# Laser Definition and 132 Discussions

A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word "laser" is an acronym for "light amplification by stimulated emission of radiation". The first laser was built in 1960 by Theodore H. Maiman at Hughes Research Laboratories, based on theoretical work by Charles Hard Townes and Arthur Leonard Schawlow.
A laser differs from other sources of light in that it emits light which is coherent. Spatial coherence allows a laser to be focused to a tight spot, enabling applications such as laser cutting and lithography. Spatial coherence also allows a laser beam to stay narrow over great distances (collimation), enabling applications such as laser pointers and lidar. Lasers can also have high temporal coherence, which allows them to emit light with a very narrow spectrum. Alternatively, temporal coherence can be used to produce ultrashort pulses of light with a broad spectrum but durations as short as a femtosecond.
Lasers are used in optical disc drives, laser printers, barcode scanners, DNA sequencing instruments, fiber-optic, semiconducting chip manufacturing (photolithography), and free-space optical communication, laser surgery and skin treatments, cutting and welding materials, military and law enforcement devices for marking targets and measuring range and speed, and in laser lighting displays for entertainment. Semiconductor lasers in the blue to near-UV have also been used in place of light-emitting diodes (LED's) to excite fluorescence as a white light source. This permits a much smaller emitting area due to the much greater radiance of a laser and avoids the droop suffered by LED's; such devices are already used in some car headlamps.

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1. ### I About Direct Laser Acceleration

How does this Lawson–Woodward theorem work. I read on the wiki that the particles cannot be accelerated by lasers. But I do see acceleration of electrons with free space. I wonder how this is done. https://rdcu.be/c0fRw http://dx.doi.org/10.1103/PhysRevAccelBeams.19.021303 In addition, I have...
2. ### I Acceleration in an electron field

I read something about accelerators using nanotubes. I am a little concerned about the design mentioned in the "High Density with Perpendicular Carbon Nanotubes" part of this paper(https://doi.org/10.3390/photonics8060216). Can wakefield acceleration be done in an electron field? Or maybe I...
3. ### I Can surface plasmons be used to build GeV gamma-ray lasers?

I read a paper about coherent surface plasmon amplification by free electron pumping in an article a few days ago. It seems to work as some kind of free electron laser-like light source, and I wonder how high the energy of photons can go in this way. Also I read in another paper about...
4. ### I Negative energy when a laser goes through lithium niobate crystal?

A screenshot from a book which describes it: So I am trying to picture this one: 1. A laser is "pumped" through a cylinder made from lithium niobate which is placed at 90 degrees, perpendicularly...so that the laser passes through the body of the cylinder (and not through the 2 round ends)...
5. ### Finding Total Number of Optical Field Modes for Visible Light

ρ_kdk = k^2/π^2 dk is the density of field modes (what we are trying to solve for here), and as ρ_kdk = ρ_λdλ, and k=2π/λ, we can rearrange this to get ρ_λdλ = 8π/λ^4dλ This is where my confusion lies. I am not sure what to do next. I know this equation physically means the number of modes per...
6. ### B How far do photons travel inside common lasers?

So (wildly simplistically) lasers work by photons being reflected between mirrors gaining energy on each trip through the medium until they break through the mirror on the output end. How many trips does that typically result in? 10s, millions? And thus the total distance is that count * the...
7. ### I Qualitative description of stimulated emission & population inversion

I'm having trouble understanding stimulated emission and population inversion, and how they work together to make a laser work. I pretty much need this explained completely. 1. Spontaneous emission, they say, is when an atom absorbs and then later emits a photon. Isn't that just regular...
8. ### Spectrum of laser light absorbed and re-emitted by a white object

Hello, If I shine a red laser onto a white surface, I assume that: some of the red light will be nearly instantly reflected, some will be absorbed and converted into phonons and some will be absorbed and re-emitted. Is that correct? I know that my laser has this extremely narrow spectrum...
9. ### Does the ruby laser (the first invented laser) have nonlinear behavior?

