Questions tagged [absorption]

A transition by which the energy of at least one photon is completely transferred to a material.

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In diffraction When wavelength is less than slit width then does the scattered light gets absorbed & emitted from the wall or just rebound?

I know that when the slit width is less than that of wavelength then the slit will act as a point source and scatter the light in all directions. But my question is that during the scattering of ...
490 views

How does the reflection coefficient change with scattering and absorption?

My professor of Biomedical Optics course asked us to think upon the evolution of the reflection coefficient with the absorption coefficient $\mu_a$, the reduced scattering coefficient $\mu_s'$ and the ...
1 vote
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Einsteins Coefficient of Absorption in solid state

What solid state parameter determines the probability of absorption (Einsteins coefficient B) in a material? Is it material dependent? I think, I cannot say bandgap. Because if I have a source having ...
1 vote
225 views

Mie theory: Interpretation in terms of intensity

I'm trying to understand Mie theory. For this I'm reading the book "Absorption and Scattering of Light by Small Particles" by Bohren and Huffman. The derivation of the formulas is fine, but I'm stuck ...
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What happens after bulk gold absorbs a photon with its energy at the band gap or higher (wavelength < 500 nm)?

As is explained in the answers of this question: Why are most metals gray/silver? nicely, the responsible transition occurs between the 5d orbital and the 6s orbital, which is relativistically shrunk ...
1 vote
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How much gas is needed to produce absorption lines?

I am trying to know whether it would be possible to do an undergraduate laboratory experiment to measure absorption lines produced by a gas. The idea is to have a background source of light with a ...
2k views

Aren't places where geodesics end singularities?

So of course when stuff falls into black holes, the geodesic for anything ends in that singularity. However, isn't it technically true that a light ray that originates from the sun and then hits the ...
1 vote
502 views

Plasma Frequency of Indium Tin Oxide

What does determine the plasma frequency? The formula is: $$\omega_p² = \frac{4 \pi N e²}{m}$$ and for frequencies above the plasma frequency the material is transparent. So for indium tin oxide (...
550 views

Times associated with absorption and emission processes

I am currently reading the book "Advances in Atomic Physics: An Overview" by Cohen-Tannoudji and Guéry-Odelin. In pages 29-31 the authors discuss a two-level atom subject to a broadband radiation ...
35 views

What determines the wavelength in absorption?

When looking at absorption or reflectance spectra, say in the range of 400nm to 2500nm, you can see peaks (or dips) at certain wavelengths, that are characteristic for the material absorbing and ...
8k views

Why can't sunlight reach the very deep parts of an ocean?

Sunlight reaches the surface of the ocean and refracts. So it is still there. And its speed is about $225000$ km/s in water which is still incredibly fast. Light is a massless electromagnetic wave. So ...
71 views

Complex Refractive Indices, Absorption, and Transparency

A complex refractive index is defined as $n = n_0 + \kappa$ where $n_0$ is the "standard" refractive index, and $\kappa$ is the optical extinction coefficient. The optical extinction ...
196 views

How does silver affect transmission of energy in the visible and infrared part of the spectrum?

A common method to prevent radio frequency and microwave energy from going through windows is to apply a microscopic layer of silver to the surface of the glass, either by attaching a film coated with ...
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How do we know that the Sun is 71% Hydrogen by mass from emission/absorption spectra?

In my Intro to Astronomy ("intro" is very important, please keep responses as simple as possible) course, we're currently learning about light and electron orbitals and such, and I came ...
340 views

How to picture vibrational overtones of water?

Im trying to understand the colour of water. The absorption occurs because of some of the vibrational overtones of water. The absorption band at 698 nm (14300 cm−1) is a 3rd overtone (n=4) The ...
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Why do the proteins in our eye have a continuous (bell shaped) absorption spectrum?

From quantum physics, I would expect that seeing e.g. red would excite the 564nm energy level of the Photopsin protein. I would also expect to only see (apart from some small smeering out) that we are ...
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What is the influence of humidity on NDIR $\rm CO_2$ measurements?

