skip to main content

Title: Pressure scaling of the collisional broadening parameters of Kr 4 p 6 S 01→→5 p [3/2] 2 transition

Pressure scaling of collisional broadening parameters of krypton (absorber)4p6S01→<#comment/>→<#comment/>5p[3/2]2transition centered at 107.3 nm in the presence of nitrogenN2(perturber) is investigated. The absorption spectrum in the vicinity of the transition is obtained from the two-photon excitation scan of krypton in the presence of the perturber at different prescribed pressures varying from a few torrs to 10 atm. The absorption spectra reveal noticeable asymmetry at atmospheric pressure, and the asymmetry becomes increasingly pronounced with pressure; however, the absorption spectra at sub-atmospheric pressures tested are symmetric. The absorption spectra are fitted with synthetic asymmetric Voigt profiles across all pressures, wherein the asymmetry parameter is varied to capture the asymmetry at different pressures. The collisional shift (δ<#comment/>C), the symmetric equivalent collisional full width at half maximum (wC,0), and the asymmetry parameter (a) are determined from the synthetic fits at various pressures. All the parameters are observed to vary linearly with pressure over the entire range of the pressure values tested. The mechanisms that cause the asymmetry in the absorption spectra are also discussed.

; ;
Publication Date:
Journal Name:
Applied Optics
Page Range or eLocation-ID:
Article No. 7760
1559-128X; APOPAI
Optical Society of America
Sponsoring Org:
National Science Foundation
More Like this
  1. Temperature scaling of collisional broadening parameters for krypton (absorber)4p6S01→<#comment/>5p[3/2]2electronic transition centered at 107.3 nm in the presence of major combustion species (perturber) is investigated. The absorption spectrum in the vicinity of the transition is obtained from the fluorescence due to the two-photon excitation scan of krypton. Krypton was added in small amounts to major combustion species such asCH4,CO2,N2, and air, which then heated to elevated temperatures when flowed through a set of heated coils. In a separate experimental campaign, laminar premixed flat flame product mixtures of methane combustion were employed to extend the investigations to higher temperature ranges relevant to combustion. Collisional full width half maximum (FWHM) (wC) and shift (δ<#comment/>C) were computed from the absorption spectrum by synthetically fitting Voigt profiles to the excitation scans, and their corresponding temperature scaling was determined by fitting power-law temperature dependencies to thewCandδ<#comment/>Cdata for each perturber species. The temperature exponents ofwCandδ<#comment/>Cfor all considered combustion species (perturbers) were−<#comment/>0.73and−<#comment/>0.6, respectively. Whereas the temperature exponents ofwCare closer tomore »the value (−<#comment/>0.7) predicted by the dispersive interaction collision theory, the corresponding exponents ofδ<#comment/>Care in between the dispersive interaction theory and the kinetic theory of hard-sphere collisions. Comparison with existing literature on broadening parameters of NO, OH, and CO laser-induced fluorescence spectra reveal interesting contributions from non-dispersive interactions on the temperature exponent.

    « less
  2. The optical phaseϕ<#comment/>is a key quantity in the physics of light propagating through a turbulent medium. In certain respects, however, the statistics of the phasefactor,ψ<#comment/>=exp⁡<#comment/>(iϕ<#comment/>), are more relevant than the statistics of the phase itself. Here, we present a theoretical analysis of the 2D phase-factor spectrumFψ<#comment/>(κ<#comment/>)of a random phase screen. We apply the theory to four types of phase screens, each characterized by a power-law phase structure function,Dϕ<#comment/>(r)=(r/rc)γ<#comment/>(wherercis the phase coherence length defined byDϕ<#comment/>(rc)=1rad2), and a probability density functionpα<#comment/>(α<#comment/>)of the phase increments for a given spatial lag. We analyze phase screens with turbulent (γ<#comment/>=5/3) and quadratic (γ<#comment/>=2) phase structure functions and with normally distributed (i.e., Gaussian) versus Laplacian phase increments. We find that there is a pronounced bump in each of the four phase-factor spectraFψ<#comment/>(κ<#comment/>). The precise location and shape of the bump are different for the four phase-screen types, but in each case it occurs atκ<#comment/>∼<#comment/>1/rc. The bump is unrelated to the well-knownmore »“Hill bump” and is not caused by diffraction effects. It is solely a characteristic of the refractive-index statistics represented by the respective phase screen. We show that the second-orderψ<#comment/>statistics (covariance function, structure function, and spectrum) characterize a random phase screen more completely than the second-orderϕ<#comment/>counterparts.

