True Lab Stories: The Water Fountain

(Series explanation here.)

When I was in grad school, I worked in a lab with an incredibly high density of laser technology. We had not one but two Ti:sapphire systems, with 15 W argon ion lasers pumping Coherent 899 ring lasers, plus a pulsed YAG/ dye laser system, and a couple of miscellaneous diode lasers.

The argon ion lasers drew a great deal of current, and required water cooling to keep them from overheating and suffering major damage. The lab provided circulating water at a regulated temperature (55 F), but wherever they were getting the water from, it had large amounts of clay in it, that would eventually gum up the plumbing of the cooling system. To get around that, we put a plastic filter in the line, sticking it in between the pipe coming out of the wall and the shut-off valve on the big hoses that ran over to the laser itself.

After a couple of years of happy operation, we came in one morning to find that the weight of the valve and hose had finally cracked the filter housing. It cracked on the top side of the filter, sending a jet of water spraying out into the room, like a giant water fountain. The stream of water hit the electrical raceway suspended from the ceiling (eight or ten feet up), and rained down all over one of the Ti:sapph lasers. We're not sure how long it had been running before the problem was discovered, but there was a good half-inch of water on the floor, and the fire department had already been called by the people in the lab downstairs, who came in to find a little waterfall running over the circuit breaker boxes on one wall of their lab.

We cut the water off, and broke out the mops, and once the floor was cleaned up, we started looking at the Ti:sapph laser. The external cavity module was literally full of water-- when my supervisor picked it up and turned it on its side, it took a good ten seconds for all the water to drain out. We had to dismantle the whole thing, and clean every single surface.

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We thought we had escaped total catastrophe, though, because the main optical table (with literally hundreds of mirrors, lenses, and waveplates on it) was underneath a shelf and surrounded by plastic shielding to keep dust off. The main spray of water was blocked from hitting any of the mirrors, so once we dried the plastic off, we thought we were fine.

It turns out, though, that the electrical raceway that the fountain was hitting ran directly over the top of the main table. It filled up with water, which slowly dripped out from the lowest point in the raceway. Which just happened to be directly above the HEPA filter and fan that we used to circulate air under the plastic sheets. As water dripped down, it hit the filter, picked up a load of dust, and dripped down into the fan, which spayed a nasty mixture of dust and water all over everything. Every single optic on the table had to be removed and cleaned, in a three-step process (distilled water, then acetone, then methanol) to get all the crud off.

The really amazing thing about the whole story? The Ti:sapph worked just fine after that. There was a small amount of corrosion on one of the ball bearings in one of the mounts that made it stick a bit when you were aligning it, but that was easy to work around, but everything else worked great. Even the external cavity, which was a nearly sealed unit that we couldn't open up to clean.

As far as I know, that laser is still in use, eight years later...