# Tag Info

16

The type of headlight lenses shown in the images, with the rows of fringes, look like Fresnel lenses. This is essentially a lens with a series of fringes that act as prisms, each at a slightly different angle but with the same focal length. That has the effect of reflecting the non-directional light from the bulb in a particular direction. I'd think the ...

8

The distance where light has a circular orbit is actually $1.5r_s$ not the event horizon. This distance is known as the photon sphere. In principle a shell observer hovering at this distance could indeed see their own back. The proper distance is indeed just $2\pi r$, however the object would look bigger than expected because the curvature of spacetime has ...

8

Nobody is answering this question, so I'll take a stab at it. Consider the mirror. Suppose you started your experiment by (somehow) putting it in a nearly-exact momentum state, meaning there is a large uncertainty in its position. Now, when you send a photon at it, the photon either bounces off or passes through. If the photon bounces off the mirror, it ...

5

You are right in that there is only one set of physical things going on in diffraction. The reason people talk about two different kinds, is because there are two natural limits in a diffraction problem. The intensity of light you see at any point is the contribution from all of the points at the aperture, where the contribution from any point decreases as ...

5

There are two parts to those lights: the reflector, which gathers the bulb's output and creates as focused a beam as possible the lens, which modifies that beam as desired. A focused beam makes a lousy headlight. You only see a small patch way in front. The extra ridges in the pictured lenses are vertical, which means they will spread the beam ...

5

Any measurement of the photon's energy (i.e. frequency, or free-space wavelength though making a direct identification of particle properties to wave properties is a little sketchy) will return a single value. Every time. But ... you can't fool Heisenberg and if you have confined the position of the photons---say by insisting that it hit the detector---then ...

4

Typically sheets of laser light are usually achieved by bouncing the laser off an oscillating mirror, though you could achieve a similar effect by passing the light through an oscillating or rotating prism. If the frequency of oscillation of the mirror is fast enough persistence of vision makes it look like a steady sheet of light. Prisms broaden a beam of ...

4

Provided the prism is of high quality (broadly speaking its faces need to be optically flat, and its material free of defects), then there should be no broadening. What the prism does is disperse different colours in different directions. Since the source is monochromatic there will be no dispersion. However if the source isn't monochromatic (within a ...

4

As described in the link you provided, Raman scattering is any scattering that changes the frequency/wavlength/energy of the light by transfer of energy to or from the matter that scatters it. If the matter absorbs energy it is called Stokes Raman scattering (sometimes shortened to just Stokes scattering). If the matter loses energy it is called anti-Stokes ...

4

They are equivalent. The formal study of this kind of problem is called "The Calculus of Variations", and it requires that you have some level of understanding of integration and of partial derivatives. You may imagine parameterizing the path taken in any way you want, say $$\vec{f}(t;\, \alpha,\beta,\delta,\dots)$$ where the function describes the ...

4

Your observation is linked to the "Optical window in biological tissue". Like you already suspected, the absorption of blue light in tissue is higher than the absorption for red light. Best read the related wikipedia article, where all relevant effects are nicely illustrated. http://en.wikipedia.org/wiki/Optical_window_in_biological_tissue

4

The diffusion approximation is one solution to the radiative transfer equation. In general, the choice of applying this particular solution depends on the optical limit, as you say. For an optically thin medium, radiation will travel and may interact along the way. This is not characterized as a diffusive process, because the beam can interact with the ...

4

It is not the case that all the rays will focus at the same point. Rays with different directions will focus at different points. You are probably thinking about rays parallel the the optical axis all converging on axis, at a distance equal to the focal length from the lens.

3

I think you have some problems with the sign convention. At first, ask yourself the question "why did I need the sign convention?" For the moment, forget the sign convention and let's derive the formula related to lenses from the scratch using only geometry. Let us consider: p= distance of the object from the optical centre q= distance of the object ...

3

If the Airy disk is smaller than a pixel (rather common), then you want to defocus. Star trackers on satellites do this in order to get sub-pixel pointing accuracy. If the Airy disk is much larger than a pixel, then you probably don't want to defocus. In the latter case the situation is complicated by aberrations and the problem of modeling the shape of ...

