Light Amplification by Stimulated Emission of Radiation. A means of creating coherent light by either driving an atomic or molecular transition in an optical cavity or firing a beam of electrons through an undulator.

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69
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2k views

Why is a laserpointer able to “erase” a glow-in-the-dark sticker?

a while ago I tried to charge a glow-in-the-dark sticker using a simple red laser pointer. It was a large sticker, of the type used to mark emergency exits and fire extinguishers here in Germany. I ...
37
votes
6answers
6k views

Why do lasers cut? Is this a case of light acting as matter?

All I found in Google was very broad. From a physics models perspective, why can photons emitted from a laser cut? Does this cut mean that the photons are acting like matter?
23
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5answers
2k views

Quantum random numbers from a laser — simplest setup?

I'm a software / maths guy who would like to build a physical setup for generating quantum random numbers. I have no physics background, so bear with me. Background The project is for a public ...
23
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2answers
722 views

Why does laser light not affect glowing materials?

I have this childrens rubber ball which glows in the dark after it's exposed to light. I "charge" it with a flash light then play with my dogs at night. I thought to try a very intense green laser, ...
18
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4answers
2k views

Is it possible to observe interference from 2 independent optical lasers?

It seems that if the coherence length of a laser is big enough, it is possible to observe a (moving) interference picture by combining them. Is it true? How fast should photo-detectors be for ...
18
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1answer
1k views

Photobombing without app used by Harley Davidson

Here we see a photobombing trick, used by Harley Davidson. They achieve to incrust a logo on a photo you take. The logo is invisible with naked eyes and only revealed on the photo you take. How does ...
17
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2answers
4k views

Is the “How to break the speed of light” minute physics video wrong?

I am referring to this video, on YouTube, by minutephysics, which has quite a lot of views. In the video it states that if you flick your wrist while pointing a laser that reaches the moon, that the ...
16
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4answers
2k views

What ways are there to measure the local polarization of a laser beam?

Measuring the polarization of a laser beam is a simple enough task if the polarization is the same everywhere. You can even buy commercial polarimeters. How do you go about it if the light beam has ...
15
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2answers
2k views

What is an intuitive explanation of Gouy phase?

In laser resonators, higher order modes (i.e. TEM01, etc) accumulate phase faster than the fundamental TEM00 mode. This extra phase is called Gouy phase. What is an intuitive explanation of this ...
14
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2answers
814 views

Why doesn't the no-cloning theorem make lasers impossible?

As I understand lasers, you start off with a few photons that are in an identical state, and other photons that are created later tend to have the same quantum numbers due to Einstein-Bose statistics. ...
13
votes
3answers
5k views

Physics of Focusing a Laser

The temperature that a solar death ray can produce is limited due to the solid angle of the sun itself. Entropic arguments dictate that you can't focus the sun's light to create temperatures higher ...
13
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1answer
747 views

Is the time reversed laser really a laser?

I'm looking at the time reversed laser and I was having trouble understanding why we call this device a laser. To me this device is more like the absorbers found in FDTD codes, something like a CPML. ...
13
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4answers
4k views

Tried to do the double slit experiment, failed. Why?

I tried, and failed, to do the double-slit experiment. I thought I had a good experiment setup, but obviously I was wrong. Can anyone offer some insight in what I might have done wrong? Most of ...
12
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4answers
548 views

When lasers are used to cool atoms or ions, etc where does the heat go?

According to the first law of thermodynamics, sourced from wikipedia "In any process in an isolated system, the total energy remains the same." So when lasers are used for cooling in traps, similar ...
12
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1answer
5k views

Will high power laser penetrate mirror?

Many nations are developing hi-energy laser weapon. My question is, what if target is coated with mirror like coating? Can laser (since laser is still light) penetrate mirror? If it can then how is it ...
11
votes
4answers
259 views

Does the speed of medium affect the path of light?

Let's say I shine a laser from a stationary medium into a moving medium (suppose the water is moving very quickly) perpendicular to the interface and back to a stationary medium like this: (Note: ...
10
votes
4answers
1k views

How to build a laser in the garage?

