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Advertising with high power lasers
projected onto the sides of city
buildings is soon to become a
reality in Australia and in fact, we
lead the world in the development
of this technology. SILICON CHIP
recently took a look at these highpowered lasers which are
controlled by computer.
By LEO SIMPSON
Just when you thought that advertising had gone
about as far as it could go, a brand new technology
has popped into place to give the marketing people
another way of delivering their message. Just recently,
Sydney City Council has approved in principle the use
of Laservision for advertising on the sides of large city
buildings. And with Sydney leading the way, other
Australian cities are sure to follow.
Laservision is in fact the name of Laservision (Aust.)
Pty Ltd. They have developed and own the technology
for controlling high power lasers so thatthey can produce almost any image imaginable.
The lasers they use to project images on the sides of
buildings, the Sydney Opera House or at the State of
Origin rugby league matches are big - 5 to 20 watts.
They are also to take delivery of the world's most
powerful visible laser, capable of producing 32 watts.
While such a power rating may not seem big, in terms
of lasers it really is big. And if you think about the
really low efficiency of laser tubes, like less than
.05%, then the power input to these devices is quite
significant - tens of kilowatts.
Mirror, mirror
As you might expect, to make a high power laser
write on a wall or cliff which may be a kilometre in the
distance, you don't move the laser, you move the beam.
It's all done with mirrors. But there's no way you can
76
SILICON CHIP
accept that glib explanation and then move onto
another subject.
Laservision Australia has spent some 8 years
developing the control technology for writing with
lasers and they reckon they are still refining it. At the
moment they have the only system available
worldwide which can be programmed in real time to
control a laser display. You can sign your signature on
a digitiser panel and have it blown up to 50 metres
wide by the laser - instantaneously.
The result is that Laservision's system is booked for
advertising and media displays all around the world.
In fact, if you see an overseas sourced video news item
featuring a large laser display, the chances ar.e that it
is a Laservision show.
Animated advertising
So what are the ramifications of having permanent
laser advertising on the sides of city buildings? One of
the big advantages of laser vision advertising is that it
does not require any large supporting structure. As
long as there is a large blank wall in clear view, that is
all that is needed. There is no need for a large bulky
billboard structure which is costly to put up in the first
place and then costly to pull down when it is no longer
needed.
The second big advantage comes about because of
the immediate programmability of the Laservision
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Laservision displays can be projected from very long
distances and onto odd shaped surfaces such as the
Sydney Opera House sails. Mist and smoke from passing
ferries makes the beam itself visible.
This Laservision display during the recent State of Origin
rugby league matches used a whopping 20 watt Argon
laser. The large display is so bright that the full
sportsground lighting was able to be left on for the whole
display.
system - that enables the display to be changed
almost at will. For example, a large city Laservision
diplay could be programmed to display a multiplicity
of advertising messages which could be charged on a
timeslot basis, just the same as TV. But interspersed
with the advertising could be useful information to the
passing parade of citizens; news bulletins, traffic and
accident reports and so on.
Where the laser billboard was visible to large
numbers of motorists, as it inevitably would be, it
would be possible for the local traffic or municipal
authority to specify how much animation and how
many changes per minute there is in the advertising.
The idea behind this is that the advertising can be
made less distracting to motorists in peak hour conditions.
Actually, Laservision doesn't even need a flat wall
on which to project a recognizable image. Since a
laser beam is always in focus, it can produce an
outline image on any surface, including the curved
sails of the Sydney Opera House.
What about the drawbacks of laser advertising on
buildings? Are there any at all? Well, apart from the
need to supply the power and control requirements of
the laser, which we '11 get to in a moment, and the
possible danger of people being injured by the laser,
there aren't any real drawbacks, unless of course, you
regard the advertising itself as a drawback.
Is it possible to be injured by the laser? Absolutely.
Laservision's 5 watt laser can lighl: a cigarette at 100
metres! If it got you in the eye, you'd be blind and that
would be that. Even looking at the spot projected on a
AUGUST 1990
77
Really, when you consider the above figures, high
power lasers are hungry beasts but what little light
they put out is coherent and that's what makes laser
light so special- its concentrated beam diverges very
little over long distances and it can even write on the
clouds.
In the future, Laservision hope to be working with
solid state lasers which have much higher efficiency.
Even now, there are solid state laser arrays capable of
producing 5 watts but at present they can only work in
the infrared region.
Controlling the
light fantastic
This is the 3-phase power supply for Laservision's 5 watt
model. Rated at 14 kilowatts, it is water cooled, as is the
laser itself.
nearby wall by a 5 watt laser is painful and it can set
the wall smoking in a short time!
So clearly, the laser can only be set in such a way
that no-one is ever likely to come into contact with the
beam. In fact, there are strict guidelines set down by
the National Health and Medical Research Council of
Australia which cover the safe use of lasers.
Mind you, while the laser could light a cigarette at
100 metres and even burn a wall when focused to a
stationary spot at close range, when scanning images
at a distance there is no likelihood of damage to
buildings.
In principle, deflecting a laser beam to write a
message is simple. One mirror deflects it in the X
direction (ie, horizontal axis) while another mirror
deflects it in the Y direction (Y axis). Continuously
move both mirrors by very small amounts and the
beam can be deflected extremely rapidly to produce
an unbroken outline image which may be hundreds of
metres wide and hundreds of metres high.
Laservision's system does all this and a great deal
Laser specifications
Few people have ever come into contact with lasers
and when they have, they have usually been small
helium-neon instruments capable of putting out just a
few milliwatts. On that basis, their power supply requirements have not seemed very demanding maybe a 50 watt power supply is all that is required.
