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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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Does the SailBeam concept violate conservation of etendue?

SailBeam is a proposed method of spacecraft propulsion based on laser-driven sails. The SailBeam laser pushes on a series of "microsails," each sail having around 0.1m radius. Each microsail ...
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Moving laser beam passing over stationary circular opening

I am in need of help with the following situation. I appreciate any insight. Imagine a circular laser beam of diameter d1 moving at velocity v passing over a stationary circular opening of diameter d2 ...
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Does the coherence of light sources make a difference in exciting fluorescence?

Using LED vs laser as light sources in wide-field epi-fluorescence microscopy are both popular choices. It seems that high intensity single color LEDs (such as this one) emits high radiometric power ...
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Do lasers with optical isolator or synchrotron radiation sources allow for Rabi cycles?

In Rabi cycle two-level system cyclically transitions between ground and excited state - bringing question where their energy difference goes during these transitions? For transition from ground to ...
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What effects could cause a laser beam inside a pipe to bend?

I am seeing a deflection in a 450nm laser beam while it is being directed through 40ft of a 48"dia. fiberglass pipe (other pipe material (ie.- concrete) doesn't affect it). Why? FACT: Heat ...
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Why laser output power fluctuates after passing through two 1x2 fiber optic couplers?

When laser source is launched into two 1x2 50/50 fiber optic couplers connected as below the output power constantly fluctuates in range of 70 uW. The fluctuation happen roughly one to two times per ...
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Why do we stay at the rotating frame when considering an atom and field interaction in the Rabi problem

In the Atom-Field interaction chapter of the Steck Quantum Optics book, he considers a two level atom interacting with an elecromagnetic wave in the dipole approximation. This leads to a 2X2 ...
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Directionality of laser light in vacuum [duplicate]

It is well-known that laser light is directional because of coherence from stimulated emission. This means that the light is emitted ONLY in the direction of propagation, and not in any type of ...
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Would the use of LIPC's for Lasers avoid eye damage for bystanders?

Laser Induced Plasma Channels (LIPC) can create a tunnel of plasma in the air for a brief moment (milliseconds). But the formation of a LIPC is a process and not something instantaneous when it comes ...
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Can the laser light, in principle, take any wavelength in the EM spectrum?

Can the laser light, in principle, take any wavelength in the EM spectrum? I don't think there is what prevent this in principle, right?
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Laser resonance phase shift

I understand in classical mechanics, for an driving force to be resonant with the oscillator and give force to it, there must be a $\pi/2$ phase shift (lag). My first question: is this the same for ...
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Spherical laser beam terminology

I am currently seeking the correct terminology for a beam that expands linearly from a fixed point, resulting in its wavefronts forming spherical surfaces. However, the beam does not expand in all ...
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What is the function of a concave lens in a laser pointer?

In my cheap laser pointer I found a concave lens in front of the LED. I expected a convex lens. If I remove the concave lens the beam is much less collimated. The same if I replace the concave lens ...
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Coupling a single mode laser to multimode fibre - does this reduce coherance?

If I have a single mode laser coupled to a multimode fibre with imperfect overlap between the laser mode and the fibre core, the light will propagate in several LP modes. In this case, does the light ...
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How does doppler cooling work?

I have trouble understanding how doppler cooling works. I understand that an atom moving towards laser sees the laser light blue-shifted and if the laser frequency is slightly below the atom's ...
python3 programmer's user avatar
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Beam displacement at focal point

I'm working on a project that uses galvanometers with mirrors. They're configured to have a focal point of 175mm. The motors rotate at 1 mechanical degree per 500mV, that will be 2 degrees optical per ...
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Question about lasers [closed]

In a laser, how the beam is almost non-divergent? When stimulated emission happens , does it copy the photons which is used for the medium to get pumped, or does it copy the photons of spontaneous ...
Prantar Biswas's user avatar
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Can X-rays compress plasma for fusion?

