New answers tagged

-1

What experimental proof do we have for the hypothetical Lorentz (without t) condition or similar Gupta Bleuler condition? The whole theory of non-existing longitudinal vacuum waves/photons is based on theoretical hypothetical assumptions, c'mon this is not physics, no matter "how advanced" your math theory is. There is plenty of experimental evidence that ...


4

Photons, as each massless particles, are characterized not by spin (which is defined as total angular momentum at rest, and mathematically corresponds to irreducible representation of the little group of representation), but by helicity $\lambda$ - the projection of total angular momentum on the direction of motion. Actually, the Casimir operator, which ...


7

By definition of spin $S$ it is a positive integer number or zero. Not to confuse with the spin projection possible values $S_z$, which may run from $-S$ to $S$.


3

Spin 1 just means that the spin in any direction can assume values out of {-1,0,1}. The 0 is only possible for massive particles, so the photon can have spin -1 or +1. That's like clockwise and anticlockwise circular polarization


5

A circularly polarized light state can be thought of as a superposition, with equal magnitude weights, of $x$ and $y$ linearly polarized light states, with the $y$ component either leading or lagging the $x$ by a quarter of a period. Therefore, you can extinguish a beam of such light with linear polarizers in several ways, of which two are: Method 1 Pass ...


2

You are correct in asserting that unpolarized light contains a mixture of many polarizations. However, each of these polarizations can be expressed as a combination of horizontally and vertically polarized light. Diagonally polarized light can thus be seen as containing both horizontally as well as vertically polarized light. When a horizontal beam of ...


2

In your final two paragraphs you have it backwards. At Brewster's angle the reflected light is totally polarized, but the total polarization of the transmitted light is usually rather weak. Compare reflection coefficients $r$ and transmission coefficients $t$ from the Fresnel equations: Reflected light is completely polarized at Brewster's angle because ...


0

I'm assuming your input photon has a known polarization (say horizontal). You won't see interference, because the polarizers act as a "which-path" measuring device. If you erase the polarization information, the interference pattern will appear.


1

From a theoretical point of view, you can get arbitrarily close to 100% transmission by using more and more linear polarizers. As the angle between each gets closer to zero, you get less polarization loss even as the number of filters increases. Unfortunately for you, while the theoretical loss goes down, the efficiency of real filters are not 100% and the ...


0

You want to read the classic paper by Richard Beth, Mechanical detection and measurement of the angular momentum of Light, Physical Review 50 115 (1936). Beth used bright circularly polarized light to drive a torsion pendulum in a vacuum chamber, and was able to observe torques due to circular polarization of order $10^{-16}\rm\,N\,m$. This was with a ...


1

The polaroid sheet consists of a polymer into which a dye, originally iodoquinine sulfate, is dissolved. The film is aligned by stretching, and this causes the molecules of iodoquinine to align along the pulling direction. Photons are absorbed by the iodoquinine whose electric (or transition) dipole is aligned along the long axis of the molecule, but only if ...


3

All of your claims are essentially true. The angular momentum of light, in both its orbital and spin varieties, is indeed angular momentum that can be transferred to matter to make it spin and give it the garden variety of mechanical angular momentum. This is well explained in the relevant Wikipedia section, with good references for experiments that show it. ...


1

I don't know about sources that emit polarization-entangled photon pairs, but polarization-entangled pairs can be obtained from a polarized source in many ways. One example is Spontaneous Parametric Down Conversion (SPDC). Quoting from Wikipedia: In a commonly used SPDC apparatus design, a strong laser beam, termed the "pump" beam, is directed at a BBO ...


1

On selection rules: Say the Zeeman effect targets an atom with a ground state of angular momentum $J=0$ and an excited state of angular momentum $J=1$, such that the magnetic field splits the excited state into 3 sublevels corresponding to $M=0,\pm1$. The selection rules for transitions to/from the excited states are imposed by conservation of angular ...


0

quantum experiments are probabilistic (weird non-classical thing): they take a mixture of states the result of the experiment is one of the states each result occurs with a probability proportional to the amplitude of the states after the experiment, the system assumes the state that was observed well known example: probability that an electron hits a ...


1

What is the difference between "observed" and "true" angles of rotation? What I think you mean is that the "true" angle is "specific" to the compound. It is defined like absorption coefficient $\beta$ as a constant of proportionality : $absorption \space A = coefficient \space \beta \times concentration \space C \times path \space length \space L$ $...


1

For your first question you want to find a way to express the observered angle in polarization in a form that is independent of the concentration of the molecule and pathlength of the light. In other words you are looking for units of angle per concentraion pathlength and you need to divide by the concentration and pathlength. Of course when you want to ...


0

This figure helps to get an intuition of how light is made up of photons Left and right handed circular polarization, and their associate angular momenta. The purple sticks in the middle are the photons which build up the macroscopic light. The individual photons, as elementary particles are point like, and are characterized by their spin , +/-1, and ...


1

Unpolarized light is more properly called light with random polarization. That makes it more clear what it means: the polarization state (circular, linear, elliptic) varies randomly over space, wavelength, and time. Consider the scenario below, where a diffuse light source is converted to a collimated beam with a narrow range of wavelengths $\lambda\pm\...


1

I tried to confirm the suggestion of @Peter Shor in the comments by creating a simple program that generates vectors by randomizing the angle $\phi$ from $0$ to $2\pi$ of a vector $\vec A_i = A\hat r_i$ that lies on a x-y plane. All the vectors have the same amplitude $A$. The program adds (by vector addition: summing all x-components and y-components) n = ...


4

One way of thinking about it is to consider light as made up of lots and lots of photons. You're not going to see destructive interference unless the polarizations of all of these photons are lined up and they all undergo destructive interference at the same time. If they're random, some of them will interfere destructively, some of them will interfere ...


1

I will try a classical light wave explanation and hope that someone smart will come up with a full quantum mechanical description to enlighten me as well. Lets imagine we have a light source which is providing unpolarized light at a single frequency. When we measure the lights intensity, we are actually measuring the absolute value of the electric field ...


1

There are two types of angular momentum of light, which are exactly analogous to their counterparts for massive particles. Light can have orbital angular momentum (OAM), which is associated with helical wavefronts, that is, with a nontrivial rotational structure in the spatial dependence of the beam. Usually this comes in the form of Laguerre-Gaussian ...


0

Yes, it is possible to use a standard liquid crystal display to switch the polarization state of light. But, it may be impractical to do so, especially with modern thin LCD construction. LCDs make use of two polarizing filters, 90 degrees to each other. The wikipedia article for LCDs has images and explanations of this. In principle, you could ...



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