# 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. ### Uses for laser light in measuring hair width

I have a question that I feel I cannot find enough on. We just did a practical in Physics class where we used a laser light shined on a single hair strand in order to create a diffraction pattern and use formulae to determine the hair's width. Because of Babinet's principle, the hair managed to...
2. ### Sketch of the electric field of a laser beam

I am trying to sketch the electric field E in snapshot of a linearly polarized laser beam. Is it correct that the E vectors bend from vertical to longitudinal near the cylindrical surface of the beam, and that all field lines within a half wave segment are closed loops?
3. ### How much can a laser burn through?

Relatively simple question, I'm new to lasers and just had a basic question. What effects what a laser can burn through? Is it wattage, nm, burn time, or what? Is there an equation for how many Joules it takes to burn through a volume of a given material using specific heat capacities? To ease...
4. ### Decreasing Laser power

Hi, So I am working with measurements using a laser. What I have noticed is that the power of the laser decreases from the time we start the laser until maybe an hour later. Today I noticed it has decreased 10%, from yesterday, which I think sounds like a lot. Does the laser have to warm up and...

Is there a possible way to redesign femtosecond lasers to reduce cost?
6. ### The collimated parallel beam of a LASER

Homework Statement Multiple-choice question: The LASER beam is a collimated parallel one, that means that its photons have the same... (i) phase (ii) direction (iii) intensity (iv) frequency Attempt at a solution I would exclude frequency because it has nothing to do with the fact...
7. ### I Determining Appropriate Focal Length

So I'm working on a project where we're deciding a new lens to use for our laser diode. I need to determine the appropriate focal length based on the equation: 1/ƒ = 1/μ + 1/σ where ƒ is our focal length, μ is the distance from the lens to image and σ is distance from lens to object. For the...
8. ### Setting up a circuit to drive a Laser Diode

Hello fellow physics friends (alliteration: always a strong opener). I am writing today because I find myself struggling to complete something which ostensibly doesn't seem that difficult to the average physics undergrad working in a lab. However, electronics and circuits are definitely a...
9. ### Designing a planocovex PMMA lens

As an electrical engineer, I am an amateur on optics, but I really could use some help. I am making a lens of PMMA, 2D. To 'convert' a rotary movement into a sweep. The lens needs to be 120mm long, with its focus at a max distance of 80mm the light traveling out of the lens needs to be parallel...
10. ### Observation of laser pulse propagation in optical fibers

Just wanted to share this, mainly because I really liked the videos (found in the supplementary section at the end). Moderators, feel free to move it to a more appropriate place. Observation of laser pulse propagation in optical fibers with a SPAD camera Recording processes and events that...
11. ### I The spin of the photon -- a weird experiment with a laser

Hello everybody, I'm playing with a ne -ne laser And i conducted an interesting experiment I did colliding beams the type of interferometer Fabry Pero between the mirrors I put the cuvette with different substances I tried to detect changes of polarization of the laser beam with the help of a...
12. ### Laser Questions

Hi! I am currently self-learning laser right now, and I have some questions about it.. 1. We know that water moves from higher to lower altitude, air moves from higher to lower pressure, electrons move from higher to lower potential. What about photons? Where would it go? 2. Why would only...
13. ### Red laser erases on glow in the dark surfaces?

Hey guys, So recently I came across a weird phenomenon... Basically, I shined a red laser on a glow in dark surface and the laser could erase it. The fun fact is that before the laser erases the are, it makes it glow for a short time. You need good goggles to see the glow despite the intense...
14. ### B 100% reflective laser cavity?

What if I replaced the half transparent mirror in a laser cavity with a 100% reflective mirror? -would all photons escape due to the quantum tunneling effect? -would the mirrors melt? Thanks :biggrin:
15. ### I Ratio between spontaneous/stimulated emission

Hi. In thermodynamic equilibrium, the ratio between spontaneous and stimulated emission is $$\frac{A_{21}\cdot N_2}{B_{21}\cdot N_2\cdot u(f)}=e^{\frac{hf}{k_B T}}-1$$ where ##A_{21}## and ##B_{21}## are Einstein coefficients. This means, that there's always much more spontaneous than...
16. ### Is it possible to collimate monochromatic light with a taper?

I am ignorant about laser physics, but i have this idea of collimating monochromatic light with an optical fiber/cable that is cone shaped: at inlet the cone has a wide diameter (several hundred microns - like an ordinary optical fiber, which might be used as a light source), on the other end it...
17. ### Is laser light polarised? In which direction?

Hello. I want to know about the polarisation of lasers and I've been reading basically two kinds of answers for the question 'Is laser light polarised?' The first one is 'yes' and the second one 'not necessarily'. Let's consider a gaussian laser. Ideally its light is monochromatic and coherent...
18. ### I Nuclear Laser?

