Even if you never find one in your Cracker Jack box, the 10-cent tunable dye laser opens up a world of possibilities. A Caltech collaboration between Demetri Psaltis, the Myers Professor of Electrical Engineering, and Axel Scherer, the Neches Professor of Electrical Engineering, Applied Physics, and Physics, has produced a microfluidic “chip” that contains such a laser, a feat that could make a variety of laboratory-grade diagnostic tests as readily available as disposable plastic thermometers.

Microfluidic devices can send very small samples through multiple simultaneous analyses, and putting a laser on the chip adds spectroscopy to the toolbox. Inexpensive, single-use devices preloaded with the necessary chemicals would be perfect for biomedical applications. “You take your spectrum and then throw it away,” Scherer says. A paper on the work, by grad students Zhenyu Li and Zhaoyu Zhang (MS ’06), Scherer, and Psaltis, will appear soon.

The group uses a process called replication molding to stamp out any number of copies from a single, precisely machined master, similar to the way the music industry made vinyl recordings available to millions. “You could do this in your garage,” Scherer says. “I have done this in my garage.”

These records are pressed in silicone rubber—clear, flexible, and very cheap. “This is bathroom caulk,” Scherer says. Inject dye into the device with a syringe, and with a boost from an external light source, your laser is ready to go. The group used the equivalent of a green laser pointer to pump the dye, but portable devices could use built-in chemical or semiconductor light sources. Yet don’t let the simple means and humble materials fool you. “This does the same job as a $20,000 tunable dye laser.”

In some ways it may even do more. All lasers emit a mix of colors, and with dye lasers that mix can be very broad. That’s what makes them tunable—if you can pick out just the narrow range of colors you want. This penny-sized device uses a series of evenly spaced pillars, running in a line down the center of the laser cavity’s fluid channel, to act as a diffraction grating. The laser is excited by an external source, and the grating allows only the light whose wavelength matches the pillars’ spacing to be emitted.

Yet rubber is flexible. Squeeze or stretch the device with your fingers and the spacing changes, as does the laser’s wavelength. Try that with your $20,000 instrument! —JA