How to emit 3.2 micrometer wavelength

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Discussion Overview

The discussion centers around the feasibility of emitting a 3.2 micrometer wavelength with high energy, particularly in a homemade setup. Participants explore various methods of achieving this emission, including the use of blackbody radiation and specific light sources, while also considering the implications for heating molecules within a confined space.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant inquires about the application and power requirements for emitting the specified wavelength, noting it falls within the infrared part of the electromagnetic spectrum.
  • Another suggests using a hot filament lamp, adjusting the voltage to emit infrared without visible light, and mentions its use in demonstrating the greenhouse effect.
  • A participant proposes the idea of a blackbody cavity with walls at approximately 900K to achieve the desired emission.
  • Concerns are raised regarding the assumption that the emission will be based on a blackbody spectrum, questioning whether the specific wavelength implies a need for monochromatic light.
  • One participant expresses a desire to heat CO2 in ambient air within a box, aiming to transfer heat to other molecules, and requests clarification on the choice of the 3.2 micrometer wavelength.
  • Another participant challenges the practicality of measuring the greenhouse effect in a small setup, suggesting that the atmospheric absorption of infrared is subtle and would require careful measurement.
  • A suggestion is made for using a narrow band IR energy source, such as a filtered halogen or LED, for practical experimentation.

Areas of Agreement / Disagreement

Participants express differing views on the assumptions regarding the emission method and the implications of the specific wavelength. There is no consensus on the best approach or the practicality of the proposed experiments.

Contextual Notes

Participants note the complexity of measuring the greenhouse effect in a confined space and the potential challenges in achieving the desired wavelength emission. There are also references to varying CO2 absorption spectra, indicating a lack of clarity on the specific wavelength's relevance.

Vincent L
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Good day!
Can anyone tell me how to emit a 3.2 micrometer(μm) wavelength with as much energy as possible? How could it be "homemade"? Is it possible?
Thank you so much
 
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Welcome to PF. :smile:

What is the application? How much power are we talking about here? It looks to be in the IR part of the EM spectrum, right?

1654103904106.png

http://www.pas.rochester.edu/~blackman/ast104/spectrum.html
 
Thank you for taking the time. My english is limited.
So i want it conceiled in a box. I want to reflect the emission so it can heat the molecules i put in the box as much it is possible.
 
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Maybe the hot filament of a lamp. You can adjust the operating voltage so that IR is emitted without visible light. I use this to demonstrate the Greenhouse Effect, by altering the temperature to give long and short wavelength IR. At long wavelengths, radiation actually comes from the hot glass of the bulb, as the glass is opaque to long wavelengths.
 
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It seems to me you want a blackbody cavity with walls ~900K
guest631096994.png
 
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Thank you all. I believe this to match with my questionning. I hope you all a good day
 
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bob012345 said:
It seems to me you want a blackbody cavity with walls ~900K
View attachment 302326
Thank you!
 
tech99 said:
Maybe the hot filament of a lamp. You can adjust the operating voltage so that IR is emitted without visible light. I use this to demonstrate the Greenhouse Effect, by altering the temperature to give long and short wavelength IR. At long wavelengths, radiation actually comes from the hot glass of the bulb, as the glass is opaque to long wavelengths.
Thank you!
 
  • #10
The problem is that the OP refers to a specific wavelength. All the above answers seem based on the assumption of a black body spectrum. If the OP were referring to spectral yellow wavelength or, say a millimetre radio wavelength, the answers would not have assumed thermal radiation.
What is it about a 3.2 micron wavelength that makes us assume that it's not monochromatic?
@Vincent L could you tell us about your choice of that particular wavelength and some more detail about your proposed experiment?
 
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  • #11
sophiecentaur said:
The problem is that the OP refers to a specific wavelength. All the above answers seem based on the assumption of a black body spectrum. If the OP were referring to spectral yellow wavelength or, say a millimetre radio wavelength, the answers would not have assumed thermal radiation.
What is it about a 3.2 micron wavelength that makes us assume that it's not monochromatic?
@Vincent L could you tell us about your choice of that particular wavelength and some more detail about your proposed experiment?
I want to CO2 to absorb it in ambient air, in a box. I want it to transfert heat to the other molecules. So I am taking the CO2 spectrum that is absorbed but not the rest Thank you for taking time
 
  • #12
Vincent L said:
I want to CO2 to absorb it in ambient air, in a box. I want it to transfert heat to the other molecules. So I am taking the CO2 spectrum that is absorbed but not the rest Thank you for taking time
Can you post a link to the ##3.2 \mu m## number that you posted? I'm finding different peaks for CO2 absorption specta...
 
  • #13
berkeman said:
Can you post a link to the 3.2μm number that you posted? I'm finding different peaks for CO2 absorption specta...
It seems to me that the OP is trying to measure the mechanism of the 'greenhouse effect'. Atmospheric absorption of IR is a very small effect, for a short path distance (i.e. a 'box'). It's pretty subtle even over the tens of km of the path through the atmosphere and many years of input power. If the effect were really that obvious we wouldn't be having difficulties with the climate change deniers.

@Vincent L 's idea is more of a thought experiment than one which would be practical. It would involve measuring a tiny temperature change, probably involving comparative readings for a box of CO2 and one with the equivalent mass of CO2-free air. A source of narrow band IR energy could be a filtered halogen or LED source, such as you can get for back pain relief. An IR photography floodlight wouldn't have the necessary power, although the spectrum could be better.

It's a good topic for discussion though and throws up a lot pf practical factors about this sort of measurement.
 

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