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Entry  Fri Nov 5 11:51:50 2021, Paco, General, Design specs, Estimate of in-air absorption near 2.05 um HITRAN_line_strenghts.pdfbroadened_spectrum.pdfPP_broadened_spectrum.pdf
    Reply  Tue Nov 16 11:47:54 2021, Paco, General, Design specs, Estimate of in-air absorption near 2.05 um PP_broadened_spectrum.pdf
Message ID: 47     Entry time: Fri Nov 5 11:51:50 2021     Reply to this: 48
Author: Paco 
Type: General 
Category: Design specs 
Subject: Estimate of in-air absorption near 2.05 um 

[Paco]

I used the HITRAN database to download the set of ro-vibrational absorption lines of CO2 (carbon dioxide) near 2.05 um. The lines are plotted for reference vs wavenumber in inverse cm in Attachment #1.

Then, in Attachment #2, I estimate the broadened spectrum around 2.05 um and compare it against one produced by an online tool using the 2004 HITRAN catalog.

For the broadened spectrum, I assumed 1 atm pressure, 296 K temperature (standard conditions) and a nominal CO2 density of 1.96 kg/m^3 under this conditions. Then, the line profile was Lorentzian with a HWHM width determined by self and air broadening coefficients also from HITRAN. The difference between 2050 nm and 2040 nm absorption is approximately 2 orders of magnitude; so 2040 nm would be better suited to avoid in-air absorption. Nevertheless, the estimate implies an absorption coefficient at 2050 nm of ~ 20 ppm / m, with a nearby absorption line peaking at ~ 100 ppm / m

For the PMC, (length = 50 cm), the roundtrip loss contribution by in-air absorption at 2050 nm would amount to ~ 40 ppm. BUT, this is nevery going to happen unless we pump out everything and pump in 1 atm of pure CO2. So ignore this part.


Tue Nov 9 08:23:56 2021 UPDATE

Taking a partial pressure of 0.05 % (~ 500 ppm concentration in air), the broadening and total absorption decrease linearly with respect to the estimate above. Attachment #3 shows the new estimate.

For the PMC, (length = 50 cm), the roundtrip loss contribution by in-air absorption at 2050 nm would amount to ~ 1 ppm.

Attachment 1: HITRAN_line_strenghts.pdf  200 kB  Uploaded Fri Nov 5 13:13:36 2021  | Hide | Hide all
HITRAN_line_strenghts.pdf
Attachment 2: broadened_spectrum.pdf  198 kB  Uploaded Fri Nov 5 13:13:47 2021  | Hide | Hide all
broadened_spectrum.pdf
Attachment 3: PP_broadened_spectrum.pdf  204 kB  Uploaded Tue Nov 9 08:31:20 2021  | Hide | Hide all
PP_broadened_spectrum.pdf
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