If you need assistance, please send an email to forum at 4hv dot org. To ensure your email is not marked as spam, please include the phrase "4hv help" in the subject line. You can also find assistance via IRC, at irc.shadowworld.net, room #hvcomm.
Support 4hv.org!
Donate:
4hv.org is hosted on a dedicated server. Unfortunately, this server costs and we rely on the help of site members to keep 4hv.org running. Please consider donating. We will place your name on the thanks list and you'll be helping to keep 4hv.org alive and free for everyone. Members whose names appear in red bold have donated recently. Green bold denotes those who have recently donated to keep the server carbon neutral.
Special Thanks To:
Aaron Holmes
Aaron Wheeler
Adam Horden
Alan Scrimgeour
Andre
Andrew Haynes
Anonymous000
asabase
Austin Weil
barney
Barry
Bert Hickman
Bill Kukowski
Blitzorn
Brandon Paradelas
Bruce Bowling
BubeeMike
Byong Park
Cesiumsponge
Chris F.
Chris Hooper
Corey Worthington
Derek Woodroffe
Dalus
Dan Strother
Daniel Davis
Daniel Uhrenholt
datasheetarchive
Dave Billington
Dave Marshall
David F.
Dennis Rogers
drelectrix
Dr. John Gudenas
Dr. Spark
E.TexasTesla
eastvoltresearch
Eirik Taylor
Erik Dyakov
Erlend^SE
Finn Hammer
Firebug24k
GalliumMan
Gary Peterson
George Slade
GhostNull
Gordon Mcknight
Graham Armitage
Grant
GreySoul
Henry H
IamSmooth
In memory of Leo Powning
Jacob Cash
James Howells
James Pawson
Jeff Greenfield
Jeff Thomas
Jesse Frost
Jim Mitchell
jlr134
Joe Mastroianni
John Forcina
John Oberg
John Willcutt
Jon Newcomb
klugesmith
Leslie Wright
Lutz Hoffman
Mads Barnkob
Martin King
Mats Karlsson
Matt Gibson
Matthew Guidry
mbd
Michael D'Angelo
Mikkel
mileswaldron
mister_rf
Neil Foster
Nick de Smith
Nick Soroka
nicklenorp
Nik
Norman Stanley
Patrick Coleman
Paul Brodie
Paul Jordan
Paul Montgomery
Ped
Peter Krogen
Peter Terren
PhilGood
Richard Feldman
Robert Bush
Royce Bailey
Scott Fusare
Scott Newman
smiffy
Stella
Steven Busic
Steve Conner
Steve Jones
Steve Ward
Sulaiman
Thomas Coyle
Thomas A. Wallace
Thomas W
Timo
Torch
Ulf Jonsson
vasil
Vaxian
vladi mazzilli
wastehl
Weston
William Kim
William N.
William Stehl
Wesley Venis
The aforementioned have contributed financially to the continuing triumph of 4hv.org. They are deserving of my most heartfelt thanks.
Registered Member #1667
Joined: Sat Aug 30 2008, 09:57PM
Location:
Posts: 373
radhoo wrote ...
So you're saying I can simply use one of these: and forget about the vacuum pump at all?
Well, see for yourself:
The higher the pressure, the narrower the pumping window, we're talking about ~1ns for nitrogen at atmospheric pressure. There exists a relation for the lifetime of the excited level as a function of the operating pressure: A peaking capacitor is introduced to compensate for the "slow" marx bank. In my opinion, it is worth reducing the pressure to buy some time to pump the laser medium. Cut 6 doorknob capacitors in the design and you'll have the money to buy a single stage vacuum pump off ebay.
The cool thing with peaker caps is that you can put a coaxial cable in between the laser head (tube and peaker cap) and the pulse generator itself.
ps. just read the wiki article that now covers some quite interesting topics. I haven't thought of diffraction limits yet. I like the thought of having graded index refocusing lenses inside my laser made entirely out of plasma! (a parabolic radial fall-off of the index of refraction is ideal for lenses and behaves much like an aspheric lens.
Registered Member #1938
Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 699
hboy007 wrote ...
