612nm Multiline HeNe score

[ultimatekaiser]

1.5 -2.1mW depending on how hot I let the tube get it increases in power as it warms to a point then drops again when it gets hot.

Sounds about right. though I've seen some do more.

You sure When It first arrived on cold start it was TEM00 before it split into TEM01 and then again into TEM01*

I've already explained this. :tinfoil: its because the tube is expanding. TEM00 and TEM01* are both symmetrical, meaning that its in alignment. the only difference between them is that their spacing has changed. They're probably just on the hairy edge of being between TEM00 (circle) and TEM01* (torus), and as the tube expands from heat, it shifts modes. the TEM01 (double dot) is usually not possible on HeNes easily, but is probably the mirror going out of alignment briefly as the tube warms up. Generally all specs are only considered after 30min or more of warmup. Anything before that is not paid attention to anyway. but the torus beam is aligned. it isnt an alignment problem generally. though if you push lightly on the OC, you can limit the amount of mirror space the beam is using, intentionally misaligning it slightly and that will usually force it to a lower order mode (TEM00) as long as the bore is thin enough to keep it from changing to a TEM01 or a non symmetrical mode.

 

[bloompyle]

How can you tell just by this that its aligned? Not saying based on TEM alone, that's no reason to realign a tube, however, my LHOR increased from 1.2mw OC and 2/3rd that on the HR - to 2.1mw on the OC and 1.7 or 1.8 on the HR. Made all the extra lines really come in, and also allowed the 609 to lase.

Courtesy Sam using a key wedged in the mirror mount to lightly bend the mount. It's now my go-to method (except I use a flathead screwdriver).

 

[ultimatekaiser]

Its possible you could get a bit more power out of it, but not likely too much. I believe yours was bare to start with, and sounds like it was out of alignment from the get go from that power level. This is one of the hard to open sealed OEM heads, and its not going to have left the factory without good alignment for starters, so unless someone used it as a hammer, its not likely to have changed enough to matter.

Lazer isn't greatly knowledgeable on taking apart these heads either and trying to do so risks the tube, and for someone always asking me which end is the cathode, I dont think it'd be wise to try taking it apart. Plus, breakage aside, REO uses very thin metal mirror stems unlike the rigid wide MG ones, so every time you bend the mirror mount, you stretch it out and make it weaker, which eventually causes the mirror mounts to 'droop' and can no longer hold themselves rigid, which is a common problem on all REOs. REO heads are usually never perfect, and there's a margin of error acceptable. Plus, removing it from the head makes it unstable from even tiny drafts of air, and exposes it to continual HV and breakage dangers. The cylinder is put around the tube for a reason.

Also, think about the mirror structure. If its symmetrical, its unlikely to be out of alignment simply by nature of the reflective structure. Walking the mirrors instead may help a bit if not aligned with respect to the bore perhaps, but its already doing over its rated power, so its not really needed. If it was really out, it'd still be TEM00 due to limiting mirror access, or some other non-symmetrical mode (multiple beams from multiple reflections internally). TEM01* is basically just an expanded TEM00 because the mirrors are spaced too far apart, so it is resonating without the center. If spaced even further apart you'll actually get a dot in the middle of the torus. I know countless REO heads that behave this way, and actually even one of my HeCds is like this, being right on the verge between TEM00 and TEM01* (torus) due to the tube mirrors being ever so slightly too far apart by a hair's width-likely due to manufacturing error. So it's kinda like a shallow TEM00 with a weak center, almost TEM01* but not quite there. the reason the 604.6 is resonating in TEM01* is likely due to the extreme lack of gain in the medium as the 611.8 is hogging all of the gain medium. I'll never understand why REO uses an HR that isnt totally reflective on most of their tubes. but by carefully designing an external resonator with most of these you can do interesting things. I've actually made my LHYR-M do all the lines at once except green with extra mirrors, including a relatively strong and consistant emission at 609nm, rather than waiting for it to play on its own terms. :tinfoil:

Basically. If it ain't broke, dont try to fix it. I've broke more than one tube scrambling for that extra quarter milliwatt. It isn't worth it.

 

[LSRFAQ]

REO uses 4750 steel welded to Kovar for the optics mounts. 4750 is no where near as flexible as the pure Kovar, and has horrible hysteresis when you bend it. However it lets them use precise BK7 glass for the mirrors instead of an exotic mix that is harder to polish... They did that for a good reason, reducing surface scattering losses so all these exotic lines will lase.

Moral of the story, avoid repeated bending of REO stems. They are very stiff.

The double ended tube is lasing multimode because it is designed that way for maximum power extraction. As Kaiser said, don't remove it from the head. I have one where the previous owner extracted it, and it will only lase at full power if mounted at two points, and with one specific side up. It looses power if lased on a flat table. Steve

 

[joeyss]

My mells gritot does 2mw on my lpm at 612 when it warms up. I really wish there was another line.