Optics is the study of light, and its interaction with matter. It includes topics such as imaging systems, fiber optics, lasers, quantum optics, and more.

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Does ordinary refraction exert a couple on the refracting medium?

Refraction gives rise to a momentum change orthogonal to the propagation direction. This must result in an equal and opposite change to the medium at the boundary. Entry and exit cancel, and the ...
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393 views

What is fidelity in experimental QM?

I often comer across the term high fidelity in QM papers. Does fidelity imply ratio of entangled photons / total photons? Is there some other metric to measure how good the source is?
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Wave or particle in the end

In Young's double slit experiment I put a convex lens after double slit and direct interference pattern on to a fibre. Then I expose the other end of fibre to a screen. What will I observe - the ...
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278 views

Why Negative refractive index is negative

$n=\sqrt{\epsilon \mu }$ Negative refractive index happens when permittivity ($\epsilon $) and permeability ($\mu $)of a material is negative. My question is, if permittivity and permeabilitity of a ...
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3D coherence of light speckles- difference between Airy and gaussian speckles

In this article, http://www.dfm.uninsubria.it/laboferri/web_page/articoli_pdf/PRA_2009-Magatti-Three_dimensional_coherence_of_light_speckles-experiment.pdf, the 3D-coherence properties of light ...
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How would I perceive a purple ball when traveling at relativistic speeds

I have a 'thought experiment' which I'd like to ask about. I was thinking what speed I would have to drive towards a crossing to see a red light as a green light - pretty easy, using the doppler ...
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What's the size of the smallest possible CCD/CMOS pixel size?

For a given wavelength $\lambda$, is there a limit on the size of the sensor pixel, regardless of the optical equipment attached to the sensor?
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Why is this way of calculating the diffraction pattern valid?

I've seen that in some books (Fowles) the intensity of the diffraction pattern is calculated in the following way. We place the source $S$ and the point at the screen $P$ in the line perpendicular ...
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Output of a beamsplitter with photon number (Fock) state inputs

Given a beamsplitter drawn below, where $\hat{a}$ and $\hat{b}$ are input modal annihilation operators, transmissivity is $\tau\in[0,1]$, and output modal annihilation operators are ...
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Smaller Airy disk with another lens?

Is it possible to reduce the airy disk size produced by one lens with another lens placed after the previous one? For example, parallel ray incident on first lens L1 (without aberration), then there ...
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152 views

How does one align a laser using two adjustable mirrors?

Suppose we would like to get a laser beam to pass through a particular point in space in a particular direction. At our disposal we have a laser, two adjustable mirrors (can rotate up/down and ...
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How do laser rangefinders work when the object surface is not perpendicular to the laser beam?

I find the functioning of a laser rangefinder confusing. The explanation usually goes like this: "you shine a laser beam onto the object, the laser beam gets reflected and gets back to the device and ...
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Is the number of rays projected by a source of light finite?

Take a source of light which gives out infinite number of rays, each ray with finite number of photons and each photon with a finite amount of energy, Then, Aren't the number of photons become ...
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Free Optics Simulation Programs

I'm having an extremely difficult time finding an optics program that is easy to use and offers accurate physics simulations. I'm not asking for much, I just want to be able to simulate a laser going ...
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Are telescopes with a concave lens useful for astronomy?

Are telescopes with a concave lens (instead of convex ones) ever useful for astronomy? And if so, where are they used? Do they ever affect resolving power?
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238 views

Why does the point of intersection of two shadows look brighter?

When I sit in my garden during the day I always keep looking at the two intersecting shadows of two rods. It looks something like this: What I find weird about it is that at the point of ...
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Human perception of distance

When we see things around us, distant objects look smaller to our eyes than nearby objects do. Is there any physics-related reason why our eyes or brain perceive things like this? Or if this is ...
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276 views

Visibility of moon-based laser from Earth

If someone (or some robot) on the moon were to point a laser at the Earth, how many watts would the laser need, to be easily seen with the un-aided eye from Earth? Obviously this depends on a number ...
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389 views

Seeing one's back on the event horizon

If we would hypothetically be exactly on the event horizon, we should see our own back, because of the circular motion of photons on the event horizon, right? But what would be the image size, or $-$ ...
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Could the speed of light change outside our solar system

Theory: The speed of light changes when it enters or exits the solar system due to a difference in medium (dark matter possibly). Potential problem 1: refraction If there was a speed change at the ...
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Thin lens formula

Can someone help me or guide me how the thin lens formula: $$\frac{1}{s_1}+\frac{1}{s_0}=\frac{1}{f}$$ can be proven? I was trying to prove it on my own using similar triangles, only to fail.
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Lasing in a 2-Level system?

What exactly is the difference between 2-Level, 3-Level and 4-Level systems? Why can we not achieve stimulated emission in a two-level system using optical pumping?
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In optics, how does the vacuum state compare to thermal radiation?

In quantum optics, a perfect absorber of light is said to emit the "vacuum field". In practice, any beam dump will be at finite temperature, so it will emit blackbody radiation. How do these fields ...
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What is the meaning of “CW” in LASER?

