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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14
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1answer
213 views

Why is Terahertz radiation so hard to generate?

This paper (and many others I've read) claim that searching for ways of producing THz radiation is a high-interest research topic. However, something I've just never understood is why it's so hard ...
1
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0answers
21 views

Why does a glass acts like a mirror in viewed at an angle? [duplicate]

There is a conference hall , glass door parallel to my desk. whenever the door is open, I can see reflection of images perpendicular to the viewing angle. But when the door is closed, I can’t see any ...
2
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3answers
75 views

Could the sky on a planet theoretically be any color?

The sky on the Earth is blue. Could the color of the sky on a planet with an atmosphere be of any color theoretically? Which colors are the most likely? I think it would be really awesome to have ...
4
votes
1answer
50 views

Options to correct rectangular laser beam profile?

We recently switched to a 405 nm laser diode which has a terrible beam profile -- it is a well-defined rectangle with an aspect ratio of about 10:1. The image below shows the collimated beam which ...
1
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0answers
28 views

Insect Eyes Vs Human Eyes?

Humans have frontal eyes. Less field of view. But better resolving power. Insects have lateral eyes. This means they have a large field of view. In some female insects the lateral eyes have much more ...
0
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1answer
18 views

doppler cooling temperature limit

Wikipedia shows a heating effect that causes minimum temperature achievable in doppler cooling as: "The atom performs a random walk in momentum space with steps equal to the photon momentum due to ...
0
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0answers
21 views

How much cheaper and smaller on average is SiPM technology over conventional PMTs?

I've heard it said that some of the major advantages of silicon photomultipliers are its low cost and compactness when compared to widely used photomultiplier tubes, but haven't found much information ...
1
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1answer
52 views

Lens with a mirrored coating [closed]

A biconvex lens of refractive index $n$ and radius of curvature $r$ and focal length $f$ floats horizontally on liquid mercury such that its lower surface is effectively a spherical mirror. A point ...
0
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2answers
24 views

Laser beam sensed by scattering

Can a laser beam, whether it is a IR laser or of the visible to human eye spectrum, be seen/sensed by an electronic eye like a photosensor/photodetector, not human eye, if the beam is just in air? For ...
12
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1answer
125 views

Sun in front of horizon after sunset; mirage or reflection?

The day before yesterday, I observed sunset while flying over the eastern Mediterranean. After the sun set, it seemed to 'continue' in front of the horizon. I managed to snatch a picture (sorry for ...
0
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0answers
25 views

How far away are we from a UV LED operating at around 100nm?

So far, we are down to around 250nm for UV LEDs. If I could get one at around 100nm that would ionize air I would find it very useful. Any ideas on whether this wavelength is feasible for a LED?
5
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0answers
159 views

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 ...
-1
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0answers
18 views

Optics..caustic curve equation

I went through this article: http://users.df.uba.ar/sgil/physics_paper_doc/papers_phys/ondas_optics/caustica1.pdf But I think that when we do F=0, we are assuming the centre of the curve to be the ...
1
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0answers
20 views

Fresnel equations of S and T waves and Isofrequecy Curves: Feeling confused

First of all sorry for my (probably) bad english. I've been studying propagation of light in anisotropic media from the Born and Wolf and from Landau "electrodynamics in continuous media" and I'm ...
0
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0answers
19 views

Implementation of Expectation Maximisation tomographic reconstruction

I'm trying to implement iterative expectation maximisation reconstruction for emission optical computed tomography, very similar to SPECT reconstruction. The algorithm given in the literature is ...
3
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4answers
60 views

Focusing and collimating laser light on a table top scale

I am looking for a summary of practical methods of focusing and collimating laser light, which I guess are contradictory objectives, or are they? For example, when I use typical small diode lasers, ...
0
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0answers
27 views

In Young's double slit experiment how can we determine the shape of fringes formed?

