pulse, spectral broadening can be minimized, and the peak on-axis brightness of the emitted radiation is increased by a factor of approximately 5.

High-resolution molybdenum K-edge X-ray absorption spectroscopy analyzed with time-dependent density functional theory

Abstract: X-ray absorption spectroscopy (XAS) is a widely used experimental technique capable of selectively probing the local structure around an absorbing atomic species in molecules and materials. When applied to heavy elements, however, the quantitative interpretation can be challenging due to the intrinsic spectral broadening arising from the decrease in the core–hole lifetime. In this work we have used high-energy resolution fluorescence detected XAS (HERFD-XAS) to investigate a series of molybdenum complexes. The sharper spectral features obtained by HERFD-XAS measurements enable a clear assignment of the features present in the pre-edge region. Time-dependent density functional theory (TDDFT) has been previously shown to predict K-pre-edge XAS spectra of first row transition metal compounds with a reasonable degree of accuracy. Here we extend this approach to molybdenum K-edge HERFD-XAS and present the necessary calibration. Modern pure and hybrid functionals are utilized and relativistic effects are accounted for using either the Zeroth Order Regular Approximation (ZORA) or the second order Douglas–Kroll–Hess (DKH2) scalar relativistic approximations. We have found that both the predicted energies and intensities are in excellent agreement with experiment, independent of the functional used. The model chosen to account for relativistic effects also has little impact on the calculated spectra. This study provides an important calibration set for future applications of molybdenum HERFD-XAS to complex catalytic systems.

Velocity and Temperature Measurement in Supersonic Free Jets Using Spectrally Resolved Rayleigh Scattering

Abstract: The flow fields of unheated, supersonic free jets from convergent and convergent-divergent nozzles operating at M = 0.99, 1.4, and 1.6 were measured using spectrally resolved Rayleigh scattering technique. The axial component of velocity and temperature data as well as density data obtained from a previous experiment are presented in a systematic way with the goal of producing a database useful for validating computational fluid dynamics codes. The Rayleigh scattering process from air molecules provides a fundamental means of measuring flow properties in a non-intrusive, particle free manner. In the spectrally resolved application, laser light scattered by the air molecules is collected and analyzed using a Fabry-Perot interferometer (FPI). The difference between the incident laser frequency and the peak of the Rayleigh spectrum provides a measure of gas velocity. The temperature is measured from the spectral broadening caused by the random thermal motion and density is measured from the total light intensity. The present point measurement technique uses a CW laser, a scanning FPI and photon counting electronics. The 1 mm long probe volume is moved from point to point to survey the flow fields. Additional arrangements were made to remove particles from the main as well as the entrained flow and to isolate FPI from the high sound and vibration levels produced by the supersonic jets. In general, velocity is measured within +/- 10 m/s accuracy and temperature within +/- 10 K accuracy.

Comb-linked, cavity ring-down spectroscopy for measurements of molecular transition frequencies at the kHz-level

Abstract: We present a low uncertainty measurement technique for determining molecular transition frequencies. This approach is complementary to sub-Doppler saturation spectroscopies and is expected to enable new frequency measurements for a wide variety of molecular species with uncertainties at the kHz-level. The technique involves measurements of Doppler broadened lines using cavity ring-down spectroscopy whereby the probe laser is actively locked to the ring-down cavity and the spectrum frequencies are linked directly to an optical frequency comb that is referenced to an atomic frequency standard. As a demonstration we have measured the transition frequency of the (30012) ← (00001) P14e line of CO2 near 1.57 μm with a combined standard uncertainty of ∼9 kHz. This technique exhibits exceptional promise for measurements of transition frequencies and pressure shifting parameters of many weak absorbers, and indicates the potential for substantially improved measurements when compared to those obtained with conventional spectroscopic methods.

Spectral broadening in anatase titanium dioxide waveguides at telecommunication and near-visible wavelengths.

Abstract: We observe spectral broadening of femtosecond pulses in single-mode anatase-titanium dioxide (TiO(2)) waveguides at telecommunication and near-visible wavelengths (1565 and 794 nm). By fitting our data to nonlinear pulse propagation simulations, we quantify nonlinear optical parameters around 1565 nm. Our fitting yields a nonlinear refractive index of 0.16 × 10(-18) m(2)/W, no two-photon absorption, and stimulated Raman scattering from the 144 cm(-1) Raman line of anatase with a gain coefficient of 6.6 × 10(-12) m/W. Additionally, we report on asymmetric spectral broadening around 794 nm. The wide wavelength applicability and negligible two-photon absorption of TiO(2) make it a promising material for integrated photonics.

