Questions tagged [optical-materials]

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94
votes
6answers
86k views

Why is glass transparent?

Once I asked this question from my teacher and he replied "Because it passes light.". "And why does it pass light?" I asked and he said, "Because it is transparent.". The same question again, Why ...
17
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1answer
1k views

How can the refractive index be below 1 in a dielectric?

Upon checking the optical properties of different dielectrics, I found the interesting case of $Al_2O_3$. It seems to be reported with a refractive index below 1 in the infrared range of $10 - 12~\mu ...
8
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2answers
339 views

What are the current experimental limits on the polarizability of the vacuum?

Many (all?) materials are polarizable at some level; meaning that when we apply an electric field across the material, there is an induced dipole moment $$ \vec{p}=\alpha(\omega)\vec{E}, $$ where $\...
7
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2answers
1k views

Slowing down light in an opaque crystal for a whole minute

I just read about a team of physicists at the University of Darmstadt, Germany, that managed to completely slow down a beam of light that traveled through an opaque crystal (article here). How is it ...
6
votes
1answer
267 views

Why is $\textbf{D}$ the response to $\textbf{E}$?

In the text Wooten, equation 2.69 shows $\textbf{D}$ being the response to $\textbf{E}$ with $\epsilon$ as the response function: $$ \textbf{D}(\textbf{r},t) = \int d\textbf{r}^{\prime} \int dt^{\...
5
votes
1answer
324 views

Why does aluminium-on-glass mirror work without distortion?

I have read an article about glass (zerodur) with low thermal expansion coefficient. It is mentioned that large casts of such glass are covered with reflective layer of Aluminium and used as mirrors ...
5
votes
1answer
194 views

Optical Retroreflectors: How Are the Faces So Accurately Righted?

This question is about Optical Retroreflectors (corner cubes) and how the extreme precision in their manufacturing is achieved. I suspect there is interesting basic physics involved, which is why the ...
4
votes
2answers
98 views

Are there any real-world examples of refraction of light by magnetic permeability?

The question Fresnel Transmission Coefficient for Magnetic Field is interesting. Thinking about it led me to reflect upon what little I know of the history of optics, with refraction by lenses and ...
4
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2answers
801 views

Is the visible light spectrum from “red-hot glass” at least close to Blackbody Radiation?

Briefly, for visibly transparent materials like glass, you can see through then even while they are glowing red hot. Most glasses have plenty of absorption in the IR, so there is plenty of absorption ...
4
votes
1answer
96 views

Periodic multi-layer scattering of neutrons

I am trying to understand the reflectivity plot on slide 26 of Neutron optics,Soldner lecture. 1.Is the peak from $\theta$=0.0 to 0.4 due to total external reflection from the first upper surface?. ...
4
votes
2answers
893 views

Why does “liquid glass” putty turn cloudy when deformed?

What physical process is taking place to make it look cloudy? What's changing to make it turn back to clear over time? While they seem pretty secretive about the exact composition, but I did find ...
4
votes
1answer
222 views

Why does the refractive index not mirror the Lorentzian peak shape of the absorption index?

In the characterization of materials, there are many methods used: One of them is infrared spectroscopy. In a lab we saw the indices of refraction and absorption of a certain (semiconductor) solid ...
4
votes
1answer
83 views

Why are birefringence materials so rare?

By symmetry, most crystals will show birefringence. But the effect is very minute. So the question is actually, why is the birefrigence effect in most low-symmetry materials so small?
4
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2answers
1k views

Why are there direct bandgaps?

This Question has been bugging me for sometime. Some semiconductors have direct bandgaps and indirect bandgaps. So what causes a direct bandgap to occur? The physics behind ,why there are direct ...
4
votes
0answers
47 views

Difference between permittivities eps-opt and eps-inf?

Very often in materials physics we are interested in the relative permittivity at optical frequencies, which is usually denoted by $\varepsilon_\text{opt}$ or $\varepsilon_\infty$. But I'm confused ...
3
votes
2answers
152 views

Can you burn invisible jelly balls with a laser?

