What is Absorption: Definition and 531 Discussions

Absorption spectroscopy refers to spectroscopic techniques that measure the absorption of radiation, as a function of frequency or wavelength, due to its interaction with a sample. The sample absorbs energy, i.e., photons, from the radiating field. The intensity of the absorption varies as a function of frequency, and this variation is the absorption spectrum. Absorption spectroscopy is performed across the electromagnetic spectrum.
Absorption spectroscopy is employed as an analytical chemistry tool to determine the presence of a particular substance in a sample and, in many cases, to quantify the amount of the substance present. Infrared and ultraviolet–visible spectroscopy are particularly common in analytical applications. Absorption spectroscopy is also employed in studies of molecular and atomic physics, astronomical spectroscopy and remote sensing.
There are a wide range of experimental approaches for measuring absorption spectra. The most common arrangement is to direct a generated beam of radiation at a sample and detect the intensity of the radiation that passes through it. The transmitted energy can be used to calculate the absorption. The source, sample arrangement and detection technique vary significantly depending on the frequency range and the purpose of the experiment.
Following are the major types of absorption spectroscopy:

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  1. Leo2024

    Optimal thin absorber of electromagnetic energy

    Hi, I am a material engineer and have a question about a formula derivation relative to microwave absorption. I really cannot figure it out after days of trying. This should be simple for a specialist. In this attached paper, how could one derive Eq(10) based on Eq (8) and (9)? Is k_2 in Eq...
  2. polyglot

    Question about Absorption Laws in Boolean Algebra

    According to my notes, the absorption law states that p ∨ (p ∧ q) = p, p ∧ (p ∨ q) = p I have found a video where they were discussing a partial absorption such as ¬q ∧ (¬p∨q) = ¬q ∧ ¬p This is not in my notes, but is this correct? specifically, is the terminology used to decribe this property...
  3. C

    A Calculating the optical depth of an inhomogeous gas

    My question emerges from my desire to calculate the optical depth, which should be unitless, for an inhomgeneous cloud of radius ##r##. For a homogeneous medium, the optical depth can be defined in terms of the density of a cloud relative to the density of the condensed medium: $$\tau = \alpha...
  4. Paul Howard A

    I Do Emission and Absorption Spectra Match? A Non-Physics Minded Tourist's Guide

    Basic stuff. Do emission and absorption spectra match? If so, why wouldn't hot stellar atmospheres exhibit both, cancelling? I'm a tourist...not physics minded..
  5. Leureka

    I How does EM wave geometrical attenuation affect atomic absorption?

    Let's say we have a point source of an EM wave in a vacuum of total energy E, and an absorber atom at some distance from this source, whose first excited state is at the energy B, with B < or = E. The energy of the wave is constant as a whole, but at each point around the source the energy...
  6. S

    I Collision-induced free-free absorption in fluids and superfluids

    Lone homonuclear diatomic molecules have vibrational excitations and rotational excitations. However, due to lack of transitional dipole moment, these are strongly forbidden to absorb IR. Lone atoms don´t have the above excitations in the first place. Now, when a diatomic molecule collides with...
  7. J

    Chemistry Electron Transitions after Absorption of Photon

    When a photon is absorbed, electrons move from a lower energy level to a higher energy level, so my answer is a, b, c, and f. I don't understand why the solution is b, c, d, e. Can electrons in this case move from a higher to lower energy level? Thank you.
  8. M

    I Absorption and emission spectroscopy of atoms

    Hello ! As I understand it, the different isotopes of the same atom have a slightly different spectroscopic absorption and emission where, for example, Deuterium absorbs slightly shorter wavelengths than Protium. My question is if two isotopes of different atoms, for example Tritium and Helium...
  9. L

    I How does atomic absorption spectroscopy work

    I did a prac where we tried to calculate the rydberg constant for hydrogen. We had a hydrogen lamp and we used a spectrometer that was hooked up to a photomultiplier tube to detect the wavelengths of light corresponding to the balmer series. In one section I need to write up a brief summary of...
  10. P

    Absorption coefficient and Linear Optical Susceptibility

    ##\alpha## is considered to be the absorption coefficient for a beam of light of maximum intensity ##I_0##. It's related to the complex part of the refractive index as we have shown above. Now, I have a doubt. Should I solve for ##k## from the quadratic equation in terms of the linear optical...
  11. D

    I What determines the time between atomic absorption and emission of photons?

