Convergence of light rays and Optical Path Length (OPL)

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SUMMARY

The discussion centers on the convergence of light rays and the concept of Optical Path Length (OPL). It establishes that rays from a planar source do not necessarily travel the same OPL when converging at a point, as this depends on the intended application. The maximum difference in OPL can be estimated using the formula δL = D[(1+(d/D)²)^{1/2}-1] ≈ d²/2D, where D is the distance to the convergence point and d is the largest dimension of the planar object. This difference, while small compared to D, poses challenges when compared to the wavelength of light.

PREREQUISITES
  • Understanding of Optical Path Length (OPL)
  • Familiarity with light ray convergence principles
  • Basic knowledge of geometric optics
  • Proficiency in mathematical concepts related to optics
NEXT STEPS
  • Explore the mathematical derivation of Optical Path Length in different media
  • Investigate the effects of wavelength on light ray convergence
  • Learn about applications of OPL in optical systems design
  • Study the principles of geometric optics in greater detail
USEFUL FOR

Optical engineers, physicists, and students studying optics who are interested in the behavior of light rays and their applications in optical systems.

pardesi
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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)
 
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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):

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

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
 

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