- #1
nightvidcole
- 25
- 12
- TL;DR
- Spectral region straddling the boundary between UV and X-rays has unique challenges - everything is opaque. I argue it deserves "promotion" to a spectral region of its own.
I propose a pedagogically useful, and physically and economically descriptive region between UV and X-rays (or, if you like, straddling the boundary between the two).
The basic physics here is dramatically different from both "traditional" UV and "traditional" X-rays, because of one very important thing - all normal matter, made of atoms, is extraordinarily opaque in this spectral region due to the photoelectric effect. A single millimeter of air, or a micrometer of solid or liquid, blocks the vast majority of this radiation. There is no other spectral region like this.
In fact, the photoelectric absorption is so strong that even astronomical observations can be suppressed due to extremely tiny amounts of intervening matter.
This means that until EUV lithography became a thing, commercial applications for this radiation were nearly nonexistent, as its use is limited to outer space and vacuum chambers. Yet, science textbooks simply place UV next to X rays, as though there is a smooth transition from suntans to radiographs. But they leave out the fact that both suntans and radiographs are possible only because at least some matter is partially transparent for "traditional" UV and "traditional" X-rays, and there is this unmentioned region in between where nothing like either is possible.
One could argue that we already have names like "XUV" and "soft X rays". This is technically true, but it doesn't really quite do justice. One could also argue that terahertz radiation never needed a designation because it was "just" mm-wave on one side and far infrared on the other. But this would downplay the unique challenges with this region. Likewise, the unique nature of the UV/X-ray boundary region is downplayed by not recognizing it as distinct.
I would even go so far as to argue that there is somewhat of a "gap" in this region just as there is a "gap" for terahertz technologies. To be specific, ordinary "optical" technologies cannot be extended cleanly into this region because they do not work when all matter has such high attenuation. "X ray" technologies would be extremely inefficient when operated in this region, as (non-thermal) bremsstrahlung energy efficiency is tiny for photons of such low energy. Just like with Terahertz, we are left with only extremely inefficient, low-power, or non-compact sources for this region.
Thoughts?
The basic physics here is dramatically different from both "traditional" UV and "traditional" X-rays, because of one very important thing - all normal matter, made of atoms, is extraordinarily opaque in this spectral region due to the photoelectric effect. A single millimeter of air, or a micrometer of solid or liquid, blocks the vast majority of this radiation. There is no other spectral region like this.
In fact, the photoelectric absorption is so strong that even astronomical observations can be suppressed due to extremely tiny amounts of intervening matter.
This means that until EUV lithography became a thing, commercial applications for this radiation were nearly nonexistent, as its use is limited to outer space and vacuum chambers. Yet, science textbooks simply place UV next to X rays, as though there is a smooth transition from suntans to radiographs. But they leave out the fact that both suntans and radiographs are possible only because at least some matter is partially transparent for "traditional" UV and "traditional" X-rays, and there is this unmentioned region in between where nothing like either is possible.
One could argue that we already have names like "XUV" and "soft X rays". This is technically true, but it doesn't really quite do justice. One could also argue that terahertz radiation never needed a designation because it was "just" mm-wave on one side and far infrared on the other. But this would downplay the unique challenges with this region. Likewise, the unique nature of the UV/X-ray boundary region is downplayed by not recognizing it as distinct.
I would even go so far as to argue that there is somewhat of a "gap" in this region just as there is a "gap" for terahertz technologies. To be specific, ordinary "optical" technologies cannot be extended cleanly into this region because they do not work when all matter has such high attenuation. "X ray" technologies would be extremely inefficient when operated in this region, as (non-thermal) bremsstrahlung energy efficiency is tiny for photons of such low energy. Just like with Terahertz, we are left with only extremely inefficient, low-power, or non-compact sources for this region.
Thoughts?