Tweaking a He-Ne laser.

I've got a few melles-griot tubes and by the looks of them, there are 2 ruby rods at both ends, and in the tube itself is a He-Ne lamp.

The power is about 1 MW, so that's peanuts.

I was thinking of removing the middle part, and putting a Xenon bulb like used in automotive lightning between the two end-caps holding the ruby rods, resulting in more output power.

The question is, am I likely to do something useless, or not?

This is the tube in question.

The HeNe mix is emitting the light. There are no ruby rods.

Your modification will permanently destroy the laser.

-Trevor

That's what I call a swift reply, I always thought that in these kinds of lasers ruby was involved, my bad then.

Thanks for the heads up.

Love these little bare-tube HeNe's though. They're gems; enjoy it.

-Trevor

Yep. Trevor is correct. Just leave them alone, there is nothing you can do increase power and anything you try will likely kill the tube. These are gas filled tubes no rubies involved.

Still begs the question, how come the emitted light is red, and what are the rods made of, any idea?

Google "Sam's Laser FAQ."

HeNe lasers do not have any rods. A high voltage discharge is pumped into the HeNe mix. That excites the gases to higher energy levels. Without going into a ton of detail, the amount of energy released when an electron in a neon atom drops back to its normal state corresponds to the photon energy of one of your red photons.

No laser rods. The "rods" you see contain the high reflector and the output coupler.

-Trevor

i believe the lens at the end dictates the light output. the hene mix i've read puts out all wave lengths. all tubes glow red. even a 543nm green.

michael.

chipdouglas said:

i believe the lens at the end dictates the light output. the hene mix i've read puts out all wave lengths. all tubes glow red. even a 543nm green.

michael.

Click to expand...

Correct. The mirrors are coated to be reflective at the wavelength that should be allowed to resonate within the cavity.

-Trevor

READ...Sam's Laser FAQ
READ...LPF.(the search area is a HUGE wealth of information)

It can be very rewarding if you are really interested in a subject to read as much as you can. You will also learn a lot you did not even think of to begin with.

The questions you are asking are the very basics of HeNe laser technology, it just seems that so many people are just looking for a quick easy answer to their every question without doing even the most basic research on their own.

Yep Sam's is a great place to gather information. Admittedly it's sometimes a little dry reading and a bunch of it is still over my head.

Think of it this way butthead. You wouldn't expect a ruby to be inside a neon "Open Sign" and many of those glow red. As has been already said, it's really just a gas being turned into plasma via high voltage. The mirrors that are involved help turn this plasma into a laser beam.

Never got the chance to try this, but adding a string of magnets to a He/Ne
can bring the output up a bit..

Sam's Laser FAQ - Helium-Neon Lasers

wannaburn said:

Never got the chance to try this, but adding a string of magnets to a He/Ne
can bring the output up a bit..

Sam's Laser FAQ - Helium-Neon Lasers

Click to expand...

I remember reading about this....it's a neat idea and combines two of my favorite science do-dads.....magnets and lasers!

I honestly thought this post was a joke at first. Yes, stop right now and read the FAQ, it could save you from injury or at the very least, save you from coming off as a fool. Your HeNe tubes will also be better off if you have at least a basic understanding of how they work and how to care for them.

A 1MW tube would be 1,000,000 Watts, and would be impressive indeed. Clearly you meant 1mW, in this case capitalization makes a BIG difference.

Neon has several different gain lines that can be made to lase. Which one you get is determined by the wavelength the mirrors are designed to reflect. The ratio of bore diameter to tube length and gas fill pressure are also optimized for a specific wavelength. With the exception of one of the (boring) IR lines, red has the highest gain of any. While there are a few exceptions, small "other color" tubes are exceptionally rare. There just isn't enough gain to get meaningful green, yellow or orange output in a tube under about a foot in length.

With larger tubes you can occasionally get flashes of colors other than what the tube is designed to produce by fiddling with carefully aligned external mirrors, I've coerced brief flashes of green out of my yellow HeNe and orange out of one of the larger red ones but there is no practical way to change the beam color of an existing tube. The tubes you have were made for barcode scanners which used HeNe tubes up until the mid 90s or so. If you want one to take apart and play with, contact Sam Goldwasser, he gave me numerous dead tubes for display and experimentation.

^^The only downside to extending the cavity like you mention, is that you can only go one way. You can't really get a 543 tube to spit out any yellow or red.



Neat trick though. I will have to find myself a proper mirror first..

That may be true, I haven't got it to go the other way but I'm not sure if it's possible or not. I think it depends a lot on the HR as well, if it's too wavelength specific you would need an external mirror on the back end too.

I used a small dichro I got out of a DVD burner sled. I turned an aluminum disk and drilled it to fit the end of a laser head and put small springs on the screws so I could adjust the alignment. It's not stable by any means but I have managed to get flashes of pure green as well as mixtures of green and yellow sustained for several seconds at a time out of a yellow tube. The alignment is extremely critical and it takes patience to get anything. It's useless, but neat.