Interaction of THz radiation with matter

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Discussion Overview

The discussion revolves around the interaction of THz radiation with matter, specifically focusing on the search for suitable materials for THz detectors and the equations governing the absorption of THz radiation in these materials. Participants explore the challenges of achieving high absorption rates and the implications for detector design.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant seeks equations linking the absorption of THz radiation in materials and how absorption varies with wavelength, expressing frustration at the lack of available information.
  • Another participant notes that absorption is a material property that is difficult to predict ab initio and suggests looking into established theories for radio wave absorption, particularly for metals, while cautioning that absorption alone may not be sufficient for effective detection.
  • A participant mentions plans to use a dedicated THz radiation source and filters to ensure that the detector primarily receives THz radiation, aiming to measure temperature changes in a microbolometer made from Vanadium Oxide.
  • Concerns are raised about the practicalities of achieving 100% absorption, with one participant explaining that absorption is generally statistical and suggesting that aiming for near-total absorption may be more realistic.
  • There is a request for recommendations on literature regarding electromagnetic radiation interaction with matter, highlighting the need for more resources on the topic.

Areas of Agreement / Disagreement

Participants express differing views on the feasibility of achieving complete absorption of THz radiation and the practical implications of detector thickness. There is no consensus on the best approach or the specific equations needed for absorption calculations.

Contextual Notes

Participants acknowledge the complexity of absorption as a statistical process and the potential trade-offs between absorption efficiency and response time in detector design. The discussion highlights the need for further exploration of existing theories and materials.

Who May Find This Useful

This discussion may be of interest to researchers and students involved in the development of THz detectors, materials science, and those studying electromagnetic radiation interactions in various media.

jgrant333
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hello.

I'm studying a project on Thz radiation and have to establish what material would make a good THz detector.

To this end I've tried to find equations linking the aborption of THz radiation in matter and how the absorption varies with wavelength (one of the things I'd like to eastablish is how thick I need to make my detector to get 100% absorption of the THz radiation).

Anyway up until this point I have been unable to come across any such equations...seriously frustrating (perhaps I need to refine how I search for informartion).

Could anyone help me out?

Many thanks!
 
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If no one else replies I'll give you my 2 cents. Absorption is fine and all, but not so useful, but first things first:
Absorption is a property of a material, just like color. It's a ***** to predict ab initio (i.e. from the theoretical ground work). For many material classes there are established theories. As THz radiation is basically normal non ionizing radio waves, you might want to look into radio wave absorption. For metals in bulk for example there should be plenty of theory, but metals also reflect a lot.
Now about the absorption: If you simply use an absorbing material it will only get warmer. You wouldn't know if you are really measuring THz waves or microwaves, or something else that is absorbed by your material. With radio waves you use antennas, and separated charges, with light you can use electron excitations in semiconductors, there are many more things imaginable where your material shows some effect A under THz radiation and you have a good detector for A. So I would look at the techniques already in use for measuring radiation, and for molecules on the length scale of the wavelength, that can resonate. Theory will not deliver what you are searching for.
 
Thank you for your response.

I take your point about differentiating between Thz waves and other electromagnetic radiation. However I plan on using a dedicated Thz radiation source along with suitable filters so that the majority of the EM radiation striking my detector is Thz.

I actually would like to fabricate a focal plane array microbolometer - i.e. just as you say in your post I want to measure how much the detector heats up when Thz radiation is impingent on it.

In many papers Vanadium Oxide is used as a detector material (it has a high temperature coefficient of resistance) however in no paper can I find an explanation giving % THz radiation absorbed with thickness of detector material.

Obviously I'd like 100% absorption of Thz radiation in my detector material to obtain maximum detector responsivity.

As a side note could anyone recommend any books on EM radiation interaction in matter?

Many thanks
 
jgrant333 said:
[...]However I plan on using a dedicated Thz radiation source along with suitable filters so that the majority of the EM radiation striking my detector is Thz.

Interesting, since I think finding filter materials is pretty much the same problem, as finding absorbers.

[...]
In many papers Vanadium Oxide is used as a detector material (it has a high temperature coefficient of resistance) however in no paper can I find an explanation giving % THz radiation absorbed with thickness of detector material.

Obviously I'd like 100% absorption of Thz radiation in my detector material to obtain maximum detector responsivity.

The way you phrase your question I am not sure if you know what you are searching for. Absorption is generally a statistical process, with an exponential behavior, so you are actually looking for 99.999% absorption or so, otherwise the detector must be unreasonably long to "catch the last photon". But not even really that, because it will probably ruin your response time if you need to heat up or cool down a thick block of material, in the end you'll probably want "most radiation absorbed" or "just enough radiation absorbed".

As a side note could anyone recommend any books on EM radiation interaction in matter?
[...]

Yes but only for molecules and quantum dots. So that doesn't help. I hope you are familiar with Maxwells equations in media, and complex valued permitivity, then you could check out the links in http://en.wikipedia.org/wiki/Dielectric_spectroscopy"
Took me about 5 minutes to find, but I don't really know what level of physics you're at.
 
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