If I pass a laser light through 100, 110, 111 or polycrystal sheet, will scattering, diffraction happen or not?
As when x-ray pass through different planes, it happens.
Can anyone suggest the phenomena or concept?
As laser have higher wavelength than x-ray, so .
Will it pass without any scattering or diffraction?
The following text is useful for concept of diffraction and scattering of high frequency electromagnetic waves in different directions.
http://eprints.maths.ox.ac.uk/452/1/fozard.pdf
The guiding principle of diffraction is the Bragg condition:
n*lambda = d*sin(theta)
where lambda is the wavelength, d is the spacing between the diffracting objects, theta is the angle of diffraction, and n is an integer. For each n you get another allowed diffraction direction, and that is what makes the spots in a diffraction pattern.
In crystallography d is the distance between planes of atoms. If there were only planes in one dimension the diffraction would make lines. The pattern of atoms in a crystal can be seen to make lots of different sets of planes in different orientations, and that is why the diffraction makes spots. These are the intersections of the diffraction patterns that you would get from all the different sets of planes. Nevertheless the spacing of the spots in any one direction in the pattern is just the Bragg condition for the atomic planes in that dimension.
Now consider the Bragg condition for visible light. The atomic spacing might be 0.5 nm while the wavelength of, say, green light is 500 nm. That means that the angle between the zero order undiffracted spot and the first order diffracted spot is:
sin(theta) = 1/1000
Certainly the small angle approximation applies, so the spacing of the diffraction spots is about 1 mrad. So you can see that the diffraction pattern is very small and wouldn‘t show up in most measurements. This is the reason crystallography is done with the much shorter wavelengths of x-rays
Now that is where the spots will be, but there is another condition that determines how bright the spots will be. That is determined by the scattering function of a single atom or crystal unit. For particles much smaller than the wavelength of light this is described by Rayleigh scattering. You can look it up, but basically the scattering angle is a very strong function of the ratio of the size of the scatterer (or really the size of its electric dipole moment) and the wavelength going as d/ lambda ^4. You can picture ocean waves crashing into a boulder at the shore. If the boulder is on the order of the distance between wave crests the wave crashes around the boulder introducing lots of directional change. However the wave rolls right past a pebble (or perhaps a thin vertical rod would be a better example) almost completely unperturbed.
in our visible light example d/lambda^4 is on the order of 1e-12. The light doesn’t scatter off the individual elements, so no light is diffracted into even the first order Bragg diffraction spots. In short visible light does not diffract from crystal lattices. This is the even stronger reason crystallography is done with x-rays
Oops! I screwed up and inverted d and lambda. The Bragg condition isn’t sin(theta) =1/1000. It’s sin(theta) = 1000 which is impossible.
Sorry. I shouldn’t answer questions when I first wake up.
Just search google "scattering optical electromagnetic waves" and you certainly find a lot of explanations, enough for you to read and learn.
You only get significant scattering into a diffraction pattern when the spacing is similar to or larger than the wavelength, so that reflections from adjacent molecules or atoms are at significantly different phases. For optical waves the wavelength is more than 400 nm which is much larger than the molecular period, so the effect is too small to see. The wavelength of x-rays is similar to the period, so there is a diffraction pattern.
Every atom or molecule scatters, probably with a cardioid pattern or similar, nearly omnidirectional. If there are lots of scatterers per wavelength then the sum of all of them is only significant in the forward direction. Once the spacing is more than half a wavelength there are other directions where the sum is significant.
There are two different cases.
At first, if you will have PERIODIC structure of scatters like atoms or other objects, to have diffraction on such structure you have to fulfill following condition:
d*(sin(theta_inc) - sin(theta_scatt)) = k*lambda/n,
where d is distance between scatters, theta_inc and theta_scatt are angles of incidence and scattering, k and n are order of diffraction and index of refraction. So, diffracted (scattered) beam exist even for the case of grazing incidence if d>=lambda/(2n). This is the reason why for crystallography one used X-rays with
d ~ lambda.
Second case is realized if you will have SINGLE object on the ideal plane or into homogeneous bulk. In such a case you will have scattered wave even for the case of atom as scattering object, because incident wave will produce oscillation of dipole (and other) momentum and field of such oscillation will be in fact scattered light. For the case of single atom, of course, it will be very weak, but it will exists in any case.
Some time ago we have observed such kind of scattering by atomic surface structure:
Article Atomic structure display of a real silicon surface under lig...
- Badges
- Science topic