Stoney's First Argon - ILT 5490A

[Stoney3K]

Small update since I figured the head could use a bit of TLC, also giving me plenty of chance to make a few internal shots.



View of the head's guts with the cover removed. I was surprised by the lack of dirt inside the laser head, given the amount of air flow going through it at run time. A few nooks and crannies had some dust collected on them, but nothing serious, and the only major cleaning I had to do was clean the fan blades and remove some grease residue from the cover. Nothing a damp cloth couldn't fix.



Shot of the anode end of the head. The OC is just out of frame on the lower left half of the picture. Also note the teflon blocks covering the Brewster stems, and a set of lines going to a pair of can-shaped objects between the fans (one leading to the cathode, one to the anode end): Could these be gas refill ampoules? In that case, I'm very happy, since both of them seem to be untouched.

The tube serial number is #49622-1 with an argon fill.



Shot of the light control and starter card. Compared to the medical board in a water cooled 5500WL, this could hardly be called a circuit board.



And a beauty shot on how this machine should look like! Given this thing is a quarter of a century old, I am still surprised by the toughness of it. There are still a few minor bits and bobs to fix on the head, for example, the resonator cover on the OC end is still missing a few screws, which weren't present when I bought the unit.

Unfortunately, every war has its casualties, though:



This is what's left of the beam splitter supplying the light sensor with a pickoff beam. No serious harm done, but it was cracked when I was slightly too careless to replace the aperture cover and tightening the screws.

The only obvious result is that the light sensor is now non functional: Not that I really need it, however, it means I need a small modification to the PSU to make it run in current regulation mode. Right now it will just give the head everything it's got, which is 12 amps at 110 volts. Sure, it makes for an impressive display of laser power, but the tube doesn't like it for very long. On the brighter side (literally!), it also means the beam isn't obstructed by another piece of glass anymore and the full 300mW of coherent photons is at my disposal.

Since the PSU still needs a bit of work anyway, it's not a major disaster. If I can find a replacement piece of glass that will fit, I may repair the light sensor and restore the whole head to its former '87 glory, but right now, I'm glad it works. I've reconfigured the PSU to run in 'standby' mode (idle current) and adjusted it for a permanent 6,7A on the tube. Once I can find or build a proper remote I can always go for current control instead.

Mixedgas: Which pins on the remote connector do I need to control the tube current?

The PSU still needs a bit of a cosmetic rework and some adjustments, including replacement of the main (solid state) relay that supplies the laser with power, but I need some components for that. If anyone has a dead PSU which contains a similar relay capable of switching 240VAC / 20A, just let me know.

[DancingMolecules]

Hi everyone,
Thanks for your great help and interest in this tank of a laser.

I recently acquired this laser in a non-working condition. The first issue was the radiator was dirty and the thermal grease had dried up. I took apart the radiator, cleaned it, put on new thermal grease to get it stable and working. After tweaking for a while I got it working great. My model has a Littrow prism in the back that allows tuning between 514 and 488nm with a SLIGHT turn of the mirror gimbal screws.

One day, when going back and forth between the wavelengths for my experiments, LASING disappeared. After careful adjustments back to the original mirror positions, there was no lasing. Then I did what you are NEVER supposed to do and I adjusted all the mirrors and probably F'ed this thing up completely.

I have checked all the electrical outputs and everything seems to be the values you guys have and the power source seems to be working fine. I am assuming I have completely mis-aligned the cavity. I checked a few places, and someone suggested shooting a HeNe laser down the cavity to monitor the reflections, but I can not see the important reflections and any adjustments of the mirrors dont seem to do anything to the HeNe beams that I can see.

QUESTION::Can misalignment damage the tube in anyway by current spikes or????????

So, anyone have some information or the patience to help me out??? This was a fantastic laser when it worked.

Also, I have a digital copy of the manual for the ILT 5400 series that I got from a tech company. I am new to this forum, so if you tell me how to upload it, I will do so with pleasure. However, it sounds like you all know more than what the manual tells!!!

Enjoy.

[DancingMolecules]

Enjoy. THEY REQUIRE AT LEAST 15 CHARACTERS PER MESSAGE

[Mel]

Really annoying I guess... If you was fiddling with the wavelength when it suddenly refused lasing it would make sense that the littrow prism had lost its correct position... also a sudden gas-out I guess, but perhaps you don't want to think about that reason!

