[HN Gopher] The terahertz gap: into the dead zone
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       The terahertz gap: into the dead zone
        
       Author : losfair
       Score  : 48 points
       Date   : 2022-12-04 17:14 UTC (5 hours ago)
        
 (HTM) web link (www.chemistryworld.com)
 (TXT) w3m dump (www.chemistryworld.com)
        
       | rich_sasha wrote:
       | 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 wrote:
         | > 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 wrote:
         | 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.
        
       | can16358p wrote:
       | 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 wrote:
         | Metric: centimicrometer
        
         | was_a_dev wrote:
         | 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.
        
       | boulos wrote:
       | (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 wrote:
         | 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.
        
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