Dear Nick,

Thank you very much for your kind and prompt help!

As you have worried about, mixing of coherent beams in incoherent mode will lose the phase value of the beam and will give us different result than the coherent beam.

I tried to check by putting one GW beam of below.

INCOHERENT

!GW            1.0      0.0015       0.0015        0        0      0.0      0.0        0.0        1.0

GW            1.0      0.0015       0.0015         0        0     0.0      0.0        1.0        0.0

This is the same beam as below.

But, as you see, it gives different result.

Will there be any way to do POP calculation for the doughnut beam in coherent mode?

Is there any definition in 'Laguerre-Gaussian' beam for the doughnut beam which is 01* mode?

Kiho

Hi Kiho,

I noticed there is a support request email you sent to support@zemax.com with same question as well, please allow me to answer your question at here instead.

As Nick descibed, dount beam profile should be modeled with ZMM file above with incoherent way. In my knowledge, that is the most direct way we can define donut beam in POP with its intensity profile, which means donut beam can be only modeled by sum TEM01 and TEM10 incoherently. If you sum TEM10 and TEM01 coherently, result beam is something other than dount:

As you may know, Gaussian Waist beam in OpticStudio is defined with Hermite- Gaussian, there is no direct way to model beam with Laguerre-Gaussian except using DLL to program the beam profile. For more information about DLL beam in POP, you can refer to help manual section below:

The Analyze Tab (sequential ui mode) > Laser and Fibers Group > About Physical Optics Propagation > Defining the Initial Beam > DLL

Also, we have a sample C code for Laguerre-Gaussian, which can be found at:

C:\Users\XXXXXXX\Documents\Zemax\DLL\PhysicalOptics\Laguerre beam.c

I am not very familar with Laguerre-Gaussian mode and I did some online search. If my understanding is correct, the donut beam in Laguerre-Gaussian should be 1,3 based on figure below:

For your other question, the reasone why you observed beams are not corresponded with Multimode and Gaussian Waist is surfaces you used to observe the beam are not same (surface #5 and #40). I tested if surface are exactly same, beam profiles are same as well. Princlples of beam modeling behind GW in ZMM and Gaussian Waist are exactly same.

Hope the answer can help you, please feel free to let us know if you have further questions.

Best regards,

Haosheng

Hi Haosheng:

Thank you very much!

Yes, I should have seen at the same surface.

The latter surfaces up to 40 is the direct imaging lens to make the conjugate.

When, I re-do the calculation at the same surface, the results are different.

Please see below.

I was using the 'Laguerre-Gaussian' DLL for the beam simulation but still having problem finding beam shape doughnut and M2 value around 2.

Sincerely,

Kiho

Hi Kiho,

Thanks for your follow-up here!

I've set up similar starting points using a modified 'donut.zmm' file (I believe you commented out the first GW command) and a Gaussian Waist beam definition that is equivalent. As we can see, the starting irradiance profile of the two beams are identical:

But, if we take a look at the phase data, we can see they aren't identical, and therefore we can't expect identical propagation between the two, I think:

So, it seems like the difference in propagation is due to the difference in initial phase definition due to the INCOHERENT command for the .ZMM file.

As for using the Laguerre Gaussian DLL to get the donut beam you'd like, I also wasn't able to produce the 01* mode as you're looking for after trying a few different COHERENT sum definitions using the 'Laguerre beam' DLL. I suspect the best route forward to make the most comprehensive representation of this beam definition is likely to write a DLL which would generate the necessary irradiance profile and phase definition for proper propagation.

Please let us know how these thoughts work out for you!

~ Angel

I know I’m late to the party here but I ran into this same problem a while back. As people mentioned above Zemax defines the beams in a Hermite space, but both Hermite and LG form complete basis so you can describe one (eg LG 10) with the proper combination of HG beams. For the LG 10 mode you need an HG 10 and HG 01 but with a phase shift added in as well. This picture shows what I’m trying to describe

So in Zemax terms to model the LG 10 mode you need to include the 90 phase rotation in the .zmm so it looks like

COHERENT

GW            1.00000000000        1.0        1.0        0.0        0.0        0.0        0.0        1.0        0.0
PHASE 90
GW            1.00000000000        1.0        1.0        0.0        0.0        0.0        0.0        0.0        1.0

Here’s the POP of the collimated LG 10 beam

Here’s the phase

And then here’s the focus from a cylindrical lens which forms a split line focus (sorry about the aspect ratio I just threw this together)

Here’s what the POP looks like without that Phase 90 term in the .zmm

and the phase

Hope this helps!!