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26 votes
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Why does light bend after travelling half of the lens?

It changes on both E and the exit point of the beam (see image below). source My understanding is that refraction occurs at any boundary that there is a change of the wave propagation velocity. The ...
NMech's user avatar
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18 votes
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Can a very bright light attract an incoming laser guided weapon?

No. It might blind it but it would not attract it. Laser guided weapons aren't just laser versions of heat-seeking weapons. You would modulate the targeting laser so that it could be differentiated ...
DKNguyen's user avatar
  • 5,641
13 votes

Why aren't screens round instead of rectangular?

The earliest CRT displays were in fact round. However, that was more due to manufacturing tradeoffs of making large glass envelopes with vacuum inside than a desire for the display area to be round. ...
Olin Lathrop's user avatar
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8 votes

Why does light bend after travelling half of the lens?

You are right, rays refract at both the entry and the exit points. That drawing is just a simplified diagram, frequently used in textbooks about geometrical optics. It helps to illustrate concepts ...
g.kertesz's user avatar
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7 votes
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How can I build a micrometer diameter laser beam from a common laser diode?

Why this is hard One micron is on the border of what is theoretically possible. You cannot create a parallel ray at this scale. One micron is almost as small as the wavelength of the light you are ...
Jack B's user avatar
  • 398
7 votes
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Alternatives to laser line?

A few points that don't fit into a comment but could help you: Get a better laser source than a 4 \$ laser diode. "Better" means a laser with higher beam quality. When you look at a laser's ...
OpticalResonator's user avatar
5 votes

Transparent, hard material that lets infrared through

Acrylic and glass do let 800-900 nm IR radiation through quite well (see, e.g., here). However, your problem is probably that part of the light gets reflected at each of the surfaces. This is ...
jpa's user avatar
  • 1,953
5 votes
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Periscope camera with a mobile phone, how to make walls not visible on the camera/alternative solution?

Ok let me draw some pictures you right now have the following situation: If you add a convex lens to this setup you get: Which does work. However you may want to add a concave lens after the convex ...
joojaa's user avatar
  • 3,577
5 votes

How is a parabolic mirror made by hand?

Large telescope mirrors are made by spinning a disc of molten glass so its surface assumes a parabolic shape, and then slowly cooling it while spinning so it retains that shape after it solidifies. ...
niels nielsen's user avatar
4 votes

Why aren't screens round instead of rectangular?

X-Y addressing and raster scanning are both much simpler when addressing a rectangular area. So either you need to lose (waste) the corners or adopt a fundamentally different addressing scheme. ...
user_1818839's user avatar
  • 1,620
4 votes

How to see through an opaque mask?

Just a lot of pinholes (without lenses) will be enough. With a high enough density Your eyes and brain will be able to compensate the lack of complete vision pretty dang well. It'll be darker and you ...
ratchet freak's user avatar
4 votes
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How can I detect black spots?

The simplest method will be a multi-step approach. The first step will be a defective product detection, that gathers general data about the product stream and quarantines defective products. On a ...
Mark's user avatar
  • 5,333
4 votes

Would connecting 100's of small telescopes into one huge telescope make for a significantly better telescope?

There are two issues here, noise and resolution. Combining the optical images from multiple telescopes would reduce the overall noise. This is because each image is independent of the others, so all ...
Olin Lathrop's user avatar
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4 votes
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Does this type of lens or light guide exist?

If you have access to a CO2 laser or a makerspace which has one, you can cut the profile of your light guide from acrylic sheet of suitable thickness. You don't have to have the rather expensive thick ...
fred_dot_u's user avatar
  • 7,227
3 votes

Device that emits a safe beam of light - doesn't have to be visible (Like laser, but safer)

There are eye-safe lasers, both in the visible and IR. For your detection system, make sure you understand the power required for your target (receiver) to register a hit. Pretty much any ...
Carl Witthoft's user avatar
3 votes

Periscope camera with a mobile phone, how to make walls not visible on the camera/alternative solution?