    « less
  3. A study of short-gated 10 nanosecond (ns), 100 picosecond (ps), and 100 femtosecond (fs) laser induced breakdown spectroscopy (LIBS) was conducted for fuel-to-air ratio (FAR) measurements in an atmospheric Hencken flame. The intent of the work is to understand which emission lines are available near the optical range in each pulse width regime and which emission ratios may be favorable for generating equivalence ratio calibration curves. The emission spectra in the range of 550–800 nm for ns-LIBS and ps-LIBS are mostly similar with slightly elevated atomic oxygen lines by ps-LIBS. Spectra from fs-LIBS show the lowest continuum background and prominent individual atomic lines, though have significantly weaker ionic emission from nitrogen. A qualitative explanation based on assumed local thermodynamic equilibrium and electron temperatures calculated by theNII(565nm)andNII(594nm)emissions is presented. In studying line emission ratios for FAR calculation, it is found thatHα<#comment/>(656nm)/NII(568more »width='thickmathspace'/>nm)is best for FAR measurements with ns-LIBS and remains viable for ps-LIBS, whileHα<#comment/>(656nm)/OI(777nm)is optimal for the ps-LIBS and fs-LIBS cases. Due to low continuum background and short time delay for spectra collection, fs-LIBS is very promising for high-speed FAR measurements using short-gated LIBS.

    « less
  4. We report on spectroscopic measurements on the4f76s28S7/2∘<#comment/>→<#comment/>4f7(8S∘<#comment/>)6s6p(1P∘<#comment/>)8P9/2transition in neutral europium-151 and europium-153 at 459.4 nm. The center of gravity frequencies for the 151 and 153 isotopes, reported for the first time in this paper, to our knowledge, were found to be 652,389,757.16(34) MHz and 652,386,593.2(5) MHz, respectively. The hyperfine coefficients for the6s6p(1P∘<#comment/>)8P9/2state were found to beA(151)=−<#comment/>228.84(2)MHz,B(151)=226.9(5)MHzandA(153)=−<#comment/>101.87(6)MHz,B(153)=575.4(1.5)MHz, which all agree with previously published results except for A(153), which shows a small discrepancy. The isotope shift is found to be 3163.8(6) MHz, which also has a discrepancy with previously published results.

  5. Properly interpreting lidar (light detection and ranging) signal for characterizing particle distribution relies on a key parameter,χ<#comment/>p(π<#comment/>), which relates the particulate volume scattering function (VSF) at 180° (β<#comment/>p(π<#comment/>)) that a lidar measures to the particulate backscattering coefficient (bbp). However,χ<#comment/>p(π<#comment/>)has been seldom studied due to challenges in accurately measuringβ<#comment/>p(π<#comment/>)andbbpconcurrently in the field. In this study,χ<#comment/>p(π<#comment/>), as well as its spectral dependence, was re-examined using the VSFs measuredin situat high angular resolution in a wide range of waters.β<#comment/>p(π<#comment/>), while not measured directly, was inferred using a physically sound, well-validated VSF-inversion method. The effects of particle shape and internal structure on the inversion were tested using three inversion kernels consisting of phase functions computed for particles that are assumed as homogenous sphere, homogenous asymmetric hexahedra, or coated sphere. The reconstructed VSFs using any of the three kernels agreed well with the measured VSFs with a mean percentage difference<<#comment/>5%<#comment/>at scattering angles<<#comment/>170∘<#comment/>. At angles immediately near or equal to 180°, the reconstructedβ<#comment/>p(π<#comment/>more »stretchy='false'>)depends strongly on the inversion kernel.χ<#comment/>p(π<#comment/>)derived with the sphere kernels was smaller than those derived with the hexahedra kernel but consistent withχ<#comment/>p(π<#comment/>)estimated directly from high-spectral-resolution lidar andin situbackscattering sensor. The possible explanation was that the sphere kernels are able to capture the backscattering enhancement feature near 180° that has been observed for marine particles.χ<#comment/>p(π<#comment/>)derived using the coated sphere kernel was generally lower than those derived with the homogenous sphere kernel. Our result suggests thatχ<#comment/>p(π<#comment/>)is sensitive to the shape and internal structure of particles and significant error could be induced if a fixed value ofχ<#comment/>p(π<#comment/>)is to be used to interpret lidar signal collected in different waters. On the other hand,χ<#comment/>p(π<#comment/>)showed little spectral dependence.

    « less