Suppose you have some jelly balls with similar refractive index as that of water, like in this video. You put them in water, making it invisible. So, the optical behavior of the balls should be ...
3
votes
2answers
2k views

Diameter of a lens vs Diameter of the circular Aperture of the lens vs Aperture of the lens

I was reading about resolving power in which it is said that "a is the diameter of the circular aperture or the diameter of the lens, whichever is smaller" . So, I don't understand how are they not ...
3
votes
1answer
180 views

Is it possible to make an optical lense that is an analog to a gravitational lense?

There are many lenses that do all sorts of things. eg. horshoe lenses twist light, meta material lenses can boggle the mind. Is it possible to make an optical lense that is an analog to a ...
3
votes
1answer
131 views

Are special relativity calcs affected by media?

Time dilation, increase in mass, Lorentz contraction calcs all involve velocity of light in vacuum. But in optical media light slows down. So what of relativity calcs in media? Do we ever need to ...
3
votes
2answers
717 views

Why do everyday plastic items interfere with light polarizers?

I recently bought a few pieces of linearly polarized film (the one intended for smartphone LCD screens). At first I was confused because I could not make the polarizers work as they should - no matter,...
3
votes
2answers
298 views

Are all fluorophores dipoles?

Lately I'm reading about surface enhanced fluorescence. In many articles I can see that fluorophores are called "dipoles". Is it because that they can be modelled by a vibrating electric dipole? Or ...
3
votes
4answers
7k views

What is the connection between the refractive index of a material and its transparency?

From my understanding, refractive index is an indication as to how the speed of light changes when it passes through a material. However a professor has asked me how would I determine whether or not ...
3
votes
2answers
75 views

Is there super-transmissivity?

I have little knowledge about quantum phenomena, but I have read about super-conductivity and super-fluidity. The first involves zero resistance and the second involves zero viscosity. I suddenly ...
3
votes
1answer
564 views

Why grating is an essential part of a monochromator?

From looking at these two images, it appears that the dispersed "rays" of the reflected light could be manipulated just as well if the reflecting mirror would be turned to a fixed angle. So why is ...
3
votes
2answers
1k views

Anodized aluminium reflectivity at 10.6 um

I wonder how I can model anodized aluminium reflectivity in ray tracing-based optical simulation. I know that the parts my company is using are anodized to get covered with a ~20 um (as specified) ...
3
votes
1answer
44 views

Why air spacing for high power beam splitters?

Ordinary glass cube beam splitters are constructed with a dielectric or hybrid coating on the hypotenuse of a right angle prism which is then cemented to another right angle prism. These fail in ...
3
votes
1answer
41 views

Where to find known dielectric functions of materials?

I've done a lot of experimental work in materials science and solid-state physics, but I'm currently venturing into the computational realm. I'm trying to compute optical constants ($n$ and $k$) for a ...
3
votes
1answer
128 views

Optical signal filters

Are there any optical filters which filter the signal's frequency and not based on the wavelength of the light? So what I mean is, if I have a modulated/pulsating light signal riding on a large DC ...
3
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0answers
78 views

Identifying diagrams for optical processes

I was reading some papers on the study of the optical properties of some metals and came upon these conference proceedings by Hopfield from 1972. They are on the study of the infrared properties of ...
3
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0answers
184 views

optical scattering cross section and polarization tensor

The optical scattering and absorption cross sections are well known to be $$ C_{sca} = \frac{k^4}{6\pi}|\alpha|^2 \qquad C_{abs} = k\Im (\alpha) $$ where $k$ is the wavevector and $\alpha$ is the ...
3
votes
0answers
190 views

Are there Optical Magnetic Mirrors (OMMs) which reflect via interaction with the magnetic field?

The most familiar mirror relies on reflection from a metal, where the very strong interaction of the electric field component of the EM wave with the conduction electrons produces a reflected wave. ...
2
votes
1answer
315 views

Metamaterial : Snell's law and Fermat principle

How do we deduce Snell's law using Fermat's principal in case of metamaterials? Metamaterials have negative refractive index. This makes the refracted ray of light bend on same side of normal as ...
2
votes
3answers
289 views

What is so special about calcite that it has double refraction?

