Menu
Home
People
Places
Arts
History
Plants & Animals
Science
Life & Culture
Technology
Reference.org
Helium–neon laser
open-in-new
<p>A helium–neon laser or He–Ne laser is a type of <a href="/facts/Gas_laser/1eIYl75j">gas laser</a> whose high energetic gain medium consists of a mixture of <a href="/facts/Helium/yRul93TG">helium</a> and <a href="/facts/Neon/5bF1FwGL">neon</a> (ratio between 5:1 and 20:1) at a total pressure of approximately 1 <a href="/facts/Torr/Y83YBu34">Torr</a> (133 <a href="/facts/Pascal_(unit)/Am1To2Qm">Pa</a>) inside a small <a href="/facts/Electrical_discharge/06wCdIrV">electrical discharge</a>. The best-known and most widely used He-Ne laser operates at a center wavelength of 632.81646 nm (in air), 632.99138 nm (vac), and frequency 473.6122 THz, in the red part of the visible spectrum. Because of the mode structure of the laser cavity, the instantaneous output of a laser can be shifted by up to 500 MHz in either direction from the center. </p>