Recent research work on the J-TEXT tokamak

Abstract: An overview of the recent research work on the J-TEXT tokamak over the last two years is presented. A series of experiments and simulations of the interaction between resonant magnetic perturbations (RMPs) and plasma were carried out on the J-TEXT tokamak. The results show that the m/n = 2/1 (m and n are the poloidal and toroidal mode numbers, respectively) mode locking is obtained with sufficiently large RMPs. And suppression of the m/n = 2/1 tearing mode by moderate magnetic perturbation amplitude is also observed. With experimental parameters as input, both mode locking and mode suppression by RMPs are simulated by nonlinear numerical modelling based on reduced magnetohydrodynamic equations. The simulations are in good agreement with the experimental observations. Density modulation using gas puffing is carried out on J-TEXT to evaluate the particle transport parameters in a typical J-TEXT discharge, including diffusion coefficient and convective velocity. Inverse sawtooth-like activity caused by neon gas injection is observed. The inverse sawtooth-like activity occurs only when the amount of neon impurity exceeds a threshold. Nevertheless, other impurities such as helium and argon cannot trigger such events. With the aid of a soft x-ray detector array, the runaway electron beam following disruptions is visible directly. A high-resolution far infrared polarimeter/interferometer, based on a three-wave technique, was developed and it observes the perturbations associated with sawtooth and tearing mode activities; the first result of the current density profile reconstruction is provided. An x-ray imaging crystal spectrometer is designed to receive the Kα line of Ar XVII and its satellites. The electron temperature obtained from line ratios of the W line to its satellites is 750 eV, and the ion temperature deduced from the Doppler broadening of the W line is 330 eV.

Density of atoms in Ar*(3p54s) states and gas temperatures in an argon surfatron plasma measured by tunable laser spectroscopy

Abstract: This study presents the absolute argon 1 s (in Paschens’s notation) densities and the gas temperature, Tg, obtained in a surfatron plasma in the pressure range 0.65 10 mbar, for which the pressure broadening can no more be neglected. Tg is in the range of 480-750 K, increasing with pressure and decreasing with the distance from the microwave launcher. Taking into account the line of sight effects of the absorption measurements, a good agreement is found with our previous measurements by Rayleigh scattering of Tg at the tube center. In the studied pressure range, the Ar(4 s) atom densities are in the order of 1016−1018 m−3, inc...

Finding the peak velocity in a flow from its doppler spectrum

Abstract: The signal backscattered by blood cells crossing a sample volume produces a Doppler power spectrum determined by the scatterers' velocity distribution. Because of intrinsic spectral broadening, the peak Doppler frequency observed does not correspond to the peak velocity in the flow. Several methods have been proposed for estimating the maximum velocity component-an important clinical parameter-but these methods are approximate, based on heuristic thresholds that can be inaccurate and strongly affected by noise. Reported here is a method of modeling the Doppler power spectrum of a flow, and from that model, determining what Doppler frequency on the descending slope of the power spectrum corresponds to the peak velocity in the insonated flow. It is shown that, for a fully insonated flow with a parabolic velocity distribution, the peak velocity corresponds to the Doppler frequency at the half-power point on that slope. The method is demonstrated to be robust with regard to the effects of noise and valid for a wide range of acquisition parameters. Experimental maximum velocity measurements on steady flows with rates between 100 and 300 mL/min (peak velocity range 6.6 cm/s to 19.9 cm/s) show a mean bias error that is smaller than 1%.

Mode excitation and supercontinuum generation in a few-mode suspended-core fiber.

Abstract: We have studied the excitation of higher-order modes and their role in supercontinuum generation in a three-hole silica suspended-core fiber, both experimentally and numerically. We find that pump coupling optimized to highest transmission can yield substantial excitation of higher order modes. With up to about 40% of the pump power coupled to higher order modes, we have studied supercontinuum generation in this fiber. In agreement with experiments, simulation results based on the multimode generalized nonlinear Schrodinger equation confirm that the spectral width is determined by spectral broadening in the fundamental mode, whereas the numerical analysis reveals that intermodal nonlinear interactions are strongly suppressed.

