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Questions tagged [laser]

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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42 views

Why do lasers require at least 3 energy levels?

I don’t yet understand why 2 energy levels aren’t enough as they can still emit photons (even when B12 and B21 are equal). By the way, I’m talking about stimulated emission.
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What effect will moving one light source closer to the screen have on the diffraction pattern of two coherent light sources?

Say that you have two coherent light sources to begin with, each the same distance away from a screen, but then, you move one of the light sources closer to the screen by a fraction of the wavelength ...
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Will a magnet diffuse/defocus a laser?

I have read through hundreds of questions here and we discuss why light is not bent by an electric or magnetic field (at least not at easily visible levels in the classical sense), but that there is ...
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Why does the laser reflect like a semicircle?

I was having fun with my laser. What causes this reflection? Edit: I had an idea and tilted the surface of this plaque by 90°. I now get a straight line, such as the reflection from the plaque below: ...
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Basics of camera calibration

I tried to find some useful explanation about camera calibration and stereo camera setup in the web but was completely overwhelmed by the hairiness of the content: but seriously though, does it have ...
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Why do objects reflect laser light?

Why do non-red objects reflect red laser light? The color of things explained as "Objects reflect in the color that we see them, and absorb other colors." But if to illuminate, say, a yellow thing ...
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Laser book for physics GRE

The recent physics GRE exams have some questions on lasers. Does anyone know of a good book which goes briefly through different types of lasers?
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Is it possible to produce shock waves in air using low intensity pulsed lasers?

Air has about 0.04% carbon dioxide. Carbon dioxide has a very strong absorption band around 4.2µm. Let's say I used a nanosecond pulsed 4.2µm MIR source and targeted it into air, part of this would be ...
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42 views

How can increasing the speed and/or mass of a particle reduce, not increase, it's frequency?

In a Physics World article called 'Neutrons on a Lab Bench', from 30 January 2013, it says, '...Yin and Albright calculated that a very intense laser beam should be able to boost the speed of ...
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Principle of a pyrometer

How does a pyrometer work? Especially how do I ensure that the temperature of a single spot is measured (where the laser points at)? Here is a scheme of the structure but I guess it's not really ...
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35 views

Laser beam versus activly cooled armor. Who will win?

I'm interested in space warfare from a hard sci-fi perspective. Usually I ask these kind of questions on Worldbuilding SE, but I felt that this one fits this SE better. Recently read this post on the ...
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Design and construction of a system identifying molecular nitrogen and water

I have read papers that use LIDAR-like and LIDAR-Raman systems that detect elements. I want to measure the vapor water ($\rm H_2O$) and $\rm N_2$ of trees/agriculture using Arduino and low cost ...
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26 views

Open source software or Matlab toolboxes for simulation of pulse chirping

I am trying to simulate the effect on the waveform of pulse chirping a Gaussian pulse from a femtosecond laser by various mechanisms (e.g. prism, grating, grism, fiber optical cables). I have tried ...
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A Problem about Line Broadening and Absorption coefficient

I am reading my textbook, Lasers by Anthony E. Siegman, and I just could not understand a point he made. In the chapter section about inhomogeneous broadening, he used a figure to show the transition ...
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When assembly of atoms is influenced by EM wave only few of them get excited not all? Why?

In laser when assembly of atoms is influenced by em wave, only few of the atoms get excited not all? why it happens
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Calculating Laser Beam Intensity Absorbtion

This question pertains to the ability to calculate the laser beam intensity , at a particular point in time when using lasers for the purposes of Cutting and Engraving Materials. The parameters at ...
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How do I obtain coherence length of a monochromatic laser with data about the visibility?

I am using a Michelson interferometer and have obtained data about the visibility. However, I am now having trouble knowing what to plot in order to find the coherence lenghth of the laser. I thought ...
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Creating some sort of optical transistor

Is there a way to create an optical transistor that runs using a cheap laser and made using mirrors and lenses? My point of using that is to make an optical logic gates, but there is another problem ...
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Does hydrogen gas laser exist? If not, why?

I have searched the internet, and this forum, but can't find a mention of hydrogen gas laser. There does, however, exist the hydrogen maser that used the 21cm radiation. Also there exist Nitrogen gas ...
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Derivation for number of photons assigned to to an electromagnetic field amplitude

I am trying to understand a derivation concerning the number of photons associated with an electromagnetic field which is irradiated on some probe. The point is to get a expression that connects the ...
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1answer
50 views

Sci-Fi weapon: Satellite shooting laser beams down to earth? [closed]

The range of one of these is stated to be 700m. Since it sends out electromagnetic waves the only problem I see with limited range is the beam divergence. Atmospheric absorption is minimal so slapping ...
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1answer
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Optical Logic Gates using Polarisers [closed]

I am trying to build an optical logic circuit using the horizontal or vertical orientations of light as the two binary states and laser as the source. Before I ask you my question I wanted to first ...
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Focusing a vibrating laser source

I am wondering about the relation between vibrations on the collimated laser source to the change in the focal position, if I focus it using a lens. My system will include a RC telescope to focus the ...
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1answer
21 views

Do dieletric mirrors and other reflective surfaces have a maximum intensity to which the absoprtion coefficient increases?

That is, if you shine a laser at a dielectric mirror so that the intensity(photons/seconds*cm^2)becomes sufficiently large, the scattering of the photons off the electrons in the surface atoms becomes ...
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Which bonds are broken when we use high laser energy?

If we suppose as in the picture that a laser with high energy been used to break down the bounds, what exactly happens? Is there anything to do with molecular orbitals? or?
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73 views

Will laser scanning system miss photons when the mirror scans too fast?

