# Tagged Questions

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### 3 mW laser dangerous [closed]

I bought a laser for airsoft. i want to know how dangerous it is when I aim at people(there is a chance I hit thier eyes) on the sticker it says it is <3mW and has a wavelenght: 635-670nM. (class ...
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### How is photon time of flight/range over sub-millimeter distances measured?

I was reading a paper that described how the force a low-thrust torsion pendulum was measured. In it, the paper states a laser is bounced off a mirror and the displacement is "...based upon the beam ...
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### Modeling the free space propagation of laser beams using Fourier transforms

I am trying to model the propagation of a laser beam in free space. I have an initial field $E_{in}(x,z=0)$ (a Gaussian beam) and need to find the fields at other points on the optical axis $E(x,z=d)$ ...
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### Rotating a Gaussian Beam

I need to see how the phase fronts of two gaussian beams interact when they intersect with each other. The two beams are tilted towards each other so that they intersect each other at their respective ...
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### Is single photon perfectly monochromatic?

Now, we do have equipment to generate single photon at a time, and LASERs are nearly monochromatic. While typing the question, am realizing that successive photons in case of single photon ...
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### 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 ...
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### Conservation of energy (or lack thereof) in Doppler cooling [duplicate]

I did not find my question answered elsewhere, so here it is. I'm doing a project in my first optics course, and we are reading a bit about Doppler cooling. I understand that a laser is tuned to a ...
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### 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: ...
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### Is glass considered as a linear optical medium?

My research, which is mainly related to communication, involves the use of optical sources (mainly lasers). However, my background in photonics and optics is not yet solid, so my question might be a ...
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### What is the amplifying medium in a laser diode?

I know it seems like a trivial question, but I can't seem to find the answer anywhere. So - what is the amplifying medium in a laser diode? Meaning: In a classical laser resonator, there a substance ...
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### What makes a material a good lens for CO2 lasers?

I read on Wikipedia that zinc selenide and germanium make good lenses for $\mathrm{CO}_2$ lasers. My question is, Why?
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### In what applications are lasers necessary vs. just convenient?

I’m trying to understand, given the wide array of current laser applications: Which applications actually require laser characteristics, as opposed to just use lasers because they are the most ...
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### 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, ...
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### 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 ...
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### Resonance condition in confocal cavity

In a confocal cavity, a beam traverses the length of the resonator 4 times between two transmissions along the same ray. . For example, in the above figure, path difference between two beams that ...
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### Ultrafast Lasers

The main idea of femtosecond or Attosecond lasers is to achive the high energy or do we have any other parameters achieved by ultra-fast lasers ?
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### What is the meaning of “CW” in LASER?

I am reading a user's manual, and the word appears here. At first, I think "CW" means "center wave". But later, I find that the meaning of "CW" is "continuous wave". It makes me confused. ...
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### Silicon Laser and Laser mirrors

If I will place Silicon as the active medium to create a Silicon Laser. Why I cannot achieve Lasing ? secondly, why do we always consider Laser mirrors in an standing position along the optical axis ...
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### Laser Transverse/Longitudnal Modes

When we say Laser transverse modes. Is that mean what we will get at the output spot of laser beam ? secondly In practice , what TEM01 or TEMnm means ?
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### 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?