laser table

Phone app user controlled UV laser point on a glow-in-the-dark surface

the origin

The laser table was born out of playing with cheap and dangerously powerful lasers bought from China in my friend’s room, who happened to have those greenish glow-in-the-dark stars stuck to his ceiling. The particular laser light used was UV, which emits particularly high energy photons (as opposed to red which is on the low energy end of the visible light spectrum). As a result the laser light instantly activated the phosphorescent dye in the stars, making them glow brightly and leaving a trail behind wherever the laser point had been (which is to say red laser light, even if it was incredibly bright, would not have produced this effect. here’s a really grainy video showing this principle from the royal society of chemistry). Not terribly unlike an old school oscilloscope screen if you’re into that kind of thing, except replace the beam of electrons with a beam of UV photons.

The physics department at Brown University has a wonderful burgeoning tradition of putting together a yearly “Physics Art Show” to showcase talents generally unseen and unappreciated. My friends and I decided to make a glow-in-the-dark surface users could draw on by directing a laser point whose movements tracked those of the user’s finger position on a phone app.

I thought it would be fun to have a blank canvas where people could draw what they want with lasers. Everything drawn is inherently ephemeral giving the whole thing a bit of a graffiti feel, and the ethereal glow of phosphorescence is something I personally can stare at for hours. Plus, dangerously powerful lasers 😉

the build

The idea is to be able to draw on your phone and have those movements replicated on the surface of a coffee table of sorts (shown on the right with a beautiful space-themed curtain to protect people from getting an eyeful of blinding UV light). If no one is in control the table defaults to cycling through a few preset patterns (the random-walk being my personal favorite). When someone goes to the website and touches their screen, they can start to draw. If someone else is already controlling the laser, the newcomer’s phone starts with a red screen that turns yellow when they touch their screen indicating they’re now in line. The website cycles through everyone, and indicates it’s a new users turn when their screen turns green.

We fixed the UV laser to point at a piece of mirror that has been hot glued to two Arduino-controlled servos which have also been hot glued together. Everything was then mounted to some scrap 2 x 4 wood. We built a short table out of scrap wood which we wrapped with some space-themed cloth. The table’s surface was a big piece of acrylic which we coated with the contents of several cans of glow-in-the-dark spray paint. A web server was made with Node.js which collected finger positions on phone screens, sent them through a serial port to the arduino, which translated them into servo angles and adjusted the mirror to the updated position.

Here is a lil movie we made showing the whole thing off 🙂

the team other than me, Will Maulbetsch, this is my website

Ben Wiener – fellow (at the time, and now graduated) grad student working in the same biophysics lab as me and on whose github the web app code lives.

Phil Zucker – also fellow (and now graduated) grad student working in theoretical condensed matter physics.

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