Dear FLUKA experts,
I found a simple model that use optiphot pass through a section of air (or water ), my question is
Why optiphot can not pass through the section, even I changed its energy?
The card “OPT-PROP” with type=METAL(for air), if I set the 3rd parameter=0, does it means that air’s reflective=1 and refractive almost equal to 0 because of the fomula r=(n1-n2)^2/(n1+n2)^2 (here r represent reflective, n1 and n2 represent refractive)? then refractive=0 seems unbelievable!
The attachment is my file, look forward to your help.
Materials declared as METAL are meant to be partially or fully reflective. This means that optical photons will either be reflected or absorbed at the surface of the material, but in no way will they traverse the boundary. If you wish optical photons to traverse the boundary, you should not declare air as metal.
The reflectivity parameter is equal to 1-r, meaning if equal to zero, the surface is perfectly reflective, if equal to one, all optical photons are absorbed at the interface.
I changed the region from air to aluminum and still can not traverse the section
I mean that if I use two cards “OPT-PROP”, one is type=metal with 3rd parameter=0 and other is type=blank, the first parameter(refractive) have to zero according to the formula. It seems unreasonable.
Optical photons cannot traverse material declared as metal, therefore they cannot traverse the aluminum part.
Because optical photons cannot penetrate in a metal, you should not define for that material the index of refraction, photon are not going to penetrate anyway. If type=metal and 3rd 1-r = 0, all optical photons are reflected.
Dear @blefebvre ,
1.No matter I use air, water or Aluminum, even delete the card OPT-PROP with type=metal, optical photon still can not pass through the section
2. If 1-r=0.5, does it mean that optical photon will partly pass through the section? If it yes, the refractive resulted from the formula is still unreasonable.
Dear @horvathd,
I found a formula that r=(n1-n2)^2/(n1+n2)^2, where r is reflectivity and n1, n2 is refractivity. I mean if I use OPT-PROP two times, one set type=metal, r=1, so 1-r=0, the optiphot from vacuum to region, n1=1, that is to say according to the formula, n2 almost equal to 0, it does not make sense.
Now the other card set type=blank. the first parameter is refractivity, it is n2, so does this two cards won’t conflict?
That is to say, If I set first OPT-PROP card with 1-r, the material’s refractive is decided(and does not make sense), the next OPT-PROP card’s parameter set of refractivity won’t confilict with the first card?
If you set a material METAL, then the optical photons only reflected or stopped at the boundary even if you specify a refraction index on a consecutive card.
If you only set the refraction index (using OPT-PROP cards with no type / SDUM) to both materials on the surface, you will get the reflection according to the formula automatically.
Dear @horvathd
I understand partly, if I set a material METAL, 1-r=0 means full reflective and a consecutive card of OPT-PROP does not make sense, 1-r≠0 means part reflective, the consecutive card (type=blank) should give absorption and diffusion coefficient only, first parameter refractivity is automatically calculated, right?
Second question is if I not use any OPT-PROP card, the optiphot still can not pass through the material, I do not understand it why.
as I said before if you set a material METAL, then the optical photons only reflected or stopped. The refraction, absorption, and diffusion values set to this material are meaningless since no optical photons can propagate in this material.
If you don’t use any OPT-PROP card for a material (except vacuum) then no optical photon transport will take place in that material.
You should not use two OPT-PROP cards together, one with type blank and the other with type METAL, for the same material. It does not make sense to do that in FLUKA. You use one or the other.
And if you are wondering about Fresnel reflections, they are handled by FLUKA provided the two materials are not defined as type=METAL. In that case, however, you cannot tune the reflectivity.
Dear @horvathd,
I understand it, one OPT-PROP card with METAL and other with blank will conflict, but do not use any OPT-PROP card can not transport optical photon.
Thank you for your help.
