Hi all, I need help, something looks like magic to me. Is it ?...

I am wondering about Kirchoffs law and the design of antireflective
coatings.

As you probably know:

If you have two different media, say air(refractive index n1) and
glass(refractive index n2) and want to minimize reflexes from the
glass surface for a single incoming frequency of electromagnetic
radiation, the way to do it is to insert a quarterwave dielectric
window in between, with a refractive index of sqrt(n1*n2).

The rays that have gone in and out of the coating, are then 180 degree
out of phase with the rays reflected at the surfase.

My question is if there's any magic in this...
I mean here on actually use the reflections from coating/glass
interface that are transmitted back to the air to cancel the
reflections from the air/coating interface.
If I minimize the amount of reflected energy, according to Kirchoff
the amount of absorbed radiation a(lambda) or transmitted radiation
t(lambda) or both should increase.

The *nice* here is that a part of reflections from coating/glass
interface are used to cancel reflections from air/coating
interface...The amount of transmitted and absorbed energy must
increase by the same amount as the amount as the reflected energy
decreases according to Kirchoff !!!

It sounds like magic !
Does it really work that way or did I miss something ?
Can I really increase a and t by decresing reflected energy by letting
reflection1 cancel reflection2 ???????

Kindest regards,
Lasse

P.S. I think we should be possible to include LaTeX when writing in
this forum...

On 11 Jan 2004 15:02:20 -0800, (Lasse)
wrote:

What is your idea of "absorbed energy" ?
Each glass absorbs some energy, say 0.01 % for example,
for a given thickness,
so, if I increase the radiation flux 100%,
I will get 0.02% absorbed energy using the same glass,
while coating the glass both sides will give some almost 8%
more throughput, and little less than 16% more if I double the
incoming intensity, One Colour Ounly, Ouf Course.
Ah...., what was the question?
w.
Hi all, I need help, something looks like magic to me. Is it ?...

I am wondering about Kirchoffs law and the design of antireflective
coatings.

As you probably know:

If you have two different media, say air(refractive index n1) and
glass(refractive index n2) and want to minimize reflexes from the
glass surface for a single incoming frequency of electromagnetic
radiation, the way to do it is to insert a quarterwave dielectric
window in between, with a refractive index of sqrt(n1*n2).

The rays that have gone in and out of the coating, are then 180 degree
out of phase with the rays reflected at the surfase.

My question is if there's any magic in this...
I mean here on actually use the reflections from coating/glass
interface that are transmitted back to the air to cancel the
reflections from the air/coating interface.
If I minimize the amount of reflected energy, according to Kirchoff
the amount of absorbed radiation a(lambda) or transmitted radiation
t(lambda) or both should increase.

The *nice* here is that a part of reflections from coating/glass
interface are used to cancel reflections from air/coating
interface...The amount of transmitted and absorbed energy must
increase by the same amount as the amount as the reflected energy
decreases according to Kirchoff !!!

It sounds like magic !
Does it really work that way or did I miss something ?
Can I really increase a and t by decresing reflected energy by letting
reflection1 cancel reflection2 ???????

Kindest regards,
Lasse

P.S. I think we should be possible to include LaTeX when writing in
this forum...

In article ,
Lasse wrote:
Hi all, I need help, something looks like magic to me. Is it ?...

I am wondering about Kirchoffs law and the design of antireflective
coatings.

As you probably know:

If you have two different media, say air(refractive index n1) and
glass(refractive index n2) and want to minimize reflexes from the
glass surface for a single incoming frequency of electromagnetic
radiation, the way to do it is to insert a quarterwave dielectric
window in between, with a refractive index of sqrt(n1*n2).

The rays that have gone in and out of the coating, are then 180 degree
out of phase with the rays reflected at the surfase.

My question is if there's any magic in this...
I mean here on actually use the reflections from coating/glass
interface that are transmitted back to the air to cancel the
reflections from the air/coating interface.
If I minimize the amount of reflected energy, according to Kirchoff
the amount of absorbed radiation a(lambda) or transmitted radiation
t(lambda) or both should increase.

The *nice* here is that a part of reflections from coating/glass
interface are used to cancel reflections from air/coating
interface...The amount of transmitted and absorbed energy must
increase by the same amount as the amount as the reflected energy
decreases according to Kirchoff !!!

It sounds like magic !
Does it really work that way or did I miss something ?
Can I really increase a and t by decresing reflected energy by letting
reflection1 cancel reflection2 ???????

Kindest regards,
Lasse

P.S. I think we should be possible to include LaTeX when writing in
this forum...


Dialectric coatings are used on camera lenses to improve transmission.
Losing light isn't as important a problem as the loss of contrast when
light starts bouncing back and forth from one lens surface to another.
Dialectric mirrors are also made, designed for a small range of
wavelengths but with reflectivity far higher than you could get from a
simple reflective surface like an aluminum film.

That is to say, letting reflection 1 cancel reflection 2 works so well
that it's been extensively commercialized.

--
"In any case, don't stress too much--cortisol inhibits muscular
hypertrophy. " -- Eric Dodd