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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Rate of absorption, how is it used in laser theory?
Let's consider an atom with two non degenerate energy levels, $E_1$ and $E_2$, that is interacting with an monochromatic EM wave. The wave function can be expressed as $\psi=a_1(t)\psi_1+a_2(t)\psi_2$
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What is the physical meaning behind negative slope of laser characteristics?
Sometimes I measure LIV curves of many semiconductor lasers with the same material and width and different cavity length.
There should be positive slope and intercept of Threshold current vs inverse ...
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1answer
26 views
Increase viewing angle of laser line
I'm thinking of a project that would send a laser beam through a powell lens to create a horizontal laser line. But I also want the line to have a certain vertical viewing angle. So just as an example ...
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1answer
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Why does the LASER beam quality factor (M^2) use squared value?
Why does the LASER beam quality factor (M^2) use squared value? Why not using just M?
i.e., Why define beam quality factor as
$M^2 = \frac{BPP_{Real}}{BPP_{fundamental}}$
not
$M = \frac{BPP_{Real}}{...
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1answer
63 views
Laser line safety
I'm a researcher at University Federal of Santa Catarina Brazil and I work with lasers.
I'm looking for information about how to calculate the Nominal Ocular Hazard Distance (NOHD) to a laser line and ...
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16 views
What is the coherence length of Hermite-Gaussian Modes?
Can one derive the coherence length of a Hermite-Gaussian Mode just from the field
\begin{equation}
\small
E_{m,n}(\vec{r})=E_0\frac{w_0}{w(z)}H_m\left(\sqrt{2}\frac{x}{w(z)}\right)H_n\left(\sqrt{...
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Is Making a laser diode at a home workshop impossible?
I love to play with laser diodes and they have always been a fascinating thing for me. Usually, I play with $0.1$mW laser diode pointer (Which are just toys) . From some physics textbooks and videos , ...
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Generating very large area gamma rays by other ways other than large accelerators
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 ...
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Is characteristic temperature $T_0$ of a semiconductor laser geometry independent?
Can I compare $T_0$ of one laser to another one, with different length and width?
For example, let's say there are two lasers:
Laser A
Width: 20 $\mu m$
Length: 500 $\mu m$
$T_0$: X
Laser B
Width: ...
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24 views
Does it make sense to speak about a wavelength of the modes in a rectangular cavity?
Let's consider the modes of the em field for an empty rectangular cavity.
In the electric field expression the physical meaning of $\nu=\omega/2\pi$ is clear, it is the time frequency of the wave.
On ...
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52 views
Force on a relativistic laser source
Consider a laser source emitting a laser beam in the horizontal direction. If we are given the power of the laser source, we can calculate the force on the laser beam.
Now consider that the laser beam ...
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32 views
How is the lifetime of the other level taken into account in natural broadening?
The width of a spectral line due to natural broadening is given by the sum of the decay rates of both the upper level and the lower level. However, in a perturbation theory approach, how is the decay ...
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19 views
Q-factor in a laser cavity and second derivative
I found the following text regarding laser cavities. But I do not understand why they use the second derivate instead of the first. Since the second can take any positive or negative value.
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1answer
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Fresnel-Kirchoff integral and Huygens principle
Consider a monochromatic, uniformly polarized, EM wave:
$$E(x,y,z,t)=\tilde E(x,y,z)e^{iwt}$$
If on a certain plane $z=z_1$ the field $\tilde E(x_1,y_1,z_1)$ is known, we can find $\tilde E(x,y,z)$ on ...
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Why doesn't the field autocorrelation contain phase information?
in the text books its written that the fourier transform of the interferogram is just the spectrum of the incident beam and therefore contains no additional phase information. Why is that? Why does ...
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1answer
50 views
For radiation from a laser, what part of the EM wave is interesting?
On page 1 of the book "Principles of Lasers and Optics” by William Chang, the author, speaking about radiation from lasers, says that:
For devices with structures that have dimensions very much ...
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26 views
Why when looking at a laser's reflection the laser appears to have a ring of noise around the central beam?
When pointing my presentation laser at a semi glossy object like stained wood or my skin I see noise, almost like TV static (it also appears to be moving). Is this a property of the laser's refraction ...
