Re: [CAD_CAM_EDM_DRO] Laser Project ( was Re: Laser links ?

John wrote:

> > Description says it is used for rangefinding, (RANGEFINDING WHAT?
> > LIKE THE FRIGGEN MOON MAYBE?)
>
> Good joke but you're probably quite close! :-)

No, probably ships at sea and at least 15 miles distant, with one pulse.

>
> > so I don't know if it can be converted
> > into something more useful, I would think one could lower the output
> > and increase the pulse rate proportionally, somehow or someway maybe?
>
> I worked that out as 1MJ per second but then I was using windoz calculator
> and I may have gone mad counting the 0's. That's a substantial, and very
> nice looking, laser. I think Jon is right that the price will go up on this,
> and even if it doesn't the power supply might be a bit nasty. You must be
> careful when powering these lasers because the crystal is pumped optically
> via the flash-lamp(s) on these older ones. With such a lamp, amp slopes,
> voltage slopes, discharge time and all the rest come into play such as
> energy density within the bulb. They all have an effect on the temperatures
> of the light emitted and the crystal can only be pumped using a certain band
> of the spectrum. Even though you may only want say a quarter of the actual
> power the laser can emit, inputting just one quarter of the energy may see
> you getting an 1/8th or something out due to the light emitted by the lamp
> changing the spectrum it emitts the strongest in.

No, it is VASTLY more nonlinear than that. If you reduce pump input by
10%, the output may drop by 90% or more! Most of the energy from the flashlamp
is lost as heat in the crystal and other losses. It is just barely enough energy
to cause a "population inversion" in the crystal, where slightly more than 50%
of the active medium atoms (or molecules) are in the desired excited state.
If less than 50% are excited, then the light emitted by the excited atoms will
all be absorbed by the ground-state (or lower energy state) atoms, and you
will get NO light out. If you manage to get much more than 50% of the atoms
excited, the crystal explodes.

The power supply appears to be in the laser enclosure, as expected. You can't
ship 15+ KV kiloamp pulses around on long wires, never mind the safety
implications.

The pump wavelength MUST be shorter than the laser emission wavelength,
in just about all cases of optical pumping. There are some combinations
where the active medium won't absorb particular wavelengths well. The
YAG laser is typically pumped with a Xenon flash tube, which emits essentially
blackbody radiation with a color temperature of something like 10,000 K.
There are some spectral lines in it, but they are not particularly significant.

> The newest crystal lasers are pumped with diodes, in fact, the nice
> expensive weld a car up ones are done precisely this way and then pulsing is
> easy at H.F. The diodes emit the exact band the crystal wants to absorb so
> you see the laser getting a massive efficiency of input to output
> conversion.

Not much better efficiency. In fact worse, as you're pumping a laser with another
laser. But, they can run for thousands of hours without trouble, and losing a
pump diode doesn't bring the whole laser down, you just lose a few % output.
Getting away from high voltage underwater and exploding flashlamps made
these laser a lot more accepted in industry.

> El probolem is the price tag and supply used for the diodes. You
> may buy a gold plated diode array that can output something stupid like 200
> watts in a single band (And it'll fit in your palm), but that costs evil
> amounts of money and the supplies are usually about the same price. Crystal
> lasers look beautiful inside with all those gold mirrors! :-)

The diode laser bars are not really that much more expensive than the commercial
YAG-flashlamp systems, at least if you include the operational costs. But, yes,
WAY out of the price range for the home shop!

Jon