Focused homemade nitrogen laser?

I've seen the designs for low-cost home-built nitrogen lasers. But
these were for unfocused beams.
Is there a low-cost method to focus the beam to a spot in the range
of
say a few hundred microns wide?


Bob Clark

The divergence of a nitrogen laser can be as low as 1 mrad if I
recall
correctly. LSI used to sell a "near diffraction limited" version of
their
sealed tube nitrogen laser (they may still). It use an unstable
resonator
with the output mirror covering only 1/4 of the output aperture and a
I'm
not sure if the rear mirror was flat or curved. I did some work
using such
a laser focused to about a 50 micron diameter for laser ablation.

Bret Cannon

...
Uncle Al overstates his case a bit.
Why dont we try numbers instead of words..............
Forget 'mode structure' for most N2 lasers, there is essentially
none, they
are single pass. But neither is it *quite* 'a flasbulb'.
To a pretty good approximation crude nitrogen lasers have a
divergence
which is about d/L where d is the 'tube' (discharge, often
transverse)
diameter & L the length.
If you focus it with focal length F your spot diameter is just F*d/L

So, if you want 0.1mm, d is maybe 5mm & L maybe 200mm you would need
a 4mm
focal length, which is operating at F~0,8
You might get a UV transparent microscope objective (at a price) that
gets
near that, but its pretty challenging to put it mildly.

With a longer, thinner laser, and relax it to 'a few' hundred um
spot, and
you would get into just about achievable regimes.
With longer focal lengths, the F number falls, & aberrations are
rapidly
less of an issue - its rather far from diffraction limited!
Lens UV transparency at 337nm is an issue, especially for a thick
short
focus lens.

Harvey

...

For these homemade nitrogen lasers the tube is just filled with
air
and made of transparent plastic, so is quite cheap. Then you could
have
a tube length say the full length of your basement, say 10 meters,
10,000mm.

And you're going to excite this laser how? :)

Then for a diameter of 25mm, you would only need a focal length of
40mm to get a spot diameter of 0.1mm. How are 40mm focal length,
25mm
diameter UV lenses pricewise?

4 mm f/l lenses are quite common. That's not the problem.a

...

rgregoryclark_at_yahoo.com writes:

Sam Goldwasser wrote:
...

For these homemade nitrogen lasers the tube is just filled
with
air
and made of transparent plastic, so is quite cheap. Then you
could
have
a tube length say the full length of your basement, say 10
meters,
10,000mm.

And you're going to excite this laser how? :)

Then for a diameter of 25mm, you would only need a focal
length of
40mm to get a spot diameter of 0.1mm. How are 40mm focal
length,
25mm
diameter UV lenses pricewise?

4 mm f/l lenses are quite common. That's not the problem.a

...

How does input energy scale with the size of laser tube?

I would expect it to be linear. However, it's not only the energy,
but
the timing - getting the excitation pulse to be in sync with the
light
pulse is not trivial over any distance.

...