Fire the Maser!

No that’s not a typo.  The maser is the laser’s less cool, older brother.  While laser stands for Light Amplification by Stimulated Emission of Radiation, maser stands for Microwave Amplification by Stimulated Emission of Radiation.  If you remember your electromagnetic spectrum from school, you might wonder what’s the difference, or if the maser is really a specialized laser.  The technical answer is that there isn’t much of a difference.  Masers came around first and really could only work in the microwave spectrum (and actually the first lasers were called optical masers).  Now it’s more complicated, because masers generally emit radiation besides microwaves, and we now have lasers that work outside the optical range of light.  Fun fact:  One idea from decades ago on making the names make sense was to change the letter before ASER for every part of the spectrum, so you’d have masers, lasers, uvasaers (for ultraviolet light), irasers (infrared), grasers (gamma rays), and the incredibly unfortunate xaser (x-ray), which might be unique having both x and s make a /z/ sound with no actual z in the word.

But enough distraction.  I’m supposed to be telling you why masers are the Betty White of the applied physics world and became sexy again after several decades.  Why were masers less cool before?  (Note:  The analogy breaks down here, because Betty White was always cool)  They work by the same mechanism as a laser (that stimulated emission), but weren’t ever as easy to use, either requiring vacuum chambers or refrigeration to a few degrees above absolute zero to work consistently.  While the first few lasers were cumbersome, now they’re small enough to fit in all kinds of everyday devices.  So why the interest in such a frustrating machine?  Because modern technology doesn’t just work in the visible part of the light spectrum.  The whole process of stimulated emission is great at amplifying weak signals, and amplifiers in the microwave/radio range could have a lot of uses in biology and medicine, as well as communications (your cell phone signal is waves in this part of the spectrum).

So what’s new?  In 2002, a group of Japanese chemists published a paper about the energy transitions between different quantum states in several organic molecules.  One material they focused on was p-terphenyl, doped with another organic molecule, pentacene.  “Doping” might sound like a weird word here, but if your first thought is wondering if this is like athletes doping, you’re not entirely off.  In materials science, we “dope” lots of things to improve properties, though currently most of the interest is in electrical properties.  For example, most electronics contain silicon infused with a small amount of boron to add additional charge carriers and provide reliable currents.  Doping works best when the molecules you’re working with have electrons arranged in similar ways.  Although I can’t find an explanation for the exact way pentacene dopes p-terphenyl, I would assume the fact that both molecules are slightly different chains of benzene has something to do with this.  (All the doping I’ve ever heard of has been with elements, so I’m a bit fuzzy on the details of how you dope with molecules.)

Mark Oxborrow from the United Kingdom’s National Physical Laboratory, recently read the Japanese paper and realized the energy transitions that were described could also be used in the stimulated emission process for a maser.  Somewhat amusingly, Oxborrow and his colleagues ended up making a machine almost entirely out of spare parts, including the terphenyl.  However, they were hesitant, because the whole process felt too easy (which seems understandable when you’re working in an area filled with six decades of disappointment).   What finally inspired Dr. Oxborrow to run the maser was an argument with his wife, which encouraged him to go

Even burned, the pentacene-doped terphenyl has a lovely hue

to the lab as “therapy”.  And then he probably needed some additional therapy when the maser exceeded anyone’s expectations:  the signal was a 100 million times more powerful than any known maser.  And he thinks he can do better, because not being much of a chemist, he accidentally burned the crystal while making it.  So here’s to firing more masers.

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