So I wonder if it is any how possible to build laser at home. A powerful one to melt brick.
10
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1answer
635 views

Can a burning laser be directed through fiber optics?

Can a laser powerful enough to cut(100w for example) be redirected using fiber optics ? What issues need to be considered? To be clear it should retain the ability to cut after exiting the fiber.
10
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2answers
3k views

Why do green lasers appear brighter and stronger than red and blue lasers?

This is mostly for my own personal illumination, and isn't directly related to any school or work projects. I just picked up a trio of laser pointers (red, green, and blue), and I notice that when I ...
10
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2answers
2k views

Amateur moon laser ranging

Questions first, then my rough estimations: 1) Is it possible to perform moon laser ranging with amateur motorized 114mm telescope? My calculations suggest that for 1mJ laser it should receive ~2 ...
9
votes
7answers
6k views

Why is a 1mW laser dangerous?

In our Physics lab we have a 1 milliwatt (0.001W) helium neon laser. Despite the low power, we were cautioned not to even look at reflections of the beam as it could cause permanent eye damage - why ...
9
votes
3answers
2k views

Is it possible to make laser beams visible midair without smoke?

My question is: Is it possible to make laser beams viable midair without smoke? I thought it would be a great idea to have a (second) smartphone or pc screen without having a solid screen. The reason ...
8
votes
6answers
3k views

Why does a laser beam diverge?

I was wondering why a laser beam diverges. If all the photons are in the same direction, I would imagine that it would stay that way over a long distance. I am aware that a perfectly collimated beam ...
8
votes
4answers
2k views

Can radio waves be formed into a pencil beam?

Laser beams are said to have high "spatial coherence". This means that the beam is highly concentrated even at long distances (low spread). Can this be achieved with radio waves (much longer waves) ...
8
votes
3answers
628 views

Why use lasers for intense, localized heat instead of some other light source?

Lasers are used in various industrial processes that need intense, localised, heat (3d printers and laser cutters come to mind). My question is: why use lasers? There are many other (cheaper, ...
8
votes
1answer
1k views

Why do we see laser beams?

A laser produces a coherent beam of photons with particular $\mathbf{k}$ and $\mathbf{\omega}$. So, if there is no particular $\mathbf{k}_0$ directed toward our eyes, why do we see laser beams? I ...
8
votes
2answers
1k views

What exactly is the difference between a sychrotron light source and a free electron laser?

Cyclotron radiation is radiation emitted by a charged particle being bent by a magnetic field. The only difference between cyclotron and synchrotron radiation is that the latter occurs at relativistic ...
8
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1answer
301 views

Graphene as optical and UV mirrors

One usually hears about graphene as a good thermal conductor, and good light absorber due to its tunable bandgap properties. But i haven't heard about its aplicability as an optical mirror. In fact, ...
8
votes
0answers
99 views

mode-locking a laser on prime-powers' frequencies

Being rather a theoretician than an experimental physicist, I have a question to the community: Is it experimentally possible to mode-lock a laser (fixed phase relationships between the modes of the ...
7
votes
1answer
402 views

Huygens wave theory not applicable to lasers or parallel beams of light?

According to Huygens wave theory, every point on a wavefront acts as a secondary source of waves. Using this principle we can never have pretty narrow parallel beams of light right? Like lasers? ...
7
votes
2answers
572 views

How does infrared light 'erase' phosphorescence on zinc sulfide?

I found some sheets of zinc sulfide in my basement that phosphoresce green for up to 24 hours or so after exposure to bright light in the violet range or shorter. One of the first things I tried was ...
7
votes
1answer
159 views

does the beam of a laser have 'throw'?

