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Hello all,



I have encountered some issues using the Physical Optics Propagation feature for wider beam inputs.



I am simulating a 12.8mm beam diameter input into a 25.4mm focal length lens, which also has an aperture of 25.4mm (THORLABS LA1951-B). The wavelength is 1030nm. Having used a 2.6mm beam diameter the Gaussian shape of the beam was maintained across the entire propagation range. However, with the 12.8mm beam diameter the beam suffers from what appears to be Fresnel boundary reflections after the curved lens surface (observed through 4-fold symmetry), even after altering the X- and Y-widths within the Lens Data window (under the 'Physical Optics' tab for a surface). This then distorts the beam shape towards the focus.



I have used the 'Automatic' feature under the 'Beam Definition' tab within the Physical Optics propagation (which it is calculating as 513 for both the X- and Y-widths) and increased this by about 10% as within the OpticStudio help function it warns that under the 'Defining the initial beam' page that maintaining a 'guard band' (empty space around the beam) is essential to stop this from happening.



Beam at surface 3





Beam at surface 4





Beam at surface 41 (focus)



Hi Donald, POP can be a bit tricky to set up sometimes. I would first recommend checking that the pilot beam is adequately sampled (see https://support.zemax.com/hc/en-us/articles/1500005488601-Using-Physical-Optics-Propagation-POP-Part-1-Inspecting-the-beams). Following this, I would suggest saving the beam at each surface and checking the intensity and phase (see https://support.zemax.com/hc/en-us/articles/1500005488621-Using-Physical-Optics-Propagation-POP-Part-2-Inspecting-the-beam-intensities and https://support.zemax.com/hc/en-us/articles/1500005488641-Using-Physical-Optics-Propagation-POP-Part-3-Inspecting-the-beam-phases for details on how to do this).

Hi there,



Thanks for the pointers!



 



Upon checking the phase profile for surface 3 (first/planar lens surface), nothing seems to be appearing - any idea why this could be?



Surface 3 - Irradiance





Surface 3 - Phase





I believe this is what causes the distortion of the beam profile at surface 4 (the curved surface of the lens).



Surface 4 - Irradiance





Surface 4 - Phase





Thanks for your time!

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