I know in ICF fusion, generally lasers are used to generate X-rays inside a holhraum to compress a duetirium tritium fuel pellet until it generates fusion reactions. I was wondering if the same ...
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Penning trap laser cooling

In the penning trap, I know that there is a quadrupole electric field and a magnetic field. This results in three eigen motions with three eigen frequencies: magnetron freq, modified cyclotron freq, ...
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How CCD receives lasers in laser machining?

The diagram below illustrates the system uses a beam splitter that sends the beam to a camera for real-time measurement. What I'm curious about is how the laser beam is directed onto the ccd, will it ...
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How laser gain bandwidth is calculated?

I was reading about mode-locking from Wikipedia and there is an explanation of cavity modes. The following sentence confuses me: For example, a typical helium–neon laser has a gain bandwidth of about ...
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Why does scanning a barcode off a mobile phone screen work?

I recently went to a store and showed the loyalty card on a picture taken on my phone. As the cashier moved to scan the barcode, I figured that this won't work. Laser light is presumably coming out of ...
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Which method of laser diode operation is less likely to cause mode hopping: constant current or constant power?

If a laser diode is uncolled and operates in a CW mode then which method of operation is less likely to cause mode hopping: constant current or constant power?
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Converting laser irradiance into volume energy density

If I want to convert a laser's irradiance of $10^{20} \,\text{W}/\text{cm}^2$ into a volume energy density, do I just divide it by the speed of light $c$?
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Einsteins Coefficient of Absorption in solid state

What solid state parameter determines the probability of absorption (Einsteins coefficient B) in a material? Is it material dependent? I think, I cannot say bandgap. Because if I have a source having ...
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What is a laser spectrum?

What is a laser spectrum? How many wavelengths can we see in it, and why? For a regular laser, the red ones you can buy at the store, is there just one red wavelength in the laser? Or are there ...
qris's user avatar
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Measuring duration of ultra-short laser pulses

I read that the duration of one ultra-short laser pulse in a pulse train can be measured with autocorrelators or more sophisticated methods like Frequency-Resolved Optical Gating (FROG). In principle ...
Ang's user avatar
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Why fiber optic Sagnac interferometers don't produce multiple interference fringes

I have seen a few Sagnac fiber optic interferometers however, those that I've seen don't produce multiple fringes but rather just one luminant dot with varying intensity. Even if a beam expander is ...
Jimski's user avatar
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What is the meaning of a fiber cutoff wavelength when given as a range?

Many polarization maintaining fibers (for example Corning PM 1550) have a cutoff wavelength specified as a range (for example 1300-1440nm). What is the meaning of this range from the physics point of ...
Jimski's user avatar
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Question about coherent population trapping

In coherent population trapping, if we denote the ground states in a $\Lambda$-like system as $|0\rangle$ and $|1 \rangle$ and the excited state $|2 \rangle$, there is a linear combination $|d \...
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In the He-Ne laser, if the collisions between the He and Ne atoms are inelastic, where does the lost energy go?

In the He-Ne laser, if the collisions between the He and Ne atoms are inelastic, where does the lost energy go? Does it go into heating the cavity?
Jack's user avatar
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Why self-phase modulation can prevent mode-locking?

Several sources claim that Self-Phase Modulation (SPM) can prevent mode locking (ML) in fiber lasers (e.g. rp-photonics). I have experience of a silica fiber laser based on active ML where steady ...
Ang's user avatar
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Does the beam image invert on each round-trip through a hemispherical laser cavity?

When one creates a hemispherical laser cavity, using one flat and one concave mirror, does the beam image invert each time it makes a round trip? I know when passing through the focus of a lens/mirror,...
Bo Mungton's user avatar
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1 answer
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Why are laser linewidths in frequency domain?

I am learning about the lasers and I find one thing confusing about the lasers. I understand that there is a range of wavelength laser, it is never exactly monochromatic. So, I understand the concept ...
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Why is the $\cos^2$ envelope much more popular than $\cos^4$ to approximate the shape of a Gaussian laser pulse?