Well, see for yourself:
Very inspiring, the topic in this thread becomes more exciting with each day. I would also want to try this, given the fact that I also have some 30KV doorknob capacitors, and maybe also try to reduce the pressure by using a fridge compressor . I am tempted in trying to seal the lasing chamber, so it would not require the pump . Any comments on this?
It would be great if you could put more pics of your setup, including some close-ups. A simplified circuit diagram would also be appreciated.
Registered Member #1667
Joined: Sat Aug 30 2008, 09:57PM
Location:
Posts: 373
I also planned to seal the laser but the first reservoir I built was kinda lame so I left it out.
A few words to the schematic drawing. One of the builders claims that the spark gap in parallel to one of the caps forms a resonant circuit and produces a negative half-wave pulse that adds to the voltage drop across the tube. This may be a contributing factor. A quick estimation (nano Farad caps, nano Henry parasitic inductance, T/2 = pi*sqrt(LC)) suggests that the negative pulse occurs on the nanosecond scale.
However, I think that for low pressure laser tubes, the breakdown voltage is reached before inversion can occur. A 30cm long tube can be ignited with around 10-15kV and when using the resonant circuit as a voltage source in series to the "main" capacitor C2, it should be C1 >= C2 (don't forget the energy dumped into the spark gap plasma). Still there arises the question what time scale we are talking about. A typical discharge may last 100-200ns with the laser terminating at 20ns after the pumping process begins. Assuming the negative half-wave contributes to the active pump phase, inversion would have to occur within 10ns after the SG fires. Even SGs themselves aren't that fast, they have a rise time of a few to a few tens of ns.
Effective usage of an inversion effect may rely on small capacitors and a high resonant frequency of the series peak voltage source. Assuming the laser operates at higher pressures, higher voltages are needed to ignite the tube and reach inversion. Then a parasitic resonant circuit may be a promoting factor for laser operation. As for my design (C2 > C1), I assume that the energy from C1 is burnt up in the SG flash to some extent, leaving C2 connected to the tube terminals with a low resistance plasma path. A fraction of the energy stored in C1 is stored in and radiated from the magnetic field around the conductors.
Operation modes could be investigated by changing the C2/C1 ratio and their values in respect to the operating pressure and the time window implied by the pressure.
Registered Member #1938
Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 699
Thank you for the well documented explanations, as well for the quality circuit diagram. Just a suggestion, you could edit the first thread to make it contain all the vital info: working principle, formulas, schematics, etc. Some readers appreciate to have everything concentrated in one post, instead of having the info scattered through all the thread.
Off-topic: how to do cut the plexiglass to get clear, clean edges? Is there any good transparent adhesive for plexi?
Can you provide more details on heating the epoxy as well, I see that you have a special technique for making the mixture better. Since epoxy is one of the key ingredients of this design, I believe it might prove useful.
Registered Member #1667
Joined: Sat Aug 30 2008, 09:57PM
Location:
Posts: 373
Looking back at the documentation I wrote for myself there is definitively a need to write it all up again. That would also require to work through some literature again and aggregate the references. Please be patient, I'm currently finishing a (commercial) software project that will help me finance my study. Apart from that, I'm working on a motorized tripod head (I'm a passionate photographer and love 360° panoramas). There is a lot more to do for my homepage, two other projects need documenting. When I pick this up, I shall take the time and rewrite some articles in English, too.
Getting plexiglass clear is a bit of a pain. It can be sanded in multiple steps and the finishing is done by flame polishing. This in turn leaves strong tensile forces in the surface layer of the plexiglass sheet that lead to cracking when gluing, fusing or cleaning the material with solvents.
The gold standard for plexiglass processing is diamond polishing. I have yet to find a company that accepts prototype and low volume jobs. The guys I found via youtube, e.g. were not cooperative.
As for the epoxy, I have both worked with "Uhu Endfest 300" which is a 2K glue and a resin flooring mixture. It may be quite instructive to get a pack of epoxy compounds for electronics potting. Compared to the glue, it is affordable to play around with. I've seen epoxy harden within a few minutes after a runaway chemical reaction. Larger volumes can reach temperatures in excess of 100°C.
The glue liquefies when being heated, then starts to cure. I'd have to try that again to tell you exactly what it looks like when it's done but at least you can stop heating when the curing becomes noticeable.
ps. there are fusing agents that glue plexiglass faces without leaving marks. You can also try Methacrylate glue that polymerizes.