Hello Everyone! I read about the function of the ruby laser which made from ruby crystal and has three energy levels. There is radiationless transition to what so called metastable level and then the electrons there stimulated to transit to ground energy state. The question is: does this...
10. ### Optical Compact Device For Measuring Speed of Light

Hi. This is an idea which I just happened to think of, and I was curious if it would be at all feasible. Here's a quick sketch I drew: The two curved mirrors should have a laser attached on one end and a video camera attached on the other. The laser would be tilted very slightly above...
11. ### I Is a LASER a classical light source or a coherent state in quantum mechanics only?

My question is the physics behind the LASER such as stimulated emission can be only explained by quantum mechanics only. We can represent LASER as coherent state in quantum mechanics only. Then how can we say LASER can be thought of a classical light source?
12. ### B Gamma rays over very large areas

According to this link https://apps.dtic.mil/dtic/tr/fulltext/u2/a351472.pdf, HERMES III at Sandia National Labs can generate very large area gamma rays by converting the electron beam into bremsstrahlung radiations after hitting the tantalum target. As we can see in the isodose contours in the...
13. ### A Laser Ablation of a fused silica surface

I read in couple of articles, like this one: https://link.springer.com/content/pdf/10.1007/BF00324203.pdf that regions of fused silica surface can be ablated by laser... I have two questions: 1- Why does the ablation occur? 2- does the ablation happens when the laser waist point is under the...
14. ### What is the meaning of polarization ratio?

I was trying to research about polarizing lasers for an experiment, and there were some things that were confusing? A website said, I was wondering if the polarization ratio was the same as the extinction ratio? Also, I was curious because I thought 100:1 would be a lot, and not much light...
15. ### I Photon induced magnetic effects

Hello all: Reading about HB-11 start up and they mentioned laser induced magnetic field : How is that created and the size of the magnetic field is in kilo Tesla range anyone heard of that Best Hagop
16. ### Optical Laser to refract/reflect water vapor and smoke.... angles?

Building visibiity sensor... What is best angle to detect water vapor reflection from laser, and refraction? I plan to have two open cylindrical containers painted flat black and put inside each other so the overlap is about 0.5-1" (adj to limit ambient light vs airflow). Laser is cheap red...

Hello, I'm looking for the governing equations for the laser radiation on a surface. I understand there are several types and methods. I was wondering if there is an equation to show all the parameters in calculating a surface temperature after laser radiation for a specific time. Some of the...
18. ### Misc. How can I enlarge the light produced by a laser?

I need to enlarge the light produced by a small laser beam that I have for a science project. I can't buy a larger laser because they're too expensive and not in the right color. Any suggestions? Thanks!
19. ### Measuring the Distance between the Fringes of a Diffraction Grating

I have been preparing for a physics practical on diffraction. More specifically, we will use a CD as a transmission grating (by peeling off the reflective layer), and measure the distance between the fringes for a specific distance between the CD and the viewing wall. However, it is unclear...
20. ### Why is milk smoother and flatter than water?

I have conducted an experiment involving projecting a laser beam onto a surface and observing speckles that move relative to us. Those speckles become less visible (maybe smaller?) when the surface is smooth and that is especially the case with milk. I have dyed milk and water to see whether in...
21. ### I Trying to Generate Entangled Photons

I've been trying to generate entangled photons using KTP laser pointer that normally produces green light at 532 nm. I was hoping that after removing the IR filter, I could add a reflective coating (right now the coating I have is a glittery metallic green nail polish) to reflect the green light...
22. ### I Minimum number of cycles in a short pulse laser

Hello to all, In a short pulse laser emission setup, can a pulse be emmited with beam length shorter than one wavelenght? (can a pulse have a duration shorter than its period?) Lets say a laser emmiter shoots a quarter cycle pulse, what would happen to this short beam? (lets supose the...
23. ### Laser cavity

