A fresnel is a unit of
frequency
Frequency is the number of occurrences of a repeating event per unit of time. It is also occasionally referred to as ''temporal frequency'' for clarity, and is distinct from ''angular frequency''. Frequency is measured in hertz (Hz) which is eq ...
equal to 10
12 s
ā1. It was occasionally used in the field of
spectroscopy
Spectroscopy is the field of study that measures and interprets the electromagnetic spectra that result from the interaction between electromagnetic radiation and matter as a function of the wavelength or frequency of the radiation. Matter wa ...
, but its use has been superseded by ''terahertz'' (with the identical value 10
12 hertz
The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), equivalent to one event (or cycle) per second. The hertz is an SI derived unit whose expression in terms of SI base units is sā1, meaning that on ...
). It is named for
Augustin-Jean Fresnel
Augustin-Jean Fresnel (10 May 1788 ā 14 July 1827) was a French civil engineer and physicist whose research in optics led to the almost unanimous acceptance of the wave theory of light, excluding any remnant of Isaac Newton, Newton's co ...
the physicist whose expertise in
optics
Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behaviour of visible, ultraviole ...
led to the creation of
Fresnel lens
A Fresnel lens ( ; ; or ) is a type of composite compact lens developed by the French physicist Augustin-Jean Fresnel (1788ā1827) for use in lighthouses. It has been called "the invention that saved a million ships."
The design allows the c ...
es.
Scientific Unit Conversion: A Practical Guide to Metrication
Cardarelli, F. 1999. Springer Science & Business Media.
References
Units of frequency
Obsolete units of measurement
Non-SI metric units
Spectroscopy
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