I've been thinking... Is there any way that there could be sort of a one-time use pulse laser that uses something like a mini atomic bomb to create a super high energy laser? I found stuff about a Nuclear pumped laser and "Project Excalibur", but I wanted to ask actual people who know a lot...
19. ### Rotating coherent laser beam

if a coherent laser beam rotates about an axis at very high angular frequency can a light dot with radiant glow (of short radius) be obtained due to persistence of vision ?
20. ### Hair/wire laser diffraction interference pattern

Hair/wire laser diffraction interference pattern - does it follow single-slit or double-slit? for single-slit interference, the equation nλ = d (y/D), (d is the width of the single-slit, y is the distance between central BRIGHT fringe to the nth DARK fringe, D is the distance from slit to...
21. ### I Is it possible to image individual air molecules?

I was wondering if it is possible to image the motion of individual air molecules? What I am picturing is using a laser to illuminate a volume of air, and using scattered light to measure the velocity of individual air molecules through the doppler shift of the scattered light. It seems that...
22. ### Class Making a T.E.A. Laser-- we have questions....

I run a Maker group for teens in Florida at the Pensacola MESS Hall. We are building a T.E.A. Laser powered by a Wimshurst machine along the lines of a Rimstar project we found on YouTube. But, we have some questions about the laser it will produce: (1) I read that the TEA Laser has high...
23. ### I Planck formula and density of photons

Hello! Let's consider again a system of atoms with only two permitted energy levels E_1 and E_2 > E_1. When electrons decay from E_2 level to E_1, they generate a photon of energy E_{21} = E_2 - E_1 = h \nu. The number of photons (per unit frequency, per unit volume) emitted by such a system in...
24. ### NIR modulated laser system - Need advice

I'd like to perform experiment on NIR laser (around 800nm) with modulated signal (varying duty cycle), with peak power around 1000mW, the output is desired to be connected to fiber optic. I am new to laser technology, and have googling around but can't find suitable laser module (complete set)...
25. ### Index of refraction of the material

Homework Statement A laser is fired into a wet paper placed ontop of a glass plate of thickness ##d## and an angle of ##0## degrees. When the light hits the paper and goes through the plate it forms a circle of light of radius ##R##. What is the index of refraction of the glass plate? Homework...
26. ### Combing Lasers To Create One Mega Laser

Hello, I am pretty new to physics but have a large amount of experience with Calculus and other sciences like chemistry. The theory I have come up with is that if I combine 6-8 5w laser beams together in a convex lens that can be moved forward or backward to change the focal point distance, I...
27. ### HeNe Laser Power Supply Components

I recently salvaged a Melles-Griot HeNe laser from an FTIR system. I neglected to save any of the electronics except for what I think is the step-up transformer attached to the laser tube. The laser is "05-LSC-708-540" and the transformer is "05-LPM-850-045". I have a 12V power supply, but was...
28. ### Is it possible to magnify light heat?

Is it possible for me to make a flash light into a "laser" hot enough to burn through paper. Here is what I have: a light prism, 2 light splitters,(the can separate light so it goes 2 ways) 2 magnifying glasses, and a microscope.(I don't want to use it though) If there is any thing else you...
29. ### Zero group refractive index

Homework Statement .[/B] I am attempting to determine the group refractive index of a laser cavity at it's resonance frequency. Homework Equations .[/B] \begin{align*} \frac{2\omega n L}{c} &= 2m\pi \end{align*} \begin{align*} n_g &= n + \omega \frac{dn}{d\omega} \end{align*} 3. The attempt...
30. C

### Camera which measures distance?

Hi all, I'm having trouble finding something online which isn't a very complicated device, but I don't know if it has a specific name, which would help me in a google search. I have a motor in an MBE which moves the sample, and I need a camera which can read to a computer what the distance is...
31. ### Optical Probe Clarity

I work in a lab that uses laser probes to test for vibration and other data, currently the lab techs hook up the probe to a laser source and check to see how bright and clear the beam spot is. I have been working on having a signal power budget created for each probe using a laser source and...
32. ### Shortest possible pulse duration

Hey guys, I really need your help. I got the following task: "Sketch the output spectrum of a mode-locked Ti-Sapphire laser (assuming eg. gaussian shape) and calculate the shortest possible pulse duration by Fourier transformation." So the spectrum is gauss shaped but I have no clue how to get...
33. ### I Diffusion of carriers in a double heterostructure

Hello! Double heterostructures are used in LEDs and lasers to provide both the confinement of the charge carriers and the confinement of the generated light. This image is a comparison between a homojunction and a heterojunction. As regards the unbiased junctions, when the n region and the p...
34. ### I Photoluminescence Excitation (PLE) vs PL spectroscopy