Measurement of 87 Rb Rydberg-state hyperfine splitting in a room-temperature vapor cell

Abstract: We present direct measurements of the hyperfine splitting of Rydberg states in 87Rb using electromagnetically induced transparency (EIT) spectroscopy in a room-temperature vapor cell. With this method, and in spite of Doppler broadening, linewidths of 3.7 MHz FWHM, i.e., significantly below the intermediate-state natural linewidth, are reached. This allows resolving hyperfine splittings for Rydberg s states with n=20,...,24. With this method we are able to determine Rydberg state hyperfine splittings with an accuracy of approximately 100 kHz. Ultimately, our method allows accuracies of order 5 kHz to be reached. Furthermore, we present a direct measurement of hyperfine-resolved Rydberg-state Stark shifts. These results will be of great value for future experiments relying on excellent knowledge of Rydberg-state energies and polarizabilities.

Supercontinuum generation in water doped with gold nanoparticles

Abstract: We report enhanced supercontinuum generation in water doped with gold nanoparticles of different shapes under modest ultrafast (35 fs) laser excitation. Reasonably, flat supercontinuum spectra covering ∼1.45–2 eV (855–620 nm) are observed with as much as ∼161 meV (63 nm) increase in the visible extent compared to pure water for dopants whose surface plasmon resonance (SPR) overlaps the excitation laser spectrum. We use a phenomenological self-phase modulation model to rationalize our results, taking cognizance of plasma contributions to the third-order susceptibility of water along with SPR-induced field enhancement. Such large spectral broadening may be useful for several applications involving imaging or microscopy with modest incident intensities.

Spectrally tailored mid-infrared super-continuum generation in a buried waveguide spanning 1750 nm to 5000 nm for atmospheric transmission

Abstract: We show how nonlinear spectral broadening in a buried chalcogenide mid-infrared waveguide can be used to reshape the spectrum of a femtosecond pulse train at 4260 nm in order to reduce the effects of atmospheric absorption due to carbon dioxide. The nonlinear spectral broadening results in the source with −20 dB spectral width spanning over 3500 nm, from 1700 nm to 5200 nm. This represents a potential route to tailored sources for long-range mid-infrared applications.

Statistical properties of ultrafast supercontinuum generated by femtosecond Gaussian and Bessel beams: a comparative study

Abstract: We present a comparative experimental study of spectral broadening and supercontinuum (SC) generation in 3-mm-thick sapphire crystal using 800 nm, 130 fs pulses in low-numeric-aperture focused Gaussian and axicon-generated Bessel beam geometry. Despite the markedly higher input energy used in the case of the Bessel beam, the dynamics of spectral broadening appears to be very similar in both cases, eventually producing a flat SC spanning across the visible and near-infrared spectral range with low shot-to-shot fluctuations (standard deviation ≤1%) of the spectral intensity. The statistical analysis performed at different stages of the spectral broadening reveals that shot-to-shot fluctuations of the spectral intensity are associated with four-wave-mixing-induced spectral correlations.

A revised uncertainty budget for measuring the Boltzmann constant using the Doppler broadening technique on ammonia

Abstract: We report on our on-going effort to measure the Boltzmann constant, kB, using the Doppler broadening technique. The main systematic effects affecting the measurement are discussed. A revised error budget is presented in which the global uncertainty on systematic effects is reduced to 2.3 ppm. This corresponds to a reduction of more than one order of magnitude compared with our previous Boltzmann constant measurement. Means to reach a determination of kB at the part per million accuracy level are outlined.

Pulse Compression of Ultrashort UV Pulses by Self-Phase Modulation in Bulk Material

Abstract: The bandwidth of ultrafast pulses in the UV is limited by the finite acceptance bandwidth of the nonlinear crystals used for their generation. For fundamental laser pulses it is well established that spectral broadening can be used to overcome intrinsic bandwidth limits. We show that self-phase modulation of UV pulses in bulk materials leads to large spectral broadening and allows for a significant reduction of the pulse duration. We find that for pulse energies in the range of a few μJ, a thin crystal is favorable due to the strong dispersion in the UV and the limitations set by self-focusing. In contrast to spectral broadening in gaseous media, the self-focus has to lie outside the crystal to avoid beam break up. We focus UV pulses into a 1 mm thick CaF2 crystal. For moderately short input pulses, a shortening factor up to 2.4 is achieved: the 120 fs long third harmonic output of a Ti:sapphire amplifier is compressed down to 50 fs FWHM. For a central wavelength of 315 nm, we generate pulses as short as 14.9 fs after compression with an UV pulse shaper. In both cases the resulting beam shape is close to Gaussian and fully usable for spectroscopic experiments. We use the pulses in a collinear 2D-UV experiment and clearly resolve vibronic off-diagonal peaks of the S2 1B2u vibronic progression of pyrene.