The Question I would like to use an NDIR $\rm CO_2$ sensor to measure $\rm CO_2$ in the 0.1-3% range. However, in the course of my experiments, humidity may vary from ambient (50-60%) up to nearly 100%...
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Infrared pass material thermal camera

I have a situation in which I need to use a thermal camera in a rain enviroment, the camera is mounted on a gymbal and can rotate 360 degrees, so I tought it may be an option to build a dome in order ...
974 views

Does sound absorption depend upon the amplitude of a sound wave?

I can understand the mechanism of frequency dependent sound absorption by most materials but does the sound attenuation also depend upon the amplitude (sound pressure or rather loudness/sound ...
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Where does light energy end up? [closed]

Here's a gedankenexperiment: In situation A you run $P$ watts of incandescent bulbs in a closed room for time $t$ (light and heat cannot escape the room). The room starts a temperature $T$ and ends at ...
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Neutron double differential capture cross section

Can one define what is the double differential capture cross section for a neutron, and how one would construct an experiment to calculate the double differential cross section as a function of energy ...
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How can daylight have a higher colour temperature (e.g. 6500 K or D65) than sunlight in space?

Supposedly, daylight at midday has a colour temperature of 6500 K. This reference is also the standard for calibrating computer screens (that's how I fell into this). However, outside the atmosphere ...
1 vote
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I was reading Baumann's book on cosmology (topic: Effective three level system). There it is said that in the epoch of recombination to form Hydrogen molecule two type of transition happens. $$2S \to ... 1 vote 1 answer 318 views How does light interact with atoms? [closed] I've read this answer regarding the difference between mere reflection and absorption followed by emission and I am struggling to understand some concepts. To begin with, we have some matter-light ... 1 vote 1 answer 88 views 450nm peak absorption [closed] I am looking for an oxide compound (metal oxide, or similar preferably inorganic) which shows light peak absorption at 450 nm. I have troubles in finding the right compound, as most of the oxides have ... 0 votes 0 answers 27 views Absorbance spectrum of common metal oxides I am looking into metal oxides particles, and I wonder where can I find the absorbance spectrum of visible light of common avaiable metal oxides? 2 votes 1 answer 66 views Why we typically see no deeper into an atmosphere for an optical depth of 1? In An Introduction to Modern Astrophysics (p.243), Carroll and Ostlie say that for a optical depth \tau = 1 the intensity will decline by a faction of e^{-1}. I_\lambda = I_{\lambda,0}e^{-\tau} ... 1 vote 1 answer 107 views Refractive index of titanium dioxide films as a function of wavelength for 400 C ° annealed films I used UV-Vis/NIR spectrophotometer to extract the measurements of refractive index %R corresponding with wavelengths in the range of 190-1100 nm of TiO2 thin film deposited on FTO glass substrate. ... 1 vote 1 answer 177 views Formation of emission lines, absorption spectra If we spectroscopically observe a cloud of hot gas, which is on the whole not very absorbent, and which is not illuminated by a source behind it, we observe emission lines. How does this type of ... 0 votes 1 answer 63 views Convolution or addition? Proper way to model overlapping absorption line profiles Suppose you obtain a measured spectral line shape (let's call it 'envelope') which appears as a skewed/asymmetric voigt profile. You know physically that the envelope line profile has this skew ... 0 votes 0 answers 15 views What effect, if any, does dissipative absorption have on aurora borealis? Why don't we see more colors as a result? According to wikipedia, the aurora borealis is primarily caused by charged particles from the solar wind being redirected to the poles by earth's magnetic field and slamming into the nitrogen and ... 2 votes 0 answers 42 views Physcial interpretation of term neglected in Rotating Wave Approximation Consider an atom as a two-level system |1\rangle, |2\rangle with energy separation \hbar \omega_0, which is interacting with a classical electric field \vec{E}=\vec{E}_0 \cos(\omega t). This ... 8 votes 2 answers 2k views What is cross section? I am learning about unit Barn, it is a unit of cross section. I know it means how likely a particle is to interact with the material, it's like opacity or transparency in optics. What I don't ... 