6 ms·

The terahertz gap: into the dead zone (2007)

75 points by losfair 4y ago

rich_sasha 4y ago
Why would THz waves offer higher resolution in imaging that IR? I understood that the shorter the wave, the higher the (lower bound on) attainable resolution? Also, unrelated but no point in commenting twice: millimetre wave astronomy is a big topic of the last decade or two. How does the THz technology described here link to what's used in mm wave detection?
- was_a_dev 4y ago
  > It beats infrared light for resolving power because it suffers less Rayleigh scattering, imaging details less than 1 millimetre wide. While the wavelength of THz is larger than IR, and hence leads to a worse spatial resolution due to diffraction. This comment is about the scattering of light through a medium, which acts as a low pass filter leading to loss of higher spatial frequencies and therefore lower spatial resolution. > millimetre wave astronomy is a big topic of the last decade or two. How does the THz technology described here link to what's used in mm wave detection? They are effecitevely the same band (1mm ~ 0.3THz). The difference between astronomy and other applications is photon flux. Distant astronomical objects are faint, therefore detection methods only need to detect a small number of photons/s. One popular detector is cryogenic bolometers, which measure a temperature increase due to absorbed energy from a THz photon. These work well in low-flux applications.
- adrian_b 4y ago
  I do not know if this claim is true, but in the article it is said that infrared light imaging is affected by Rayleigh scattering, which limits its resolution. According to this claim, many common materials would diffuse the infrared light so that the image would look like looking to something through translucent glass or through fog, which would diminish the resolution. I assume that this refers to imaging through visually opaque materials, i.e. through clothes, like for airport security, not to looking through the air with an infrared camera.
boulos 4y ago
(2007) Can people comment on what has happened since? 15 years is a long time in the research world. Did the hoped for things come to pass?
- wolfram74 4y ago
  If I'm remembering correctly, most of the interesting work in archaeology recovering palimpsests (reused canvas/media for multiple works) has been done with THz stuff, so that's one place it's come up.
- bloggie 4y ago
  There has been a lot of technological progress, but the sector remains a niche one. Many new THz sources have been built and improved, including coherent sources like the QCLs mentioned. Microantennas may play a big role in the future, and now there are technologies to build them. Optics and detection have also improved. THz equipment still remains expensive, demanding, fragile, and scientific, although much improved from 15 years ago and with many more people working in this field. It's even being considered for 6G communications by some [1] [2] but I do not think this is realistic given the state of technology and optical technologies will probably 'win' [1] https://opg.optica.org/abstract.cfm?uri=OFC-2022-M3C.6 https://opg.optica.org/abstract.cfm?uri=OFC-2022-M3C.6 [2] https://en.wikipedia.org/wiki/6G_(network) https://en.wikipedia.org/wiki/6G_(network)
  - boltzmann-brain 4y ago
    We talk about high-GHz to low-THz technology in the Tektronix / Hewlett Packard [1] Discord [2] every now and then; there's even a push in the community to talk about such cutting edge stuff (separate room, lists of resources, etc). When it comes to high GHz bands, the consensus always is that what's prohibitive to the average non-state-funded lab are exactly the sources / generators - not just the price, but also availability. [1] two companies with historically the largest impact on electronics testing equipment, and largest and oldest enthusiast communities, so we have this discord [2] https://discord.gg/wQAzp4qm https://discord.gg/wQAzp4qm
can16358p 4y ago
Technically speaking, what should EM in that range called? Not visible light, as it's not visible. Not exactly microwave either, or is it?
- downvotetruth 4y ago
  Metric: centimicrometer
- was_a_dev 4y ago
  0.3-3.0THz is given usually named just THz, given surrounding bands are already named. Another convention is sub-mm, given the wavelength is just that, being on the order of microns.
  - Dylan16807 4y ago
    "Named", yes. Ugh. I mean, find a random person on the street and ask them to sort "Extremely", "Super", and "Ultra", and how confident they are.
    - was_a_dev 4y ago
      I don't understand your point. Every part of the EM spectrum is "Named"
      - Dylan16807 4y ago
        My point is that the names are awful and hard to remember, so they're almost worse than using the numbers by themselves.
        was_a_dev 4y ago
        Maybe - I work in the THz field, so it might seem more intuitive to me. But naming is hard by the admission of software engineers, right?
    - 4y ago
twawaaay 4y ago
"THz radiation is non-ionising, so it’s safe to use on humans" Great logic. "This cheeseburger does not contain arsenic and so it is safe for consumption." It would be much better to say "We haven't really done much study about it but as of now we do not know of any side effects at reasonable power levels."
- CamperBob2 4y ago
  At some point, the burden of proof falls on the OOGA BOOGA brigade.
  - boltzmann-brain 4y ago
    UV is non-ionizing, and gives you skin cancer.
    - coryrc 4y ago
      Your antecedent is incorrect, some UV is ionizing.
- wanda 4y ago
  Sure, the cheeseburger is bad for you if you eat 10 every day, never exercise etc. But that kinda goes without saying right? Just like you might say that a lawnmower is compliance tested against electrical faults before sale and is thus safe to use, despite having some sharp rotating blades on the bottom that could ruin your day pretty quickly if you put your head in it and turned it on. The way EM radiation works is that it's classified as ionising if it's sufficiently energetic and penetrative (read: high frequency/short wavelength) to enter human tissue and detach electrons in the atomic structures that make up that tissue. The danger that ionising radiation presents is that detaching electrons in DNA can cause carcinogenic mutation i.e. cause cancer. Radiation in high-frequency ultraviolet and above in the EM spectrum is considered ionising, and everything from low-freq UV below is considered non-ionising. This is because the energy carried by EM waves of lower-than-UV frequency is not sufficient to ionise atoms in human tissue. I don't know the exact numbers on that, but I do know that the lowest threshold for ionising any atom is 3.9eV (low f UV) to ionise a caesium atom — and obviously we aren't made of caesium. And this is backed up pretty well by the fact that if visible light were dangerously ionising EM radiation, life would not exist as we know it, and even if it made it this far, we'd all have a lot of cancer. And since visible light is ostensibly higher frequency/higher energy than this "terahertz radiation" (presumably a buzzword for high freq microwave/infrared?) we can safely say that it won't hurt us in the way that a thousand chest X-rays might. Now it's true that you can burn your food in the microwave and you can blind yourself with a laser, but this isn't because you ionised your chicken beyond core cooked temperature, it's because you subjected it to intense microwave radiation which excites the atoms. Sufficiently intense visible light will burn your skin, but it won't mutate your skin. You get skin cancer from excessive exposure to ultraviolet, not from light. Cellphones, wifi and 4G/5G have all been used by those who profit from scaremongering, but if you think about it, if any of it were true, there would have to be some new science to describe the mechanism by which they cause harm.
deleted 4y ago
[deleted]
Sporktacular 4y ago
The article puts the lack of development down to technology but it's arguably the lack of applications that came first. We've developed solutions for most of the spectrum (anything below cosmic gamma rays) because we needed to and the tech followed. As we find applications it will follow. Also, not to be pedantic but about the terminology, the spectrum below the terahertz range is generally called radio (with optical or light for above it) not 'electronic', while the technology for producing frequencies above it is called photonics (with electronics for below it), not 'optics'.