I am reading a user's manual, and the word appears here. At first, I think "CW" means "center wave". But later, I find that the meaning of "CW" is "continuous wave". It makes me confused. ...
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Make a semi transparent mirror with copper

The question: How would you make a semi transparent mirror (50% reflection, 50% transmission) with glass with a layer of copper. For light $\lambda$ = 500nm Try to be as realistic as possible What ...
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Why are non-linear optics called non-linear?

Looking at the wikipedia article on nonlinear optics you can see a huge list of frequency mixing (or multi-photon) processes. What makes these different from single-photon interactions? More ...
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Possibility of making an experiment in a classroom to simulate DNA diffraction

I am a TA in a structural chemistry class. The professor want me to show students how Watson and Crick determined the structure of DNA from X-ray diffraction results of DNA crystals. The professor ...
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Optically thick media

What does "optically thick media" mean? Does this property depend on the length of an enclosure? Why is the diffusion approximation for the radiative transfer equation applied to optically thick ...
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What is the difference between the words transparent and translucent?

Merriam Webster defines transparent as: Having the property of transmitting light without appreciable scattering so that bodies lying beyond are seen clearly. And translucent as: ...
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Difference in perception of unpolarized and polarized light

What is the difference in perception of polarized light and unpolarized light? What difference does polarized light cause to our eyes?
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Why would an object appear a different size when in water?

A friend of mine has a homework question and we're having some trouble figuring out what physical mechanisms come into play for this. An underwater swimmer sees a spherical air bubble that appears ...
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697 views

Goldfish perspective

What does the world look like from the Goldfish point of view, from inside a spherical aquarium? If our eyes were inside, would we be able to see the straight lines, focus on different objects and ...
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How to make the projected image smaller by adding one ore more lenses in front of the built in projector lense?

I have a projector that creates a large image, even if the distance to the screen is short. The device is very small, approximateley 10x10 cm if you look from above. The height is only 3 cm. I ...
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If I reflect light from a projector using a mirror, then is the reflected image real or virtual?

I am in a great confusion about this question. In our school, we have been taught that: A real image is an image which can be obtained on a screen. It is always inverted. A virtual image is ...
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Why don't fogbows appear on clouds?

As far as I know clouds are lot of small droplets condensed in air. If droplets are large enough we see a rainbow. If they are small we see a fogbow. Although the size of the droplets are big enough ...
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Shape of the rainbow

I have watched Walter Lewin's lecture(http://www.youtube.com/watch?v=6QVbE_tU2sA) which was about the rainbows. But there is still a question bothering me. I understood the first part of the ...
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Fourier transform of two pulses of light

I have laser beam path that fires two pulses of light in a gaussian distribution, so the intensity graph over time is two identical gaussians separated by a distance $t_0$. In other words, a gaussian ...
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Polarization of Light

How do materials polarize light? I know that they polarize light in the same plane, but light has two perpendicular directions with the two fields, so which direction is reflected and why? And if ...
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Diffraction through one slit?

When Thomas Young first conducted his double slit experiment to prove the wave nature of light, he shone light through two slits, creating an interference pattern. Apparently he then covered up one ...
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778 views

Why can't I see far when I look in a mirror?

I'm myopic. It's a fact. I understand exactly how it works because Internet told me light rays encounter themeselves too soon in my eyes... that is why I can't see far objects even if I see near ...
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Why does shining a laser into an iPhone camera create these shapes?

When I shine a laser light into an iPhone 6 camera I get these weird shapes: The shapes are in no way in the background behind the laser. What causes these to appear? I know about typical lense ...
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Can there be a string so thin as to be invisible, but that can still support a visible weight?

A spider web thread is very thin, yet it can support a spider. Given that the human eye visual acuity is finite, are there materials, natural or man-made, sufficiently thin that a string made from ...
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Does optical fiber preserve the angles of incoming light?

I am reading up on optical fibers and there's one thing I haven't understood yet: Does an optical fiber preserve the angles of incoming light? For example, if we light two LEDs in front of an ...
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Three polarizers, 45° apart

If light is passed through two polarizing filters before arriving at a target, and both of the filters are oriented at 90° to each other, then no light will be received at the target. If a third ...
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What's the name for taking pictures of air flow in a normal room?

There is a way to photograph air in a room. It makes convection, breathing and movement visible. The result looks a bit like a soap bubble. This is some kind of optical effect. No special gases or ...
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Diffraction Pattern on LCD Screen

I was up late working with my red LED headlamp on and when I was looking at the black part of my LCD (Apple Retina Macbook Pro) screen I noticed this interesting diffraction pattern. I'm confused ...
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Is the IoR of water exactly $4/3$?

The index of refraction of water is commonly cited as $n \approx 1.33$, to varying numbers of decimal places. I've never seen a decimal expansion for this value with any digit other than $3$ past the ...
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174 views

Why does sea colour differ from place to place?

If you notice the colour of sea changes from place to place. At some places it is of blue or green and even different in beach. What must be the reason?
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Does diffraction occur before interference?

In the double slit experiment, light passes through two slits and the waves interfere and form an interference pattern. A single slit is required for diffraction. So, I was thinking about whether ...
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Counterpropagating beams in a ring cavity lasers

Ring cavity lasers usually has a intracavity element like a optical diode to forbid standing wave pattern and, consequently, spacial hole burning and related instabilities. So, my question is: why to ...