Transparency and translucency: Difference between revisions

Revision as of 20:31, 9 December 2023

Revision as of 03:00, 29 January 2024

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Most of the time, it is a combination of the above that happens to the light that hits an object. The states in different materials vary in the range of energy that they can absorb. Most glasses, for example, block ultraviolet (UV) light. What happens is the electrons in the glass absorb the energy of the photons in the UV range while ignoring the weaker energy of photons in the visible light spectrum. But there are also existing special [[glass]] types, like special types of [[borosilicate glass]] or quartz that are UV-permeable and thus allow a high transmission of ultra violet light.

Thus, when a material is illuminated, individual photons of light can make the [[Valencevalence electron|valence electrons]]s of an atom transition to a higher electronic [[energy level]]. The photon is destroyed in the process and the absorbed radiant energy is transformed to electric potential energy. Several things can happen then to the absorbed energy: it may be re-emitted by the electron as [[radiant energy]] (in this case the overall effect is in fact a scattering of light), dissipated to the rest of the material (i.e. transformed into [[heat]]), or the electron can be freed from the atom (as in the [[photoelectric effect|photoelectric effects]]s and [[Compton scattering|Compton effects]]).

===Infrared: Bond stretching===

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Most [[Insulator (electricity)|insulators]] (or [[dielectric]] materials) are held together by [[ionic bond]]s. Thus, these materials do not have free [[conduction electrons]], and the bonding electrons reflect only a small fraction of the incident wave. The remaining frequencies (or wavelengths) are free to propagate (or be transmitted). This class of materials includes all [[ceramic materials|ceramics]] and [[glass]]es.

If a dielectric material does not include light-absorbent additive molecules (pigments, dyes, colorants), it is usually transparent to the spectrum of visible light. Color centers (or dye molecules, or "[[Dopant|dopantsdopant]]s") in a dielectric absorb a portion of the incoming light. The remaining frequencies (or wavelengths) are free to be reflected or transmitted. This is how colored glass is produced.

Most liquids and aqueous solutions are highly transparent. For example, water, cooking oil, rubbing alcohol, air, and natural gas are all clear. Absence of structural defects (voids, cracks, etc.) and molecular structure of most liquids are chiefly responsible for their excellent optical transmission. The ability of liquids to "heal" internal defects via viscous flow is one of the reasons why some fibrous materials (e.g., paper or fabric) increase their apparent transparency when wetted. The liquid fills up numerous voids making the material more structurally homogeneous.{{Citation needed|date=July 2013}}

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[[Image:Zblan transmit.jpg|thumb|Light attenuation by ZBLAN and silica fibers]]

[[Attenuation]] in [[Optical fiber|fiber optics]], also known as transmission loss, is the reduction in intensity of the light beam (or signal) with respect to distance traveled through a transmission medium. Attenuation coefficients in fiber optics usually use units of dB/km through the medium due to the very high quality of transparency of modern optical transmission media. The medium is usually a fiber of silica glass that confines the incident light beam to the inside. Attenuation is an important factor limiting the transmission of a signal across large distances. In optical fibers the main attenuation source is scattering from molecular level irregularities ([[Rayleigh scattering]])<ref>I. P. Kaminow, T. Li (2002), Optical fiber telecommunications IV, [https://books.google.com/books?id=GlxnCiQlNwEC&pg=PA223 Vol. 1, p. 223] {{webarchive|url=https://web.archive.org/web/20130527231335/http://books.google.com/books?id=GlxnCiQlNwEC&q&f=false&pg=PA223 |date=2013-05-27 }}</ref> due to structural disorder and compositional fluctuations of the [[Amorphous solid|glass structure]]. This same phenomenon is seen as one of the limiting factors in the transparency of infrared missile domes{{Citation needed|date=November 2010}}. Further attenuation is caused by light absorbed by residual materials, such as metals or water ions, within the fiber core and inner cladding. Light leakage due to bending, splices, connectors, or other outside forces are other factors resulting in attenuation.<ref>{{cite journal|author=Smith, R.G.|title=Optical power handling capacity of low loss optical fibers as determined by stimulated Raman and Brillouin scattering|journal=Appl. Opt.|volume=11|issue=11|pages=2489–94|year=1972|doi=10.1364/AO.11.002489|pmid=20119362|bibcode=1972ApOpt..11.2489S}}</ref><ref>{{cite journal|author1=Archibald, P.S. |author2=Bennett, H.E. |editor-first1=Stephen A. |editor-first2=Geoffery |editor-last1=Benton |editor-last2=Knight |name-list-style=amp |title=Scattering from infrared missile domes|bibcode=1978SPIE..133...71A|journal=Opt. Eng.|series=Optics in Missile Engineering |volume=17|page=647|year=1978|doi=10.1117/12.956078|s2cid=173179565 }}</ref>

==As camouflage==