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26 views
Laser spot size with pinhole
I am currently trying to find the focus of an IR laser beam by using a 300 $\mu$m pinhole. Now, when I am scanning the pinhole across the beam and plotting the pinhole position vs the laser spectrum ...
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Why doesn't the acousto-optic frequency shift depend solely on the velocity of sound in the medium, if it is a form of Doppler shift?
Many optics books make the statement that the frequency shift of a laser beam from the acousto-optic effect can be thought of as a Doppler shift from a traveling index of refraction grating (pressure ...
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2answers
62 views
Is there such a thing as a white laser pointer? [duplicate]
I can't seem to find a white laser pointer for sale anywhere. Is it just me or is it somehow not possible to make it? I see only color laser pointers like red, green, blue, etc.
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Can a “lightsaber” be scientifically possible? [duplicate]
Can a lightsaber be made in real life?
If yes, how can you make it?
If no, why is it impossible to make it?
I know there is another question on it, but I feel like I need better answers :)
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1answer
20 views
Reflectivity coefficients at dielectric interface
In the book Principles of Lasers by Orazio Svelto, at chapter 4.3 "Wave Reflection and Transmission at a Dielectric Interface", the author tells that
If the wave is initially in the medium ...
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21 views
Calculate if a beam of light will pass through a given point?
I'm not sure this should be in math or physics so i'm asking in both.
Given a laser beam at closed reflective surface where point $(x,y)$ being the source of a laser bean which hits a reflective ...
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39 views
How to derive the equation relating the Laguerre Gaussian mode to the Hermite Gaussian mode of a laser beam
Please help me derive the last equation, any tips are welcome. The $u^\text{LG}$ refers to Laguerre-Gaussian mode while $u^\text{HG}$ refers to the Hermite-Gaussian mode.
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Radiative transfer equation for a three-level system
I am trying to derive the radiative transfer equation for a three-level system, which is supposed to be given by:
$\frac{dI(\omega,x)}{dx}+N [\alpha\rho_{11}-\beta( \rho_{22}+\rho_{33})]I(\omega,x)=\...
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1answer
38 views
Setting a laser cutter focus in the meters range
Apologies if this is the wrong Stackexchange. All the laser-cutting searches led to graphicdesign.stackexchange.com. ?!?!?!?
I have access to a laser cutting rig, a 200W CO2 beast, that needs to do a ...
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1answer
28 views
Proof of the paraxial law for Gaussian beams in laser design [closed]
How does one proof that the complex beam parameter $q_1$ of a Gaussian beam is altered according to
$$q_2=\frac{Aq_1+B}{Cq_1+D}$$
when passing through an arbitrary optical element with a known ABCD (...
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3answers
88 views
Will a beam of laser light, in an infinite and ideal vacuum, diverge in time?
Picture this: a localized, collimated laser-beam, say one light-second long (there is a range of different frequencies or TE/TM modes), is sent into an infinite ideal vacuum. By an ideal vacuum, I ...
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What is box shape in ion beam drivers for ICF?
What is the meaning of box shape in the ion beam pulses?
i mean in plasma we say the ion beam irradiating the capsule is box shaped. what does it mean?
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What is the difference between ion beam and laser?
What is the difference between laser beams and ion beams, especially in inertial confinement fusion?
In inertial fusion, we use lasers as well as ion beams for driving the reaction. What is the ...
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Why alkali metal vapours are widely used in laser spectroscopy?
I've read, that because they are readily ionized and strongly interacting with the laser light, they could be used to study interconversion mechanisms between photon, chemical, thermal etc. energy. ...
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Photonic devices assembly (Passive optical alignment) online lectures/books
I started a new internship recently in a photonic devices company, I have a background in physics but not that much in optics (I know the basics). So there are a lot of terms that I don't understand ...
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Should also laser beams be tried as detectors in Double Slit Experiments?
If we know that a photon scatters an electron should it be tried as an indirect detector to say a deflector at one slit which can help to deduce the 'which path' information as only an electron that ...
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1answer
30 views
Why $1/e^2$ of maximum intensity is used to calculate beam diameter?
I was confused between FWHM and $1/e^2$ to find beam diameter of laser beam. Why $e^2$ and not $e $?
