Focused homemade nitrogen laser?

[[email protected]]

...
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.
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?



Bob Clark

 

[Sam Goldwasser]

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

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[[email protected]]

...

And you're going to excite this laser how?


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?



Bob Clark

 

[Sam Goldwasser]

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.

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[Harveyx]

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.

They 'could'; but given the very rapid discharge needed, it will have to be
transverse excited, & either a rather complicated delay system & one spark
gap, or lots of spark gaps...........

Realistically, a metre is a pain, & anything more pretty impractical.
250-500mm is far more the norm.

Harvey

Then for a diameter of 25mm,

Do any N2 lasers have that big a gap? Maybe, but Ive not seen one.

you would only need a focal length of

 

[Sam Goldwasser]

They 'could'; but given the very rapid discharge needed, it will have to be
transverse excited, & either a rather complicated delay system & one spark
gap, or lots of spark gaps...........

Realistically, a metre is a pain, & anything more pretty impractical.
250-500mm is far more the norm.

Harvey


Do any N2 lasers have that big a gap? Maybe, but Ive not seen one.

I think what he means is that once the beam spreads to 25 mm.....

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[[email protected]]

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.

...

OK, the problems with just using air at standard pressure may be
insurmountable for my application.

However, this page suggests homebuilt nitrogen lasers can be used for
micromachining with the lasing gas at low pressure:

The Nitrogen Gas Laser.
"This laser produces intense, short, pulses of UV radiation at 337.1nm
and is useful for applications ranging from microcutting to pumping dye
lasers. This is one of the easiest gas lasers to build 'from scratch'
although the electrical discharge circuitry must be carefully
designed."
http://www.technology.niagarac.on.ca/people/mcsele/lasers/LasersN2.htm

The page suggests a vacuum pump to get the nitrogen down to 25 torr,
about 3% of standard pressure, is simple and low cost.
This company has prices for low cost UV lenses:

UV Optics - PCX.
http://www.hiteckint.com/product/optics/leans-pcxuv.htm

They give a price for a 6mm diameter, 9 mm focal length UV lens as
about $5.00. This is a Hong Kong company however.


Bob Clark

 

[nightbat]

nightbat wrote

OK, the problems with just using air at standard pressure may be
insurmountable for my application.

However, this page suggests homebuilt nitrogen lasers can be used for
micromachining with the lasing gas at low pressure:

The Nitrogen Gas Laser.
"This laser produces intense, short, pulses of UV radiation at 337.1nm
and is useful for applications ranging from microcutting to pumping dye
lasers. This is one of the easiest gas lasers to build 'from scratch'
although the electrical discharge circuitry must be carefully
designed."
http://www.technology.niagarac.on.ca/people/mcsele/lasers/LasersN2.htm

The page suggests a vacuum pump to get the nitrogen down to 25 torr,
about 3% of standard pressure, is simple and low cost.
This company has prices for low cost UV lenses:

UV Optics - PCX.
http://www.hiteckint.com/product/optics/leans-pcxuv.htm

They give a price for a 6mm diameter, 9 mm focal length UV lens as
about $5.00. This is a Hong Kong company however.

Bob Clark

nightbat

Thanks for the relative posted subject info Bob, reference
links, and all additional info from contributing posters. Could be
useful for possible low cost contruction of initial Star Race D.R.I.L.L.

the nightbat

 

[Zak]

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?

What about using a reflector?


Thomas