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N2 Pumped Dye Laser

Anthony P

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Over the years, I have constructed several Lasers based on the Scientific American Amateur Scientist articles (Light And It's Uses). The original version of the N2 laser was word for word identical to the articles. This version 2.0 has several modifications which greatly improve performance.
In the photos, notice the most significant improvement in the use of the fire engine red paint (just kidding). First, the plexiglass plates were replaced with 2" PVC pipe. It was split by clamping it into a length of angle iron and running through table saw. This was done in 2 separate pieces due to the thickness of the saw blade. The capacitor plate was etched from FR4 board which is better than the G10 from SciAm. It has higher dielectric strength and greater heat resistance... not to mention that is much easier to find these days. Everything was assembled using JB weld. The silicon recommended by the article is a horrible choice for vacuum work. I have tested JB Weld vs Torr Seal in many a projects and the JB Weld performs as well, if not better in most cases. The power supply is a variac controlled Neon Sign transformer 3000V. When pk-pk voltage and a slight overdrive from the variac are factored in, output is 5000 VAC. This is fed into a simple 4 stage multiplier circuit for 20KVDC max. Performance is optimized when spark gap is set at 5.5-6.5mm. The final improvement is the use of actual polished quartz windows.
The cell is pretty straight forward. Pump light enters through a quartz window and laser exits through glass microscope cover slips. 1" width seemed to perform the best. No resonator is necessary, though an ordinary DCX lens at the output greatly enhances divergence.
2 special optics were used to focus the N2 beam onto the dye. The N2 beam has a bar shape which is familiar to any diode laser enthusiast. This passes through a quartz cylinder lens with a 50.8mm FL. At the back side of the N2 is a 2" dia, 20"FL concave UV enhanced Al mirror from Edmond Optic$. While not 100% necessary, it does significantly improve output.
The beam shots were difficult to photograph from a pulsed laser and I considered making a short video. Fortunately, I got lucky and was able to get some decent shots.
Finally, the dye is rhodamine 590 chloride often referred to as 6G. Concentration 1.5g/l. I have also used coumarin 450 for remarkable blue beams. The solvent was 200 proof reagent ethanol... cocktails anyone?

 



mojo_1234

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Awesome laser builds. Also have some plans to build my own TE nitrogen laser. But as usual time is limited (family & kids). When ever I'm on some business trip close to your home I would be happy to meet you and to see some of your projects. -mo-
 

Anthony P

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Thank you to everyone for your comments.
I feel obligated to warn people about the addictive nature of dye lasers. It requires only a modest effort to achieve good results... then begins the pursuit of great results.
I am in design phase of rebuilding the flash-lamp dye laser. I plan to encase the lamp in a water jacket to reduce IR emissions. A spark gap trigger will be added. I am also considering a tiny tesla coil as a trigger circuit to ionize the lamp. I fear the expense of an OC for yellow, but I will likely make the investment when the time comes. As always, I am open to suggestions.
 

paul1598419

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Did you see planters dye laser from a few years ago? If not, it is on YouTube and might be worth a watch to you.
 

Anthony P

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Did you see planters dye laser from a few years ago? If not, it is on YouTube and might be worth a watch to you.
Yes, I have watched his videos. While I am not afraid to spend some money on good laser parts, he is out of my league.:(
 

paul1598419

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I don't know if you are interested, but planters video on his dye laser included specifications for the lamp drivers. I saw it quite awhile back and hadn't actually thought that the capacitor bank needs high power discharge caps as they basically see a short circuit as they discharge to the point that the capacitor's plates deform. IIRC, planters purchased three specially made capacitors, two of which were to be used as backups when one failed.

More recently I have read Walter Koechner's Solid State Laser Engineering, which I have in a hardcover edition. It is filled with much of the information you'll need to design a good circuit for these. If you have the requisite math skills to follow along it makes much more sense, but even if you don't it is so valuable it is worth getting one.
 

Anthony P

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Thanks for the tip, Paul. I will re-watch the video looking for the cap info. My discharge will only be a fraction of what he is doing. My original version (SciAm) was simply a 5KV 15microfarad cap right into air lamp. The whole system was a little touchy, but It made super intense yellow when adjusted. This version will have higher voltage and lower capacitance, also a sparkgap switch. I will try close coupling of lamp to dye cell which should simplify the system. The elliptical reflector design is difficult to get right.

As far as the book, I will look into it. As for math, I have forgotten more math than most people ever learn. The key word there is forgotten! If I look up my old notes I can usually figure out what I need.
 

Hemlock_Mike

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It's been years for me on N2 lasers - Too Noisy!
Great work on your projects. I'm impressed.
HM
 

paul1598419

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That's great, Tony. When I was in school we used a large mainframe computer to evaluate Bessel functions that couldn't be evaluated conventionally. It was fast, but still took several minutes to get a final value. Not all the calculus is that advanced, so you shouldn't have too many problems with it. The book is worth every penny you spend to get a copy.
 

ultimatekaiser

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Did you see planters dye laser from a few years ago? If not, it is on YouTube and might be worth a watch to you.
Yes. I helped make one. There's a very similarly designed one out here I used to run. It's been long since retired though, and it does orange not yellow.
 

Alaskan

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What do you guys know about using polymer dye cells? Appears they aren't useful to make yellow unless using a wavelength doubled Q-switched ND:YAG. Anyone know the least amount of peak power possible to efficiently produce yellow with these?

 




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