One for the physics guru's

[i_got_a_mohawk]

Trying to calculate the dielectric constants for two substances. One with refractive index 1.51, one with refractive index of 0.47.

Using in a system where 670nm light is being used.

670nm is 1.85eV (I think).

I'm looking over the equations and I'm just lost and confused. Anyone got any advice or a simple walkthrough of how to approach the problem?

Cheers!

[machine gewehr]

I called you nerd a few days back and you denied it.
Now,I'm studying computers and I tell you its not easy at all but what you posted,man...You're one big nerd.



j/k

[GeoffByrne]

I know nothing about this, but......

someone must have done a spreadsheet for this so you can just plug in the numbers.........

Try university sites.

[i_got_a_mohawk]

Ok, ok.

I know I'm a nerd , heck, yesterday with the missus, was down to my backup rubber (blueberry!) and made a Dr Manhattan comment .

[i_got_a_mohawk]

Originally Posted by GeoffByrne

I know nothing about this, but......

someone must have done a spreadsheet for this so you can just plug in the numbers.........

Try university sites.

I've tried looking and can't find anything other than the equations I need to use. I just can't figure out how to do it tho. Damned complex numbers.

Heck, even if I could just figure out what to do with this extinction coefficient part I'd be able to plug away at it , wish I knew how to use things like matlab now

[machine gewehr]

Just keep the thread on top so some one will surely help,lots of sharp minds here.

Last week,I learned I had to submit a java work just 2 hours before the deadline.First thing I did was come here and start writing for help.Luckily my friend was able to help me before I hit the post thread button.

[i_got_a_mohawk]

Lucky

I've had this for a while, deadline is still a while away. It's part of a greater report, but I'm just stuck on this part

[CDRhom]

Your help, or a different explianation may lie in MIT's open courseware:

http://ocw.mit.edu/OcwWeb/web/course...ex.htm#Physics

http://ocw.mit.edu/NR/rdonlyres/6A67...solid_prop.pdf

Since you have been provided a constant for the refractive index you may be able to work backwards through the equations. (yes, you remember correctly 670 nm is 1.85ev)

[fdeck]

Originally Posted by i_got_a_mohawk

Trying to calculate the dielectric constants for two substances. One with refractive index 1.51, one with refractive index of 0.47.

Using in a system where 670nm light is being used.

670nm is 1.85eV (I think).

I'm looking over the equations and I'm just lost and confused. Anyone got any advice or a simple walkthrough of how to approach the problem?

Cheers!

I'm a physicist, and have taught electrodynamics, but I don't want to just give away the answer. So I will offer just a faint hint instead. We throw around a whole bunch of different parameters... permeability, permittivity (both "absolute" and "relative"), refractive index, dielectric constant, and so forth. It would be worth finding all of the definitions and relationships between those quantities that you can find in your textbook or a trustworthy online reference. Stare at those relationships and see which variables you can eliminate.

[i_got_a_mohawk]

I'm not looking for just an answer, I'm more looking for help on how to crack it, so your help is very much appreciated.

The main thing I really don't understand is the ik (imaginary number and extinction coefficient?).

I've had a look about and just can't seem to find a solid way in which to work out the imaginary part of the equations. On saying that, I have a hard enough time working with regular numbers, let alone complex ones (well, this is the first time I've ever done anything with complex numbers, really wish I had taken a masters more in the vein of my undergrad)!

[i_got_a_mohawk]

Originally Posted by CDRhom

Your help, or a different explianation may lie in MIT's open courseware:

http://ocw.mit.edu/OcwWeb/web/course...ex.htm#Physics

http://ocw.mit.edu/NR/rdonlyres/6A67...solid_prop.pdf

Since you have been provided a constant for the refractive index you may be able to work backwards through the equations. (yes, you remember correctly 670 nm is 1.85ev)

I know that if done simply, the dielectric constant is the root of the refractive index, which is the way I tried to go backwards in order to get the answer. But it seemed to mess with the results quite a lot by missing out the imaginary component.

Cheers for the links

If it's of any interest the experiment is to do with surface plasmons.

