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longitudinal excitation nitrogen laser

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hboy007

Mon Mar 30 2009, 02:10PM

Registered Member #1667 Joined: Sat Aug 30 2008, 09:57PM
Location:
Posts: 373

Now here is one of my recently finished projects I want to share with you, it's a LE nitrogen/air laser with an optical resonator working at 1-10mbar and 25-30kV.

It took me about 15 months to get this laser finished, mainly because I am occupied with my studies but as time tells I managed to get it done. So here are a few pieces of information about this laser:

I use three pulse capacitors rated 1nF/40kV, one in parallel to the enclosed spark gap, 2nF in series. The end points of this circuit are connected to a choke and the discharge tube.

the laser channel consists of a 120mm glass capillary with a bore of 2mm

the resonator consists of a first surface aluminium mirror (~87% reflectivity at 337nm) and microscope slide (~8% reflectivity)

The main concept was to completely seal the tube by soldering tubes and using epoxy glue. I am still looking for a pressure reservoir, so far the laser remains connected to my double-stage rotary vane vacuum pump. I am looking forward to operating the laser without a pump.
Mirror and output window are glued to brass tubes that can be precisely adjusted and sealed to copper tubes that connect to the capillary. I performed adjustment using a 2mW HeNe tube, one can see good resonator alignment when observing the screen image of the widened, reflected and transmitted beam because the optical resonator can also work as a Fabry Perot interferometer when multiple orders interfere.

Once the tubes are glued air-tight to each other, only minor optimisations are possible (but that has proven to be enough).

LE nitrogen lasers are hard to find on the net, I know of only 3 other people that built this type of laser because higher output powers can be achieved using a "TE" topology and from different variations of a technology only the strongest ones survive. Back in the days when I started this project, 405nm laser diodes were quite expensive, now I bought two laser diodes for the price I paid solely for the parts of this laser.

Videos
I made a video from the running device

and a little presentation that illustrates the process of creation

I would be delighted to see more LE lasers... If you find or build one, please let me know.
Have a nice day

hboy007

plazmatron

Sat Apr 04 2009, 01:23PM

Registered Member #1134 Joined: Tue Nov 20 2007, 04:39PM
Location: Bonnie Scotland
Posts: 351

That is VERY cool.

I have never tried an LE Nitrogen Laser before, since as you say much higher powers are available with TE.
Mine is at:
http://www.fineartradiography.com/hobbies/lasers/nitrogen/index.html

Tell me, Have you tried pumping dyes with this it? A compact Nitrogen pumped Dye laser would be neat!

Leslie

hboy007

Sat Apr 04 2009, 06:43PM

Registered Member #1667 Joined: Sat Aug 30 2008, 09:57PM
Location:
Posts: 373

Thank you, Leslie. I remember your page, I happened to visit it about a year ago when I was searching the net for more nitrogen laser builders' sites and you did a great job. Hopefully I will manage to build an external trigger for the spark gap. I will then test how high the pulse rate can be pushed without suffering deexcitation problems and thermal lensing that seem to plague static fillings. I do however not have high hopes to be successful in pumping a dye laser or if I manage to get a dye to lase, the output will not be overwhelming. Single pulses on the photos look very bright and they actually are but I imagine a lot of trouble exciting a dye solution in a longitudinal setup ( these dielectric mirrors will be fun to get hands on for a reasonable price ).

The schedule for the longitudinal laser looks as follows:
- include sg trigger
- finish alignment process (there is still potential for improvements)
- build a simple 2-axes cnc table
- expose PCBs, photo paper, blueprints, ... do lots of fun stuff like hardening paint and so on

even with my 405nm laser diode lying around on my desk right now I can't withstand the temptation to see the initial plan work out in the end.