In this video is explained how the double refraction occurs. But it explains that if the ordinairy ray is horizontal and the extraordinairy is vertical that the first one gets less delayed than the ...
2
votes
1answer
736 views

Plasma frequency

I have a neutral plasma and I need to solve Maxwell equations given the charge and current densities on the plasma. In order to do it I need to know the electrical permittivity $\varepsilon$, I've ...
2
votes
1answer
114 views

Optics, What is a Foil?

I was using a program for simulating optical elements; mirrors, gratings, foils, crystals, slits, and zoneplates are what it mentioned. Does anyone know what a foil is in terms of optics? I know what ...
2
votes
3answers
610 views

How can fiber optic image conduits consist of only fiber core, no cladding?

Looking at fiber optic image conduits, I found that they have a packing fraction (the ratio of the fiber core's area to the total area) of 100% (source here). In other words, they consist only of ...
2
votes
2answers
224 views

Temperature-induced wavelength shift of optical coatings?

Optical coatings designed for reflection or anti-reflection are made of many thin layers which will expand when heated. What will the effect be on the wavelengths the coating will reflect when the ...
2
votes
2answers
634 views

Why is this laser beam being scattered(and not)?

I was shining a laser beam through a liquid filled test tube(an ester particularly),and I found this phenomenon rather intriguing.Have a look. Now when I passed the laser straight through the upper ...
2
votes
1answer
277 views

Why is GaN better than Si as a substrate for ZnO thin film?

in an attempt to grow a thin film using ZnO, I found many researches use silicon as a substrate and others use GaN. by further research I found that GaN is preferred than silicon but I don't know the ...
2
votes
1answer
600 views

Optical Waveguide's “Base Bandwidth”

Consider a dielectric slab waveguide (lossless, isotropic) illuminated transversally from the vacuum (with coherent, monochromatic light). We define the base bandwidth of a waveguide (or optical ...
2
votes
1answer
68 views

Focal plane of ideal thin lenses and spherical mirrors

Recently I was studying about optical instruments and in my book I came across a point which stated that When non axial parallel rays are incident on an ideal spherical mirror at a small angle or a ...
2
votes
2answers
113 views

Is there such a material that only emits, or “sends out” the same color light that was “taken in” (absorbed)?

For example, glow-in-the-dark materials (photoluminescent) only emit a green hue regardless of the color of the light shone on the material. Is there such a material that emits the color of the light ...
2
votes
2answers
4k views

What plastic-like materials allow IR to pass through them? [closed]

What plastic-like materials allow IR to pass through them? Material should be solid and plastic like. Does't care if it is transparent to light or not. IR ray is emitted by Sharp distance center so it ...
2
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3answers
303 views

See through material for IR camera

I have an IR camera that I'm trying to hide behind an opaque or fine meshed material (plastic?). Any idea? Thanks!
2
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1answer
37 views

Is magneto-optic Kerr effect discernible for material with natural optical activity?

Magneto-optic Kerr effect requires a system with internal magnetism or external magnetic field and exhibits, say, circular dichroism for reflection measurements. Natural optical activity can have ...
2
votes
1answer
80 views

Is there a material that allows light to pass perpendicular to the surface, but reflects at an angle?

This is inspired by Michael Steven's new video about optics. He shows off Selenite, which has the property that light entering on one side travels perpendicularly down the crystal until it exits the ...
2
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0answers
45 views

How to decide between sizes of particles for maximum light intensity for scintillation?

Are nanoparticles or microparticles or quantum dots better suited as scintillation materials as far as light yield intensity is concerned? I was unable to find literature that compares micro vs ...
2
votes
0answers
639 views

Bandwidth-length product of an optical fiber

A multimode step index fiber has a numerical aperture of 0.2 and a core refractive index of 1.47 . Estimate the bandwidth-length product for the fiber assuming only intermodal dispersion when: (a)...
1
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2answers
101 views

Why can't ultraviolet light pass through glass?

What factor determine whether a body behaves like a transparent object for EM waves of a particular frequency?
1
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2answers
304 views

Magnifying power of a microscope for a farsighted person

I was doing some problems on optical instruments and in one of the questions it was asked that if a simple microscope(magnifying glass) has a magnifying power 5X for a normal relaxed eye.. what will ...