Introducing inkjet-printed disposable lasers

The humble inkjet printer can create organic laser components so cheaply, easily and efficiently, the parts can be swapped out like disposable razor blades.

Researchers from France and Hungary, led by Paris 13 University's Oussama Mhibik, mixed commercially available dyes and inks and printed them onto clear quartz panels. These "lasing capsules" produced a tunable beam from yellow to deep red.

The beauty of an inkjet printer, says senior study author Sébastien Sanaur from Mines Saint-Etienne, is "you print where you want, when you want, without wasting raw materials". Nor does it require special protective equipment, such as masks, it can be done at room temperature and can also print onto flexible materials.

Lasers are fairly simple gadgets, comprising an input light source, usually called the "pump source", a "gain medium" which, among other things, changes the light's wavelength and produces the characteristic narrow, single-colour beam, and an "optical resonator" usually consisting of at least two mirrors to bounce the beam back and forth.

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A schematic of the laser setup (OC = output coupler and FP = Fabry-Pérot etalon, which are partial and full mirrors), and the actual ‘lasing capsules’. – Sanaur, et al / JAP

In organic lasers, the gain medium is made of a carbon-based material. While they're less common than inorganic lasers – which include lasers in optical computer mice and CD/DVD players – they can cover a wide range of wavelengths.

The drawback is they degrade relatively quickly. But what if they were so cheap and quick to make they could be tossed out after each use? 

Mhibik, Sanaur and colleagues rose to the challenge with an unlikely weapon: an inkjet printer.

Inkjet printers work by squirting small jets of fluid onto a surface. Scientists use them to print electronic circuits and even living cells. 

For their laser gain medium to work, the researchers knew they needed an ink that, when printed, would dry flat to ensure a light beam passing through isn't diverted. So they tested a variety of commercial inkjet inks and eventually found one that set smooth and flat.

The next step was to test various dyes which dictated the colour of the beam. The dye had to mix well with the ink, keep the nozzle clog-free, not splash when squirted and keep the ink's flatness when it dried.

Two laser dyes, which absorb green light while letting wavelengths either side to pass through, ticked the first three boxes.

What about the smoothness of the dried ink? To test this, 50-millimetre-squared patches were printed onto clear quartz. The researchers measured pockmarks and bumps of only 1.5 nanometres (or 1.5 billionths of a metre) on the dried ink's surface.

Each "lasing capsule" could be made for only a few cents each.

While their inkjet-printed laser produced yellow and red light, the researchers say other dyes could cover the blue and green parts to create a tunable laser across the whole visible light spectrum.

The work was published in the Journal of Applied Physics.

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