A laser that BURNS!!
Since getting into lasers, I've always wanted one which will actually BURN STUFF. apart
from a pathetic little 200mw 980nm diode I had which would just about burn a pinpoint spot
into black paper, I knew a CO2 laser was what I needed, preferably a sealed tube type to
avoid all the vacuum pump and gas mix hassles.
I've been keeping an eye on a regular medical auction house here in the UK, and last week
spotted a Sharplan 1025 in their catalogue. A little research on the net showed this to be
a 25 watt sealed CO2 unit - Time for an early start to drive the 3-hour trip down there.
I knew from past sales that it was likely to go pretty cheaply (the last sale saw an 80W
YAG go for £150), and the saleroom was less busy than usual due to holidays. There was
only one other bidder interested in the laser - the auctioneer started at £200, I held my
breath for him to drop it when there were no bids, and when he went to £100, the other
bidder chipped in. After what seemed like loads of bids, I won it for £230 (£257 after
the buyer's premium). Of course I was taking a bit of gamble as I had no idea of the
condition of the tube, but figured out that if it was totally shot I could get some money
back by selling the optics and PSU on Ebay.... fortunately this proved not to be
nceessary...!
Of course the first thing to do was pull the cover off. I was amazed
at how big the tube was - just over 2 feet long. For no particularly good reason,
I'd always pictured them as being the same size as HeNe tubes. A small spider had made its
home in a corner of the case...!
Before anything more could be done, I had to 'take care' of the key switch as there was no
key (right). Inside, I was surprised at how much stuff was crammed into the very compact
case (about the size of 2 upright vacuum cleaners strapped together). Apart from the huge
tube, there is a closed-circuit liquid cooling system, power supply, HeNe tube for aiming,
and assorted control circuitry etc.
A nice little surprise - on opening a little door in the top I found a
collection of accessories, including the all-important lens that focuses the bam into a
concentrated spot. The very long 10.6 micron wavelength of CO2 lasers means that very few
materials are sufficiently transparent to use as optics. Zinc selenide is one such
material - I suspect this is what the lens is made of.
there were also a few guide tubes and mirror attachments for burning round corners...
OK, time to rock.... but first some protective eyewear (right) most
materials are opaque to the long 10.6um wavelength of a CO2 laser, so apparently clear
goggles provide good protection (until they get a hole burned through them...).
On applying power, it made some assorted clicky noises, and then a continuous gentle
gurgle as the cooling system started pumping coolant around the tube. The pump sounded
like it was having a bit of a hard time, and the display said "low coolant
flow", but it seemed happy to power up anyway, and allow a power level to be set.
I set the power level at 5W and aimed a short pulse at a cardboard box, and was rewarded
with a little brown burn-mark - YES...! IT WORKS!!!!
Time to crank up the power....
(left) At 20 watts, the focussed beam produces an instant fire-spot
on a block of hardwood
>Writing my name in fire..!
Removing the lens allows stuff to be burnt at a distance - (left)
cardboard box at 3 feet, (right) fax paper at 8 feet.
In pulse mode (50ms pulses) it blew cute smoke rings from a plastic
bottle - the plastic fumes were a bit nasty though (cough, splutter!).
>Talking of nasty fumes - it's fun to be able to drill holes in foam rubber...
< Drilling holes in 3mm acrylic (Plexi)
sheet - a good demo that the long CO2 wavelength does't pass through clear plastic. Before
firing, you can see the red HeNe beam coming out the other side, but the instant the laser
is fired, the HeNe spot disappears as the surface of the plastic distorts.
Internal view. Tube is vertically mounted
on the left, mostly obscured by all the other gubbins like cooling etc.
(right). I started blasting various flammable things around the garage, including this cardboard box, but in the excitement of looking for other stuff to attack, I didn't notice that one of the burn marks had also developed a little flame, and soon noticed a strong smell of burning as the flame took hold.... now where did I put that fire extinguisher....?
