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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64
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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 ...
23
votes
2answers
602 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, ...
15
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2answers
2k 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 ...
15
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4answers
1k 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 ...
13
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4answers
1k 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 ...
13
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2answers
502 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
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6answers
3k 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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3answers
4k 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 ...
12
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2answers
1k 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 ...
11
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0answers
524 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. ...
10
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4answers
485 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 ...
10
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4answers
975 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
525 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
1k 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
4k 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 ...
8
votes
3answers
1k views

Can radio waves be formed into a pencil beam?

Laser beams are said to have high "spacial 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
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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
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1answer
1k 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 ...
8
votes
1answer
236 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
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0answers
80 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
2answers
583 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 ...
7
votes
2answers
459 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
128 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
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2answers
337 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
2answers
2k 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 ...
6
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4answers
223 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
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1answer
278 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? ...
6
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4answers
509 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
1answer
355 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
2answers
139 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 ...
5
votes
6answers
1k 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 ...
5
votes
2answers
520 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
359 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
1answer
2k 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?
5
votes
3answers
724 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
3answers
638 views

How do “holographic plates” work?

I asked a question about laser stage lighting over at Audio Video Production, and received an excellent answer that explained that laser clusters are generated from a single beam via something called ...
5
votes
2answers
280 views

Did anyone claim that quantum theory meant lasers would never work

I've been reading 'How the Hippies saved Physics', which describes a design for a superluminal communication device, of which the crucial part was a laser which duplicated an incoming photon many ...
5
votes
3answers
608 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 ...
5
votes
1answer
1k views

Laser cutting/drilling of copper

In industry, it's common to cut steel using 50-200 W $\mathrm{CO}_2$ laser. Meanwhile, for making holes in PCB (35 $\mu$m of Cu), DPSS 355 nm laser is usually used and secondary $\mathrm{CO}_2$ to ...
5
votes
1answer
176 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 ...
5
votes
1answer
121 views

Optical laser pumping and reflectors

Let's say we are building Nd:YAG laser. It is optically pumped by some linear xenon flash lamps, it absorbs light around 750nm and 800nm, and emitted light is at 1064nm. The question is why doesn't ...
5
votes
1answer
63 views

what general physical arguments discredit induced emission of nuclei?

trying to read a bit about "quantum nucleonics", i've encountered this rebuttal from people at Livermore that induced radiation stimulation of Hafnium nuclei is possible. Something that catches my eye ...
5
votes
2answers
229 views

What reflective media do laser shows use?

I am having a hard time in finding out what exact light media laser shows use. I am trying to build a laser show myself. I know that the laser light is reflected off these particles in such a way that ...
5
votes
1answer
368 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 ...
4
votes
4answers
176 views

Why do lasers require mirror at the ends?

Laser uses mirrors to reflect photons in order to stimulate atoms to emit photons, but why this is so?. I mean, why does a photon stimulate atoms to produce more photons? If a photon made an atom to ...
4
votes
3answers
13k 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 ...
4
votes
2answers
117 views

How can laser communication be faster than microwave?

My textbook states that "Laser communication is much faster than microwave communication." But, how can that be? Both are electromagnetic waves with different frequencies but, how can the speed be ...
4
votes
2answers
267 views

Laser beam shaping

Hi I like to build a laser pointer that reflects different shapes for a project I am working on. I know this can be done with Diffractive Optical Elements. Are there other options? DOEs are expensive. ...
4
votes
3answers
460 views

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?
4
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2answers
1k 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 ...