    What determines the time between atomic absorption and emission of photons? Is there a correlation to blackbody radiation?
  12. A

    I Schwarzschild Metric & Particle Absorption

    The Schwarzschild metric implies a potential different from that of Newtonian gravity. Is there a relationship between it and the process by which particles can be absorbed by other particles? (I haven't studied QFT yet)
  13. D

    I Experimental demonstration of an absorption spectrum

    Hello, is there a convincing experiment to visualize absorption spectra? At disposal I have: - Halogen lamps - Lenses - Straight view prism - transmission grating - slit, iris, screen - Sodium vapor lamp and mercury vapor lamp Unfortunately, I do not have a sodium vapor cell or anything...
  14. C

    A Absorption and emission spectrum in quantum optics

    The emission spectrum or resonance fluorescence for a quantum dot, atom or defect center are discussed in many quantum optics textbook, for example see "Quantum Optics" by Marlan O. Scully and M. Suhail Zubairy Chapter 10 , "Quantum Optics" by D. F. Walls and Gerard J. Milburn Chapter 10 and...
  15. A

    I Balmer Absorption Lines in Different Temperature Stars

    Hi all I couldn't find on the web anywhere but what I'm looking for is a real image of strong Balmer absorption lines for a 10,000° Kelvin star and also a real image of a weak Balmer absorption lines for both a much colder or hotter star that shows how the absorption lines are weak. Does...
  16. B

    Vapour Absorption Cycle Questions

    Hi all, I'm doing some research on vapour absorption cycle machines, mainly water ammonia refrigerators. I've got a few questions. 1. What is the role of the water absorber? ie why do we need the water? 2. In the absorber we have a water ammonia solution. Is the ammonia a gas in the solution...
  17. C

    I Assumptions for blackbody spectra vs. emission spectra vs. absorption spectra

    Hi there, I am a physical oceanographer teaching an introductory undergraduate Earth science class that has a unit on astronomy. I have a physics undergraduate background, took a few astronomy classes at the undergraduate level back in the day, and did a bit of undergraduate research in...
  18. B

    I Probe absorption and dressed states

    Hello! I am reading about dressed states, and I am presented a situation in which we have a laser (the pump laser) on resonance with a 2 level (atomic) transition, and a second, weak laser (probe laser) that is scanned over a frequency range. The absorption spectrum of the probe laser, for...
  19. J

    B Photon absorption -- What happens to the excess energy?

    Wikipedia: "When a photon has about the right amount of energy to change the energy state of a system (usually an electron changing orbitals), the photon is absorbed." What happens if a somewhat higher energy photon arrives?
  20. PainterGuy

    I Some questions about absorption lines

    Hi, I was watching the following video. I need your help to clarify few important points. Thanks a lot in advance! Question 1: I'm not able to understand picture #1 below. I think that the frequency increases vertically downward but what about the horizontal scale? Compared to picture #1...
  21. Haorong Wu

    I Where does this formula for 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 $$\sigma_a =\frac {1} {| \mathbf E_i|^2} \int_V k \epsilon^{''}_r | \mathbf {E} |^2 dV = k \epsilon^{''}_r |\frac 3 {\epsilon_r +2}|^2 V.$$ Where does...
  22. S

    A Absorption of an Exciton and Exciton propagation

    I read articles talk about the absorption of the exciton in a solvent, such as TIPS Pentracene in toluene. My question is does the absorption spectrum keep the same for aggregate TIPS Pentracene , in case if I want to know for a layer of TIPS Pentracene?! My second question is: let's say I know...
  23. S