And on that note, something has just clicked and I may have this . . .

[i_got_a_mohawk]

Ok, maybe not. Bugger.

Looking for an angle around 80-90 degrees. Got my answer to (theta) = Sin(-1) 1.08.

I realised I had made a daft mistake earlier on in the maths. But sadly, looks like I still need the imaginary part to knock it down a bit to get under 1

[hbarcat]

Ahem . . .


Other terms for the relative static permittivity are the dielectric constant, or relative dielectric constant, or static dielectric constant. These terms, while they remain very common, are ambiguous and have been deprecated by some standards organizations. The reason for the potential ambiguity is twofold. First, some older authors used "dielectric constant" or "absolute dielectric constant" for the absolute permittivity E rather than the relative permittivity. Second, while in most modern usage "dielectric constant" refers to a relative permittivity, it may be either the static or the frequency-dependent relative permittivity depending on context. - Wikipedia

[i_got_a_mohawk]

Most of that is over my head. It might be because I've been working away on one thing or another for the best part of the day and it's almost 1:30 am and my brain is shutting down .

However, I'm pretty sure it's frequency dependant, if not, I don't understand why we're to make use of the wavelength of the laser.

I dare say, if I only fail this one thing . . . it wouldn't be toooo terrible . . .

[Eric Perry]

Originally Posted by i_got_a_mohawk

Trying to calculate the dielectric constants for two substances. One with refractive index 1.51, one with refractive index of 0.47.

Using in a system where 670nm light is being used.

670nm is 1.85eV (I think).

I'm looking over the equations and I'm just lost and confused. Anyone got any advice or a simple walkthrough of how to approach the problem?

Cheers!

My brain hurts.

[Dertygen]

.

Originally Posted by Eric618

My brain hurts.

http://hyperphysics.phy-astr.gsu.edu...elefie.html#c3

[Eric Perry]

Originally Posted by Dertygen

.

http://hyperphysics.phy-astr.gsu.edu...elefie.html#c3

Cheesus Haych!

[fdeck]

Originally Posted by i_got_a_mohawk

I'm not looking for just an answer, I'm more looking for help on how to crack it, so your help is very much appreciated.

The main thing I really don't understand is the ik (imaginary number and extinction coefficient?).

I've had a look about and just can't seem to find a solid way in which to work out the imaginary part of the equations. On saying that, I have a hard enough time working with regular numbers, let alone complex ones (well, this is the first time I've ever done anything with complex numbers, really wish I had taken a masters more in the vein of my undergrad)!

This is just slightly involved. The solution to the wave equation for the electric field has something like exp(i(k x - w t)) where k is the so called propagation vector and w is the angular frequency. I don't know where you are at with this stuff, but is this familiar?

If k is real, then the entire exponent is imaginary, and it is just the plane wave that propagates forever.

Now let k be a complex number a + i*b. Now if we put this into the wave solution, we get:

exp(-b x)*exp(i(a x - w t))

This is the plane wave again, but with a simple exponential decay term in front of it. Thus, you have an expression for the electric field in a medium where the wave is being extinguished as it passes through the medium. An example is trying to shine a light through a piece of metal. Many common metals have tabulated values for complex refractive index.

Is this useful? Yes. The complex refractive index is used in computing the detailed behavior of reflection from metal surfaces, or transmission through thin metal films such as mirror sunglasses.

My suggestion is: Work through the derivations a few times until you are comfortable with the complex exponential notation. It's your friend. Note that the "hyperphysics" site is pretty cool, and most of the Wikipedia entries on physics are decent.

[fdeck]

Originally Posted by i_got_a_mohawk

Lucky

I've had this for a while, deadline is still a while away. It's part of a greater report, but I'm just stuck on this part

It's good to spend a bit of time and see if you can crack this nut, but if you really get up against a wall, let me know.

[i_got_a_mohawk]

It looks kinda familiar. I see a similarity with the complex number k and the dielectric constant equation where:

E = E' + i*E''

(where E is epsilon)

I need to wake up a bit and come back to this, thanks again for all the help so far !