75 points by losfair 4y ago

Why would THz waves offer higher resolution in imaging that IR? I understood that the shorter the wave, the higher the (lower bound on) attainable resolution? Also, unrelated but no point in commenting twice: millimetre wave astronomy is a big topic of the last decade or two. How does the THz technology described here link to what's used in mm wave detection?

was_a_dev 4y ago
> It beats infrared light for resolving power because it suffers less Rayleigh scattering, imaging details less than 1 millimetre wide. While the wavelength of THz is larger than IR, and hence leads to a worse spatial resolution due to diffraction. This comment is about the scattering of light through a medium, which acts as a low pass filter leading to loss of higher spatial frequencies and therefore lower spatial resolution. > millimetre wave astronomy is a big topic of the last decade or two. How does the THz technology described here link to what's used in mm wave detection? They are effecitevely the same band (1mm ~ 0.3THz). The difference between astronomy and other applications is photon flux. Distant astronomical objects are faint, therefore detection methods only need to detect a small number of photons/s. One popular detector is cryogenic bolometers, which measure a temperature increase due to absorbed energy from a THz photon. These work well in low-flux applications.
adrian_b 4y ago
I do not know if this claim is true, but in the article it is said that infrared light imaging is affected by Rayleigh scattering, which limits its resolution. According to this claim, many common materials would diffuse the infrared light so that the image would look like looking to something through translucent glass or through fog, which would diminish the resolution. I assume that this refers to imaging through visually opaque materials, i.e. through clothes, like for airport security, not to looking through the air with an infrared camera.

boulos 4y ago

(2007) Can people comment on what has happened since? 15 years is a long time in the research world. Did the hoped for things come to pass?