Hi everyone,
Thanks for your great help and interest in this tank of a laser.

I recently acquired this laser in a non-working condition. The first issue was the radiator was dirty and the thermal grease had dried up. I took apart the radiator, cleaned it, put on new thermal grease to get it stable and working. After tweaking for a while I got it working great. My model has a Littrow prism in the back that allows tuning between 514 and 488nm with a SLIGHT turn of the mirror gimbal screws.

One day, when going back and forth between the wavelengths for my experiments, LASING disappeared. After careful adjustments back to the original mirror positions, there was no lasing. Then I did what you are NEVER supposed to do and I adjusted all the mirrors and probably F'ed this thing up completely.

I have checked all the electrical outputs and everything seems to be the values you guys have and the power source seems to be working fine. I am assuming I have completely mis-aligned the cavity. I checked a few places, and someone suggested shooting a HeNe laser down the cavity to monitor the reflections, but I can not see the important reflections and any adjustments of the mirrors dont seem to do anything to the HeNe beams that I can see.

QUESTION::Can misalignment damage the tube in anyway by current spikes or????????

So, anyone have some information or the patience to help me out??? This was a fantastic laser when it worked.

Also, I have a digital copy of the manual for the ILT 5400 series that I got from a tech company. I am new to this forum, so if you tell me how to upload it, I will do so with pleasure. However, it sounds like you all know more than what the manual tells!!!

Enjoy.

[Stoney3K]

Really annoying I guess... If you was fiddling with the wavelength when it suddenly refused lasing it would make sense that the littrow prism had lost its correct position... also a sudden gas-out I guess, but perhaps you don't want to think about that reason!

I agree: The cavity is probably misaligned and it is possible to re-align it. Also check Sam's Laser FAQ for a good starting point on realigning a gas laser from scratch.

Misalignment won't damage the laser tube, unless you abuse the mirror gimbals to an extent that the Brewster stems snap off. You're going to need one hell of a lot of force to do that, though. If the tube is up to air, the PSU would never be able to start it.

If the PSU has no problems and the plasma tube runs as it should (about 103V at 8A, depending on the amount of gas) then the problem is optical and you can look at re-aligning the cavity. I don't know if there are any specific procedures on realigning the HR when there's a Littrow prism present -- you may need to consult Steve (mixedgas) on that matter as he's the local neighbourhood ion guru.

[medusa]

Hi all,

may I intoduce myself: I just signed up to this forum for I was really surprised to see a small ILT 5490 fan community developing here. I owe 2 of them (see below for details). Normally I'm on the german laserfreak.net forum (same nick, same avatar).

Both of my 5490s I got in a very poor state. About the first one (an ACM) and its restoration history I wrote on my webpage (english version at http://www.diane-neisius.de/laser/index_E.html#ilt5. It is really sad how careless some people are about this nice old pieces of technical art. Some idiot ruined its case by a very crude addition of a big top fan. Despite of tons of dirt I removed. And missing resonator covers. Strange long screws sticking out of the resonator. Light sensor? What light sensor?
Meanwhile it is well again. It is still able to do 100mW at Imax. And, did you know a surplus ALC60 light sensor can be modified to work in a 5490 (do that only for current-regulated units like the 5490ACM!!). Even a replacement for the beam stopper cap can be made from a cut-off BNC connector.

The second one (an A, probably modified) is a still more tragic case. I bought it as "dead for parts" since I still missed original parts as light sensor and resonator covers. However, gave it a try with my PSU and cable and it still lased (weakly). The guy who sold it told me it has only 40 hours but had an air-leak in 2004. Some well-known german laser refurbisher did a rework of the tube. I checked for, you still can see the welding on the cathode bell (due to the airleak, they had to replace the cathode). The story sounded like he had a lot of trouble to get the laser back. In the end, it did only 40mW max, plasma burns at 90-95 volts. In idle mode at 6A, it puts out only 5mW.
I had not the heart to rip this poor old cripple apart to save parts for the other one. As long as it is able to squeeze out some coherent blue photons, I will keep it and grant it its monthly maintenace run (it just gets one while I'm typing this).

~medusa.