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New method to establish frequency calibration of FTS with multireflection cells

Röske, Christian and Birk, Manfred and Wagner, Georg (2018) New method to establish frequency calibration of FTS with multireflection cells. 15th Biennial HITRAN Conference united with 14th ASA conference, 13.-15. Jun 2018, Cambridge, Massachusetts, USA.

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Abstract

In laboratory FT spectroscopy in the infrared region, instrumental line shape (ILS) determination and the associated frequency calibration is necessary for accurate measurements. For high pressure measurements, both can be obtained from a previous measurement of a calibration gas at low pressure, preferably under otherwise similar conditions. However, especially in combination with a multireflection cell, a subsequent change in pressure causes an alteration in the adjustment of multireflection cell due to mechanical deformations and change of refractive index. The beam path and profile are thus shifted, which especially comes into effect for high absorption paths. An unavoidable correction of the adjustment then usually causes a deviation from the original ILS and thus from frequency calibration. ILS contributions are distributed over the infrared beam in the spectrometer optics and therefore the adjustment can influence the ILS. Especially the detector and detector window exhibit a strong angular dependence of reflectivity, thus influencing the ILS. The known method of using a small cell with a calibration gas in series with the multireflection cell fails when narrow band filters are applied for obtaining good signal to noise ratios and there is no calibration gas available with strong lines in the spectral region of interest. Here, a method is presented by which the re-adjustment of the instrument can be performed in a way to restore the previous ILS and frequency calibration for large absorption paths and pressure changes of about 1 bar. Explained is the detailed restoring procedure as well as exemplary results using a multireflection cell of 0.8 m base length set to an absorption path of more than 100 m, where a secondary reference cell was used to validate the method.

Item URL in elib:https://elib.dlr.de/119856/
Document Type:Conference or Workshop Item (Poster)
Title:New method to establish frequency calibration of FTS with multireflection cells
Authors:
AuthorsInstitution or Email of AuthorsAuthors ORCID iD
Röske, ChristianChristian.Roeske (at) dlr.deUNSPECIFIED
Birk, ManfredManfred.Birk (at) dlr.deUNSPECIFIED
Wagner, GeorgGeorg.Wagner (at) dlr.deUNSPECIFIED
Date:June 2018
Refereed publication:No
Open Access:No
Gold Open Access:No
In SCOPUS:No
In ISI Web of Science:No
Status:Published
Keywords:Fourier Transform Spectroscopy, Multireflection cell, Infrared Spectroscopy, Laboratory Spectroscopy, Frequency calibration
Event Title:15th Biennial HITRAN Conference united with 14th ASA conference
Event Location:Cambridge, Massachusetts, USA
Event Type:international Conference
Event Dates:13.-15. Jun 2018
Organizer:Harvard-Smithsonian Center for Astrophysics
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Space
HGF - Program Themes:Earth Observation
DLR - Research area:Raumfahrt
DLR - Program:R EO - Erdbeobachtung
DLR - Research theme (Project):Vorhaben Spectroscopic Methods in Remote Sensing
Location: Oberpfaffenhofen
Institutes and Institutions:Remote Sensing Technology Institute > Experimental Methods
Deposited By: Röske, Christian
Deposited On:22 Jun 2018 12:32
Last Modified:22 Jun 2018 12:32

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