Intro. colour optics (cont. of Optimizing Fire in Modern RB (FIC) thread) - calling Garry H. and our

[yssie]

Garry-



http://www.cutstudy.com/cut/english/comp/scint1.htm
Very cool link(thanks Serg)! I had a fun morning, also did some digging in the archives, let''s see if I''ve got this:


1. In the programme I''m looking at a setup of a narrow spot-lighting beam, unmoving (observer) surface above diamond. Programme tilts diamond with source light – changes fire patterns.. fire patterns modelled are the result of example scenario in which entering ray is reflected (glare, not seen here) and refracted *once*, internally reflected (assume crit. angles achieved) and refracted again back to observer – the results of this first refraction are large VFs..IRL ray is refracted multiple times, so many more smaller VF subdivisions, but the majority of the ray’s initial energy must be preserved in that first refraction, and the reflection has much less energy (diamond RI 2.4, higher RI then less energy in refraction and more in reflection) - so these are the rays that disperse into strong intense fire. Secondary and higher order refractions will create… what? Interference w/ first-generation wavelengths in some cases, in others short, small bursts of colour rather than big bold flashes..

 

[yssie]

-Green hard to see b/c pupil must be positioned in front of exactly the right wavelength(s) to see green, can see red/blue (perhaps violet at the extremity) much more easily b/c there’s a much wider angle through which to view these colours

-Simple case – move your head in front of yellow output at distance A, you see only yellow b/c range of emissions that brain interprets as “yellow” spans pupil.


ETA: colours are dreadful! you know what they're supposed to be..

 

[yssie]

- 1) What if two (or multiple *distinct*) point-source (narrow) white rays hit the same facet at same time? At distance A from diamond surface, regular expected spectrum. At distance B depending on your angle, will see addition of colours..

 

[yssie]

- 2) What if infinite distinct point-source white rays (so one thick ray/diffuse light)? At any point in space, at any time there are an infinite number of rays of every colour that together add to white, so bright white light return… pupil expands in dim point-source lighting, but it doesn’t matter, you'll see fire b/c single ray incident on a single facet, so no colour addition possible

 

[yssie]

-Yellow diamond - material absorbs complementary wavelengths so no blue fire, but will still have bluish-green fire, bluish-purple fire.. tinted yellow (L/M/N?) then different colour absorbed.. fluoro – smaller uv wavelength absorbed, ss longer ‘blue’ wavelength emitted, visible light refracts into component visible lights but uv component absorbed, so yellow-tinted stone will appear to have different body colour but will still NOT emit blue fire of the missing wavelength

 

[yssie]

Now back to the original model (link in OP), which is much more interesting

question - Does the model consider polarisation? we know diamond material is polarizing, so we know parall. rays to surface mostly reflect, perp. mostly refract, if refl. perp. refr then refl ray polarized parall and refr ray polarized perp. So if refracted ray incident on diamond interior >critical angle, all light must bounce back. If ray incident on diamond interior at crit. angle, some refl (polarised parallel) and some refracted (polarised perp.)…refracted light is dispersed into different wavelengths - some allowed to escape and reach your eyeball, some not, which will also affect colour distribution… How significant is the effect..?


another question - Snell’s law which I have been using is for a wave incident on an infinite surface, which is certainly not the case for say a bezel facet, and it ignores incident wave polarization. A safer model would be huygens principle..? Explicitly consider the fact that an incident wave is a series of waveforms created along boundary (or boundary-to-be), and each point is single lightsource that diffuses outward w/ refl and refr components – slower in new diamond medium w/ higher RI. Superimpose, get waveform that forms alongside approaching incident ray… one more step of complexity is to consider that multiple rays approach sequentially…I’m not feeling up to a nonlin. calculation. Is there a programme/module for this?


Most important question - does it matter?

 

[Garry H (Cut Nut)]

Date: 1/30/2010 5:11:54 PM
Author: yssie
- 1) What if two (or multiple *distinct*) point-source (narrow) white rays hit the same facet at same time? At distance A from diamond surface, regular expected spectrum. At distance B depending on your angle, will see addition of colours..

This can not happen with a singly refractive material Yssie because the rays can never ''mix'' by definition.
With doubly refractive materials like caclite (as shown below) this happens and you would know that you have never seen these second order colors in a diamond.

Also in order to see green you need your pupil to be far enough away to not allow a mix of red and blue into the eye.

Finally if one eye sees a blue flash from a VF and the other eye perchance happens to see a flash from an entirely different light source or a part of a larger source, then I think what happens is that one will naturally be brighter than the other and that is what would be recorded. Sergey has studied this intensly and could better clarify it though.

 

[yssie]

Date: 1/30/2010 10:28:18 PM
Author: Garry H (Cut Nut)

Date: 1/30/2010 5:11:54 PM
Author: yssie
- 1) What if two (or multiple *distinct*) point-source (narrow) white rays hit the same facet at same time? At distance A from diamond surface, regular expected spectrum. At distance B depending on your angle, will see addition of colours..

This can not happen with a singly refractive material Yssie because the rays can never ''mix'' by definition.
With doubly refractive materials like caclite (as shown below) this happens and you would know that you have never seen these second order colors in a diamond.

Also in order to see green you need your pupil to be far enough away to not allow a mix of red and blue into the eye.

Finally if one eye sees a blue flash from a VF and the other eye perchance happens to see a flash from an entirely different light source or a part of a larger source, then I think what happens is that one will naturally be brighter than the other and that is what would be recorded. Sergey has studied this intensly and could better clarify it though.

Ah, I see... huh.


Thanks for taking the time to help the newbie

 

[Serg]

Hi Yssie,

Please check http://www.gemology.ru/cut/english/grading1/index.htm

We did test for polarization 10+years ago. For round diamond we found what difference( if we account partial polarization during reflection in LR is minor and we do not account it)
We decide work without partial polarization to reduce raytracing time calculations ( 10 years ago computers were much more slowly )

May be we will return polarization in 2011. Polarization gives minor effect because standard consumer light sources have not polarization and diamond is isotropic material