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Absorption (electromagnetic radiation)

About: Absorption (electromagnetic radiation) is a research topic. Over the lifetime, 76674 publications have been published within this topic receiving 1381221 citations.


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Book ChapterDOI
TL;DR: In this article, the authors compare the performance of Mossbauer spectroscopy and ultraviolet spectroscopic methods, and show that the differences in spectra can be attributed to the hyperfine interactions; the interactions between the nuclear charge distribution, and the extranuclear electric and magnetic fields.
Abstract: Publisher Summary Mossbauer spectroscopy can be likened to ultraviolet spectroscopy. Both techniques employ a source of radiation, an absorber and a detector. In Mossbauer spectroscopy, we consider transitions between nuclear energy levels with the emission and absorption of y rays; whereas, in ultraviolet spectroscopy, we consider the transitions between electronic energy levels with the emission and absorption of ultraviolet radiation. To observe resonance, a range of source photon energies is scanned: in ultraviolet by the use of a prism or grating, and in Mossbauer by employing the Doppler effect. The energy of the y ray (E,) is varied by the well-known Doppler formula d E = (V/C)E, where AE = change in energy of y photon, 11 = velocity of source relative to the absorber, and c = velocity of light. As in ultraviolet, absorption is plotted versus the energy of source photon (usually in velocity units for Mossbauer). Different compounds of one isotope give different spectra— that is, the nuclear energy levels are sensitive to the extranuclear environment. These differences in spectra can be attributed to the hyperfine interactions; the interactions between the nuclear charge distribution, and the extranuclear electric and magnetic fields. These hyperfine interactions give rise to the isomer shift (IS.) , the quadrupole splitting (Q.S.), and the magnetic Zeeman splitting.

208 citations

Journal ArticleDOI
TL;DR: In this article, femtosecond laser pulses were used to fabricate straight and bent through-channels, which had diameters on the order of tens of microns, high aspect ratios, and good wall-surface quality.
Abstract: Ultra-short-pulse lasers have proved to be effective tools for micromachining a wide range of materials. When the ultra-short laser pulse is focused inside the bulk of a transparent medium, nonlinear absorption occurs only near the focal volume that is subjected to high intensity. Three-dimensional structures can be fabricated inside transparent materials by taking advantage of this volumetric absorption. In this paper, femtosecond laser pulses were used to fabricate straight and bent through-channels. Drilling was initiated from the rear surface to preserve consistent absorption of the laser pulse. When the debris was not removed efficiently, variation of the channel diameter and occasional termination of the drilling process were observed. Machining in the presence of a liquid and additional use of ultrasonic wave agitation facilitated the debris ejection. The machined channels had diameters on the order of tens of microns, high aspect ratios, and good wall-surface quality.

207 citations

Journal ArticleDOI
TL;DR: Fluorescence quenching and excitation spectra indicate that the singlet energy transfer is efficient for the dyad triplet photosensitizers, and Nanosecond time-resolved transient absorption spectroscopy has confirmed that the triplet excited states of the dyads are distributed on both the energy donor and acceptor.
Abstract: Resonance energy transfer (RET) was used for the first time to enhance the visible light absorption of triplet photosensitizers. The intramolecular energy donor (boron-dipyrromethene, Bodipy) and acceptor (iodo-Bodipy) show different absorption bands in visible region, thus the visible absorption was enhanced as compared to the monochromophore triplet photosensitizers (e.g., iodo-Bodipy). Fluorescence quenching and excitation spectra indicate that the singlet energy transfer is efficient for the dyad triplet photosensitizers. Nanosecond time-resolved transient absorption spectroscopy has confirmed that the triplet excited states of the dyads are distributed on both the energy donor and acceptor, which is the result of forward singlet energy transfer from the energy donor to the energy acceptor and in turn the backward triplet energy transfer. This ‘ping-pong’ energy transfer was never reported for organic molecular arrays, and so it is useful to study the energy level of organic chromophores. The triplet ...

207 citations

Journal ArticleDOI
TL;DR: In this paper, a series of high-quality silica glasses doped with 0.01 to 0.1 wt% of each transition element (V through Cu) was prepared by a vapor hydrolysis technique.
Abstract: The optical absorption of 3d transition elements in fused silica was studied. A series of high-quality silica glasses doped with 0.01 to 0.1 wt% of each transition element (V through Cu) was prepared by a vapor hydrolysis technique. Their optical spectra were measured, and their practical absorptivities were calculated between 200 and 2000 nm. In the proposed waveguide use range (∼ 850 nm), V and Cr appear to absorb most (apract= 2.6 and 1.2 dB/km ppbw−1 (metal), respectively) and Cu the least (apract≃0). Comparisons are made with data for conventional glasses.

207 citations

Journal ArticleDOI
TL;DR: In this article, the absorption of high-energy γ-rays in intergalactic space has been studied by calculating the absorption properties of 10-500 GeV γ rays at high redshifts.
Abstract: In this paper, we extend previous work on the absorption of high-energy γ-rays in intergalactic space by calculating the absorption of 10-500 GeV γ-rays at high redshifts. This calculation requires the determination of the high-redshift evolution of the intergalactic starlight photon field, including its spectral energy distribution out to frequencies beyond the Lyman limit. To estimate this evolution, we have followed a recent analysis by Fall, Charlot, & Pei, which reproduces the redshift dependence of the starlight background emissivity obtained by the Canada-France Redshift Survey group. We give our results for the γ-ray opacity as a function of redshift out to a redshift of z = 3. We also give predicted γ-ray spectra for selected blazars and extend our calculations of the extragalactic γ-ray background from blazars to an energy of 500 GeV with absorption effects included. Our results indicate that the extragalactic γ-ray background spectrum from blazars should steepen significantly above 20 GeV, owing to extragalactic absorption. Future observations of a such a steepening would thus provide a test of the blazar origin hypothesis for the γ-ray background radiation. We also note that our absorption calculations can be used to place limits on the redshifts of γ-ray bursts; for example, our calculated opacities indicate that the 1994 February 17 burst observed by EGRET most probably originated at z ≤ ~2.

207 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2022185
20213,106
20202,866
20192,953
20182,876
20172,679