Registered Member #2941
Joined: Fri Jun 25 2010, 08:08AM
Location:
Posts: 143
radhoo wrote ...
Cedric, I have a few questions regarding your test as well.
cedric wrote ...
I get it to laze, with the fridge pump !!!
Can you elaborate on this part, and maybe provide more pictures, videos, details? How good is a fridge compressor for this purpose? I have one at hand, and it would be my first option in trying this kind of laser. Also can poor vacuum be compensated by higher voltages?
cedric wrote ...
I am not there yet,the lazing is very hieratic ,the beam is not so bright and the beam profile is not very nice ,but all together ,now that I know how to do it ,I am planing to build one bigger (10 cm tube with internal diameter of 6 mm),same capacitor ,and steadier construction, of course I will need better vacuum . I also think this type of setup is perfect for pulse multigas laser (given enough power and a resonator it's possible to laze about anything
Can you try adding a little NaHCO3 inside the tube, the plasma should heat it up and release CO2. I am curious if it changes anything having CO2 inside (2NaHCO3 → Na2CO3 + H2O + CO2 → Na2O + 2CO2 + H2O ) Or adding a little mercury for a mercury vapor atmosphere inside the tube. Just a few ideas, to see if it would still laze.
sorry it took me a bit of time to answer, I don't have any picture or video of the working laser with the pump and since I disassemble it to make a new better one I can not take picture anymore. the fridge compressor is just a regular fridge compressor ,to my understanding it work in this case because the channel in narrow (2.5 mm) and short (7 cm),I think that if I had a better pump it would work better. I notice that while running it ,lasing would take place only if I archive a discharge through the tube and not just ionization,in tea laser ,it's not a requirement .as hboy007 mention it ,nitrogen is a really high gain medium ,a spark in between two mirror might be enough to get lazing ,the big difference in between atmospheric pressure and low pressure laser is about the rising time of the electrical pulse .with a conventional spark gap the rise time is about 10 ns,and the time for population inversion with low pressure nitrogen in about 20 to 30 ns ,witch mean that for low pressure laser ,much more of the electric pulse can be use to pump the medium. I join some picture of the pump and the new laser...
I am building a new prototype ,much better done ,using ceramic tube and a vacuum reservoir ,I am looking forward to test other gas ,like co2 ,argon ,krypton ,the difficulty is to find suitable optic ,I won't try mercury since the electrode are in aluminum and that would lead to there destruction.
Registered Member #1667
Joined: Sat Aug 30 2008, 09:57PM
Location:
Posts: 373
I was wondering, too. I hope the aluminium tape / foil is just a means of protection during construction.
As for the window, I've tested and approved of BK7 microscope slides:
My power supply is a homebrew offline flyback converter base on a TV flyback transformer and a BU2508AF transistor with signal generator and driver circuitry.
Registered Member #2941
Joined: Fri Jun 25 2010, 08:08AM
Location:
Posts: 143
well of course the aluminum tape is not part of the optic it was there to protect the laser channel from dust, for the tube I use ceramic because I had one tube of the right length and because my previous glass tube broke du to arcing (at list this one is a good dielectric )it's a bargain, I agree with hboy007 that a narrow channel is better for lazing ,but if the vacuum is deep enough large bore might work just as well. also and it might sound trivial ,with my previous one I get lazing photon bouncing from the wall cavity giving this weird half circle near the dot, I south at list I won't have this problem, + the optic tuning should be more easy with a large tube. I also integrated a vacuum container and a vacuum valve in the aluminum block at the end ,so fare the vacuum since to hold ,but I will know only once I get a decent pump... the power supply is fly-back base ,with a pwm switching a laptop power supply ...
the last picture is a (very bad) x-ray of the valve, the vacuum tank is visible under it, close by a steel ball..
This site is powered by e107, which is released under the GNU GPL License. All work on this site, except where otherwise noted, is licensed under a Creative Commons Attribution-ShareAlike 2.5 License. By submitting any information to this site, you agree that anything submitted will be so licensed. Please read our Disclaimer and Policies page for information on your rights and responsibilities regarding this site.
longitudinal excitation nitrogen laser
