Spectra Physics-107 fine alignment help?

So this is my pride and joy of my gas lasers, my Spectra Physics 107 (Resonator Length 95cm).
I'll use this thread to try to document my endeavor to improve the power and to ask some questions.


First I'll show some pics.


laser^


OC Mirror mount^


getter^ (I think?)


IR suppression magnets ^

It came out of a projector from a planetarium, and has a sticker on it that says " 38mW 1/23/? " . The year has a scratch on it so I can't tell what year.

Now that I just borrowed a nice LPM I can do more precise alignment on it.
Both of the mirror mounts course adjustment 7/16 nuts have been adjusted to give max output. I have not touched the fine adjustment set screws at all.
I find that if I pull up on one or both mirror mounts that I can get a max increase of about 40% (18mW -> 25mW, Actual power may be different). I'm not sure how to keep it at that max, or if there are other options.

And the questions:
-Can you run it continuously(>20min). Rephrase: do I have to worry about it over heating? After a few minutes I can tell the tube is warm but the resistors are HOT. I'm pretty curtain it can be run for continuously, but I want to be sure.

-Does it need to be cleaned (Brewster windows & the outside of tube)? Does cleaning the brewster windows increase the power much? And would cleaning the outside of the tube be safe enough?

-Is it hard sealed, I believe it is from 1989-1987. To my understanding all newer tubes are hard sealed.

-Are there any other tips/info I should know



Some links to Sam's laser FAQ that I found interesting:
Sam's Laser FAQ - Commercial Unstabilized HeNe Lasers
Sam's Laser FAQ - HeNe Laser Testing, Adjustment, Repair

The reason why lifting it helps the alignment, is something known as "cathode sagging".

Think of it like to tennis players having a volley. In a perfect tube, that ball would never tough the ground.

In this analogy, the tennis players are mirrors, the ball is a photon, and the ground is the bore wall. In your situation, the light is being reflected around the bore, and bouncing off the bore, etc. If you were to watch your output in ultra slow motion, you may even see a spiral form.

If the mirrors were planar-planar, it wouldn't matter where the mirror was, as long as it was parallel. However, in this case, their is a curve in them. One, or both, is concaved. So if light doesn't hit dead center, it gets all squibbly.

The only reason your tube still lases well has to do with the immense cavity length. There are a lot of tennis balls being hit around.

I haven't had the opportunity to play with a 107/127 hands-on. However, if there is an adjustment for elevating a mirror, that may be your best bet. Large frame HeNes share this issue with the noble gas ions as well. I believe there are remedies for this issue, but I've never needed to locate one.

Try searching around for "laser cathode sagging" in Google or PL.

Best of luck!!!

I can help you with this. Do you have Skype? It's hard to type it all out it's pretty long. But if it's already lasing it's easy with some care. The anode end is obviously the OC , and is concave and the HR is on the cathode end, and it is planar.

Generally you shouldn't have to clean or realign it at all. All the surfaces are covered by the rubber boots. But I'd start with bore alignment. It sounds like the bore is out, and the ends have been pushed down. You can adjust them easily with certain screws on the resonator. I have a 127, so I can walk you through it. I'll warn you that it takes a lot of patience, and you run the risks of critically damaging it. I was going to post a guide on it soon, I've just not had time to write it and upload the tons of pics. It'll be like a short novel...

Edit: no the tube shouldn't overheat if it's being driven properly. It will get hot however, so do note not to touch too much. Your getter also looks somewhat weak, so it's possible it's just lost some power with age. And yes they are hard seal tubes.

Unfortunately I do not have Skype. Home computer doesn't have a camera, but I might be able to use a smart phone.

Yeah most smartphones have it as an app. Or if not a phone call perhaps. It's just easier to talk about it, rather than type it out. I'm making a guide, but I'm not sure when I will be finished with it.

I know it's hard to know for sure, but approximately how much time would it take to align it. <5hr, >10hr?

It depends on weather you have done it before and how good you are at it. Myself, for instance, it would
take an indeterminate amount of time spanning weeks or months, depending on how many times I
dropped the mirror and any potential replacement mirrors. :banghead:

Generally a couple hours if you're in a clean room and with proper equipment. At home on the floor....? Whole different ball game. I'm doing mine as we speak. And it's quite a pain in the ass, and is an ongoing project to perfect it. The tube is so long there is maybe a tenth of a turn at most of any nut, before a total loss. And that's with the other mirror perfect. General alignment wise....far less. Let's put it this way - if you're seeking alignment by randomly twisting the nuts, your odds of getting a beam at all are probably on par with winning the lottery jackpot.

Maybe from scratch takes a few hours your first time, but if it's already lasing it's a lot quicker. <20 minutes is my wild guess.

