How to use a laser to light a Christmas tree

Make sure it's a small tree, nanoscale for sure, digitally simulated if you want publishing credits instead of fire alarms.

A nanoscale virtual Christmas Tree bright with laser light.
Credit: Gonoskov, et al

A group of Swedish researchers who were absolutely focused on the serious questions in their field and not at all looking for something interesting to do during the long, dark Scandinavian winter, decided to see what happens when you point a terawatt laser the laser at a Christmas tree.

Because they were looking for a little professional diversion rather than mayhem, however, they used a very small tree -- nanoscale, in fact. And even it was digitized as part of a test to see what effect odd angles, shapes and inclusions had on the ability of a randomly shaped target -- like a Christmas tree, for example -- might have on the target's ability to absorb laser light of the kind that might come out the end of a fiberoptic cable or from one photon-driven data connection to another within an optical computer.

The test wasa huge success, according to the paper posted to the science-research archive arXiv Dec. 19 by researchers at the Dept. of Applied Physics at Chalmers University of Technology in Gothenburg, Sweden. The question they were trying to answer by virtually lasing a virtual Christmas tree was, of course, directly relevant to the development of optical networking and computer chips, which carry data using laser lite flowing through fiberoptics.

There are a lot of unanswered questions about how to control individual photons within optical networking and optical computing environments, how to delay or hold lite-borne data and how the intensity, accuracy and efficiency of the laser light being used to carry it is affected by the inner walls of the fiberoptic cable and shape or characteristics of the target the light will hit to complete its connection and deliver its data.

It turns out that a Christmas Tree-shaped fiberoptic target may not be the most efficient possible shape, but is a lot more effective than you would think, and a lot more festive than you'd normally associate with optical physics, nanotech (and Sweden in winter).

The curving shape of the tree's branches, its pointed tips, the little ornaments and star at the top all seemed to increase the ability of the target's shape to absorb lite compared to one that was flat and less holiday shaped. The sharp curves and points of the branches were likely to be the most reactive areas, but it turned out that the top of the tree, which had curves, points as well as ornaments and a star, were even more effective.

The whole thing gets a little gimmicky in the discussion, where the authors describe discovery of a GIFT (Absorption Gain In Fir-tree Targets) and describe the lingering light at the ion-dot ornaments and tree-branch edges as a "warm fireside glow." That doesn't do a lot to bolster the credibility of the whole paper, despite the semi-serious conclusion that shapes characteristics similar to the top of the experimental Christmas tree "may constitute a viable means of accelerating particles."

arXiv is an archive and repository for scientific research papers both before and after publication, so the experiment and analysis of the nano-scaled Christmas-tree laser-target simulation didn't have to undergo a rigorous peer review before publication.

It's unlikely a nanoscale laser-target Christmas tree, however successful, will influence the development of either optical computing or the direction of plasmonics research, though there's no reason to think that people who do this kind of work when they're goofing off aren't a lot more on target the rest of the time.

The paper and the research that went into it have apparently done their bit to keep people with access to powerful lasers occupied and out of trouble, however, even if they don't appear to take the results as more than a really complicated way to create a Christmas display.

In the Acknowledgements section of the extremely short paper titled "Lighting up the Christmas tree: High-intensity laser interactions with a nano-structured target," the authors stated specifically that they "are grateful for the spare time we had during which this research was conducted."

It's a good bet the other residents of Gothenburg are grateful it was a virtual tree the team decided to light up. No matter how dark it gets in the winter, there's a limit to how involved most people want to get with a warm, cheery glow created with a big laser.

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