Thank you. I calculated the problem now, but the solution is lengthy and I guess it'll be easier to just try it out with the accordant waveplates :rolleyes: :smile:
I figured that I only need two waveplates to produce any desired linear polarisation. A quarter-wave plate will turn elliptical...
With a combination of wave plates in the order \lambda/2 - \lambda/4 - \lambda/2 it should be possible to achieve any polarisation. But I don't understand why: the first wave plate switches the polarisation direction, the second changes linear to circular polarisation and vice versa, and the...
hello.
I've got a gaussean beam, which is collimated with a diameter of 2mm, and a wavelength of 1112nm. I need to focus it to a beam waist of 25µm, but my lens with the smallest focal length I have is still f=300mm, so I need to build a telescope:
---collimated beam (w0)-----|lens f)-----beam...
The idea behind it is:
Before it gets doped, the semiconductor is perfectly happy with its electron distribution. Then it gets, e.g., p-doped. Nothing holds the extra hole anywhere except for the potential of the doping atom, so you can calculate its effective Bohr radius as said above, taking...
Semiconductors and isolators are only different in that the energy gap of the former is smaller than 2eV, and of the latter it is larger. I can change the energy gap by doping - but can I make any isolator a semiconducter? What are the limitations?
If you use the envelope wave function, you get an H-atom like energy spectrum (e.g. for n-doping):
E_D(n) = E_C+\frac{m*}{c^2 m}E_H = E_C - 13.6 eV \frac{m*}{j^2c^2m}
where Ec is the energy of the conduction band, m* the effective mass of an electron, and j an integer.
From that, you get an...
Yes I know it sounds a pretty stupid question, but it just seems to be opaque to my understanding.
Thanks for your answers so far (*notes* effective mass, velocity of sound)
If, say, I had an exam about solid state physics and plasma physics and I were asked to draw and explain dispersion...
Dispersion relations have the tendency to confuse me.
In general, I know what dispersion is, but trying to apply it to crystals, I just "can't see the forest among all those trees". :uhh:
In phonon dispersion, acoustical and optical phonons have quite a different dispersion behaviour. Why is...
So I seem to have mixed up the 2fold degeneracy of the conduction band with the 3fold (2fold) degeneracy of the valence band.
Thank you for your answers, it all makes more sense now.
Hm, I was thinking too one-dimensionally. Cheers.
But wait. Why are there only different valleys (or directions) if the band gap is indirect?
There is no valley degeneracy in GaAs, and it has the same crystal structure as Si except that it has a basis of two different atoms and Si a basis of...
Hiya,
trying to learn something about the band system of semiconductors, I found that the conduction band is degenerated at the minimum by valley degeneracy.
Do you know where this comes from? In how far is it dependent of the form of the band gap (i.e. direct, indirect)?
I would be...
Hello,
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I have got a Michelson interferometer and measure a laser beam (HeNe @ 633nm). I move the mirror with a step motor of unknown step length and measure the intensity of the beam. I get a nice beat pattern out of that, with "wavelength" of the carrier wave being 14 steps and of the...
No, work is not a state function, only U is. As said above:
U = Q + W
You can get the same value for U for many different combinations of Q and W. In this special case, Q = 0 so U = W.
It is not the water that is travelling: the water particles are only moving upwards and downwards. The formula you quoted is for phase speed:
v = \nu \lambda = \frac{\lambda}{T}
because a wave propagates exactly one wavelength \lambda far in the period T=1/\nu
In general, the velocity of...