Convergence of light rays and Optical Path Length (OPL)

Click For Summary

Discussion Overview

The discussion revolves around the convergence of light rays and the concept of Optical Path Length (OPL), particularly in the context of rays originating from a distant source and converging at a point. Participants explore the conditions under which these rays may or may not travel the same OPL, considering both theoretical and practical implications.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant asserts that all rays from a distant source converging at a point need to travel the same OPL.
  • Another participant counters that this requirement depends on the intended use of the rays at the convergence point.
  • A different participant suggests that rays from a planar source do not typically travel the same OPL.
  • One participant provides a mathematical estimation of the maximum difference in OPL for rays from a planar object, indicating that while the difference can be small compared to the distance to the convergence point, it can be significant relative to the wavelength of light.
  • A question is raised about the scenario where rays originate from the same point source, implying a potential difference in OPL under those conditions.

Areas of Agreement / Disagreement

Participants do not appear to reach a consensus, as there are multiple competing views regarding whether rays converging at a point must travel the same OPL and under what conditions this may or may not hold true.

Contextual Notes

There are limitations regarding the assumptions made about the source of the rays and the geometrical configurations involved, as well as the dependence on definitions of OPL and the specific conditions of convergence.

pardesi
Messages
337
Reaction score
0
Why do all rays coming from far off distance from a source(may be planar)... converging at a point need to travel the same Optical Path Length(OPL)
 
Science news on Phys.org
They don't have to - it depends on what you want to do with them at the point.
 
pardesi said:
Why do all rays coming from far off distance from a source(may be planar)... converging at a point need to travel the same Optical Path Length(OPL)
Usually they don't travel the same OPL.
 
pardesi said:
Why do all rays coming from far off distance from a source(may be planar)... converging at a point need to travel the same Optical Path Length(OPL)
For a truly planar object with its plane is normal to the direction of the rays, then you can estimate the maximum difference in the OPL from its largest dimension (say 2d) and the distance to the point of convergence (call this D):

[tex]\delta L= D[(1+(d/D)^2)^{1/2}-1] \approx d^2/2D[/tex]

This number is tiny compared to D, but it's much harder to make it small compared to the wavelength of the light.
 
but is it true if they start from the same point source
 

Similar threads

Undergrad Image construction with concave and convex mirrors
  • · Replies 4 ·
Replies
4
Views
2K
Graduate Looking for trigonometric ray tracing software for optics
  • · Replies 22 ·
Replies
22
Views
3K
Graduate How to model converging illumination through object plane (in ZEMAX)
  • · Replies 1 ·
Replies
1
Views
1K
Undergrad How to couple light from a very small source into spectrometer?
  • · Replies 10 ·
Replies
10
Views
2K
Graduate Calculating the optical depth of an inhomogeous gas
  • · Replies 1 ·
Replies
1
Views
3K
Graduate Strategy for interference problems
  • · Replies 2 ·
Replies
2
Views
1K
Undergrad How does an eye reconstruct an image?
  • · Replies 9 ·
Replies
9
Views
3K
Undergrad Digital Micromirror Device based optical setup
  • · Replies 7 ·
Replies
7
Views
3K
Undergrad Image appears outside of q -- Lens Maker's Equation confusion
  • · Replies 17 ·
Replies
17
Views
4K
Optical path difference between two reflected rays
  • · Replies 4 ·
Replies
4
Views
988