The
helium neon laser(HeNe laser) is a
discharge pumped
gas laser. It consists
of a
glass tube filed with a
low pressure mix of
helium and
neon.
There are also
electrodes in the tube and a
mirror in each end.
One of the
mirrors is only
partialy reflective, and will let some of the
light at
the
laser output frequency,
through. To use the
laser a high
voltage
(about 1000VDC) is
connected to the
electrodes and a starting pulse(10000V+) is
administred.
This causes the
neon to
emit photons. Some of the
photons will be
reflected by the
mirrors. These
photons will hit the
gas atoms and cause further emission, And thus more light.
This
process creates light with in
narrow frequency band, and with high
coherence(this means that the light waves
move in
phase).
This
laser type were used in
laser printers, laserdisc players and barcode
scanners
but has been
replaced by the
cheaper, more
power efficient and much smaler
laser
diode. But is still used in
applications like interferometers and holography
where the higher
coherence is wanted. The HeNe
laser is easily
recognized due to
a more
orange(a wavelength of about 632.8
nano meters) light than the
laser diode. HeNe
lasers
commonly has an output of
between 0.5mW and 5mW, but larger laboratory lasers may have up to about 0.3W.