But when you scale up the power demands to feed a 5
watt laser, you realise just how inefficient these
devices really are.
Laservision commonly employs a 5 watt Argon
(blue-green) or Krypton (red) laser. These are large instruments typically measuring 114cm long, 16.5cm
wide and 18.6cm deep. They are heavy, weighing over
46 kilograms (102lbs). They use a 3-phase rack mounting power supply which looks reasonably impressive
but it is not until you look at its power input specifications that you realise just what's involved: 40 amps
per phase at 208 volts AC; that's just over 14
kilowatts!
To supply that requirement from Australian 415V
AC 3-phase mains supply takes a whopping
transformer that weighs over 95kg!
Where does all that power go'? Well, we said before
that lasers are highly inefficient devices and so virtually all that power is ultimately turned into heat by
the laser tube and its associated plasma coils. To get
rid of the heat, the laser and the power supply must be
water-cooled and in fact is fed by a substantial hose at
8.5 litres per minute.
78
SILICON CHIP
This is the 5 watt Argon laser, sitting on top of its
carrying case. In the future, solid state laser arrays will
be much more efficient and a very small fraction of the
size of this model.
This view of the laser shows the two galvanometer
scanners and their dichroic mirrors which are used to
deflect the beam. Ordinary metallised mirrors are no
good for this task as they are not sufficiently efficient as
reflectors - the laser would burn a hole straight through
them!
Moving the mirrors
While this tunnel effect looks spectacular, it is easily
produced by a laser and a rotating mirror - no fancy
laser scanning software is needed.
more. For example, in every Laservision display
(whether text, script or graphics), the image is unbroken. At no point does it start or finish - it is continuous. The control software does not reduce the apparent laser light output by blanking the laser during
a retrace line from start to finish of an image; the software cleverly makes the laser spot write the image in
such a way as to avoid any need for a retrace period.
By doing so, they not only avoid reducing the apparent light output but they also avoid the need for the
extra complication of an electronically controlled
shutter.
As you can imagine, the mirrors which deflect the
laser beam must be controlled with extreme precision.
And before we go any further we should perhaps
describe the mirrors. The mirrors used to deflect the
beam are not mirrors at all. They look like small pieces
of glass and are, in fact, dichroic filters, similar to
those used for beam splitting in colour TV cameras.
At the light wavelengths for which they are designed, dichroic filters act as more efficient reflectors
than conventional silvered (or aluminized) glass mirrors. This is important because low reflector efficiency quickly translates into heat rise and conventional
mirrors would quickly burn out - the laser literally
burns a hole right through them.
The two small dichroic mirrors are each moved
back and forth by devices which are referred to as
galvanometer scanners. In essence, these are the
same as the pointer deflection coil used in analog
multimeters. In fact, they are virtually the same as the
mirror galvanometer, a very precise instrument which
is virtually a laboratory curiosity.
Like the mirror galvanometer, these galvanometer
scanners have a centre rest position and the mirror
can be deflected symmetrically from each side of this
centre rest position. The difference is that while mirror galvanometers were very sensitive, responding to
mere microamps of current, these laser deflectors are
high power devices with very fast response times.
As well as having a fast response time, the
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galvanometer scanners have positional feedback [via
separate coils) and temperature compensation so that
the laser beam does not drift from its initial set-up
position as the temperature changes. To provide the
temperature compensation, the galvanometers have
been provided with external heaters and thermocouples.
The other reason for having positional feedback and
temperature control is to make sure that the laser
always follows the same path when scanning out a
pattern - if it did not continually follow the same
precise path [within a few millimetres at a distance of
1 kilometre) the image would be blurred and not as
bright.
In addition, the drive circuitry defines the limits of
horizontal and vertical deflection of the laser beam
[the scan "window"). This is an inbuilt safety feature
so that even if the driving software goes awry the
laser beam will not be deflected anywhere but at the
target wall.
The time for the laser to make one complete scan of
the image is typically 20 milliseconds although it
depends on how complicated the image is. Larger and
more complicated images take longer to scan but once
the scan frequency gets down below 20 Hertz or so,
flicker begins to become a problem. Interestingly, the
scan rate can be set to avoid flicker problems when
the display is being recorded on film or video and the
programming has time code facilities so that a laser
display can be precisely choreographed into a video
production schedule.
80
SILICON CHIP
Laservision can project very complex images such as this
one for a well known magazine. The images are vector
scanned in outline and not "raster scanned" as in video
technology. Note that this image is being produced in real
time, direct from the digitiser tablet.
Another interesting aspect of the software includes
the ability to "keystone" the display so that it can be
projected onto oblique roofs or for example, on the
Sydney Cricket Ground during the recent State of
Origin series. As well, images can be rotated, and
animated to blend from one to another, expand, contract and so on. It is this ability to rapidly change images which make the Laservision display so entertaining to audiences at large entertainment venues.
Apart from the power amplifiers, power supplies
and other analog control circuitry, Laservision's control hardware includes a full size digital to analog control card which fits into a Toshiba T3200 laptop computer with a plasma display. It is used in conjunction
with a digitiser panel for direct programming of the
laser display.
The photos included in this article show some of the
spectacular displays which Laservision has produced.
For us though, one of the most satisfying was the setup they did specially for the SILICON CHIP logo. They
say there is nothing like having your name up in lights.
With Laservision, that's especially true.
Acknowledgement
Acknowledgement: our thanks to Paul McCloskey of
Laservision [Aust) Pty Ltd for his assistance in the
preparation of this story and for supplying the photos.
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