Glycerin as index matching fluid

Dichromated Gelatin.
Tony DCG
Posts: 147
Joined: Thu Jan 08, 2015 1:47 pm

Glycerin as index matching fluid

Post by Tony DCG »

I am considering trying an index matching fluid between my DCG plate (non coated side) and a resin block.

I know glycerin can be used as index matching fluid
Glycerine: 1.473
Glass =1.52
Resin + 1.5 to 1.6
Real expensive optical index fluid = 1.8

Question is glycerin OK enough to use?
Is there a cheap material I can use?
What is the rule of thumb for using index matching fluid

Thoughts?
Dinesh

Glycerin as index matching fluid

Post by Dinesh »

We use mineral spirit for index matching, but I'm not a fan of index matching, so I don't do it a lot.

In terms of the numbers you give, use the Fresnel equations to determine the efficacy of the material. The reflectivity (for normal incidence) is:

R = [ {n(1) - n(2)}/{n(1) + n(2)} ]^2

and the angle of refraction is, of course, Snell's Law:

n(1)*sin(theta-in) = n(2)*sin(theta-ref).

For an air-glass (index ~1.5) interface, the reflectivity for normal incidence is:

R = [(1.0 - 1.5)/(1.0 + 1.5)]^2 = (0.5/2.5)^2 = 0.2^2 = 0.04 (or, 4%)

For your glycerin,

R = [( 1.52 - 1.473)/(1.52 + 1.473)]^2 = (0.016)^2 = 0.0002 (or, 0.02%)

For refraction between the media:

sin(theta-in)/sin(theta-ref) = 1.47/1.52 = 0.96 (ie, the two angles, in and refracted, are almost equal and there's practically no refraction)
I would say this is pretty adequate as an index matching fluid!
Arturo
Posts: 126
Joined: Thu Jan 08, 2015 4:48 am

Glycerin as index matching fluid

Post by Arturo »

I guess this discussion should be copied in the wiki! :)

Dinesh wrote:We use mineral spirit for index matching, but I'm not a fan of index matching, so I don't do it a lot.

In terms of the numbers you give, use the Fresnel equations to determine the efficacy of the material. The reflectivity (for normal incidence) is:

R = [ {n(1) - n(2)}/{n(1) + n(2)} ]^2

and the angle of refraction is, of course, Snell's Law:

n(1)*sin(theta-in) = n(2)*sin(theta-ref).

For an air-glass (index ~1.5) interface, the reflectivity for normal incidence is:

R = [(1.0 - 1.5)/(1.0 + 1.5)]^2 = (0.5/2.5)^2 = 0.2^2 = 0.04 (or, 4%)

For your glycerin,

R = [( 1.52 - 1.473)/(1.52 + 1.473)]^2 = (0.016)^2 = 0.0002 (or, 0.02%)

For refraction between the media:

sin(theta-in)/sin(theta-ref) = 1.47/1.52 = 0.96 (ie, the two angles, in and refracted, are almost equal and there's practically no refraction)
I would say this is pretty adequate as an index matching fluid!
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