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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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Journal ArticleDOI
TL;DR: In this article, the authors present a detailed characterization of the output of optical limiters using photogenerated carrier defocusing within the material to limit the output fluence and irradiance.
Abstract: We present a detailed characterization of the output of passive semiconductor-based optical limiters. These devices utilize two-photon absorption along with photogenerated carrier defocusing within the material to limit the output fluence and irradiance. In addition to protecting downstream optical components, the focusing geometry combined with these nonlinearities makes the devices self-protecting. Such devices have a broad working wavelength range since both the initial two-photon absorption and the subsequent carrier refraction are slowly varying funtions of wavelength. For example, ZnSe should have a useful range of from 0.5 to 0.85 μm. In this material we have observed the onset of limiting at input powers as low as 80 W when using 10-nsec, 0.53 μm input pulses. At the same wavelength, when 30 psec pulses into a monolithic ZnSe limiter are used, limiting begins at ≃300 W or 10 nJ. We also monitored the output spatial energy distribution along with the temporal response at each position, using a 2-psec-resolution streak camera. We found that the output fluence along with the output irradiance is effectively limited below detector damage thresholds over an input range of 4 orders of magnitude. Additionally, since both two-photon absorption and the associated self-defocusing increase with decreasing band-gap energy, similar devices using narrow-gap semiconductors should have considerably lower limiting thresholds.

213 citations

Journal ArticleDOI
TL;DR: Strong two-photon absorption and nonlinear scattering are found to be responsible for good optical limiting characteristics in these nanoparticles.
Abstract: The nonlinear optical absorption, scattering and optical limiting properties of CdS nanoparticles dispersed in dimethylformamide (DMF) are investigated. The nanoparticles are synthesized using the standard chemical synthesis method with thioglycerol as the capping agent. The investigations are carried out at 532 nm in the ns regime. Strong two-photon absorption and nonlinear scattering are found to be responsible for good optical limiting characteristics in these nanoparticles.

213 citations

Journal ArticleDOI
TL;DR: In this paper, the effect of an external electric field on the optical absorption associated with a direct transition between bands is studied and an expression for the absorption constant for photon energies below and above the band gap is given.
Abstract: The effect of an external electric field on the optical absorption associated with a direct transition between bands is studied. Expressions are given for the absorption constant for photon energies below and above the band gap. The formation of discrete levels in the presence of the electric field produces oscillations in the absorption.

213 citations

Journal ArticleDOI
TL;DR: Findings suggested that photographic ir sensors were more suited to remote sensing of moderate to high biomass levels or vegetational density in a grass canopy than were sensors operating in regions of the spectrum where strong absorption occurred.
Abstract: The asymptotic nature of grass canopy spectral reflectance has been evaluated from field experimental data collected over the wavelength region of 0.500–1.000 μm at 0.005-μm intervals. The spectral reflectance of green vegetation against a soil background decreases in regions of absorption and increases in regions of minimal or no absorption as the vegetational density increases until a stable or unchanging spectral reflectance, called the asymptotic spectral reflectance, is reached. Results indicated spectral reflectance asymptotes occurred at significantly lower levels of total wet biomass, total dry biomass, dry green biomass, chlorophyll content, and leaf water content in regions of strong pigment absorption (low detectability threshold) than in the photographic ir region where absorption was at a minimum (high detectability threshold). These findings suggested that photographic ir sensors were more suited to remote sensing of moderate to high biomass levels or vegetational density in a grass canopy than were sensors operating in regions of the spectrum where strong absorption occurred.

213 citations

Book ChapterDOI
TL;DR: In this article, the spectral-line absorption coefficient and radiative transfer expressions appropriate for calculating absorption and emission by atmospheric gases are formulated, and problems associated with the calculation of absorption by these two molecules are discussed.
Abstract: Publisher Summary This chapter focuses on absorption and emission by atmospheric gases. At centimeter and shorter wavelengths, absorption and emission by atmospheric gases can significantly affect the propagation of electromagnetic radiation through the atmosphere. At frequencies from 1 to 300 GHz, referred to as “microwave frequencies,” absorption by atmospheric gases is dominated by water vapor lines at 22 and 183 GHz, oxygen lines near 60 GHz and at 118 GHz, and relatively narrow and weaker ozone lines above 100 GHz. Non-resonant absorption by water vapor and oxygen has significant effects in the window regions away from the dominant lines. The radiative transfer expressions appropriate for calculating absorption and emission by atmospheric gases are formulated. The general expressions for the spectral-line absorption coefficient are provided, followed by specific expressions for calculating absorption by water vapor and oxygen. Problems associated with the calculation of absorption by these two molecules are discussed. The absorption by microwave lines of ozone and other minor constituents is considered. Finally, the results of calculations of atmospheric absorption and emission, as well as the measured values are presented in the chapter.

213 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