Download - Royal Australian Navy

NAVY ENGINEERING BULLETIN MARCH 2003
57
Focus on Laser Safety in
the RAN
How do we use lasers in defence?
Lasers are already commonplace in defence forces around the world,
and their numbers and uses are increasing. Their military applications
are numerous and can range from optical communications to highenergy
weapons. Accurate range finding is currently the most common
use, and it is a capability that we implement on many RAN platforms
(ANZAC 9LV, FFG EOTS, and MHC EOSS). We also use hand held laser
thermometers in damage control to determine the temperature of
objects from a safe distance, without having to touch the potentially hot
surface. We use a system known as Laser Airborne Depth Sounder
(LADS) to perform ocean depth surveying using lasers operated on
board an aircraft. RAN ships have even used laser designators to guide
beam-riding missiles. These applications are only the beginning. As the
technology matures we will begin to see laser systems used for hard and
soft kill point defence systems, low power line of sight communications
with very high bandwidth, LIDARs that construct real-time threedimensional
images of distant targets, one day we may even have to
learn ceremonial light-sabre drill.
LEUT CHRIS DAVIDSON NAOS
What are the dangers?
Apart from the obvious danger
involved with an inbound laser
guided missile, there are other
risks to personnel involved with
the use of lasers. Laser radiation
is non-ionising (ie, will not result
in radiation sickness or genetic
abnormalities), but it can burn
flesh, and eyes are especially
susceptible. Even a 100 mW
laser is powerful enough to blind
you permanently. A person can
happily stare at a 100 W light
globe because it emits noncollimated
light. That means that
the power is dissipated in every
direction, so only a tiny fraction of
the total power emitted enters the
eye of any single observer. Laser
light on the other hand is highly
collimated (every ray has
approximately the same direction
of travel). So if a laser beam is
pointed at an observer, the full
power of the laser is concentrated
onto the small spot on the skin
where the laser beam strikes.
What makes the eye even more
susceptible to damage than skin
is the ‘Spot Size effect’. This
refers to wavelengths in the
optical hazard region (not only
visible wavelengths from 0.4 –
0.7 micrometres, but also the
near infra-red from 0.7 – 1.4
micrometres), which are bought
into sharp focus onto the retina
of the eye. This concentrates the
full energy of the laser beam onto
an even smaller spot,
superheating that point on the
retina. Depending
on the wavelength,
and duration of
exposure to the
laser, the resultant
super-heating can
cause damage
ranging from
temporary dazzle
to blind spots to
total blindness.
Eyes can be put in
further danger if
magnifying optics such as
binoculars are used. Binoculars
have a much larger aperture than
the eye, so they have the ability
to collect a lot more laser
radiation from beams with a large
diameter, and focus this radiation
into the eye.
What is being done about laser
safety in the RAN?
The Defence Laser Safety
Committee (LSC) is a tri-service