Modification of the MOOG Spectral Synthesis Codes to Account for Zeeman Broadening of Spectral Lines

Abstract: In an attempt to widen access to the study of magnetic fields in stellar astronomy, I present MOOGStokes, a version of the MOOG one-dimensional local thermodynamic equilibrium radiative transfer code, overhauled to incorporate a Stokes vector treatment of polarized radiation through a magnetic medium. MOOGStokes is a suite of three complementary programs, which together can synthesize the disk-averaged emergent spectrum of a star with a magnetic field. The first element (a pre-processing script called CounterPoint) calculates for a given magnetic field strength, wavelength shifts, and polarizations for the components of Zeeman-sensitive lines. The second element (a MOOG driver called SynStokes derived from the existing MOOG driver Synth) uses the list of Zeeman-shifted absorption lines together with the existing machinery of MOOG to synthesize the emergent spectrum at numerous locations across the stellar disk, accounting for stellar and magnetic field geometry. The third and final element (a post-processing script called DiskoBall) calculates the disk-averaged spectrum by weighting the individual emergent spectra by limb darkening and projected area, and applying the effects of Doppler broadening. All together, the MOOGStokes package allows users to synthesize emergent spectra of stars with magnetic fields in a familiar computational framework. MOOGStokes produces disk-averaged spectra for all Stokes vectors ( I, Q, U, V ), normalized by the continuum. MOOGStokes agrees well with the predictions of INVERS10 a polarized radiative transfer code with a long history of use in the study of stellar magnetic fields. In the non-magnetic limit, MOOGStokes also agrees with the predictions of the scalar version of MOOG.

A Study of Sea Surface Range-Resolved Doppler Spectra Using Numerically Simulated Low-Grazing-Angle Backscatter Data

Abstract: A numerical study of sea surface range-resolved Doppler spectra using low-grazing-angle backscatter measurements is described. Backscattered fields as a function of frequency are computed using the method of moments (MOM) for a single realization of a 1-D oceanlike surface profile as the realization evolves in time. Transformation into the range-Doppler domain enables examination of properties of the resulting Doppler spectra (for both HH and VV polarizations) and their relationship to properties of the surface profile. In general, a strong correspondence between the “long-wave” orbital velocity of the surface projected along the radar line of sight and the Doppler centroid frequency is observed for visible portions of the surface, as well as some evidence of relationships between the “width” of the Doppler spectrum and variations of the projected velocity in time at a given range point. Evidence of similar relationships even in some shadowed portions of the surface is also provided. Doppler spectra from HH and VV polarizations are qualitatively similar, despite differences in total power levels, although the portion of shadowed surface points from which Doppler information is available is somewhat larger in VV polarization. A further examination is conducted using backscattered fields computed with a single-scattering method, which neglects shadowing and any multiple-scattering effects. The remarkable similarities observed between MOM and single-scattered Doppler spectra even in some shadowed portions of the surface suggest that non-line-of-sight propagation effects do not significantly influence Doppler properties in such regions.

Turbulence driven by structure formation in the circumgalactic medium

Abstract: The injection of turbulence in the circum-galactic medium at redshift z = 2 is investigated using the mesh-based hydrodynamic code enzo and a subgrid-scale (SGS) model for unresolved turbulence. Radiative cooling and heating by a uniform Ultraviolet (UV) background are included in our runs and compared with the effect of turbulence modelling. Mechanisms of gas exchange between galaxies and the surrounding medium, as well as metal enrichment, are not taken into account, and turbulence is here driven solely by structure formation (mergers and shocks). We find that turbulence, both at resolved and SGS scales, impacts mostly the warm-hot intergalactic medium (WHIM), with temperature between 10 5 and 10 7 K, mainly located around collapsed and shock heated structures, and in filaments. Typical values of the ratio of turbulent to thermal pressure is 0.1 in the WHIM, corresponding to a volume-weighted average of the SGS turbulent to thermal Doppler broadening bt/btherm = 0.26, on length scales below the grid resolution of 25 kpc h 1 . In the diffuse intergalactic medium (IGM), defined in a range of baryon overdensity δ between 1 and 50, the importance of turbulence is smaller, but grows as a function of gas density, and the Doppler broadening ratio is fitted by the function bt/btherm = 0.023 × δ 0.58 .

Pulsed Mid-infrared Radiation from Spectral Broadening in Laser Wakefield Simulations

Abstract: Spectral red-shifting of high power laser pulses propagating through underdense plasma can be a source of ultrashort mid-infrared (MIR) radiation. During propagation, a high power laser pulse drives large amplitude plasma waves, depleting the pulse energy. At the same time, the large amplitude plasma wave provides a dynamic dielectric response that leads to spectral shifting. The loss of laser pulse energy and the approximate conservation of laser pulse action imply that spectral red-shifts accompany the depletion. In this paper, we investigate, through simulation, the parametric dependence of MIR generation on pulse energy, initial pulse duration, and plasma density.

