The measured 10μm refractive index of some simple molecules (CO, H2O, CH4, C2H2) and their calculated extension to the whole IR frequency region

Marchetti, S.; Simili, R.

doi:10.1016/j.infrared.2005.05.002

Cited by 2 publications

(3 citation statements)

References 11 publications

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“…experiments on moist air in the visible [3,9,18,53], 2. experiments on pure water vapor at 3. 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.…”

Section: Scopementioning

confidence: 98%

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: 98%

Refractive index of humid air in the infrared: model fits

Mathar¹

2007

J. Opt. A: Pure Appl. Opt.

111

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“…In this way the instability of the resonators and the laser is removed. Nevertheless to derive accurate measurements, a particular procedure is required to remove the residual relative cavity drift (about 0.35 fringes/°C) due to the air in the reference resonator and to the ZnSe windows of the cell [2].…”

Section: Resultsmentioning

confidence: 99%

“…(1) contain the results of [1] when the right terms are neglected being (X + X i ) ) (X À X i ). At frequencies higher than the microwaves we have (X + X s ) ) 1 and we can approximate Dn i as in [2] also for the SF 6 because also for the spherical tops we have the conditions N P Jþ1 ffi N R J and l P Jþ1 ffi l R J that allow to summarize, the cumulative effect of all the rotovibrational absorption lines in the simple expression…”

Section: Introductionmentioning

confidence: 99%