Steve B
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 Feb 8 comment Maxwell equations and symmetry Don't forget about vectors versus pseudovectors, when you're doing the P transformation. Feb 1 comment About partially polarized light and the degree of polariztion #3 - No. For example, if you mix 1 watt of circularly polarized light with 1 watt of unpolarized light. Jan 30 comment Do holes have wavefunctions? Normally people bypass the whole discussion by making the single-particle approximation, i.e. not talking about Slater determinants in the first place, but instead treating each electron or hole as an independent particle. Many-particle-effects are taken into account semi-heuristically (if you need higher accuracy) by "exchange forces" and "pauli blocking" etc. etc. (You asked about Slater determinants, so I answered, but this whole topic is not the usual approach.) Jan 30 comment Do holes have wavefunctions? An electron-hole excitation is another way to say "move an electron from the valence band to the conduction band". So you would replace one of the valence-band wavefunctions with a conduction-band wavefunction in the Slater determinant. Jan 29 answered Do holes have wavefunctions? Jan 29 answered Maximising entropy when energy is shared between systems Jan 29 comment Why does $E=\nabla\phi$ follow from $\nabla\times E=0$? en.wikipedia.org/wiki/… - click "show" in the gray box to see a proof Jan 15 answered If you “disobey” the constraints of the Kramers-Kronig relations, what happens? Do you get non-physical results? Jan 15 revised Is coherent light required for interference in Young's double slit experiment? more on temporal coherence Jan 6 awarded Custodian Dec 29 comment Fermi level in equilibrium and non-equilibrium situations Possible duplicate: physics.stackexchange.com/questions/68162/… Dec 19 answered Understanding Wikipedia's “Semiconductor Band Structure” diagram where the bandgap appears to increase with increasing density of states Dec 5 comment Lasers and Collimation You need the correct definition, not just an unambiguous definition. For example, if you say "'neutron' is a term for any neutral particle", it's an unambiguous definition, but it's not the correct definition. :-P You can't call something a "plane wave" unless it has planar wavefronts (note the plural; one planar wavefront is not enough) AND (related to that) it has constant intensity in the lateral directions. The Naik quote is consistent with that. Again, you can look it up in any textbook or ask any expert what "plane wave" means. Dec 5 comment Lasers and Collimation "Plane wave" is a technical term with a standard definition that you can (and should) look up in any textbook. You'll see that the definition of "plane wave" is not what you think it is. (Sure, if you look around enough, you can find someone who has misused the term "plane wave". But I promise, the term "plane wave" is completely standard and unambiguous.) I'm glad you seemingly understand the physics of light propagation, but you do NOT know the terminology for talking about it, e.g. the standard definitions of "plane wave" and "collimated". Dec 3 comment Lasers and Collimation I hope you are aware that a Gaussian beam is not a plane wave anywhere, full stop. It is not a plane wave at the beam waist, it is not a plane wave anywhere else. Nor is it "collimated" at the beam waist, or anywhere else. I think you're confused about the definition of "plane wave", and "collimated". Dec 1 comment Lasers and Collimation I wrote "it's impossible to put 100% of [a laser's optical] energy into a perfect gaussian beam". This is obviously true because lasers have finite lateral size while gaussian beams do not. Are you really arguing that this statement is not true? Your comment above ("...not part of the beam") sounds like "100% of the energy goes into the gaussian beam, if you ignore the energy that does not go into the gaussian beam". Are you really arguing something so silly? If not, I don't understand you. The paper you linked to references a ~99.3%-efficient coupling, which they rounded to 100%. Dec 1 comment Lasers and Collimation @LukeBurgess - As you go away from the center of a gaussian beam, the intensity reduces exponentially, but never reaches zero in a finite distance. Therefore a finite-sized source or cavity CANNOT be 100% mode-matched to a gaussian beam. Maybe you can find a source that puts 99.99% of the energy into a perfect gaussian beam, but not 100%. Dec 1 comment Lasers and Collimation @LukeBurgess -- You have a funny definition of "collimated" if a wave can be "collimated at a single z-position". The whole point of collimating a beam is that it is supposed to stay collimated as it travels, until it hits the next lens. A beam of finite size can never be perfectly collimated. You can prove it by thinking about photons, or by working through Maxwell's equations, or by thinking about Huygens' principle, or by thinking about diffraction, or by thinking about fourier transforms and plane-wave decompositions. (Actually, these all amount to the same thing.) Nov 30 awarded Guru Nov 27 awarded Mortarboard