Challenges in Focusing X-Rays with Lenses

[cronxeh]

What are the current technical difficulties that prevent us from focusing x-rays with lenses?

 

[Claude Bile]

Just about all media readily absorb X-Rays.

Claude.

 

[chroot]

And we can focus X-rays, just not with optical glass. Instead, we have to make use of very small-angle "glancing" collisions with plane mirrors to steer X-rays around.

- Warren

 

[cronxeh]

I didnt mean diffraction, I meant actually focusing them. Thanks Claude, but Id like to know a bit more on quantum level. Are there any new advancements in high energy EM wave optics?

 

[chroot]

I'm not talking about diffraction; I'm talking focusing X-rays, i.e. bringing them a focus. This can be done with glancing reflections from plane mirrors.

- Warren

 

[cronxeh]

I'm not talking about diffraction; I'm talking focusing X-rays, i.e. bringing them a focus. This can be done with glancing reflections from plane mirrors.

- Warren

So on a smaller angle the material does not absorb the waves?

 

[chroot]

Yes; at very small angles, the x-rays are reflected, rather than absorbed. This is the principle used to design mirrors for x-ray telescopes, like Chandra:

http://chandra.harvard.edu/edu/chandra1014.html

There are a few other kinds of x-ray lenses, also. One, called a Fresnel zone plate lens, uses diffraction through a disc with concentric circular lines. A higher density of lines causes greater diffraction, so the discs are designed with lines spaced more and more closely as you go outward from the middle of the disc.

http://www.xradia.com/pro_zpl.htm

I don't doubt that there are other technologies, too.

- Warren

 

[GENIERE]

So on a smaller angle the material does not absorb the waves?

Oops! Chroot got there first!

As per Chroot’s response, the Chandra X-ray telescope uses four mirrors in a barrel shaped setup to focus the beam via very shallow angle reflection.

A cube of aluminum with a hollow center (spheroid) will focus an x ray beam, but I’m not sure of the physics of it.

 

[chroot]

Actually, I just found another technology which probably threatens to put the previous sorts of lenses out of business (note that I'm no expert in the field).

This website does a very good job of explaining the evolution of x-ray mirrors.

http://www.src.le.ac.uk/projects/lobster/ov_optics.htm

- Warren

 

[cronxeh]

I see. So suppose there was a material that had 100% reflective rate for EHF EM waves. What would be the emerging technologies (other than microscopes, high energy weapon systems, etc)?

 

[GENIERE]

I see. So suppose there was a material that had 100% reflective rate for EHF EM waves. What would be the emerging technologies (other than microscopes, high energy weapon systems, etc)?

I recall the 1980's star war program envisioned an a-bomb generating x-rays that used a large number of cylindrical tubes in a bundle to focus the beam.

 

[chroot]

I see. So suppose there was a material that had 100% reflective rate for EHF EM waves. What would be the emerging technologies (other than microscopes, high energy weapon systems, etc)?

You mean, even with perpendicular incidence, like a mirror with visible light?

Obviously, it would create new classes of telescopes and microscopes with very high resolution.

Such a material could also be used for medical imaging or radiation therapy. You can generate X-rays without any dangerous radioactive substances; if you could focus them easily and cheaply, you could use them to treat cancer.

I can't think of many communications applications -- our atmosphere absorbs x-rays, and so do almost all other substances.

Maybe you could invent an x-ray oven that could pop your popcorn in 13 milliseconds. (Who has time to wait two minutes to pop popcorn in a microwave oven?)

- Warren

 

[SciFiGuy]

I recall the 1980's star war program envisioned an a-bomb generating x-rays that used a large number of cylindrical tubes in a bundle to focus the beam.

I think that's a bit off. My research on the subject seems to suggest that the rods were the lasers, and that the bomb was the energy pump - hence the common name "bomb pumped x-ray laser". There was no means to focus the laser, or even prevent it from firing both forwards and backwards.

