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FrozenGate by Avery

HeNe Mod Hopping

daguin

daguin

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Mar 29, 2008
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I often hear people complaining about their lasers "mod hopping."

I have a HeNe that mod hops . . .

. . . and I love it.

Here are a couple of short clips so you can see how interesting it can be :angel:




Peace,
dave
 





Those are very symmetrical patterns! Those are the kind that are very neat to watch.. A lot of times with DPSS when the laser produces higher-order modes they're distended and random.
 
That is sweet.
I agree that it can be cool to watch.

A long time ago I recorded this video of some DPSS laser modes.

The camera overexposes the image a lot so the shapes are not always clear.


These are not always symmetrical, though. In reality it is much more interesting.

Thanks for sharing, Daguin. I like to see things like this.

Is this your ~40mW HeNe or a lower power one?
 
I noticed my HeNe doing weird thing like this the other night. It's much easier to see when the dot is expanded of course. I had it pointed down a long hallway, and then noticed it when I took a close look at the dot.

Is this a sign of instability? Will higher end HeNes not do this as much?
 
Most of my higher power He-Ne's mode hop to some extent, mostly in the 00-11 range. The more precise the cavity length and optical alignment the less hopping. my 20mW red tends to float from 00-10-11-00. One of my old 0.2 mW greenies(R.I.P. after 22 yrs, now has a nice purple glow) did the same.
 
That is kinda neet Dave. Never seen mode hopping in action .
 
KiLLrB said:
That is kinda neet Dave. Never seen mode hopping in action .
Click to expand...

I really like it. However, one of my motivations for recording this is that the plasma in this old tube, is getting very "pink." :cryyy:

Peace,
dave
 
KiLLrB said:
does that mean its leaking?
Click to expand...

"Leaking" isn't really the right way to think about it. Gass molecules "migrate" through the seal, being "driven" by the pressures generated by the plasma. Some gass is also driven "into" the glass and metal components of the laser. Eventually the gas mixture gets to the point where it won't lase any more. A "pinkish" plasma indicates that the percentage of oxygen in the mixture is too high

This tube was from a very old and well used particle sensor. It had MANY hours on it before I salvaged it. I have enjoyed the heck out of it for several years. However, I DO see that the end is near :cryyy: I already have to let it "sit" for increasingly longer periods to allow for the gas to "escape" from the metal so I can see it again for a short while.

Peace,
dave
 
Last edited:
This tube was from a very old and well used particle sensor. It had MANY hours on it before I salvaged it. I have enjoyed the heck out of it for several years. However, I DO see that the end is near :cryyy: I already have to let it "sit" for increasingly longer periods to allow for the gas to "escape" from the metal so I can see it again for a short while.

Is it a 1 brewster tube with a epoxy seal?
If so, have you tried the helium bag trick or the refire the getter trick, before its too late? Also you can pile on more torrseal and slow it down..

These tricks are shady, but some times they work.

Steve
 
Looks exactly like one of my mode-hopping greens. I don't mind it much, and sometimes (if i'm really bored) i'll take off the collimator and watch the funky patterns.
 
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