All Questions
Tagged with electromagnetic-radiation laser
25
questions
42
votes
3
answers
16k
views
Is it really possible to break the speed of light by flicking your wrist with a laser pointer?
Minutephysics has a popular YouTube video called "How to break the speed of light". In the video it states that if you flick your wrist while pointing a laser that reaches the moon, that the spot of ...
- 551
311
votes
2
answers
30k
views
What is Chirped Pulse Amplification, and why is it important enough to warrant a Nobel Prize?
The 2018 Nobel Prize in Physics was awarded recently, with half going to Arthur Ashkin for his work on optical tweezers and half going to Gérard Mourou and Donna Strickland for developing a technique ...
- 134k
156
votes
1
answer
15k
views
What is an "attosecond pulse", and what can you use it for?
The 2023 Nobel Prize in Physics was announced today, and it was awarded to Pierre Agostini, Ferenc Krausz and Anne L’Huillier, for
“experimental methods that generate attosecond pulses of light for ...
- 134k
14
votes
3
answers
8k
views
Why is the photon emitted in the same direction as incoming radiation in Laser?
When an atom “lases” it always gives up its energy in the same direction and phase as the incoming light. Why does this happen? How can this be explained?
How does the photon generated because of ...
- 557
6
votes
4
answers
1k
views
Energy conservation in the combination of two coherent beams
I was asked a question today by a student that I couldn't find a satisfactory answer to.
Imagine we have two identical laser beams with average electric field strength $E$. Upon combining these beams ...
- 3,819
15
votes
4
answers
2k
views
Does the speed of medium affect the path of light?
Let's say I shine a laser from a stationary medium into a moving medium (suppose the water is moving very quickly) perpendicular to the interface and back to a stationary medium like this:
(Note: ...
- 153
17
votes
4
answers
13k
views
Can radio waves be formed into a pencil beam?
Laser beams are said to have high "spatial coherence". This means that the beam is highly concentrated even at long distances (low spread).
Can this be achieved with radio waves (much longer waves) ...
- 589
12
votes
2
answers
2k
views
On the (non)linearity of electromagnetism
As a student you are typically told that Maxwell's equations (ME) in vacuum are linear. However, it seems that for extremely high electromagnetic fields the equations for electromagnetism turn out to ...
- 1,211
5
votes
2
answers
2k
views
Why are laser pulses Sech Squared in temporal shape?
Ultrashort pulses from mode-locked lasers often have a temporal shape which can be described with a squared hyperbolic secant ($\mathrm{sech}^2$) function:
$$
P(t)=P_0 \mathrm{sech}^2 \left( \frac{t}{...
- 1,934
2
votes
1
answer
482
views
Michelson interferometer with and without Gaussian beam
In this video from MIT OpenCourseWare for a Michelson interferometer are demonstrated circular fringes.
I’m curious, how the mode of the laser influences the shape of the fringes. Can one conclude ...
- 10.6k
2
votes
1
answer
712
views
Gaussian beam shape
In this diagram of a Gaussian beam, why does the radius vary with z position? Is it assumed that a Gaussian beam is always being focus by a lense? Why can the beam not go any smaller than $w_0$ and ...
- 31
40
votes
2
answers
2k
views
Why does laser light not affect glowing materials?
I have this childrens rubber ball which glows in the dark after it's exposed to light. I "charge" it with a flash light then play with my dogs at night. I thought to try a very intense green laser, ...
- 780
12
votes
3
answers
6k
views
What exactly is the difference between a sychrotron light source and a free electron laser?
Cyclotron radiation is radiation emitted by a charged particle being bent by a magnetic field. The only difference between cyclotron and synchrotron radiation is that the latter occurs at relativistic ...
- 327
11
votes
3
answers
838
views
Are non-zero-area pulses of electromagnetic radiation possible?
This is a bit of a long-standing question / bone of contention that I've seen floating around, and which I would like to ask here in the hopes of getting some outside perspectives from a broader ...
- 134k
11
votes
1
answer
2k
views
Can a Black Hole be moved by lasers?
I've read that an object colliding with a black hole will move it, as it would any other object. Could a laser continuously fired into a black hole move it?
- 719