wolfram74 4y ago
If I'm remembering correctly, most of the interesting work in archaeology recovering palimpsests (reused canvas/media for multiple works) has been done with THz stuff, so that's one place it's come up.
bloggie 4y ago
There has been a lot of technological progress, but the sector remains a niche one. Many new THz sources have been built and improved, including coherent sources like the QCLs mentioned. Microantennas may play a big role in the future, and now there are technologies to build them. Optics and detection have also improved. THz equipment still remains expensive, demanding, fragile, and scientific, although much improved from 15 years ago and with many more people working in this field. It's even being considered for 6G communications by some [1] [2] but I do not think this is realistic given the state of technology and optical technologies will probably 'win' [1] https://opg.optica.org/abstract.cfm?uri=OFC-2022-M3C.6 https://opg.optica.org/abstract.cfm?uri=OFC-2022-M3C.6 [2] https://en.wikipedia.org/wiki/6G_(network) https://en.wikipedia.org/wiki/6G_(network)
- boltzmann-brain 4y ago
  We talk about high-GHz to low-THz technology in the Tektronix / Hewlett Packard [1] Discord [2] every now and then; there's even a push in the community to talk about such cutting edge stuff (separate room, lists of resources, etc). When it comes to high GHz bands, the consensus always is that what's prohibitive to the average non-state-funded lab are exactly the sources / generators - not just the price, but also availability. [1] two companies with historically the largest impact on electronics testing equipment, and largest and oldest enthusiast communities, so we have this discord [2] https://discord.gg/wQAzp4qm https://discord.gg/wQAzp4qm

can16358p 4y ago

Technically speaking, what should EM in that range called? Not visible light, as it's not visible. Not exactly microwave either, or is it?

downvotetruth 4y ago
Metric: centimicrometer
was_a_dev 4y ago
0.3-3.0THz is given usually named just THz, given surrounding bands are already named. Another convention is sub-mm, given the wavelength is just that, being on the order of microns.
- Dylan16807 4y ago
  "Named", yes. Ugh. I mean, find a random person on the street and ask them to sort "Extremely", "Super", and "Ultra", and how confident they are.
  - was_a_dev 4y ago
    I don't understand your point. Every part of the EM spectrum is "Named"
    - Dylan16807 4y ago
      My point is that the names are awful and hard to remember, so they're almost worse than using the numbers by themselves.
      - was_a_dev 4y ago
        Maybe - I work in the THz field, so it might seem more intuitive to me. But naming is hard by the admission of software engineers, right?
  - 4y ago

twawaaay 4y ago

"THz radiation is non-ionising, so it’s safe to use on humans" Great logic. "This cheeseburger does not contain arsenic and so it is safe for consumption." It would be much better to say "We haven't really done much study about it but as of now we do not know of any side effects at reasonable power levels."

CamperBob2 4y ago
At some point, the burden of proof falls on the OOGA BOOGA brigade.
- boltzmann-brain 4y ago
  UV is non-ionizing, and gives you skin cancer.
  - coryrc 4y ago
    Your antecedent is incorrect, some UV is ionizing.
wanda 4y ago
Sure, the cheeseburger is bad for you if you eat 10 every day, never exercise etc. But that kinda goes without saying right? Just like you might say that a lawnmower is compliance tested against electrical faults before sale and is thus safe to use, despite having some sharp rotating blades on the bottom that could ruin your day pretty quickly if you put your head in it and turned it on. The way EM radiation works is that it's classified as ionising if it's sufficiently energetic and penetrative (read: high frequency/short wavelength) to enter human tissue and detach electrons in the atomic structures that make up that tissue. The danger that ionising radiation presents is that detaching electrons in DNA can cause carcinogenic mutation i.e. cause cancer. Radiation in high-frequency ultraviolet and above in the EM spectrum is considered ionising, and everything from low-freq UV below is considered non-ionising. This is because the energy carried by EM waves of lower-than-UV frequency is not sufficient to ionise atoms in human tissue. I don't know the exact numbers on that, but I do know that the lowest threshold for ionising any atom is 3.9eV (low f UV) to ionise a caesium atom — and obviously we aren't made of caesium. And this is backed up pretty well by the fact that if visible light were dangerously ionising EM radiation, life would not exist as we know it, and even if it made it this far, we'd all have a lot of cancer. And since visible light is ostensibly higher frequency/higher energy than this "terahertz radiation" (presumably a buzzword for high freq microwave/infrared?) we can safely say that it won't hurt us in the way that a thousand chest X-rays might. Now it's true that you can burn your food in the microwave and you can blind yourself with a laser, but this isn't because you ionised your chicken beyond core cooked temperature, it's because you subjected it to intense microwave radiation which excites the atoms. Sufficiently intense visible light will burn your skin, but it won't mutate your skin. You get skin cancer from excessive exposure to ultraviolet, not from light. Cellphones, wifi and 4G/5G have all been used by those who profit from scaremongering, but if you think about it, if any of it were true, there would have to be some new science to describe the mechanism by which they cause harm.

deleted 4y ago

[deleted]

Sporktacular 4y ago

The article puts the lack of development down to technology but it's arguably the lack of applications that came first. We've developed solutions for most of the spectrum (anything below cosmic gamma rays) because we needed to and the tech followed. As we find applications it will follow. Also, not to be pedantic but about the terminology, the spectrum below the terahertz range is generally called radio (with optical or light for above it) not 'electronic', while the technology for producing frequencies above it is called photonics (with electronics for below it), not 'optics'.