I'm not sure I understand what information we can get from Photoluminescence Excitation (PLE) that we don't get from regular PL. Let's imagine we have a sample with emissions between 700nm and 850nm. If I'm not mistaken in a typical PL experiment you'd just use a laser source with a wavelength...
35. ### Gases that absorb IR radiation

Hello, I'm looking for a gas (hopefully one that is readily available) that will absorb Nd:YAG laser radiation at 1064 nm. The purpose is to heat the gas to transmit heat into a glass fiber composite which normally does not absorb IR light.
36. ### Is there any relationship between light intensity and angle

Homework Statement I'm working on a project right now, which uses laser beams and part of the project requires me to find a mathematical model which relates angle of projection to the intensity of the light. Does anyone know of an equation(s) which relates the intensity and angle together...
37. ### Calculating Electric and Magnetic Field amplitude

Homework Statement A circular uniform laser beam has a power of P = 3.2 mW and a diameter of d = 8.5 mm. The beam is a form of electromagnetic raditation with both electric and magnetic field components. (a) Calculate the intensity of the beam in units of W/m^2 (b) Calculate the energy (delta...
38. ### Measurement of Focal length with Laser beam

Homework Statement Hi! I have lately come across some tricky experimental physics tasks, where no solution is given. Some of them involved parts where the focal length of a convex lens had to be measured with a laser. How do you do this? Homework Equations 1/l + 1/d = 1/f (1) where f is the...
39. ### LASERs: Why is population inversion required for amplification?

Hi, I'm doing a module on quantum optics and lasers. Most of the texts and online source I have read simply state that 'population inversion is essential for amplification in laser operation'. My question is, why? Amplification/Gain is essentially the result of stimulated emission. Can't...
40. ### Class I laser

I am doing some experimentation, for a science fair. And I want to make sure I the laser pointer I use is Class I (conceivably, I may change that, but any class of laser can be used to replicate results similar to the double slit experiment correct?). Can anyone direct me as to where I may be...
41. ### Laser beam intensity

What is the intensity in W/m² of a laser beam used to burn away cancerous tissue that, when 94.0% absorbed, puts 539 J of energy into a circular spot 2.11 mm in diameter in 4.00 s?? I've tried a couple different equations and I keep getting the answer wrong. This is due tonight, I'm super...
42. ### Laser and Metal

When blaster or laser is used to make a hole in a piece of metal is any of the matter of the metal completely eliminated from the universe?
43. ### Help in laser simulation in COMSOL

hi im supposed to simulate a vcsel laser for my thesis i got problem in selecting physics.. i should check its heat transfer and threshold current but i don't know which physics should i choose ! does anyone know about vcsel's physical structure in Comsol ? by the way does anyone know that how...
44. ### What laser should I use?

If I were to replicate this experiment http://arxiv.org/pdf/1505.04254v1.pdf but was limited to the purchase of only one laser which frequency and what power should I choose? I know the research team that conducted this experiment purchased their lasers from jetlasers.org but they unfortunately...
45. ### Possible non-burning visible beam mock-up?

To give a little idea for what I'm aiming for: I want to make a prop laser gun. It doesn't have to actually do anything, but I've decided it'd be awesome if it did. I could use a 2-5W blue laser diode like some people who make awesome contraptions with lasers show on YouTube, but I'd frankly...
46. ### Semi-classical argument for stimulated emission?

Laser action by definition requires the presence of stimulated emission in the laser medium. The typical way of treating this semi-classically is to introduce the Einstein coefficients, in essentially an ad hoc way, then derive the Einstein equations for the various level population transitions...
47. ### Low-cost low threshold optical beam limiter?

Do you guys know a low-cost low-threshold optical beam limiter, with cost somewhere ~\$100. Or if you know certain method to fabricate such. I would be greatful if you could include links and/or references. I am still noob in photonics so I am only familiar with a beam limiter that blocks the...
48. ### Laser Induced Breakdown Spectroscopy

Hi, I'm trying to use LIBS technique to figure out elemental analysis of human nails. But every time i run the experiment, i get the emission line of metal instead. The sample holder is indeed made up of metal. What should I do to overcome this problem? Since i have small size sample, I'm...
49. ### Can stimulated emissions from CO2 be absorbed?

When an excited molecule absorbs a photon two coherent photons are emitted. If one of these photons is absorbed by a second molecule, since the emission was coherent then that molecule will absorb the second photon too. If the second molecule was in the ground state then it will become excited...
50. ### Laser TEM modes

What determines which TEM mode will the laser output have? Why some lasers emit in TEM00, while other in a donut mode, and other in a superposition of multiple modes. Thank you.