Mystery of the 609.6nm line

Those aren't lasing lines, just the regular spectra, sadly.

I've started a dialog with the co-inventor of the HENE laser about this line.

If there is one person left who understands the Helium-Neon gas mixture, it is him. He's in his 80s, but still has an office.. We shall see if he replies.

It looks like a 2p4/1s4 level In Neon, and it shows as a radiative transition in all literature I've found, not a lasing line.


Steve

That sounds logical. I found a healthy multimode REO yellow I can squeeze this line out of quite well from the HR mirror along with all of the main lines using an additional mirror. It hangs around quite a lot in this particular sample. Very interested in hearing about this. I got a few good pictures but I'm at work. So I can't share them right at the moment.

Make my day and tell me you can get a spectrometer shot? I have it, but its blinking and faint. Of take it over to REO and let them ponder this...

Nothing so far, I'll call his office soon.

Steve

Yes I have a spectrometer shot of it I'll post it later. I believe I also shared it with bloom at one point. If I remember correctly it showed up exactly at 609nm on my graph.

sorry for the DP but I wanted it to update so I had to make a new post. I'm with you, I kinda wanna go run up the street and knock on their door and ask them about it.

I can't even be mad with this necro post, considering the 1:365 timing, it makes a helluva birthday gift.

Yes. The 609 line is a radiative transition line according pg.501 of Masamori Endo and Robert F. Walter's "Gas Lasers".

This is the only reference to this line that I've found outside of 'pay-per-read' scientific library sites.

EDIT: With some MacGyver-y work, I was able to isolate the line and measure it on my micrometer at 609nm, with a subtle peak at about ~609.5. This is with a setup metered to have a 2nm margin of error, metering, if I recall correctly, 2.5nm low. That said, I tested SEVERAL gas, ion, and DPSS wavelengths to gauge what the offset was, and where it peaked.

With this knowledge, I sent the output through a screen to block the bore light, followed by a second screening to isolate the 609 line. The output was funneled across a few mirrors resulting in an incredibly faint output. Double digit uW.

After that, it was simply a matter of waiting for the line the come in, and measuring it.

I took several measurements over several hours, ensuring I was getting consistent results.

This proved, without a doubt, that this is the 609.6nm line.

The science isn't as flashy or immediately forth telling as a 4-digit priced spectrometer, but with all the controls I had in place, they're hard findings to dispute.

I have all of this documented somewhere, I believe even a video displaying my setup. Though it's a fairly annoying video to watch. It was an early experiment with speaking on camera with no tangible real-time response.

The designer of the dual line tube, Dr. Knollenberg, says 2P4 -> 1S4 for this transition and mentions it in his paper "Prospects for the Helium Neon Laser Through the End of the Century*" only he says 610 nm, and does not list the specific wavelength...

Knollenberg is a founder of PMS, which Spun Off REO... He ought to know, and he mentioned this in 1987....

It does not explain a 0.5 nm discrepancy between what Sam and others have measured, and the assignment of the line, but if the tube designer says 2P4->1S4 in Paschen Notation, I'm inclined to stick with it. He was actively trying to make as many different HENE lines lase as possible, and he was good at it, for commercial reasons. Kaiser's spectrum places it right over 610, so given instrument error, 609.61 is about right. Bloom's new measurement is similar.

It took me more than two years to run this down... And I'm about to try to get in touch with a retired REO employee who would know...

*in SPIE Vol 741, Design of Optical Systems Incorporating Low Power Lasers, (1987)

Damn hard to get book...

I really had to work thru a lot of reference material to get this, and when you search Neon 2P4 1S4 on Google, if you have a university level library access, you find another paper measuring the sidelight of this transition by another scientist..... That scientist shows no population inversion at 609.61 but he has 6328 lasing. Dr. Knollenberg says that he has to partially suppress 612 nm using careful optics design to get dual line lasing with 604. So it is possible that you need a very carefully tailored optic to see the 609.61 line, because of gain competition between lines. As well his having to use a partially multimode or multimode tube, Which explains why no one else shows this as a working laser transition.

In the paper, Dr. Knollenberg also explains a lot about the external mirror particle sensing tubes, both the "Active" one Brewster Tube, and the "Passive" three mirror laser, as well as mentioing seeing seven lines in the three mirror laser... He then expanded the three mirror laser to IR as well, but he does not go into detail on that.

He also explains a lot of the mechanics of dual line tubes, as well as what you have to do to get 543 and 594...

There is the possibility of an error in Moore's wavelength tables, which is what everybody uses to find transition wavelengths. But at this rate, it might take me another six months to run this down to more digits, if I can at all... Right now it is 609.616 or 609.618 nm.



But the line is documented in a published work... And yes, Sam knows, I called him.

Steve

very interesting. Thanks for sharing

Sam is saying 608.9 to 609.1 right now... Still running down the missing 0.5 nm....

Maybe line(s) instead of line... Ie 609.6 and/or something else...

What Dr. Knollenberg does to get the massive multi-line output in the three mirror system includes Doppler Shifting the passive cavity lines using a tiny amount of motion on Mirror 3. This shifts the standing modes frequency enough to eliminate some line competition. It also reduces feedback into the tube.

Kaiser, email me for a copy of the paper...

Steve

LSRFAQ said:

Sam is saying 608.9 to 609.1 right now... Still running down the missing 0.5 nm....

Maybe line(s) instead of line... Ie 609.6 and/or something else...

What Dr. Knollenberg does to get the massive multi-line output in the three mirror system includes Doppler Shifting the passive cavity lines using a tiny amount of motion on Mirror 3. This shifts the standing modes frequency enough to eliminate some line competition. It also reduces feedback into the tube.

Kaiser, email me for a copy of the paper...

Steve

Click to expand...

PM sent instead. The tube i'm using is a multimode yellow (has the torus mode) the bore is quite wide, like most REO tubes. I havn't tried it with a red or green, but both yellow and orange tubes give me this line if placed on a rail, with a broadband mirror of any kind sending the beam back into the tube from either end. I've used both metallic mirrors (Al and Ag) as well as various dielectric ones for that spectral region. I consistently get a reading of 609 =/- .1nm with a single mode fiber on my ocean optics.

Steve, thanks so vey much for sharing this. I found it incredibly interesting.

I've been in my cave for quite some time, but I did enjoy the update.

Kaiser, what's the count on tubes you've gotten this to lase from manually? I've used broadband mirror intended for Kr+, thanks to a tip from Steve long ago, yet to ever manually get the 609 lasing. Though it has given me both 632 and 594 simultaneously from a 543. It's also lased 604 and 612 for me, though never 609.

I'll need to dig through my storage to re-test this. Over the past few moves, things have become scattered all over various boxes; haven't been very driven to retrieve much of it.

As always, Steve, thank you for the updates. Bitter-sweet that it's already "known". Though with that, I'd very much like to finally get down this rabbit hole and figure out what in the hell is happening here.