Re: Lasers - my $.25 worth ( thats 2 cents adjusted for inflation...)

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "skullworks"
<skullworks@...> wrote:

>
> Hi All;
>
> I have been using a Nd-YAg 60W 1064Nm since 1990. At his point the
> machine is a functional dinosaur.
>
> It uses a full height enclosed 19" rack mount to house all the

driver

> subsystems. The rack is cooled by a water to air intercooler and

the

> De-ionized water is run thru a water to water intercooler. The

main

> computer is a Motorola 68000 ( 8 whole MHz! ) on a VME chassis

with

> 2Mb ram... (Wow!)
>
> The beam exiting the laser cavity is a 8x6mm ellisp - in some
> applications we use a tunsten apature to trim the edges of the

beam

> to a perfect circle. The laser mirrors (99.5% and 100%) are
> watercooled and are outside the laser cavity. There is a high

speed

> shutter before the 100% mirror which is used to modulate beam

pulse

> freq up to 32KHz.
>
> The beam that exits the 99.5% mirror is run thru a beam expander -
> there are many reasons for a beam expander but the most important

one

> is that you now have a up to 60Watts hitting within a 8mm circle.
> This system uses mirrors on highspeed Galvos to direct the beam
> within the lense marking field. - If the beam was not expanded

these

> mirrors would be burned thru in a few seconds.
>
> The beam now goes thru the final lense group and at the proper

focal

> length is focused to a dot .1mm or less (about .0027") The galvos

can

> move the beam up to 999mm/sec.
>
> I have a program that draws sheet music - and plays the tune as it
> draws the notes. - People think thats neat. Its really simple, I

am

> hitting an object with energy - and can control the freq of the
> impact - works like an adjustable tuning fork.
>
> Back in 1990 the proper filtered safety glasses cost $640 each.

(They

> have dark green lenses resembling a #5 welding lense but with a

much

> more complex makeup - DON'T USE WELDING GOGGLES - THEY DO NOT

PROVIDE

> PROPER PROTECTION. )
>
> I've worked with HeNe, Nd-YAg, and some diode lasers. I still
> consider myself a rank amature... But I'm game if someone decides
> Lasers need there own forum.
>
> GAB
>

A few things to note:

Nd:Yag is 1064nm which most glass and plastics are transparent to
(it passes right through them)

CO2 lasers are 10,600nm, almost like a infrared heat ray. Glass and
plastics absorb almost all or totally all of this energy (little or
no laser light gets through unless it melts).

Nd:Yag goggles therefore have to have special coatings to allow
visible light (which is relatively close in wavelength 450-700nm)
where CO2 lasers you can use glass or plastic goggles from Home
Depot.

Your Nd:Yag laser is not actually 60 watts, but is more likely 10s
of kilowatts peak power (60 watts is the average power...but that is
high..most of them are like 20-30 watts average power). Most CO2
lasers are not q-switched like yag and therefore do not have such
extreme high power pulses. This is why you can't mark some metals
with CO2 but you can with YAG...other than the shorter wavelength
which is absorbed more readily by some metals, the high peak power
of the q-switched yag overcomes the surface reflectivity of the
metal.

On CO2 lasers you use beam expanders not so much to protect the
mirrors but because the formula for focus spot size depends on the
beam diameter...larger diameter can be focused to smaller spot
(sorta..more complicated that that really). Some people call these
optics "cut enhancers" or something.