3

Hopefully a sharper restatement of the question is: what's the difference between a mirror and a photocathode? Experimentally, in a Mach-Zender interferometer we can fold light paths with a mirror while maintaining coherent interference, but passing either beam into the photocathode of a photodetector destroys interference effects, even for photons that ...

3

$r=1.5r_s$ for the Schwarzschild solution corresponds to the unstable maximum of the effective potential for a photon, therefore you won't be able to see much in practice, since practically every photon on this orbit will either fall in the black hole or escape to infinity.

3

An optically thick medium is one for which the mean free path of a photon is low. This means that a photon won't be able to travel very far before it interacts with the matter than makes up the medium. The measure of optical thickness, optical depth, does depend on the volume of material in the medium. For example, for a material with a fixed density, ...

2

From your question, I guess the double mirror configuration is just an example you thought of. I suppose your question actually is about if a photon can be trapped. Then basically yes. A device able to confine electromagnetic wave or light or photon is called cavity. You should understand a photon does not necessarily means a propagating plane wave. It can ...

2

Yes, it's ok, but it's an explanation that has been stripped down to bare bones, and leaves out quite a bit. Here's a little more to help prop up the explanation. First, it's important to realize that in a condensed phase like a solid or liquid the light is not interacting with molecules in isolation. Light is interacting with all of the molecules. ...

2

Although the physics in the other answers is correct, their conclusions unfortunately aren't. Prisms can be used to make a laser beam wider in one dimension. This is, in fact, common practice in circularizing the output of laser diodes which are typically highly elliptical (they go by the name anamorphic prism pairs). Here is an example from Thorlabs.com. ...

2

There's no difference between plasmon and plasmon polariton. Both of them indicate the resonant excitations involving electromagnetic wave and collective electronic motions simultaneously. "surface" stresses that the excitation in many cases occurs at the interface of a metal and a dielectric. However, there exist bulk plasmons as well. So "surface ...

2

While rob is correct about the quantum mechanical picture I think that this case is at least as easy to understand in the classical description. Classically circular polarization can be described in terms of a time-varying linear polarization, so lets just look at two points on a wave. I'm going to chose a beam in the $+z$ direction at examine two points ...

2

From a quantum-mechanical perspective, circularly-polarized light is made of photons with their spins parallel to their momentum. The mirror reverses the photons' momentum but does not affect their spins, so the dot product $\sigma\cdot p$ changes sign. Both the quantum and classical approaches are examined in Beth's 1936 measurement of the angular ...

2

In the absence of noise they can both work the same (assuming you know the exact amount of defocusing, and you over-sample the Airy disk) In the presence of realistic noise, you are better off focusing the object due to the details of the noise. For intensity images, you are (likely) dealing with Riciean distributed data, and you are better off using a ...

2

It's not possible. There is a field of study called non-imaging optics dedicated to this kind of problem. See this Wikipedia page. FWIW, I don't agree that this question belongs somewhere else. I think it could live here, or in Engineering. Not sure where you would get better responses in this case.

2

Any optical fibre - and any optical waveguide in general - has a cutoff wavelength (and therefore a cutoff frequency or a cutoff energy) because wether light is confined in the film region (guided modes) or escapes to the substrate (substrate-radiation modes) depends on the propagation constant, $\beta$, which is related to frequency trough the dispersion ...

2

It's simply the diameter of the fiber core. In a single-mode fiber, only the lowest-order mode fits physically into the fiber.

2

To start with the double slit experiment gives interference even when the beam is composed by one photon at a time. The spot on the screen a photon/particle the statistical accumulation the interference seen as expected classically too. The joint comes because the photon as a quantum mechanical entity has a wavefunction that is the solutions of Maxwell's ...

1

There are many different forms of the mirror and lens formulas, each varying slightly in appearance, and each using a different set of rules as to what distances, focal lengths, and radii are positive or negative! The most important part of any formula is what I call the "wheres". Mixing one formula with another set of "wheres" leads to total chaos... In ...

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