Did you ever end up doing this? I just realigned my 127 finally, and it took about three hours from scratch + fine tuning. Since yours is already lazing I would say you should devote at least an hour. You'll also need a very sensitive LPM if you want absolutely maximize what you get. The majority of the adjustment you'll probably ever have to make are in the bore. Going to go ahead and make a new thread on the process later after I get off work, as it will be quite an extensive post.

Don't know why I missed this thread until now.

Batman - Those Wonderful Toys - YouTube

I too am interested in your results.

Also, it wasn't answered, but yes, cleaning the brewster windows will greatly help in maximizing output. Dust gets electrostatically attracted to the glass even in the cleanest environments.

Yes although in a perfect world, nothing in this laser should get dirty because it's all covered. But inevitably we all know it doesn't ever work out that way.

ultimatekaiser said:

Did you ever end up doing this? I just realigned my 127 finally, and it took about three hours from scratch + fine tuning. Since yours is already lazing I would say you should devote at least an hour. You'll also need a very sensitive LPM if you want absolutely maximize what you get. The majority of the adjustment you'll probably ever have to make are in the bore. Going to go ahead and make a new thread on the process later after I get off work, as it will be quite an extensive post.

Click to expand...

No, unfortunately I did not, and I just gave back the LPM that I borrowed back. When I get another chance and have time I'll contact you kaiser and get that done. I did verify the output on another LPM to be 18mW-19mW normally and if I press on the mounts it peaks at 26mW.

Mattronium said:

No, unfortunately I did not, and I just gave back the LPM that I borrowed back. When I get another chance and have time I'll contact you kaiser and get that done. I did verify the output on another LPM to be 18mW-19mW normally and if I press on the mounts it peaks at 26mW.

Click to expand...

Having done more of them then I'd like to remember, there are four tricks:

1. Clean the Brewsters only as a last resort, the little rubber boots crack if stretched and are irreplaceable. Wait till you get "death spiral" power levels before removing a dried out boot. These lasers have almost no gain, use of less then a USP or Chromatography grade solvent usually means leaving with less power then you began with. Cambridge Laser Labs bought the HENE line from SP, they may sell you extra boots.

2. Mount or set the laser on a stiff metal rail or really stable optical bench-top. I use aluminum "association channel" extrusion when I don't have access to a optical bench. If the laser slips around while your handing it, or it bends ever so slightly, you get horrible drift.

3. Have multiples of all the Allen wrenches so you can adjust "differentially" while walking in the power. Moving the wrench from end to end / side to side s maddening and wastes time.

4. Very slight tweeks to the fine adjust and the bore straighteners score you more power then adjusting the main mirror mounts. That said, don't crack the bore if your tube has bore straightener screws.

Give it thermal "settling time" of 30 seconds or so between adjustments.

Three hours to align from scratch, about an hour and a half for peaking for me. Considering aligning from scratch means the "cards and crosses" business card based technique, and not an alignment laser, one should take extreme care not to loose even faint lasing.


Steve

There is no *cathode* to "sag"in a 107 / 127. the cathode is an aluminum cylinder. I own four and replaced the tube on one. Alignment is a bear if you lose lasing. the central tube supports are real fun to align as well. there is a youtube video from cambridge lasers on how to align a 107 tube. I got some help from the wizards of gas lasers over the phone and in e-mail. Clean the brewsters and mirrors properly and with spectroscopic grade materials. Use Q tips that dont have glue holding the cotton to the stick. Be carefull of the high voltage leads, the high voltage is enough to immediately send you on your way to the great beyond. Read Sams laser web page to learn more.
Drop me a note if you have any questions too.
Have fun, learn and be safe. =)

VidalWolf said:

There is no *cathode* to "sag"in a 107 / 127. the cathode is an aluminum cylinder. I own four and replaced the tube on one. Alignment is a bear if you lose lasing. the central tube supports are real fun to align as well. there is a youtube video from cambridge lasers on how to align a 107 tube. I got some help from the wizards of gas lasers over the phone and in e-mail. Clean the brewsters and mirrors properly and with spectroscopic grade materials. Use Q tips that dont have glue holding the cotton to the stick. Be carefull of the high voltage leads, the high voltage is enough to immediately send you on your way to the great beyond. Read Sams laser web page to learn more.
Drop me a note if you have any questions too.
Have fun, learn and be safe. =)

Click to expand...

yeah, HeNe cathodes don't sag just ion lasers. Generally adjusting the bore is the more important bit. the best thing to do is just do fine alignment. generally the brewsters and mirrors dont get too dirty unless someone fiddled with them before. but a cotton swab and a little lab grade acetone is best for those. best thing is to just adjust the bore carefully and then walk the mirrors. sometimes a little mirror mount touchup is necessary, but generally not.