So in many applications like Optical Coherence Tomography, LIDAR, a mechanical scanning mirror is often used to reflect the laser to outside and also reflect the back scattered light to detector. ...
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Is there any incoherent collimated monocromatic light source?

I was looking for an incoherent monochromatic collimated light source. I know that if I shine a laser through some medium I'll partially lose the coherence but I will also sacrifice the collimation I ...
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Can scintillator crystals be used for solid state lasers?

For example, a theoretical design would involve a yellow Cerium-YAG scintillator crystal which emits yellow light when stimulated by ultraviolet radiation. Has this approach ever been tried and if so ...
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Bending a Laser Beam [closed]

We can bend a Laser beam by varying the refraction coefficient of the air. We can bend a Laser beam by dispersing into the air small particles that have the same effect on the Laser Beam and small ...
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Spin state of photons inside laser

Can the total spin state of photons inside a laser beam be written as a product of individual spin states ? Tentatively, the answer seems to be yes because single laser beam have a definite ...
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Why are Raman lidars and Rayleigh-Mie lidars operated at those specific wavelengths for aerosol study?

A study of several Atmospheric lidar stations around India shows that in order to study properties of aerosols, all Rayliegh-Mie lidars are operated at 532 nm, and Raman lidars are operated at 355, ...
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What are the practical reasons for have a high or low finesse value for a laser?

I was just wondering if someone could expand on what finesse of a laser cavity is, from my lecture notes I know how one would calculate it via the equation: $$F=\frac{4R}{(1-R)^2}$$ where $R$ is the ...
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Similar tool like pulse picker to decrease rep. freq. of pulsed laser?

Now the laser I'm using is with 100MHz repetition frequency. For some measurement, I need to decrease to 20MHz (or 40MHz, 60MHz, between 10MHz to 60MHz is good). Apart from pulse picker, is there any ...
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How much energy does it take to form a plasma channel with a laser?

The usage is for something like this https://en.wikipedia.org/wiki/Electrolaser I know that the laser is powered for an instant in which a plasma channel is formed for the electricity to flow through,...
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1answer
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Why is the spontaneous emission a big deal?

In spontaneous emission, an electron in an energetically higher state jumps to an energetically lower state. This seems a simple phenomenon. Why is it called a quantum mechanical effect? What was so ...
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Lasers for plasma

Recently I had the same idea as given at A question about the properties of plasma and its potential use in recycling, or a similar one, rather. The basic idea is: could you turn stuff into plasma ...
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How Gaussain beam exaclty be after diffraction between two mediums?

How it will be the refraction of the Gaussian beam, does one of its sides will go in distortion, and which equations can predict this distortion? Sure I have to use Snell's law to know the angle but ...
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1answer
31 views

Does semiconductor laser need stimulating photon to produce coherent light?

In regular laser, we need: stimulating photon => this makes the output light coherent ways to make inversion population resonant cavity in the pictures about semiconductor laser, I do not see any ...
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Optical power through a circular aperture?

I have the following situation to evaluate: A laser emitting a Gaussian beam having $ d_{63}=5 mm $, a small divergence $\theta$ and power $P_{0}$. $d_{63}$ is the diameter in which my beam has 63% ...
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1answer
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Ionization rate in atomic hydrogen

In perturbation theory (QM), i found the graph of ionization rate with various parameter like momentum of ejected electron, intensity, frequency, field strength of incident laser field. But i am ...
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Can light beams (e.g. from a laser) visibly interfere if they cross in mid-air?

I am wondering if two or more specific (in terms of frequency, wavelength etc) light sources could exist and capable of transmitting visible or invisible 'light', and where the beams intersect each ...
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1answer
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Laser power inside a vapour cell

I have a laser beam whose power I measured to be x $\text{mW/cm}^2$. Furthermore, I measured the beam profile of the laser beam and therefore can estimate its intensity. I shine this laser through a ...
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1answer
62 views

Light matter interaction (LASER) [closed]

I don't understand how a photon energy get absorbed or emitted by a electron. when photon incident on electron it absorbs photon energy and go to excited state, and when it come down it emits energy. ...
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Calculate beam radius for gaussian laser beam with lenses

So I know that the beam radius is $$w_R(z) = w_{0R}\left[1+\left(\frac{z\lambda M^2}{\pi w_{0R}^2}\right)^2\right]^{1/2}$$ for a Gaussian beam at a distance $z$. Now, I need the equation for the ...
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Question regarding demonstration of Poisson's spot [duplicate]

https://youtu.be/y9c8oZ49pFc At around 5 minutes into the video, to show Poisson's spot, the laser beam is made to go through a diverging lens. Is it necessary to use a diverging and why?
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1answer
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Identify reasons for laser intensity fluctuation

I got a Mitsubishi LPC-826 laser diode (single mode) with laser driver iC-HG. There is no cooling device, but data was captured after 30 mins switching on (which should be temporally stable). The beam ...
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1answer
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Regarding the demonstration of Poisson's Spot

This video is one by Veritasium on Poisson's Spot. https://youtu.be/y9c8oZ49pFc In the later half of the video where he does the experiment by using a laser, why does the laser beam have to pass ...
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109 views

What are the losses in a laser cavity?

I studied that to get the lasing conditions gain must overcome the losses. But what are the losses? Thanks a lot
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Why can't cavity length be minimized to spread the spacing between allowed frequencies in a laser cavity?

I came to conclusion that it is because by doing so the threshold gain for lasing increases but I'm not completely sure of that. Thanks
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1answer
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Random laser modes its Q-factor(s)

Many papers about random lasers mention the Q-factor of random lasers. Since a random laser has multiple peaks close to each other like shown in the figure. Does each of these peaks correspond to a ...