Laser Beam Diameter: Why Can't Power Be Increased?

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Discussion Overview

The discussion revolves around the limitations of achieving a laser beam diameter smaller than its wavelength and the implications for power output through lenses. Participants explore concepts related to diffraction and the behavior of electromagnetic waves in this context.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions why a laser beam cannot have a diameter smaller than its wavelength to increase power, seeking a simple explanation.
  • Another participant asserts that the limitation is due to diffraction, stating that there is no solution for electromagnetic waves corresponding to a smaller diameter.
  • A request for clarification on diffraction is made, with a focus on why light does not scatter beyond its wavelength.
  • It is noted that diffraction is distinct from scattering, and that books should be consulted for detailed explanations.
  • A participant references a Wikipedia article on diffraction, highlighting animations that illustrate how a smaller aperture leads to a wider beam spread.
  • One participant explains that if the wavefront size is much smaller than the wavelength, there will be minimal interference, affecting the wavefront's expansion.
  • A personal anecdote is shared about coding a simulation of the wave equation, revealing insights into the behavior of light and the role of interference patterns.

Areas of Agreement / Disagreement

Participants express differing levels of understanding regarding diffraction and its implications, with no consensus reached on the initial question about laser beam diameter and power increase.

Contextual Notes

Some participants reference external resources for further understanding, indicating that the discussion may rely on definitions and concepts not fully explored within the thread.

Krishnakant
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Hi Friends,
I want to know that why one can't achieve diameter of a laser less than the wavelength of the beam in order to get more power through a lens.
please explain in simple Physics
 
Science news on Phys.org
This is given by diffraction.
There is just no solution for electromagnetic waves that would correspond to a smaller diameter.
 
mfb said:
This is given by diffraction.
There is just no solution for electromagnetic waves that would correspond to a smaller diameter.
Dear mfb,
Would you please explain diffraction so that I can comprehend the diffraction?
Why light does not scatter above the order of its corresponding wavelength?
 
There are books about diffraction, I cannot replace books.
This has nothing to do with scattering.
 
Krishnakant,

check out the section "Diffraction of light" in https://en.m.wikipedia.org/wiki/Diffraction ,
particularly the animations. The size of the hole in those animations is the laser's aperture, and the "beam" is coming out to the right. You will see that the smaller the aperture, the wider-spread the beam is. The whole article explains why that is.
 
In simple terms, if the size of the wavefront is much smaller than the wavelength, there will be almost no interference between different parts of the wavefront, which is what keeps a wavefront from immediately expanding outwards in all directions.
 
A few weeks back I actually wrote some code as a fun project that simulates the wave equation on a grid, and visualized it (in C#). I futzed around with different aperture sizes and was quite stunned that from >10 wavelengths on of aperture size, the classic "beam" just comes out naturally.
It made me realize that what we think as the "obvious" behavior of light, I.e. that it will move in a straight line, is really not obvious at all, but rather an outcome of intricate interference patterns.
 
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