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prometheus
05-05-2011, 06:37 AM
Anyone who knows where to find a good reference index of the optical constants of conductor materials?

Michael

XswampyX
05-05-2011, 11:04 AM
Metal Optics

a branch of optics concerned with the study of the interactions of metals with electromagnetic waves. The main optical features of metals are a large coefficient of reflection R (for example, for the alkali metals R ~ 99 percent) over a wide range of wavelengths, and also a large coefficient of absorption (an electromagnetic wave in the interior of metals is attenuated after passing through a layer of thickness δ ~ 0.1 1 X 10-5 cm). These special features are related to the high concentration of the conduction electrons in metals.

As the conduction electrons interact with an electromagnetic wave incident on the surface of a metal, they also interact simultaneously with the vibrating lattice ions. Most of the energy they acquire from the electromagnetic field is radiated in the form of secondary waves, which combine to give the reflected wave. Part of the energy imparted to the lattice leads to the attenuation of the wave in the interior of the metal. The conduction electrons are capable of absorbing quanta of electromagnetic energy hω (h is Planck’s constant, and ω is the frequency of the radiation), no matter how small they are. For this reason, the electrons contribute to the optical properties of metals at all frequencies. Their contribution is especially great in the radio-frequency and infrared regions of the spectrum. With increasing ω, the contribution of the conduction electrons to the optical properties of metals decreases and the differences between metals and dielectrics become smaller.

The remaining valence electrons exert an effect on the optical properties of metals only when the electrons participate in the internal photoelectric effect, which occurs at hω ≧ Δε (Δε is the energy gap between the ground and excited states of the electrons). Excitation of the electrons leads to anomalous dispersion of the waves and to an absorption band with a maximum in the vicinity of the resonance absorption frequency. The absorption bands in metals are significantly broader than in dielectrics because of the strong electron-electron and electron-ion interactions. The metals usually exhibit several bands, which are located mainly in the visible and near-ultraviolet regions of the spectrum. However, a number of polyvalent metals also have absorption bands in the infrared region. At frequencies ω ≧ ωp, where ωp is the plasma frequency of the valence electrons, plasma vibrations of electrons are excited in the metal. They lead to the appearance of a region of transparency at ω ≈ ωp

The coefficient of reflection R decreases in the ultraviolet region, and the properties of metals approach those of dielectrics. At higher frequences (X-ray region), the optical properties are determined by the electrons of the inner shells of atoms, and metals no longer differ from dielectrics in optical properties.

The optical properties of metals are described by the complex dielectric constant ∑ (ω) = ∑’ (ω) − (i 4Π/ω) σ(ω), where ω’ is the real dielectric constant and σ is the conductivity of the metal, or by the complex index of refraction:

(K is the coefficient of absorption). The complex nature of the index of refraction expresses the exponential attenuation of the wave in the metal. If a plane wave is incident on the surface of a metal at an angle Ф ₋ 0, the wave will be inhomogeneous inside the metal. The plane of equal amplitudes is parallel to the metal surface, whereas the plane of equal phases is inclined toward the surface at an angle whose magnitude depends on f>. The waves reflected from the surface of the metal, which are polarized in the plane of incidence and perpendicular to it, have a phase difference. This causes plane-polarized light to become elliptically polarized after reflection. The coefficient of reflection R of the waves polarized in the plane of incidence is always nonzero in metals (in contrast to dielectrics) and has a minimum only at a certain value of Ф.

The mean free path / of the electrons becomes greater than δ in pure metals at low temperatures in the long-wavelength region of the spectrum. The attenuation of the wave ceases to be exponential, although it remains very strong (the anomalous skin effect). In this case the complex index of refraction becomes meaningless and the relationship between the incident and refracted waves becomes more complicated. However, the properties of reflected light at any ratio of / to δ are completely determined by the surface impedance Z, which is related to the effective complex indexes of absorption and refraction as follows:

For l < τ, the quantities n and K in the equations are replaced by neff and Keff, respectively.

To measure n and K of a massive metal specimen, the light reflected from its surface is studied by polarization methods (the characteristics of the elliptical polarization of the reflected light are measured) or by methods based on measurements of R over a wide region of the spectrum during normal incidence of light on the surface of the metal. Such methods make possible measurement of the optical characteristics in the infrared, visible, and ultraviolet regions with an error of the order of 0.5-2.0 percent. Measurements of the fine structure of absorption bands are performed using methods based on modulation of the properties of the metal, which leads to modulation of the reflected light, which is what is measured (thermoreflection, piezoreflection, and so on). The methods mentioned above make possible determination of R with a high degree of accuracy upon temperature changes and deformation and under other conditions (see Table 1), and also the study of the fine structure of absorption bands. Special attention is paid to the preparation of the surfaces of the specimens under investigation. Surfaces of the required quality are produced by electric polishing or by vaporization of metal in a vacuum, with subsequent deposition on a polished substrate.

http://i465.photobucket.com/albums/rr16/xXswampyXx/Constants.jpg

http://encyclopedia2.thefreedictionary.com/Metal+Optics

:stumped:

DonJMyers
05-05-2011, 11:19 AM
What service!

prometheus
05-06-2011, 02:08 AM
Is there any way this index is useful for setting values in the conductor material?

what we have to work with as I see it, It is the specularity and roughness values..

