Accurate measurement of the refractive index of CO2, N2, He, O2, and air at 10.57μ and T=23°C

Marchetti, S.; Simili, R.

doi:10.1016/j.infrared.2004.12.005

Cited by 10 publications

(10 citation statements)

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“…4 and 10.6 µm [44,48,49], 3. experiments on dry air and its molecular constituents in the visible [6,23,32,78], at 1.064 µm [56,72], up to 2.0 µm [57], up to 1.7 µm [34,54,58,59], or at 10.6 µm [43,66], 4. verification of the dispersion and higher order derivatives with astronomical interferometry [71], 5.…”

Section: Scopementioning

confidence: 92%

Refractive index of humid air in the infrared: model fits

Mathar¹

2007

J. Opt. A: Pure Appl. Opt.

111

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The theory of summation of electromagnetic line transitions is used to tabulate the Taylor expansion of the refractive index of humid air over the basic independent parameters (temperature, pressure, humidity, wavelength) in five separate infrared regions from the H to the Q band at a fixed percentage of Carbon Dioxide. These are least-squares fits to raw, highly resolved spectra for a set of temperatures from 10 to 25 • C, a set of pressures from 500 to 1023 hPa, and a set of relative humidities from 5 to 60%. These choices reflect the prospective application to characterize ambient air at mountain altitudes of astronomical telescopes. The paper provides easy access to predictions of the refractive index of humid air at conditions that are typical in atmospheric physics, in support of ray tracing [5] and astronomical applications [4,16,47,50] until experimental coverage of the infrared wavelengths might render these obsolete. The approach is in continuation of earlier work [46] based on a more recent HITRAN database [60] plus more precise accounting of various electromagnetic effects for the dielectric response of dilute gases, as described below.The literature of optical, chemical and atmospheric physics on the subject of the refractive index of moist air falls into several categories, sorted with respect to decreasing relevance (if relevance is measured by the closeness to experimental data and the degree of independence to the formalism employed here):1. experiments on moist air in the visible [3,9,18,53 [42,61,79] and eventually in the static limit [24], the refractive index plotted as a function of wavelength is more and more structured by individual lines. Since we will not present these functions at high resolution but smooth fits within several bands in the infrared, their spiky appearance sets a natural limit to the far-IR wavelength regions that our approach may cover. II. DIELECTRIC MODEL A. MethodologyThe complex valued dielectric function n(ω) of air n = 1 +χ (1) is constructed from molecular dynamical polarizabilitiesN m are molecular number densities, S ml are the line intensities for the transitions enumerated by l. ω 0ml are the transition angular frequencies, Γ ml the full linewidths at half maximum. c is the velocity of light in vacuum, and i the imaginary unit. The line shape (2) adheres to the complex-conjugate symmetry χ m (ω) = χ * m (−ω), as required for functions which are real-valued in the time domain. The sign convention of Γ ml merely reflects a sign choice in the Fourier Transforms and carries no real significance; a sign in the Kramers-Kronig formulas is bound to it. The integrated imaginary part is [28] whereν = k/(2π) = ω/(2πc) = 1/λ is the wavenumber.

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Section: Scopementioning

confidence: 92%

Refractive index of humid air in the infrared: model fits

Mathar¹

2007

J. Opt. A: Pure Appl. Opt.

111

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“…The experimental apparatus has been described in [1,3]. Briefly the interference spectra are produced by recording the transmission through two differential cavities of a frequency tuned CO 2 laser emission.…”

Section: Resultsmentioning

confidence: 99%

“…Some data of Ref. [3] are also reported for comparison. These data are converted for the 21°C temperature by means Eq.…”

Section: Resultsmentioning

confidence: 99%

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The ν3 SF6 band intensity derived from the refractive index measurement performed off-side the absorption band

Marchetti

Simili

2008

Infrared Physics & Technology

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“…In a previous work we have reported the infrared refractive index of some gases measured by means of a single mode tunable CO 2 laser and a differential interferometric technique [1,2].…”

Section: Introductionmentioning

confidence: 99%