 

[Astronuc]

I recall the 1980's star war program envisioned an a-bomb generating x-rays that used a large number of cylindrical tubes in a bundle to focus the beam.

Yep.

I think that's a bit off. My research on the subject seems to suggest that the rods were the lasers, and that the bomb was the energy pump - hence the common name "bomb pumped x-ray laser". There was no means to focus the laser, or even prevent it from firing both forwards and backwards.

Actually GENIERE is correct - that was one concept, and the term was "nuclear pumped X-ray laser". One could also use a specially designed nuclear reactor, which offers a more stability, at the cost of power density.

The problem is nuclear 'bombs' is that the energy burst is more or less isotropic (not to mention very destructive, and otherwise destabilizing), and once would catch only part of the nuclear energy. The energy, primarily gamma and X-ray radiation can be focussed (somewhat) using tubular metal structures, and the photons primarily 'go in one end and out the other'.

Anyway as for the OP, X-rays will interact with the electrons in the atom, and, if the X-ray energy is sufficient, will interact via the photoelectric effect or scatter via the Compton effect, either of which can ionize the atom, and thus X-ray energy is absorbed.

Focussing X-rays generally requires single crystals of a heavy metal, preferably with a characteristic X-ray energy higher than that of the X-rays being focussed.

 

[inha]

Capillaries are kind of lenses too. Kind of. They're not quite as good as Fresnel zone plates or Kirkpatrick-Baez mirrors at producing microbeams but on the other hand do not require as much space and can be easily used at tabletop devices.

 

[cronxeh]

Hmm.. what about biooptics that can bounce the X-rays around? Id figure the degree of reflection would be smaller, but if its organic then perhaps there could be an animal that could see X-rays, of course the circumference of such eye would have to be many times higher than humans but in principle if they had an internal material that could reflect xrays at a higher reflection rate then it could like a catadioptric telescope (Maksutov type telescope)?

No seriously is there any reason why a material could not be 100% reflective to x-rays on a molecular level? I guess that's my real question. Is there such an electron configuration that pretty much resists any EHF EM wave interaction?

 

[jack47]

No seriously is there any reason why a material could not be 100% reflective to x-rays on a molecular level?

you can find a theoretical tabulation of the 'mass-absorption coefficient' of every element between hydrogen and Uranium for X-ray energies in this link. My PhD project involves measuring some of these X-ray absorption coefficients, and the tabulation is pretty accurate.

http://physics.nist.gov/PhysRefData/FFast/html/form.html

To answer your question, pretty much every element is a strong absorber of X-rays. Particularly once you hit the metals above Z=11. This is because X-rays tend to have a nice energy to take part in photo-ionisation, where an X-ray is absorbed by one of the inner electrons in an atom, flinging the electron off the atom toward freedom! This is the main mechanism by which X-ray absorption occurs.

There is a number of interesting things that relate to this (e.g. XAFS) but i guess I won't go into that . So sorry, but just about any substance made out of protons, neutrons and electrons absorbs X-rays strongly.

 

[SciFiGuy]

The problem is nuclear 'bombs' is that the energy burst is more or less isotropic (not to mention very destructive, and otherwise destabilizing), and once would catch only part of the nuclear energy. The energy, primarily gamma and X-ray radiation can be focussed (somewhat) using tubular metal structures, and the photons primarily 'go in one end and out the other'.

Hmm...so does that mean that nukes produce coherent light?
It also means that someone should fix this Wikipedia article.
http://en.wikipedia.org/wiki/Laser_applications

 

[CGHW01]

I know this posting is rather old, but I thought I would add something.
As it happens, it is possible to focus X-rays using lenses (not just grazing incidence mirrors).
You can click here:
http://www.institut2b.physik.rwth-aachen.de/xray/references/SPIE4783.pdf

to find an article about "Beryllium parabolic refractive x-ray lenses" to be used on synchrotrons.