    Engineering Light absorption in a semiconductor

    The doped a-Si: H layers in a HIT solar cell do not contribute to the photocurrent. The light they absorb (according to their absorption curve below) is lost. For a doped a-Si: H layer at the front side of the cell that is 25nm thick, what percentage of light at 400nm will be lost due to...
  24. Elbow_Patches

    B Absorption of beta particles by lead

    Hello everyone, We conducted an experiment with a strontium-90 source and some different thicknesses of lead. With 2.1mm of lead the count rate (corrected for the background) was 0.69 counts per second, 3.0mm 19.7cps 6.8mm 15.4cps 13.8mm 10.0 cps This would...
  25. D

    I Photon absorption for an atomic electron

    Quick question: let's say we have an atomic electron in the ground state which requires, say, one "unit" of energy* to jump up to the next orbital energy state. If a photon arrives with a bit more or less than this, say 1.00003 or 0.99997 units of energy, is there some finite, non-zero...
  26. Haynes Kwon

    I Absorption lines and emission lines in stellar spectra

    Why do we see more absorption lines in stellar spectra than emission lines?
  27. bhobba

    I Why Do We Have The Effect Of Spontaneous Emission And Absorption

    Hi All In another thread I answered was a question related to this and noticed another as well, so I thought I would give the full answer in its own thread rather than write it out twice. The other question has been deleted but here is the full detail anyway. First see...
  28. A

    Deconvolve absorption from this spectrometer signal

    Hello all, I have a monochromatic laser peaking at 808 nm and some non-scattering sample. I want to measure the absorption with a spectrometer. I can use the Beer-Lambert law to do this, but since it is a monochromatic laser I have some doubts. I could do a weighted-average, taking into...
  29. A

    Understanding Radio Waves & Oxygen Absorption at 60GHz

    Homework Statement: I am having difficulty understanding what exactly is happening when radio transmissions are being absorbed by oxygen at 60GHz at the atomic level. Homework Equations: Refraction/reflection, oxygen absorptions/attenuation, frequency I have tried to find the answers online...
  30. Guilherme Franco

    A Trying to meaningfully deconvolute IR absorption spectra

    Hi I'm preparing some BCNO phosphor samples. Their basic structure is hexagonal Boron Nitride (h-BN) but it's doped with carbon and oxygen. The simplest BCNO phosphors are usually made from urea and boric acid alone, this already produces a BN structure with C and O impurities. I'm trying to...
  31. theobromine

    Exploring Black & White Materials: Absorption vs. Reflection

    True black materials theoretically absorbs all wavelengths of visible light. True white materials reflect all wavelengths of light. If a material which was black at room temperature was heated up to incandescence so that it was emitting all visible wavelengths (white light), and then light was...
  32. M

    How to Measure Impact Force / Energy Absorption

    Hi, I am a bit out of my league here, but had a question. I have 5 pieces of .25" thick foam/padding of different densities, and I wanted to measure which one absorbs the most energy (weakens the impact) when struck by a fist/punch or even a ball, how would I do that? I ran across a...
  33. darksat

    Infrared energy absorption of H20 molecules as a percentage of energy

    I eventually managed to find that a CO2 molecule can absorb about 8% of infrared energy passing through it that's radiated from Earth but its actually been incredibly hard to find a comparable figure for H2O molecules. Has anyone got a percentage figure for H2O in the form of atmospheric water...
  34. S

    Absorption Spectrum Practice problem

    Summary: The experimentally measured absorption spectrum of 1,3-pentadiene molecule exhibits a peak absorption (light absorption) around 224 nm corresponding to an electronic transition. Estimate the length of the molecule. I thought of using lambert law A = c*l*e but we have none. how do I...
  35. gmalcolm77

    MIT Material 10x Blacker Than Any Other: 99.995% Light Absorption

    Summary: MIT researchers have created a material that is 10x blacker than any other material ever recorded. The foil captures at least 99.995% of incoming light. Does this mean that there is practically no EM re-radiated?
  36. I

    I What happens to an electron's frequency during absorption of a photon?