I was thinking about Einstein's train and platform experiment and was wondering if a beam of light experiences throw? Let me explain, if I take a water hose and point it straight out and then swing ...
7
votes
2answers
366 views

Fairly Broad Spectrum Light Source Options

I tried this sight before to find filtering options and got fantastic results, so let's try again! I am setting up an experiment that requires light of two different frequencies (445nm and 350nm). ...
6
votes
4answers
19k views

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

What makes the beam of some lasers: 1-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 ...
6
votes
2answers
448 views

Homemade Spectrometer

Recently I have had ideas of how to build a spectroscope, but I'm not sure if it will work. As can be seen in the diagram, the experiment is simple: it consists of a laser that generates the light ...
6
votes
4answers
378 views

Why is laser light a cone?

What about the production of laser light disallows it to be perfectly straight as opposed to a cone? I feel like it should be a plane wave, not a very tight cone.
6
votes
3answers
722 views

Recently publicized experiment on destructive interference between two laser beams

Recently I've had several non-physicist friends ask me, independently of each other, about an experiment where two collinear laser beams destructively interfere along a certain length. Everybody wants ...
6
votes
4answers
550 views

Far-field intensity from scattering of small particles

Howdy, I'm building a simulation for looking at the light field underwater. In order to verify my simulation, I'm looking for some data showing the far-field intensity that comes from single ...
6
votes
2answers
116 views

How is the phase of the stimulated emission in a laser first “chosen”?

As I understand, once you have a population inversion and the excited atoms decay they will emit in random directions, and the ones that emit along the axis of the medium will cause stimulated ...
6
votes
1answer
665 views

Wavefront RMS errors, mirror surface roughness and Gaussian beam scattering

What I'm interested is in the scattered power of Gaussian beams reflected from mirrors with a given surface RMS. Usually the surface RMS $\sigma_{s}$ of a mirror translates in an error for the ...
6
votes
1answer
273 views

Free Electron Lasers (FEL) and limits on laser wavelength

Free Electron Lasers are based on Synchroton coherent radiation when a collimated electron beam suffers trajectory curvature due to a strong bouncing magnetic field inside an undulator. Free Electron ...
6
votes
1answer
106 views

How legit is this paper claiming to have observed Hawking radiation? [closed]

I recently stumbled upon this paper. In it, the author claims to have found a signature for Hawking radiation in a condensed matter system. I know that experimentalists have been trying to find ...
6
votes
2answers
159 views

PSF Measurements In Fluorescence Imaging

Quite a technical question! I have measured the Point Spread Function of 100nm fluorescent breads with my Olympus scanning head. I'm two-photon exciting the beads with a wavelength of 800nm and ...
6
votes
2answers
474 views

Good introductory papers and books on laser physics and pulsed lasers

I am looking for good introductory papers and/or books on the principles of lasers. In particular, I am interested in pulsed laser technology. I understand that Gould, R. Gordon (1959). "The ...
5
votes
4answers
526 views

Why isn't V. A. Fabricant given the credit for the discovery of the laser?

In another question here I asked for help in finding old Russian papers in physics and as an example I gave the founding papers on the laser by Basov and Prokhorov (from 1945 and 1954). In an answer ...
5
votes
2answers
949 views

Why is the photon emitted in the same direction as incoming radiation in Laser?

When an atom “lases” it always gives up its energy in the same direction and phase as the incoming light. Why does this happen? How can this be explained? How does the photon generated because of ...
5
votes
3answers
429 views

Will a prism widen a monochromatic beam?

The representation of the experiment which demonstrates that white light consists of many colors, invariably shows that the beam of white light is broadened inside the prism and is some what more ...
5
votes
3answers
864 views

Does there exist a laser that is tunable over the whole visible spectrum?

Does there exist a laser that is tunable over the whole visible spectrum? If so does there exist one that is solid state? This is to settle a score with my dumb workmates.
5
votes
2answers
3k views

laser pointer class III and potential eye damage

We just bought a green laser pointer on Ebay and had a discussion about the safety. The laser is low end chinese one (5 USD, free shipping :-) ) and the seller says this: Green Laser Pointer Point ...
5
votes
1answer
3k views

Why are lasers inefficient?

Why are lasers inefficient? Is it because of the heat lost during lasing? Why couldn't there be thermocouples or turbines in parts of the cooling circuits to extract something out of that heat?