As for compact nitrogen lasers, I intend to build a miniature TE laser with optical reasonator and two 470p capacitors. A three phase motor from a harddrive or laser printer could be used to force gas flow along the channel as these motors are considerably small, powerful, brushless and readily available. Using a portable power supply I aim at rep. rates as high as 50-100 Hz, the more the better. the entire setup should fit into a 50mm PP tube, giving it a "laser pointer"-like touch. If I manage to build anything useful I will let you know :)

cedric

Wed Oct 19 2011, 12:24PM

Registered Member #2941 Joined: Fri Jun 25 2010, 08:08AM
Location:
Posts: 143

very inspiring work you have done here ,
I want to make a similar project and I have most of what I need for it ,except a decent vacuum pump (I have one ,but unfortunately it run in 3 phase and I only have 220v 1 phase),I also have a fridge compressor who can pump down to -100 kpa ,but not feather,I south of a way to reduce the need for deep vacuum by making the laser tube shorter (down to about 8 cm) my question is: how did you determine the optimal tube length and diameter?
I have an other question : does the size of the electrode inside the laser tube is critical or not (right now they would be around 2 or 3 mm on each side)

hboy007

Wed Oct 19 2011, 01:15PM

Registered Member #1667 Joined: Sat Aug 30 2008, 09:57PM
Location:
Posts: 373

dear cedric, I'm very excited to hear you're going to build such a laser, too. Since you can to some extent adjust the channel current density by changing the trigger voltage of the gap and the size of the pump capacitor, the major parameter becomes the operating pressure. Have you tried the "Steinmetzschaltung"

yet? I'm operating one of my pumps with a capacitor. Forget about the fridge compressor. I observed that a degassing period is needed (no controlled air leak, good vacuum, high voltage connected). That may be enough th drive out most of the adsorbed water. A fellow laser enthuisast has built a hefty longitudinal N2 laser with a wide and long tube that is also operational (adrian-homelab.de, currently infected with malware, I've sent him a message).

As for the electrode: most lasers and low pressure discharge lamps and ion sources have electrodes with large surface areas. Sputtering may be a concern but I am not aware of a physical limitation to the field electron emission current density other than the collapse of the electrical field by space charges. It is very hard to get estimates for such influences.

So don't worry, shortening the channel will come at the expense of reduced gain but judging from the results of my experiment, there is room for that. Perhaps the threshold voltage will increase by 3-5 kV but other than that you'll be fine.

ps. there you go:

pps.: this build may be also be interesting:

radhoo

Wed Oct 19 2011, 02:06PM

Registered Member #1938 Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 699

very nice laser and project!

Turkey9

Thu Oct 20 2011, 03:17AM

Registered Member #1451 Joined: Wed Apr 23 2008, 03:48AM
Location: Boulder, Co
Posts: 661

Wow this is a very well built project. I tried to build a few different nitrogen lasers a few years back with no success. Do by any chance have a build-along or more details of construction? Again, great job!

radhoo

Thu Oct 20 2011, 09:49AM

Registered Member #1938 Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 699

Turkey9 wrote ...

Wow this is a very well built project. I tried to build a few different nitrogen lasers a few years back with no success. Do by any chance have a build-along or more details of construction? Again, great job!

Maybe the author of this project could provide more details.

hboy007

Thu Oct 20 2011, 10:05AM

Registered Member #1667 Joined: Sat Aug 30 2008, 09:57PM
Location:
Posts: 373

As for my part... a documentation exists but it was never intented for the public. I think of it as a blog entry to keep in mind what I spend my time with. Apologies for writing it in German. You can find it here

cedric

Thu Oct 20 2011, 10:14AM

Registered Member #2941 Joined: Fri Jun 25 2010, 08:08AM
Location:
Posts: 143

Dear hboy007

thanks for your fast answer,
yesterday I finish a test set up of the laser and try it(I didn't tune the resonator)
as you say ,the fridge compressor is useless,I can not even get an uniform plasma in the tube from it,I did try various way to run my vacuum pump using capacitor and it work but each time the engine get very hot in less than 5 minutes (sniff..)
I also find a way to increase the surface of the electrode ,I have now about a 1 cm2 on both side ,
my set up is a bit different than yours ,and the tube is passing very close from the positive contact plate of the capacitor (through it to be precise)it simplified a lot the construction but yesterday ,wile running test at high ppm the glass tube broke du to arcing,I instal a dielectric in between the tube and the aluminium plate to correcte this problem ,I joint a picture of the set up so people can tell me if there is any obvious flow ...

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