I know I should be helping get our Burning Man proposals in final shape, but I wanted to post some thoughts I’ve had on bubble ignition with lasers. For those of you who don’t know what I’m talking about, we’ve periodically discussed whether our hydrogen plus oxygen bubbles could be ignited remotely with a laser. I think it’s agreed that this would be pretty awesome. Unfortunately it turns out it’s probably quite hard.My initial thought along these lines was to use some kind of photochemical reaction along the lines of a demo I saw in my freshman chemistry class. If you shine blue light on a mixture of hydrogen and chlorine, it explodes, forming hydrochloric acid. You can see this in this video on youtube:This works because blue light photodissociates the molecular chlorine into atomic chlorine. The atomic chlorine is very reactive and reacts with the hydrogen in a chain reaction, forming HCl. Chlorine is photodissociated by UV - blue light in the 300 - 400 nm range.In principle you can do exactly the same thing with either the oxygen or hydrogen in our bubbles.Unfortunately, the wavelengths you need to photodissociate either oxygen or hydrogen are in the deep UV, and can only be generated by very expensive sources like fluorine excimer lasers. Even worse, these deep UV wavelengths are efficiently absorbed by the atmosphere. So direct photodissociation of H2 or O2 is probably out. One potential possibility is to dope our bubbles with something that can be efficiently photodissociated to spark the reaction (chlorine would work, but it’s pretty toxic) but this seems likely to be pretty complicated.There is another possibility: laser spark ignition. It turns out that if you focus enough laser power into a small spot, the resulting electric field is enough to ionize the air and create a spark. Once again, youtube has video of it (it’s amazing what you can find on youtube):This should ignite a bubble just as well as an electric spark (and in fact, there’s a lot of research into using laser spark ignition to replace spark plugs). There’s just a few problems. First, you need a lot of laser power. That video is using 200 mJ pulses that are probably a few nanoseconds long. That means the instantaneous power is on the order of 10 MW. The average power is only 4W, but you can imagine that if you happen to be in the way of one of those pulses you will be unhappy. So laser safety concerns preclude using this in an open space.Second, that laser is probably pretty expensive.Third, you have to have the beam come to a tight focus to get the spark. That means it’s not enough just to point the laser at the bubble, but you need to focus the spot into the bubble. That’s probably pretty hard to do.So, my initial ideas for laser ignition of bubbles seem not to be feasible … but I’ll keep thinking!

So this is the start of False Profit Labs… seems like it is off to a good one. I didn’t really know what to expect when heading over to Brett’s. I figured we were going to brainstorm some about the candelabra and the bubbles and FPL in general but I didn’t know how much work we might be doing or how directed that would be. Should I bring my own stuff to work on? I decided not too mainly because I was on my bike and was still slightly hung over and didn’t feel like dealing with figuring out a project of my own right then and just figured I would help with other people’s projects. This turned out well because most of the work right now seems to be focused on the bubbles and candelabra.I arrived as some brainstorming was going on and there was good talk of direction and different plans to frame the projects. After this we headed down to the Lab. And also immediately starting lighting things on fire. W00t! We got a demo the candelabra controller which was really fun to see working. Even if the input system seemed to have bugs. Brendan and I then started work on an ignition system based on hot wire. Put enough current through special types of wire and it gets really hot. Not too surprising but will it be hot enough to light propane? How much current do you need? How little current can you get away with? How should you shape the wire? Is it a good idea to wrap wire that you intend to get very very hot around a wood rod? While only one of these questions has an obvious answer (wood rod = no) that was the first thing we did. It worked ok. We hooked the wire wrapped wood up to 120v from a generator and waited eagerly for something to happen. The wire got warm, the wood started to smell a little funny and we had effectively made a small space heater. This clearly would not do. So we reducing the resistance of the wire by hooking up about half the length of the wire (to half the resistance) and tried again. This time the wire got red hot and the wood quickly burst into flame. Success!Now that the basic concept had been proved, we needed to refine a lot. The first place to look was a hydrogen powered toy rocket which had a wire ignition. First step, test the rocket. Instructions read, rocket fueled and ready, now time to launch. But outside there are power lines and too many houses and very little open space. So what other place to launch than inside the garage. At this point I wish I could report some exciting disaster or at least a near miss but sadly everything was quite uneventful. This is mainly due to the fact that electrolysis part of the hydrogen power rocket seemed to have been broken and the rocket would not launch. So we trying hooking up the ignition wire directly to a 12v battery and the promptly melted it. Not quite success.Eventually after much more poking we managed to light propane and hydrogen off coiled wire. We even managed to get hydrogen (not propane sadly) to light of wire powered by a battery, not 120v which means we can reduce the power considerably when making the igniters. In the mean time, other folks had been playing around with the top pipes on the candelabra and trying to figure out how to change the air mix to change the flame.Overall, we had a very good time and good progress seemed to be made and then we went and had tacos.

We’ve been hard at work in the shop, building the prototype for our new V3 Hydrogen Bubble Machine and testing a voice control interface for Kurt’s candelabra project. We now have 3 fire tubes connected via USB interface to our flame simulator software. When input comes through the microphone, it is analyzed for amplitude averages over short time periods. This is essentially a VUMeter algorithm. The analysis is displayed on the screen and simultaneously sent to a Measurement Computing USB-1024LS Digital I/O board. The pin-outs 0-5V are connected to Kurt’s amplifier board which boosts the voltage range to 0-24V. This then controls a set of solenoids connected to our 1/2″ copper flame tubes.We have been working on a good ignition system and just had some luck using nichrome wire to form a hotwire ignitor on about 8A of current. But for now, in the lab, it doesn’t seem to matter since each of the candelabra’s flame tubes seems to stay lit long enough after the solenoid closes to relight the next time it opens.Here’s some video of our 3-tube voice-controlled Candelabra demonstration:

And here’s a clip showing propane ignition with nichrome wire:

Last night (January 15, 2008) at the False Profit Community meeting we were given the official go-ahead to start using the name False Profit Labs. So, first thing I did was set up this blog, and next we’ll have a wiki and a new email list. I’ll be the Creative Director at least for this quarter, and will be speaking with everyone in our community about the labs, hoping to be the facilitator in making this endeavor inclusive and fun.

Please contact me if you have a project you want to make, especially involving fire or other science-inspired artwork. If you have ideas or feedback about False Profit Labs as an organization, it’s goals and mission, drop me a line as well.