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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What is the minimal size of the spec of dust I can see with naked eye?

When sun directly shines thru the window - I can see small specs of dusts in the air. All specs have different sizes. Assuming direct sun luminosity is 100kLux, spec is a perfect sphere, reflection ...
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5answers
3k views

Why can we see through rain?

I am gazing through my office window into a heavy rain. I am thinking that raindrops are like small lenses that bend the light. Thus I am surprised, that I can clearly see other buildings through the ...
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5 views

To approximate the uncertainty of viewing angle in Telecentric optics?

I am thinking how to approximate the uncertainty of the viewing angle in the telecentric optics when the viewing angle is less than 5 degrees. I have a Cadcam called ArtCam from a Japanese ...
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2answers
38 views

Light (Laser) operated optical switch

I have searched the web and found that optical switches are activated either through mechanical or electro/magnetics. Making them sort of Optomechanical or optoelectronic switches. Lets exclude ...
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1answer
47 views

Fraunhofer Diffraction and Lenses

Suppose we have the diffraction pattern for a single slit in the Fraunhofer approximation. In order to see this diffraction patter at finite distance we locate a converging lens. Is the diffraction ...
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2answers
23 views

Why, in order to obtain distinct interference, is a small distance between the two waves essential?

This is quoted from Concepts of Physics by H.C.Verma: In order to obtain a fairly distinct interference pattern, the path difference between the two waves originating from coherent sources should ...
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451 views

When/why does the principle of least action plus boundary conditions not uniquely specify a path?

A few months ago I was telling high school students about Fermat's principle. You can use it to show that light reflects off a surface at equal angles. To set it up, you put in boundary conditions, ...
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40 views

How to calculate the Refractive index of a glass sheet

My question is how to find the $n$ of a glass sheet with just aiming a laser beam to that. I've got lot of ways that let me find the $n$ ( Refractive index ) but I need the whole part of the ...
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1answer
18 views

Making a home made projector bur lens an issur

This got booted out if the lifehacker forum so I'll try here I read a nice tutorial here which tells you how to make a homemade projector for two quid. Lovely thinks I so I trotted down to the local ...
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2answers
53 views

Why railroad tracks seem to converge?

I stand up and I look at two parallel railroad tracks. I find that converge away from me. Why? Can someone explain me why parallel lines seem to converge, please?
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13 views

Optical fibre numerical problems [closed]

(a) What is the need for a cladding layer on the core of an optical fiber other than mechanical strength? (b) Assuming a fiber that is kept stra ight and is of length L, find the ...
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37 views

Can a person with bad vision see a blurry picture clearly? [duplicate]

I was just thinking to myself how weird it must be to have bad vision. Then I thought, I wonder if you could print a picture that would appear clear to someone with bad vision. That seemed unlikely to ...
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2k views

Is it possible to blur an image in such way that a person with sight problems could see it sharp?

If someone has short or long sight, is it possible to tune image on a computer monitor in such way, that a person could see it sharp as if they were wearing glasses? If not, will 3d monitor make it ...
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2answers
91 views

Does Fermat's principle of least time apply to sound waves?

I am reading Feynman's presentation of Fermat's Principle of Least Time, which explains the behavior of light; does it apply to waves in general? for example sound waves or waves on the surface of ...
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4answers
28k views

What makes some laser beams visible and other laser beams invisible?

What makes the beam of some lasers: visible? such as the ones used in clubs or such as the laser pointers sold at amazon which if pointed to the sky look like a solid visible beam of light ...
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2answers
156 views

Examples in which the light maximizes the optical path length

I posted a similar question about geodesics on Math.SE. Many sources (Wikibooks for instance) claim that the light could maximize the optical path length in some cases. But I don't think it's actually ...
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1answer
86 views

How does airborne laser system deflect the laser beam?

In the Airborne Laser system, the laser beam is directed from the nose of a Boeing airplane towards the target. In this system, the angle of laser beam with respect to airplane body can be changed at ...
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1answer
19 views

Fringe Width and Spacing and Number of Slits in Diffraction Experiments

In a single slit experiment, the fringes are not equally spaced and aren’t of equal widths—the central maximum is the widest, the secondary maxima grow narrower and narrower outward, and the minima ...
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2answers
199 views

Alternate young double slit experiment

What will happen in young's double slit experiment, when instead of screen I put a black screen with a hole and a second screen behind the black one. Will it still form interference pattern albeit a ...
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1answer
16 views

longitudinal magnification confusion in concave mirror

If you move a rod lying on the principal axis of any concave mirror, when the near end of the rod is at a distance equal to half it's own length from the mirror, then the instantaneous velocity of ...
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1answer
138 views

Using a laser to overhear a room conversation

Movies with science based tricks and gimmicks are generally silly and sometimes even annoying. The science based trick that I don't know enough about to judge is the following (and I have seen it in a ...
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1answer
34 views

Why does in the definition of 'optical path', only spatial phase change is taken into consideration & not that of time?

In Concepts of Physics by H.C.Verma, I got the definition of optical path. However, one thing that I couldn't understand is why only the spatial phase change is considered in its definition. As he ...
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7answers
4k views

How do we see? Where do the photons disappear?

I know that the light is reflected from a object to my eyes, but I don't understand exactly how. The photons appear from the light source and disappear in my eye! Can someone explain the phenomenon of ...
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1answer
52 views

Can one detect a single photon through measuring its impulse/momentum on a mirror?