0 votes 2 answers 2k views Why the crest of water absorb more light than the trough of water? I have done my experiment using water ripple to study the behavior of waves. I know that the crest will absorb more light than the trough so that the image created on the white paper sheet appeared to ... 0 votes 0 answers 21 views Determination of absorption and scattering coefficients, given only the attenuation length I'm attempting to write a Monte Carlo solution to the radiative transport equation in a highly anisotropic medium with known attenuation length \lambda. Due to limitations in our ability to measure ... 3 votes 3 answers 300 views Why does sound absorbing foam stop echoes, but not transmission through the wall? I understand echoes are sound reflections. But if foam absorbs sound, and if it reflects off the wall, then that means the waves travel through the foam, and if sound waves get transmitted from a ... 1 vote 0 answers 22 views Absorption Cross Section for Two-Level Spin System in an AC Magnetic Field - Photon Picture For a two-level spin with a energy difference of E = h f, where the two levels have zero dipole electric coupling and can only be driven by a magnetic field, how do I calculate the absorption cross ... 0 votes 0 answers 12 views Why do the 'colors' of liquids in differently sized glass cylinders appear similar despite varying absorption rates? For some liquids, such as cooking oil, I have observed that when filling two glass cylinders (with lids) of different diameters (e.g., one with a 5 cm diameter and another with a 10 cm diameter) with ... 1 vote 0 answers 67 views How does light absorption work for solids and liquids? I've studied in my physics class, absorption and emission spectra for gases or more "spread out" molecules like what is done in atomic absorption spectroscopy (learnt that one in chemistry). ... 0 votes 1 answer 2k views How are microwaves blocked? When a phone is inside a microwave oven and if we call it over Wi-Fi, the phone doesn't receive the call, because Wi-Fi and the microwaves generated in the oven have the same frequency and there is a ... 2 votes 0 answers 54 views Predict color of dye under a certain wavelength of light? I am picking fluorescent dyes to be put under a UV of known wavelength and would like to be able to predict approximately what color the dyes will appear under the light. I can request ... 0 votes 0 answers 17 views Water vapor: refractive index and extinction coefficient (n and k) Looking for optical properties of water vapor (index of refraction and extinction coefficient) as a function of wavelength. 0 votes 0 answers 31 views Absorption line of nitrogen at 337 nm Nitrogen laser emits a laser at 337 nm. So, I think nitrogen has a laser absorption spectrum at 337 nm, but I have not found any information such as absorption coefficients around this wavelength from ... 1 vote 3 answers 90 views What is the explanation that the same material could receives and reflects EM wave signal while another absorbs? Here is B-2 Spirit, a stealth bomber by Northrop Grumman. Another one is a depiction of a parabolic dish antenna receiver. As we knew, the B-2 is a stealth aircraft, which is not reflects the received ... 0 votes 2 answers 258 views If photons are massless, how are they reflected and blocked by something that has mass? Shouldn't they pass right through any object? If photons are massless, how do they get reflected, blocked when something comes in its way? Shouldn't the particle just pass right through any object? 0 votes 0 answers 11 views Expansion and visibility of particles because of diffusion A cloud forms as a point source containing a fixed quantity of particles and then expands according to the diffusion equation. Let's analyze how the visible size of the cloud changes with time. When ... 11 votes 1 answer 2k views Understanding the virtual states referenced in multiphoton absorption studies The Heisenberg energy-time uncertainty tells us that we can have so-called virtual states between eigenstates as long as the lifetime of these states is at most: \tau = (\frac{h}{4 \pi E_v}) Where ... 1 vote 0 answers 91 views Where does this formula of absorption cross section come from? My professor gave us a formula for absorption cross section, but he said he did not remember where he found it. The formula is given by$$\sigma_a =\frac {1} {|\mathbf E_i|^2} \int_V k \epsilon^{''}_r ...
I am not a physicist, but reading up on interference in thin films. I understood how the relation of two interfering light waves intensities $I_1$ and $I_2$ of a thin film (the first reflected at the ...
According to https://en.wikipedia.org/wiki/Ultraviolet#Subtypes Ultraviolet radiation below $200$ nm is considered to be Vacuum Ultraviolet, due to being strongly absorbed by atmospheric Oxygen. ...