Does the shape of fringe change if the type of source is changed (point source or extended source) or if the relative position of slits is changed (both lie on a line either horizontal or vertical to ...
16
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3answers
3k views

Can light emit light?

How and why does the Huygens principle really work? I mean, does it always work? The Huygens principle: Every point on a wave-front may be considered a source of secondary spherical wavelets ...
2
votes
3answers
63 views

Laser beam photon counting

I'd like to know if devices exist that are able to detect the single photon missing out of a normal laser beam. I am aware of the fact that single photon counters do exist, but I'd like to ask some ...
6
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3answers
101 views

How big would a solar sail need to be to be detected from the orbit of Pluto?

Suppose we made a solar sail out of a highly reflective material. How big would that solar sail have to be for the Hubble Space Telescope to detect it visually at the average distance of Pluto?
-1
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0answers
27 views

Fresnel to Fraunhofer limit

I'm puzzled about what happens when distance L from obstacle to screen is continuously increased from a small value (Fresnel diffraction) to infinity (Fraunhofer diffraction). Please consider four ...
-1
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0answers
36 views

Why do clothes look darker or change color when they get wet? [duplicate]

Clothes can look darker or change color when they get wet. Why does this happen?
0
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0answers
22 views

The first term of Stokes Vector of natural light is zero?

Consider the electric field of a beam of natural light: $$ E(r,t) = E_0 \cos(k·r+wt) $$ Since this beam of light is natural, the vector E has all the components possible that satisfies: ...
1
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2answers
57 views

Understanding colored shadows [on hold]

When I turn on white lights, these chairs cast a shadow. However, when blue LED lights are turned on the shadow turns yellow. Why is this? Is this due to interference of light or is it just an ...
7
votes
2answers
405 views

How do I find the right lens for my laser?

I purchased this line laser recently and I'm running into a bit of an issue. The laser shoots out at a 120 degree angle which is perfect. However, once the laser spreads to about 4.25 inches, I need ...
0
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0answers
45 views

With the new time cloak technology could it be possible to stop time for everything except one person

So I was just reading up on some new research on national geographic from the Cornell University scientists and it seems that they've managed to bend waves of light around something to hide it from ...
0
votes
1answer
46 views

What exactly is an image?

When we say several rays meet to form an image, what is that which is formed? Is it an arrangement of unknown entities? What exactly am I looking at when I see my image in a plane mirror?
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0answers
20 views

How does a, halftone screen work?

Forever I've seen explainations that say a halftone printing image is made by photographing through a screen. But I have yet to see explained how that does the trick. Apparently the screen is placed ...
2
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0answers
27 views

What could cause the gradual loss (or change) of power in a CO2 laser over a long period (e.g. a year)?

For example, if it were a 10W CW CO2 laser that were used for ~45 minutes per day over a period of a year. Would you expect a slight reduction in power with age? Does the dissociation of CO2 occur ...
3
votes
2answers
43 views

Arrow that changes direction home experiment

I saw this cool optical effect in a experiment on Youtube: https://www.youtube.com/watch?v=G303o8pJzls Could anyone explain to me why the arrow points in the opposite direction? I have read ...
2
votes
1answer
86 views

Huygens' Principle During Reflection: comparing wavelets from before reflection with wavelets from during reflection

I was recently reviewing geometric optics, during which I read about Huygens' Principle and how it could be used to prove the Law of Reflection from the "light is a wave" viewpoint. I'll quote what I ...
4
votes
1answer
46 views

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 ...
2
votes
1answer
58 views

Why does larger permittivity of a medium cause light to propagate slower?

I was wondering about what physically happens when light is transmitted through a non-magnetic medium. Specifically, I’m trying to visualize how materials slow down light as the electromagnetic wave ...
1
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1answer
38 views

Can a polarizing beam splitter cube be used to replace two polarizers?