Can one detect a single photon through measuring its impulse/momentum on a mirror? If the answer if YES or theoretically possible, photon path and interference fringes can be detected simultaneously ...
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2answers
46 views

Which photons pass through a circular annulus?

Passing light through a circular sieve: Well, actually, let’s think about radar or microwaves with a wavelength of order a centimeter or two, so you can tailor your aperture, say by etching a silver ...
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2answers
54 views

How is the virtual image reconstructed from a hologram?

To make a hologram a film is exposed to an incident plane wave and wave from the object to record the interference pattern on the film. The principle is commonly explained in a way like that in p.1212 ...
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2answers
37 views

Reflection during refraction

I have observed in a book (one that is different from the one that I study with in school) that a light ray reflects during refraction, which is a partial reflection, but when does that occur? Is it ...
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1answer
31 views

Derivation of relativistic mean free path

I am working through a short derivation found in Abramowicz 1991 regarding the mean free path of a photon. We have a fluid moving in a particular direction with velocity $v$ and in an inertial rest ...
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1answer
21 views

Experiment to test flatness of prism

I have a Prism glued to a prism plate. Let's say the method of using optical glue is good enough, and minimal human error is tolerated. What experiment would be a good to check if the prism is not ...
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1answer
25 views

Creating nanosecond pulses from a CW laser source

Experimental setup question. If anyone aware of a technique to create pulses of several nanoseconds at a around 10Hz repetition rate from a CW laser source?
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2answers
434 views

Finding the illuminance from a triangular light source

Since most light sources in games are point-like, it's pretty difficult to approximate area light sources with point sources. As triangles are a universal form to represent 3D models (thus area light ...
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2answers
44 views

Why array of telescope is used?

To increase the resolution of an instrument, smaller wavelength and larger aperture is desirable. It is mentioned in some textbooks that the "effective" diameter of a telescope can be increased by ...
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0answers
22 views

In Fermat's Principle of Least Time, how do we know that light is able to reach the end point?

From my understanding of Fermat's Principle, you decide a start point and an end point for a light ray to travel between, and the light 'chooses' whichever path takes the least time (or technically ...
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1answer
9 views

Dissolving photoconductor (TiOPc) from Laser Printer drum possible?

When I was thinking of a Lab-On-a Chip Application which combines a lensless microscope and an optical tweezers I saw the ...
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2answers
35 views

x-ray diffraction of crystals

In explaining x-ray diffraction of crystals, usually the approach is to consider the atoms absorb radiation and scatter it, at some angles constructive interference occur and bright spots can be ...
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16 views

Question about dark fringe in diffraction

In finding the angle for the mth dark fringe of single slit diffraction using Huygen's principle, they usually split the slit into equal portions. For example, to find the first dark fringe the slit ...
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0answers
2k views

How does autorefractor work?

Autorefractors are being used by eye opticians for eye diagnosis. I searched internet for articles and wiki page as well but I wasn't satisfied. I am interested to know how do they actually work. How ...
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1answer
17 views

Is it possible to “change the focal plane” of a 2d image?

Can we apply some type of transformation to 2D image in such a way that when a person looks at it directly (i.e. focuses on the paper or the computer screen which displays the image), it is blurry; ...
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3answers
142 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?
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26 views

How to measure the diameter of a Glass tube? [closed]

I'm working on something and I need to find the diameter of a glass tube. I wanted to use diffraction pattern to find the diameter of my tube. but the problem is that my tube is transparent. Anybody ...
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1answer
163 views

Why is the focal length of a convex mirror negative?

According to the Cartesian sign convention, the focal length should be positive since the convex mirror forms a virtual image to the right of mirror (positive direction) when light comes from left. ...
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11 views

Limitation of Rytov approximation for turbulence

I have been working through the textbook "Laser Beam Propagation through Random Media" by Andrews and Phillips and have arrived at an interesting dilemma. For a second-order perturbation in the Born ...
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4answers
4k views

Why does change in speed of a wave make it refract?

When a light wave enters a medium with a higher refractive index (e.g. from air to standard glass) and its speed decreases, why does that make it refract/bend? I understand that wavelength decreases ...
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2answers
195 views

Determining the refractive index of a foil

(59th Polish Olympiad in Physics, final stage, experimental part, 2010) You have at your disposal: a sample of blue foil of a homogeneous material, placed between two glass panes in a ...
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1answer
30 views

Effect of the refractive index of a transparent layer coating a particle?

I am modelling a cell as a particle coated by a layer of a material whose refraction index might change. This layer is to resemble the membrane. The purpose of the model is to simulate what happens ...
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14 views

How can I determine spatial resolution from an Airy disk diffraction pattern?

From introductory optics, the angular resolution of a lens (in radians) can be described by the Rayleigh criterion: \begin{align*} \theta = 1.220 \frac{\lambda}{d} \end{align*} This has its ...
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1answer
171 views

Third-order susceptibilities of metals?

Can anyone point me to a source for measurements of the third-order nonlinear electric susceptibilities $\chi^{(3)}$ of various metals? Specifically in relation to the AC Kerr effect, so measurements ...
3
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1answer
89 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 ...
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2answers
32 views

Slit width in single-slit diffraction

In Born's Atomic physics, he makes the comment on the single slit diffraction that For diffraction patterns to show themselves, it is necessary that the width of the slit employed should be of ...
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1answer
24 views

Absorption Magnification

I'm working on an optical project about the absorption of glass sheet and I need to measure the intensity of laser beam that has passed the glass sheet and compare that with the intensity of laser ...