Which is more beneficial FWHM or $1/e^2$?
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Can a polarizer let scattered laser light pass in order to filter ambient light?
I am currently working on a project in which I need to detect the image of a line laser (I haven't choosen the laser yet, most likely a low-cost one) with a camera (most likely basic CMOS camera).
By ...
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2answers
28 views
Spatial Light Modulator (SLM) phase-only versus amplitude-only modulation
I am reading about the phase-only vs amplitude-only modulation with Spatial Light Modulators (SLMs). I wonder if there are specialists here who do this for living.
For instance, here the authors ...
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Should two laser pointers always shine a point on the screen with same intensity? [duplicate]
Lasers are coherent beams so they can be totaly cancelled out if applied a source out of phase of 180 degrees. So the question is simple... do two different coherent lasers of same luminosity when ...
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1answer
37 views
Can you create high-energy photons using multiple low-energy photons? [duplicate]
I heard once that with a special crystal it's possible to "convert" somehow two green photons to a ultraviolet one and that some UV-lasers are based on this fact. Is this right, and even ...
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Meaning of 'linear' in linear retarder
An optical retarder is a device consisting of a birefringent material, which is used to impart a desired phase change to polarized light. Common examples include half wave plates (rotate linear ...
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How to measure the doppler effect perpendicular to the movement in laser doppler anemometry
I'm trying to grasp the principle of Laser Doppler Anemometry. I like it as it is quite genius I'd say. However, what struggles me is the circumstance that the Doppler effect perpendicular to the ...
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1answer
16 views
Validity of wave front curvature calculation for a gaussian beam depending on the focusing conditions
The curvature of a gaussian beam is usually given by
$$R(z)=z\left(1+\left(\frac{z_r}{z}\right)^2\right)$$
with $z_r$ the Rayleigh length. Is there a limitation for that curvature (similar to usual ...
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1answer
20 views
Will an infrared laser reflected back on itself lose data carried by the beam?
I'm passing a 1392nm laser through a beamsplitter, through an aresol medium hitting a retroreflector, passing back through an aresol medium, and passing it through the same beamsplitter. The two beams ...
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Clarification on $M^2$ factor
In beam optics, the $M^2$ factor is a "catch-all" single number that describes how "good" a beam is, i.e., how close it is to an ideal Gaussian beam, which by definition has $M^2 = ...
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Why can't $\rm N_2$ TEA lasers produce optical breakdown? (sparks in the air)
I've been googling around and I can't find any direct explanation of why N2 TEA lasers are never shown to be used to demonstrate optical(dielectric?) breakdown or sparks in the air.
Would someone ...
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1answer
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Band-gap engineering and semiconductor lasers
I am currently studying Physics of Photonic Devices, second edition by Shun Lien Chuang. Chapter 1.3 The Field of Optoelectronics says the following:
The control of the mole fractions of different ...
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3answers
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How does mirror create stimulated atoms in laser
I know excited atom can emit photon at any direction as long it stays consistent so the total angular momentum and spin states are conserved, this is spontaneous emission. What about stimulated ...
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2answers
39 views
Is there a beating note for a sideband modulated laser beam?
In short: A laser at frequency $\omega$ gets phase-modulated at $\Omega$ (e.g. with an electro-optical modulator), such that the lowest order sidebands appear at $\omega\pm\Omega$. If this laser beam ...
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Single-mode laser oscillation in a resonator: time-dependent power
I have some issues with the time-dependent power of a single-mode laser oscillator.
We are given the frequency $\nu$ of the resonator mode,
the amplification of one period in the resonator is given by ...
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2answers
134 views
Why is a laser beam monochromatic and coherent? [closed]
Why is laser beam monochromatic and coherent?
My reasoning: Laser is monochromatic because there is equal energy difference between metastable and ground states.
Laser is coherent because there is no ...
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1answer
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Are a laser's wavelength, spot size, energy per pulse, and pulse duration independent parameters? Or can some be derived from others?
An Nd:YAG laser that has the following properties:
$\lambda=1024$ nm (wavelength)
$d = 5.8 $ µm (spot size)
$\tau=30$ ps (pulse duration)
$E_L=50$ µJ (energy per pulse).
Given any two of the above ...
