Sequential vs Non-sequential; Which mode is more precise and reliable?

  • 1 December 2019
  • 1 reply

I simulated an optical system in both sequential and nonsequential modes. I used a Gaussian entrance beam for my system and then, compared the results of "Physical optics" in sequential mode and "coherent irradiance" in non-sequential mode.

The problem is that the results don't coincide with each other!

Now, I want to know which one is more accurate and reliable?


1 reply

Userlevel 2
Sequential mode accounts for diffraction in a lens (although simplified to the diffraction at the exit pupil not each surface).

POP (within sequential mode) accounts for diffraction at each surface and can be set up for a coherent input beam such as a Gaussian beam. 

Non-sequential mode simply traces rays.  It does not account for diffraction at surfaces or at the exit pupil.  It does, however, allow you to model diffraction at a diffraction grating.  It also keeps track of the phase of a ray and so you can model coherent interference (eg in an interferometer).

Non-sequential mode will propagate rays even if part of the beam actually misses a lens or other component.  Sequential mode will not do that.  The main application is usually illumination systems. 

I would say the best way to describe the difference is that sequential mode is important when you are interested in the micro-scale, eg spot sizes and resolution.  Non-sequential mode is best when you are not interested in the micro-scale, eg illumination from a street light.

For your case it looks like POP would be best.