    The point that I want to know is how two frequencys react with each other and does electron's frequency wait to reach to higher frequency on that fraction of second when they(photo's frequency and electron's frequency)collapse to each other than go to higher energy level or what?
  37. D

    I Photon Absorption & Electrons: Mass, Energy & Releasing Photons

    I'm not that familiar with the current theoretical standing on how electrons "absorb" photons, as in the sense that electrons in an atom absorb photons and move from lower to higher energy states. But during the absorption of a photon the electron, if you set units of c=1, gains energy and...
  38. Q

    Solar cell absorption efficiency in COMSOL Multiphysics

    Hi. I am studying the effect of plasmonic nanoparticles on solar cells. Is there a way to calculate absorption efficiency in different layers of tandem solar cells in COMSOL Multiphysics.
  39. C

    Atmospheric CO2 absorption - actual quantification?

    I have read oodles of hand wavy qualitative text about 'the greenhouse effect' and it is clearly dominated by the absorption characteristics of H2O vapour. What I struggle to understand is the part of CO2 in radiative absorption, in relative quantified terms. CO2 has absorption peaks at 2.7um...
  40. L

    Usage of absorption and magnitude mode spectra in nuclear magnetic resonance

    In nuclear magnetic resonance, when should one process spectra in absorption mode and when - in magnitude mode? What is benefit of using the first one and the second one? For example, I need to integrate spectrum. In this case, what should I use - absorption or magnitude mode?
  41. PSuran

    Acoustic resonance - Absorption vs Transmissibility

    Hi everyone. Firstly, I'm not a physicist, so relatively "intuitive" explanations would be greatly appreciated :) I'm confused by the following: Let's say we have a partition / wall, which resonates at a specific natural frequency. If the resonance is relatively high Q (low damping), then...
  42. R

    B Absorption of electromagnetic radiation

    Hi, I wonder why with electromagnetic radiation, there's some radiation that penetrates with Earth atmosphere such as visible light, while other can't like gamma radiation. What does the penetration of any em radiation on any object depends on
  43. hagopbul

    I Absorption of Radiation: Calculating Sphere Area

    Hello: Do anyone remember a law to calculate an area of a sphere ,some thing like the specific surface area but relative to absorption of radiation ?
  44. M

    Water vapor absorption in THz range

    Hi everyone! Terahertz time-domain spectroscopy (THz-TDS) is a spectroscopic technique that is using the radiation in the THz range. https://en.wikipedia.org/wiki/Terahertz_time-domain_spectroscopy A THz-TDS setup consists of an emitter and detector. The emitter creates a short broadband...
  45. sophiecentaur

    Absorption rate of CO2 in water

    So here's an interesting topic and I would appreciate some input from the assembled brains of PF to the question. Unfortunately I can't reveal the background to this but I want to know something about the rate that small bubbles of CO2 are likely to be dissolved in water under moderate pressure...
  46. Cool4Kat

    I Confusion about absorption spectra - cool gases absorb?

    So I was taught in school that heated low density gases produce spectral lines and cool low density gases absorb their spectral lines. I mentioned this to my husband and he asked me what the definition of hot and cool were and I had no idea. The more I thought about it, the more confused I...
  47. M

    On Rayleigh Scattering and UV Light Absorption

    I've read that UV light cannot "penetrate" the atmosphere as easily during winter. But what does this exactly mean? My hypothesis is that due to rayleigh scattering, since light with smaller wave lengths scatter more, the UV light doesn't end up reaching the surface of the Earth (i.e. gets...
  48. Sandeep T S

    I Photoelectric effect questions: photon absorption and electron ejection....

    Is a photon fully absorbed by a electron in metal? Ejected electron is a free electron or bonded one? Is it possible to have a zero work function? If not why? I want to study about this detaily ,can you prefer some reference papers?
  49. YMMMA

    Confused about the number of absorption lines

    Homework Statement If an atom in energy level 1, how many absorption spectral lines can an atom exhibit due to transition between 3 levels? How about 4 and 5 levels? And also in emission? Homework Equations Concept The Attempt at a Solution I am confused one book says it can absorb a photon...