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Tunable Helium Neon Laser

lasingfox

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No sources needed. I’ve done it. So I’m speaking from experience. I’m basically the HeNe guru of the forum.
ah, i'll add that to my brain. thank you HeNe guru for your insight.
 



ultimatekaiser

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Its no problem. I haven’t really been around all that much, as most of the crowd that I used to spend my time with on here have pretty much all left the forum as times have changed. I’m still around time to time though, and folks like Diachi know how to get a hold of me if they need me, so I’ve kinda become hit or miss lately.

Don’t get me wrong helium soaking CAN help tubes, but there’s a variety of factors that need to be considered beforehand. And it is a very slow slow slow tedious process. In fact the only tubes I generally recommend it on anymore are old 70s and 80s spectra physics tubes of certain makes. And such specimens are quite rare, as they must be only helium deficient and not truly leaky. Most of the time either a tube is completely up to air or it is just fine- it’s very rare for it to end up in that weird middle state were only the helium is lost.
 

lasingfox

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i'll save soaking for a last resort for anything. I just hope the higher current really has that much of an effect.
 

ultimatekaiser

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That’s probably the best course of action. If you’d like to talk to me at length about it you can reach me on discord pretty easily if you have it. I’d be happy to chat and share some know-how.
 

lasingfox

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will do. i'm always happy to learn more about these beautiful things. I think i've seen you around in a few servers i'm in so i'll give you a ding if I have any more questions. thank you.
 

LSRFAQ

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Don't soak it just yet. I have He3 on order. A former HeNe glassblower is selling me his tank. I have Ne22 on station already.
In fact don't soak it at all. Helium does not as readily diffuse through Kovar and 304, the alloys mainly used in REO type construction.
It does diffuse rapidly when ancient epoxy seals or 7740 borosilicated glass instead of 7052 aluminosilicate glass are used.

Soaking in the wrong helium isotope would cause a 20-30% loss in power on the low gain lines. Soaking in some cases is just fine for VERY old red HENES, but it will do a injustice on anything other then 633nm and 1.15 u tubes. The gain mixture for green, for example, has over twice the NEON in the tube then a 633 nm tube. Contrary to popular belief the green line will lase in the normal cheap isotope mix, , but weakly.

I'd suspect your tube has plenty of HE, and the only easy way to find out is to measure the ratios of the intensities of some of the sidelight lines and compare them to a known good, healthy, tube tunable tube.

It is also very easy to reduce the gain on the non 633 lines by over or under driving the tube. They have a much narrower "sweet spot" on the current curve. Since prior owner replaced the PSU, you don't know where your at without a lot of work.

I own quite a few multiline REOs, none with the prism, but one with the Brewster, dust and current level matter big time.. In fact 594 likes lower tube current then 633 in the same tube. Same for the green, very current sensitive.

Single Isotope neon has the main effect of reducing the number of longitudinal modes lasing for a given output power, while at the same time reducing the width of the gain curve on the competing 3.39 micron line that robs power from 632.8. So a short single mode tube will tend to have an isotopic fill, making short Tem00 tubes like bar code tubes possible. Usually Ne20 is used for this purpose.

See attached, as the gain is lower, the low gain HENE lines are strongly influenced by scatter from the optics. Hence non-red HeNes use hyperpolished mirrors of some form. So there is clean enough to lase red, and clean enough to lase everything else, which are two different things.

Steve
 

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  • Knollenberg's Gain Table HENE.png
    Knollenberg's Gain Table HENE.png
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kecked

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Like he knows what he’s talking about. I mean he only got 18 lines out of a hene. He taught one Spanish too!
If steve can’t fix your hene no one can.
 

LSRFAQ

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Like he has lased:

3.39 u
1.5 u
1.15 u
1.12 u
543
588 (four wave mixing)
594
609 [four wave mixing)
604
612
639
632

650 (raman line)
730
2 more visible four wave mixing.
4 x ir four wave mixing.
And some other weak Ir stuff I have not identified yet.

I got my hands on a few of Dr Knollenberg's unbelievably perfected sealed mirror tubes with the broadband multi-line mirrors. There are some near Ir lines that are weak mixing products i haven't identified yet, but I know are coherent. So I have one more line then Sam G, simply because he hasn't had much interest in IR four wave mixing.

Steve
 
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lasingfox

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after a long tedious journey of rotating and cleaning the prism, I finally got it to lase at full power. the main issue was a thin layer of dirt on the brewster and prism which I could wipe off and with every pass, I saw an increase in power. It was incredible! I got about 3.65mW of 632.8 and unknown powers of 612nm, 604nm, 594nm.
594nm.jpg604nm.jpg612nm.jpg632.8nm.jpgorange.jpg


Then, while I was enjoying the pretty photons (which look terrible on camera) , the universe decided I had enough fun. The power supply started screaming and then conked out.. So, I had to remove the tube from the casing and I'm now looking into finding a new supply. I'm hoping I don't have to go through too much effort realigning and cleaning but, I probably will. At least I have a feel for it now so, it should be much easier. Thanks to everyone who gave me advice. It really helped out in fixing this thing up. :)
 

LSRFAQ

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after a long tedious journey of rotating and cleaning the prism, I finally got it to lase at full power. the main issue was a thin layer of dirt on the brewster and prism which I could wipe off and with every pass, I saw an increase in power. It was incredible! I got about 3.65mW of 632.8 and unknown powers of 612nm, 604nm, 594nm.
View attachment 71825View attachment 71826View attachment 71827View attachment 71828View attachment 71829


Then, while I was enjoying the pretty photons (which look terrible on camera) , the universe decided I had enough fun. The power supply started screaming and then conked out.. So, I had to remove the tube from the casing and I'm now looking into finding a new supply. I'm hoping I don't have to go through too much effort realigning and cleaning but, I probably will. At least I have a feel for it now so, it should be much easier. Thanks to everyone who gave me advice. It really helped out in fixing this thing up. :)
CALL REO and get the real specs for the PSU, its easy to install a wrong one, which will be short lived. Also if it is killing PSUs, replace the ballast resistor with a wirewound or metal film resistor of the correct value and wattage.

Steve
 

lasingfox

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May 2, 2020
Messages
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Points
18
CALL REO and get the real specs for the PSU, its easy to install a wrong one, which will be short lived. Also if it is killing PSUs, replace the ballast resistor with a wirewound or metal film resistor of the correct value and wattage.

Steve
I read that the tube needs 2.2kV and the recommended current is 5.25mA but I just sent REO an email to verify.
 




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