The Gaussian laser pulse $$ E(t) = E_0 e^{\frac{-2\ln 2}{\tau^2} t^2} \cos{\omega t} $$ (where $\tau$ is the intensity FWHM) is often troublesome in numerical simulations due to the infinite temporal ...
Neinstein's user avatar
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Why does laser light not bend (refract) when it travels from air to water?

I passed green laser light from air to water but to my suprise the light doesn't bend towards normal even though I changed the angle of incidence.It goes undeflected ,Is it because of its higher ...
Sanjay S's user avatar
2 votes
1 answer
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What is the intuitive reasoning for Stimulated Emission?

I've been scouring the web for explanations of Stimulated emission, and have seen questions Like this one on directions and frequencies, this one on energy conservation, this one one lasers and ...
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How Does Laser Light Maintain Coherence Amid Photon-Atom Entanglement?

Laser light is known to produce "coherent state light," which consists of a superposition of different photon numbers. However, wouldn't the entanglement between the atoms and the light ...
Steven Sagona's user avatar
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Energy of electron during Tunnel ionisation

I have been studying an emission mechanism that exploits the ionization, disassociation and subsequent fluorescent recombination of nitrogen molecule by a femtosecond laser for velocimetry. The ...
Nikkhil Chander's user avatar
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What are the disadvantages of using a single mode Fabry-Perot laser diodes in interferometry, as opposed to distributed feedback laser diodes?

What are the disadvantages of using a single mode Fabry-Perot laser diodes in interferometry, as opposed to distributed feedback laser diodes? I'm specifically interested in potential problems that FB ...
Jimski's user avatar
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If lidar is used underwater, would passing through a turbulent surface into a pocket of air (e.g. a "moon pool") distort the resultant image at all?

I have zero experience with lidar systems, but I have been under clear water and looked up at the interior/ceiling of an indoor pool, and even the slightest turbulence at the surface distorts what I ...
rccapps's user avatar
2 votes
0 answers
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Deriving the dephasing operator in the master equation for atom laser interactions

Consider a two level atom where the two levels of the atom are seperated by energy $\hbar\omega_{0}$ and are coupled via the dipole interaction induced by interaction with a laser of fluctuating ...
Adrien Amour's user avatar
29 votes
2 answers
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How does a laser from Earth manage to hit the Moon with precision?

A question I've been asked is how a laser, fired from earth, would hit the moon without "leading it" (or hit it with precision). When firing a laser at the moon, it takes about 3 seconds to ...
Marco Chacon's user avatar
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1 answer
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Do high powered lasers refract differently than other light?

So I have a question: I am told that there are naval lasers that target over 100's of miles ship-to-ship (not ship to air). Someone asserted that powerful lasers would refract differently than light. ...
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Incidence angle in pulsed laser deposition (PLD)

Why is an incidence angle of 45° the best choice in pulsed laser deposition (PLD)? Why not 20 or 30 degrees, if reflection is effect or not?
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Converting time-bin diagram to second order correlation function

Considering characterization of single photon sources a second order correlation function $g(𝜏)$ is used to determine the purity of a single photon source, specifically its value at $g(0)$. Now ...
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Is it possible to make a dual-mode, multi-band laser?

Understanding how N2 and CO2 gas lasers work, Is it possible to make a gas laser (i.e. with the right gas mix and excitation source) that: has more than one mode of operation, emits light in more ...
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Measuring Temperature of Water-filled Methacrylate Capsule: Laser Thermometer Accuracy and Penetration Depth Inquiry

Imagine that I have a methacrylate capsule filled with water (8cm in diameter and 30cm in length). If I wanted to measure the temperature with a laser thermometer pointing at the capsule, what ...
Eladio's user avatar
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2 votes
1 answer
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Why some laser diodes have angled window?

Why some laser diodes have angled window? Here is an example
Jimski's user avatar
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Will a laser with low power - operating as continuous wave - generate supercontinuum in nonlinear materials?

Some nonlinear optical materials, such as for example glass doped with As2Se3 or As2S3, are able to generate supercontinuum if a single mode laser pulse, in range of a few watts, is launched into the ...
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