I guess the resonator will be stable when both focal lengths of lens and curved mirror meet. The curved mirror is fixed and it's focal length: $$f_{curved} = \frac{R_{2}}{2} = 50 \, mm.$$ Then the d should be: $$d=f_{lens}+f_{curved} = 100 \, mm.$$ I think that's also the distance for which the...
24. ### B Poisson spot madness

Recently, I started to experiment with a laser and a coin used as a lens, being inspired by an old Cody's Lab video. My initial assumption was that through diffraction, the laser will be focused onto a spot on when the coin is a certain distance away from the wall. In a way, I imagined it as an...
25. ### Laser Linewidth Calculation

Hi guys, It's one of the questions I'm asking myself needlessly but I really wonder about this ;) Say I have a laser at a wavelength λ. I can calculate the frequency by ν=c/λ. Then the linewidth Δν=cΔλ/λ2 that can be found through differentiation of two sides of the equation. The question is...
26. ### Laser gain and the saturation effects

Hello, I study laser physics, using "Laser Physics" by Eberly and Milloni. I am confused regarding the notion of gain and the saturation effect. According to the book, the gain is defined as ## g(v) = \dfrac{g_o(v)}{1+I_v/I^{sat}_{v}} ## where ## I^{sat}_{v}## is the saturation intensity and...
27. ### What is the difference between 1/2 wavelength and 2 overlapped wavelength? (pulsed laser autocorrelation)

So, I was working on autocorrelation for my pulse laser system and I started to wonder what is the difference between single wave with 400nm of wavelength and two 800nm waves overlapped. In the knowledge, I know of, is that wavelength is the length between two picks. And when it is pulse laser...
28. ### Modes and Q-factor(s) of a random laser

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 unique random lasing mode, or is it just a single mode? Similarly what is the right way to...
29. ### Controlling light diffraction angle with a holographic "lens"

I'm a physics student, and working on a class project that requires coming up with a method to control the exit angle (diffraction angle) of a monochromatic light source. For example, taking a laser (monochromatic, coherent light source), spreading the beam, and directing the light at a piece...
30. ### What is the effect of a Laser on gravity

Hi everyone, I have this topic ,and I searched all over the internet without any results what is the affect of Laser Beam on cancelling the Gravity or reducing it if anyone can refer to a reference that can help me I will appreciate it
31. ### I Single-mode vs multi-mode fiber coupling

Hi, Is coupling light from a laser into a single-mode fiber (transverse electric) more difficult than coupling to a multi-mode fiber? If so, is it due to the geometry? Does the laser light have multiple modes to begin with or it can be designed to have just one mode? Thanks
32. ### What exactly is the thermal lens effect?

Hello, i just wanted to ask if you can explain to me what thermal lens effect is? I am supposed to answer why laser beam passing through ink or soy sauce creates this effect and i can't find any information on what actually this thermal lens is. I know of course that it is a lens, but why does...
33. ### What is meant by Spectral and Spatial Shaping of a laser

Hi, I am new to the forum so apologies if I placed this in the wrong subforum though I think the subject is classical enough to be here. I was hoping to get a concise answer to what is meant by spectral and spatial shaping of a laser. My intuition says that we are modifying the amplitude of the...
34. ### Relation of laser pulse length and the Output Coupler trasmissivity

Dear all, I'm within my Ph.D. studies in laser engineering and most of the details are rather new to me. Working on short pulse systems, my advisor told me some times about the relation of the output coupler transmissivity and the outcoupled pulse length, but more as a rule of thumb. According...
35. ### Reflected Light Beam

Hello, I have a question or perhaps a few questions regarding light and mirrors. When we point light at a mirror, it gets reflected back. But we can see the point light (assuming that it is a laser for the sake of simplicity) at a surface opposite to the reflective surface of the mirror. What...
36. ### B Gravitational Redshift of a laser

If we run two identical lasers and put one at sea level and one on top of a high mountain, will they operate at different frequencies?
37. ### Laser pumping: further increasing injection above threshold?