Michael

jrandom
05-10-2011, 03:58 PM
For conductor/dielectric materials, a google search of "IOR list" usually turns up some good results (http://forums.cgsociety.org/archive/index.php/t-513458.html).

caesar
05-11-2011, 07:33 PM
I still miss in LW a good set of material presets, like in modo or maxwell render SSS presets (I know there's presetcentral.com...)

jrandom
05-11-2011, 07:39 PM
I still miss in LW a good set of material presets, like in modo or maxwell render SSS presets (I know there's presetcentral.com...)

I am working on this, although I don't know when I'll have some production-ready materials available for download.

I'm actually writing some plug-ins to help with some of the crazier node networks, and have the first one successfully running on a Mac. (I don't have a good toolchain for Windows yet, but hopefully soon!)

caesar
05-11-2011, 07:43 PM
I am working on this, although I don't know when I'll have some production-ready materials available for download.

I'm actually writing some plug-ins to help with some of the crazier node networks, and have the first one successfully running on a Mac. (I don't have a good toolchain for Windows yet, but hopefully soon!)

That would be nice!

prometheus
05-12-2011, 06:48 AM
But how does the IOR index relates to specularity and the roughness settings in a conductor material??

would it be just enough and accurate to set the same IOR values as input in the roughness channel for conductor material?

or is it necessary to feed another material node in to the conductor node with refraction index such as the delta node?

Michael

JeffrySG
05-12-2011, 08:24 AM
I have a pretty comprehensive IOR list on my site too:

http://www.pixelandpoly.com/ior.html

jrandom
05-12-2011, 10:54 AM
But how does the IOR index relates to specularity and the roughness settings in a conductor material??

The IOR is necessary for the reflective and/or refractive qualities of a surface. Roughness and specularity/reflection amounts are not necessarily an intrinsic property of a material: eg. metal can be rough or it could be polished and shiny. I don't think there's a comprehensive list of those kinds of settings.

JeffrySG
05-12-2011, 11:40 AM
The IOR is necessary for the reflective and/or refractive qualities of a surface. Roughness and specularity/reflection amounts are not necessarily an intrinsic property of a material: eg. metal can be rough or it could be polished and shiny. I don't think there's a comprehensive list of those kinds of settings.

:agree: A material can be as rough or as smooth as you make it. It's fun to see how silly putty reacts when you put in on different materials. Put it on smooth glass and it becomes almost reflective. Put in on newspaper and it becomes very dull, for example.

prometheus
05-13-2011, 12:36 AM
The IOR is necessary for the reflective and/or refractive qualities of a surface. Roughness and specularity/reflection amounts are not necessarily an intrinsic property of a material: eg. metal can be rough or it could be polished and shiny. I don't think there's a comprehensive list of those kinds of settings.

So this might just be that there´s no way of getting those properties Accurate and transfered to a conductor material..ergo no way of using the IOR index properly with the conductor material at least?

I am refering to the main help in the conductor mode where it says..

Conductor"Appropriate for simulating metallic surface finishes accurately. The appropriate values for various conductors (metals) can be obtained from published data in handbooks of optical constants."So It would be interesting to hear if there´s a way to transfer those IOR values in to the conductor material, perhaps by connecting other nodes with refraction in to conductor?

Michael

jrandom
05-13-2011, 01:13 AM
Oh! Got it! I understand the confusion. :)

For non-transparent materials, the IOR is used with the Fresnel node. Input the IOR into the Fresnel node, multiply it with your specular amount, and input that into the materials Specular input.

prometheus
05-13-2011, 04:23 AM
Oh! Got it! I understand the confusion. :)

For non-transparent materials, the IOR is used with the Fresnel node. Input the IOR into the Fresnel node, multiply it with your specular amount, and input that into the materials Specular input.


Thanks! that sounds logical, don´t know if that would be physicly correct thou? and it also makes me wonder if there in the future would be better to set values directly in the conductor material...if there´s an update to the conductor material.

Another thing Im curious about, have anyone made any good conductor material mix with the anisotrophy shaders?

Michael

jrandom
05-13-2011, 10:54 AM
Thanks! that sounds logical, don´t know if that would be physicly correct thou?

Yep, it's physically accurate. I don't remember the specific physics of it, but Fresnel reflections in the real world are determined by the material's IOR.


Another thing Im curious about, have anyone made any good conductor material mix with the anisotrophy shaders?

I've been avoiding the shaders since they only take a Normal input and no Bump Map which makes mixing materials with differing bump maps more complicated since you have to mix the bump maps separately and feed the result into the Node Editor's output.

For a conductor:


Specular and Reflection should get the same input amount
Diffuse Amount should be set to the inverse of the Reflection amount
Color Highlights should be set to 100%
While the relationship isn't exactly linear, the Reflection's "blur" amount can be set to the inverse of the Glossiness.
For more realistic results, Specular/Reflection amounts should be reduced the less glossy (more rough) the surface is.

grabiller
08-19-2012, 11:53 AM
Is there any way this index is useful for setting values in the conductor material?

what we have to work with as I see it, It is the specularity and roughness values..

Michael

Hi,

You can use the Maxwell's equation:

R = |(n-1)˛-k˛|/|(n+1)˛+k˛|

Then multiply this value with the output of the Incidence node, plug the result in the Specular input of the Conductor material.

If you have trouble setting the nodes for the Maxwell's equation feel free to ask.

As for the Roughness parameter, it's not per say a physicaly accurate parameter but more an artistic control depending on the state of the surface (dented or not, etc..), the best thing to do is to experiment with some actual metal picture, as any metal can by brushed, dented, eroded, etc..

Hope this helps.

Cheers,
Guy.