The basic answer is that the field of view (FOV) of your camera is much wider than the FOV of the periscope. Unless you add a lens system between the periscope and the phone to limit the effective ...
Carl Witthoft's user avatar
3 votes
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Is it possible to reduce the divergence of a red laser pointer beam from 40 degrees to 1 degree?

Of course, a lens with a short focal length can be used. The easiest way is to take the standard lens that comes with most laser pointers and move it a bit closer to the laser crystal. If you want ...
Han-Kwang Nienhuys's user avatar
3 votes
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Can I use an optical fiber to direct a laser cutter?

CO2 lasers cannot be coupled into standard silica-based fibres, because these fibres absorb light longer than 2.1um. You could use hollow silica fibres, but they are quite recently developed, so might ...
OpticalResonator's user avatar
3 votes

Would connecting 100's of small telescopes into one huge telescope make for a significantly better telescope?

coupling together a large number of small telescopes to emulate the behavior of a single very large telescope is an area of active research in the telescope field. to properly combine a large number ...
niels nielsen's user avatar
3 votes

Does this type of lens or light guide exist?

The term to search for is 'light pipe'. You may have luck with this question on Electronic Engineering SE (such a part would be part on an EE design). eg Search for light pipes on Digi-Key.com While ...
user85471's user avatar
  • 131
3 votes
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Heat loss in Optical Fiber

If you increase the length of the fibre, you will get more reasonable results. The losses -in my mind- need to be distributed along the entire length of the fiber . Currently, you seem to model a very ...
NMech's user avatar
  • 24.4k
3 votes
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Calculating Temperature of an Optical Fiber

If a model does not reflect reality, the model is not accurate enough for that situation. Consider some of the minutia in the workings of light. First an alternate model for the fiber: As light ...
Abel's user avatar
  • 1,352
3 votes
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How can a small screen be projected on glass but still visible near 2cm from eyes?

When you project an image on a reflective medium, you inherit the projection distance. So what you are seing is a plane that is hovering behind the glass. In essence your eyes see is the whole path to ...
joojaa's user avatar
  • 3,577
2 votes

Precision measurement of liquid levels

I believe some laser equipment does have the 20µm that you are looking for: Displacement measurement sensors This product for example has a 20µm precision, but it is said that the precision depends ...
Odano Naotake's user avatar
2 votes
Accepted

How does the Michelson interferometer measure the self-coherence function of coherent light in an incoherent background?

As you change the relative arm lengths of a Michelson interferometer, the transmission (or reflection) coefficient of the interferometer ranges from $T=0$ to $T=1$ for coherent light, but, if designed ...
Chris Mueller's user avatar
2 votes
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What happens when very bright coherent light and weaker incoherent background light passes through doubly cascaded diffraction gratings?

The original question was along the lines of: "what happens if light passes through cascaded gratings". Before that question can be answered, you have to understand what a single grating does. See the ...
Han-Kwang Nienhuys's user avatar
2 votes

Can we see a nanowire?

no, a nanometer is much smaller than the wavelength of light, so you can not even see it with an optical microscope. May be worth a note the "nano-" prefix is often abused in the literature. Things ...
agentp's user avatar
  • 949
2 votes

How can I build a micrometer diameter laser beam from a common laser diode?

If you have one convex and one concave lens, you can effectively make the laser beam smaller and more concentrated while still having a parallel ray. I believe it's called a galilean lens. It would ...
Bart's user avatar
  • 1,184
2 votes

How to focus the flashlight of a smartphone?

Focusing and collimating are two different things. Focusing means focusing into a small point (which will show the image of the light source); collimating is analogous to focusing into infinity, so ...
jpa's user avatar
  • 1,953
2 votes

rotating mirror system for shifting a beam?

You could use a slab of glass or other transparent medium with a different refractive index then air. The slab should have two surfaces which are as parallel as possible and be mounted on a two axis ...
fibonatic's user avatar
  • 1,653

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