I have a design for a setup to look at the light reflecting off the back of the human retina. I would like to remove any specular reflection that occurs at the cornea. At the moment the idea is to use ...
0
votes
1answer
28 views

Cause behind bending of light in refraction [duplicate]

I know that refraction is caused due to change in speed of light but why does it bends? I also know that during refraction frequency is constant and wavelength is decreased since speed slows down. But ...
3
votes
2answers
56 views

How do HUD optics create readable text so close to the eye?

The human eye has a minimum focal length of about maybe 50-80mm. Most Heads Up Displays (HUDs) are much closer to that, so how is the text they display visible without being horribly out of focus? ...
0
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0answers
45 views

Is there a way to cancel lens effects?

If I had 2 identical lenses, and put the two facing each other in oposite directions, would their effects be cancelled? Is there a way it could be done, maybe with fresnel lenses, so that it would ...
1
vote
4answers
102 views

How to measure the size of a laser dot?

I'm not a physicist, that's why I'm asking you if there is maybe an easy way (e.g. a mathematical law) to measure the size of a laser dot, or its diameter. The setup It contains a laser, a high ...
0
votes
1answer
27 views

How can I make an optical circulator?

I need to a single mode 1550 optical circulator at my lab. I have a varied supply of components, but no circulator. Any idea how I can make one myself? Perhaps using coupler and isolator? Thanks. -D ...
5
votes
2answers
1k views

Can spectacles converge sunlight to an extent that it burns the eyeball?

I need to know whether wearing spectacles can cause optical harm. I saw a movie where one pair of glasses was placed on table exposed to sunlight, then the sunlight converged and focused to a point ...
0
votes
1answer
60 views

light is allowed to pass through transparent objects? [duplicate]

light passes through transparent objects like water and glass ,where in case of glass the molecules are more tightly packed or concentrated then to it allows light to pass, Why?(yet reflection occurs ...
0
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0answers
14 views

Electro-Optics, Where to Start Studying

I have an opportunity for pursuing my Doctoral studies in a Electro-Optics domain. I have been chosen because I fulfilled the other criteria to secure the opportunity. I still have quite a lot of time ...
1
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3answers
56 views

Why diffraction is related to wavelength not amplitude

For diffraction, the wavelength of the incident beam should be in range magnitude of the slit length, but why the amplitude is not related to the length of the slit?
0
votes
1answer
29 views

A very basic question about optics and figuring out focal length

Focal Length of a lens - I was told that as an approximation I could simply put a sheet of paper with text on it on a table, hold the lens above it, and when I can see the text most clearly, the ...
0
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0answers
20 views

Why does Threshold current of laser increase with the increase in temperature?

Why does Threshold current of laser increase with the increase in temperature? I know that at the same current level, the power is higher at lower temperature but why?
0
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0answers
11 views

How do I derive Sommerfeld's solution of the case when the incident ray is aimed obliquely to the edge of the screen?

I already know that the Sommerfeld's solution to this problem is conical. But internet does not show me the simple of exact derivation of this solution. How do I solve this problem?
0
votes
1answer
73 views

Apparent depth and virtual image position

Why does the virtual image appear right on top of the object and not a little to the right, for example? Is it explained by some formula or just symmetry of the geometry?
0
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2answers
59 views

Why does black glass reflect better than white one?

Why does black glass reflect better than white glass? Both of them are glasses, so they reflect light. But why black glass reflects better? See below, shiny black glass.
2
votes
1answer
57 views

Spatial coherence of SLED light (width of active region?)

As far as I know, super-luminescent diodes (a.k.a. SLEDs) have a very similar structure to laser diodes, except that the front faces of the active region are tilted to prevent the sort of reflections ...
0
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1answer
45 views

How do you calculate the focal point location of a circular mirror? [closed]

I'm trying to find the focal point and center of curvature of a concave mirror. Just using the radius for the center doesn't seem to work. I know C = 2f, but I'm not sure how to find f or C, given the ...