MOTION MOUNTAIN

light sources 149
Vol. V, page 103
Vol. V, page 157
Vol. II, page 204
F I G U R E 94 A modern
picosecond pulse laser and
an industrial X-ray source,
both about 700 mm in size
(© Time-Bandwidth, SPECS).
ing, in costfromafraction ofan Euro to hundredsof millions of Euros,and in lifetime
fromafractionofasecondtohundredsofyears.
Lasers are important light sources for industry, medicine and research. Lasers can
emit visible, infrared and ultraviolet light, continuously or as light pulses, with various
powers, polarizations and beam shapes; they are explored later on in our adventure. In
the domain of imaging, lasers are used in many microscopy techniques, in scanningimagingsystems,intomographyandinholography.
Sourcesofradio waves are common in everyday life: mobile phones, radio transmitters,
tv transmitters and walkie-talkies are all sourcesof radio waves. They are used for
imaging in magnetic resonance imaging, which allows to image the interior of the humanbody,andinastronomy:Sincemanystarsareradioemitters,onecanimagethesky
atradio wavelengths. Nowadays, radio astronomy is an important part of modern astronomyandhasledtomanydiscoveries.
Radio astronomy has also been an important tool
for the precision testing and confirmation of general relativity.
On the other end of the electromagnetic spectrum, light sources that emitX-raysand
gamma rays are common. They are routinely used in medicine and materials science,
alsofor various imaging techniques.
All sources of electromagnetic radiation are potentially dangerous to humans, so that
Motion Mountain – The Adventure of Physics copyright © Christoph Schiller June 1990–November 2015 free pdf file available at www.motionmountain.net