Broad Iron Lines in Neutrons Stars: Dynamical Broadening or Wind Scattering?

Abstract: Broad iron emission lines are observed in many accreting systems from black holes in active galactic nuclei and X-ray binaries to neutron star low-mass X-ray binaries. The origin of the line broadening is often interpreted as due to dynamical broadening and relativistic effects. However, alternative interpretations have been proposed, included broadening due to Compton scattering in a wind or accretion disk atmosphere. Here we explore the observational signatures expected from broadening in a wind, in particular that the iron line width should increase with an increase in the column density of the absorber (due to an increase in the number of scatterings). We study the data from three neutron star low-mass X-ray binaries where both a broad iron emission line and absorption lines are seen simultaneously, and show that there is no significant correlation between line width and column density. This favors an inner disk origin for the line broadening rather than scattering in a wind.

Fluorescence origin and spectral broadening mechanism in atomically precise Au8 nanoclusters.

Abstract: Super-small Au8 nanoclusters have shown great potential to be used in bioimaging, biosensors and catalysis. Understanding the fluorescence origin and the spectral broadening mechanism is of critical importance for the applications. Here we investigate the fluorescence origin and the spectral broadening mechanism using steady state and ultrafast time-resolved spectroscopy. For the first time we clearly elucidate the broad fluorescence of Au8 nanoclusters consisting of an intrinsic band from the Au8 core and an extrinsic band from the surface fluorophores. The emission energy of the intrinsic band is in accord with the rule of E/N1/3 and the spectral broadening originates from ultrafast dephasing due to effective electron–electron scattering. The extrinsic band has a much larger bandwidth due to massive surface fluorophores; it is the dominant mechanism for spectral broadening in Au8. In contrast to the jellium model predictions, the overall fluorescence exhibits excitation wavelength dependence.

Spectroscopy of the three-photon laser excitation of cold Rubidium Rydberg atoms in a magneto-optical trap

Abstract: The spectra of the three-photon laser excitation 5S 1/2 → 5P 3/2 → 6S 1/2 nP of cold Rb Rydberg atoms in an operating magneto-optical trap based on continuous single-frequency lasers at each stage are studied. These spectra contain two partly overlapping peaks of different amplitudes, which correspond to coherent three-photon excitation and incoherent three-step excitation due to the presence of two different ways of excitation through the dressed states of intermediate levels. A four-level theoretical model based on optical Bloch equations is developed to analyze these spectra. Good agreement between the experimental and calculated data is achieved by introducing additional decay of optical coherence induced by a finite laser line width and other broadening sources (stray electromagnetic fields, residual Doppler broadening, interatomic interactions) into the model.

Experimental Demonstration of Quasi-Resonant Absorption in Silicon Thin Films for Enhanced Solar Light Trapping

Abstract: We experimentally demonstrate that the addition of partial lattice disorder to a thin-film micro-crystalline silicon photonic crystal results in the controlled spectral broadening of its absorption peaks to form quasi resonances; increasing light trapping over a wide bandwidth while also reducing sensitivity to the angle of incident radiation. Accurate computational simulations are used to design the active-layer photonic crystal so as to maximize the number of its absorption resonances over the broadband interval where micro-crystalline silicon is weakly absorbing before lattice disorder augmented with fabrication-induced imperfections are applied to further boost performance. Such a design strategy may find practical use for increasing the efficiency of thin-film silicon photovoltaics.

The ultimate limit to the emission linewidth of single nanocrystals.

Abstract: Measurements of the emission linewidth of single nanocrystals are usually limited by spectral diffusion. At cryogenic temperatures, the origin of this instability was revealed to be photo-induced, suggesting that the spectral peak position may be stable in the limit of vanishing optical excitation. Here we test this stability using resonant photoluminescence excitation and find there is persistent spectral broadening, which ultimately limits the emission linewidth in these materials. The spectral broadening is shown to be consistent with spontaneous fluctuations of the local electrostatic field within the disordered environment surrounding the nanocrystal.

Measurement of nonlinear refractive index coefficient of inert gases with hollow-core fiber

Abstract: A simple method of determining the nonlinear refractive index coefficient n 2 of inert gases is demonstrated. It is based on the accumulation of optical-Kerr-induced spectral broadening effect in gas-filled hollow-core fibers. By using this method, the values of n 2 of argon and neon at 800 nm and argon at 1.8 μm are determined.