Glass Transparency: What Allows Visible Light to Pass Through?

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Discussion Overview

The discussion centers around the molecular structure of glass and its transparency to visible light, exploring the mechanisms that allow light to pass through various materials, including glass and photochromatic lenses. Participants also touch on the effects of irradiation on lucite and the principles of dispersion in relation to transparency.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant inquires about the molecular structure of glass that allows visible light to pass through.
  • Another participant suggests that the lack of absorption in glass is due to electron transitions not matching the energy of visible light, similar to water's transparency.
  • A participant notes that the presence of other substances in glass can affect absorption, specifically mentioning that water absorbs infrared light and must be removed for fiber-optic applications.
  • Questions are raised about the effects of UV rays on photochromatic lenses, specifically regarding changes in molecular links and electron transitions.
  • A participant describes photochromatic dyes that break down under UV light, leading to changes in energy levels that allow absorption of visible light.
  • Another participant shares an experience with lucite that became transparent again after thermal annealing, following prior irradiation that caused discoloration.
  • A claim is made that for glass to be completely transparent, there must be no dispersion, referencing Kramers-Kronig relations.

Areas of Agreement / Disagreement

Participants express various viewpoints on the mechanisms of transparency and the effects of different materials and conditions, indicating that multiple competing views remain without a clear consensus.

Contextual Notes

Some discussions involve assumptions about molecular interactions and the specific conditions under which transparency is achieved, such as the role of dispersion and the effects of irradiation.

Who May Find This Useful

Readers interested in materials science, optics, and the chemical properties of transparent materials may find this discussion relevant.

live4physics
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What´s glass feature (molecular structure) that allow the visible light bypass it ?
:confused:
Thanks
 
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Basically there is nothing to absorb the light.
The electron transitions in glass do not match the energy of visible light and so it goes straight through - the same mechanism that makes water transparent.

Other substances in the glass can change the absorption, water strongly absorbs infrared so to make glass fibre-optic for infrared you have to remove all the water from the molten glass first.
 
In the case of photochromatic lens, how the UV rays changes the molecular links between atoms ? are there any electron transitions ?
Thanks.
 
live4physics said:
In the case of photochromatic lens, how the UV rays changes the molecular links between atoms ? are there any electron transitions ?
Thanks.

Photochromatic is a dye molecule that gets broken by UV light, this leaves a bunch of bonds with lots of loose electrons that can then change energy levels and absorb visible light.
The clever bit is finding a dye that heals itself when you take it out of UV.
 
I have a block of formerly transparent lucite that was irradiated with a 15 MeV electron beam in 1959. It was a dark brown due to F-center dislocation. Now, 50 years later, it is transparent again, due to thermal (room temperature) annealing.

For glass to be truly transparent (no absorption), there can be no dispersion (See Kramers Kronig or dispersion relations). See
http://en.wikipedia.org/wiki/Kramers-Kronig_relations
These also apply to the real and imajinary components of electrical circuits.
 
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