Above the threshold, the stimulation emission becomes dominant for lasing. If increasing the pumping, what will be the change of spontaneous emission and its contribution to the output power and FWHM of the signal, based on the threshold carrier density clamping and the threshold gain clamping...
38. ### Mirror: refractive index and thickness

Homework Statement Hello everyone ! I hope this is the correct place to ask. Here is my probem: I have to measure the refractive index and the thickness of the glass part of a mirror. The idea that I have, and that has been approved by my teachers, is the following: In order to measure the...
39. ### I Why can't there be a 2-level laser with Non-Optical Pumping

Hi everyone, I would like to understand the answer to the question in the title. I got that when we use optical pumping of a laser, the probability, given an incoming photon of adequate energy, for an atom to absorb it and for an other to produce some stimulated emission out of it are equal...
40. ### 3D subsurface laser engraving for translucent minerals?

3D Subsurface Laser Engraving works for clear glasses like Schott BK7 and B9 Borosilicate Glass. How does one do the same for relatively translucent minerals? I have read research papers on using lasers for tattoo removal and cancer radiation therapy. However, I want to know how the laser's...
41. ### Why parts of the laser ray seem brighter than other parts

Hi. When we see a laser ray, it seems that part of the ray are brighter than the other parts and they seem like they’re vibrating and moving. It also seems there are fractures in its path. I want to know why do we see like this? For example see this picture (it is from wikipedia). I circled...
42. ### Number of Photons inside a Laser Cavity

<< Mentor Note -- thread moved from the technical forums, so no Homework Help Template is shown >> Let's say you have a laser cavity with two mirrors at either end, one is considered 100% reflective, the other 99.9%, so that a wave beam is emitted through this lower reflectivity mirror. I know...
43. ### The Extreme World of Ultra Intense Lasers - with Kate Lancaster

The largest and most powerful lasers in the world can be used to make some of the most extreme conditions possible on earth. Scientists around the globe are using these lasers to try to miniaturise particle accelerators, make astrophysical conditions in the lab, and create fusion energy.
44. ### What is a "Pin-Bar" TEA Laser

Now from reading wiki i understand there are Pin-bar and non pin-bar, non pin-bar is what people have moved to today with the spark gap. but i read that "These first 'Pin-Bar' TEA lasers, operating at around one pulse per second, were easy and cheap to construct. By operating at atmospheric...
45. ### Calculating how many Joules are required to make a photon

A double covalent bond of nitrogen (N2) is 15.58eV Now let's go into a example. if i have a laser that is 477nm and i do 1240/477nm then i get 2.6eV per photon. Now if i do (15.58eV / 2.6eV) it equals ~6 photons. Now to figure out how many Joules are required for 1 photon I do (6.626*10^-34S *...
46. U

### Laser Question - Axial Modes & Gain Saturation

I am studying laser physics at the moment and there is something that confuses me. The laser output consists of the central laser mode and some axial modes due to constructive interference in the optical cavity. At first there is a high enough population inversion and while the laser works this...
47. ### Longitudinal/transverse modes in optical cavity (resonator)

I am learning about lasers and trying to clear up some blurry concepts in my head so I am not necessary using heavy math for description here so please bear with me. Let's take EM field in a rectangular box with walls that are perfect conductors (optical cavity). EM field distribution inside...
48. ### Question about missile defense systems and lasers

I was reading a news article about powerful lasers being used in missile defense systems, and I was wondering if multiple weak laser can work together to do the same job as one strong laser. For example can a thousand 1 Kw lasers in different locations be made to point at a single point on a...
49. ### If lasers cross-over, do they "add up"

Hello, If two lasers cross over, do tehy ionisate each other. If i have sensor in laser measuring ionisation going out etc can it see that laser 2 is crossing over it?
50. I

### Use of a half wave plate plus polarizer to attenuate lasers?

The combination of a half-wave plate followed by a polarizer is commonly used as a variable attenuator for polarized lasers. The idea is that the beam enters the half-wave plate, and you rotate the half-wave plate leading to a rotation of the polarization direction of the beam. As the beam is...