A tractor beam—a special beam of electromagnetic radiation that draws particles toward it instead of pushing them away—might be a concept straight from Star Trek, but scientists from the Australian Research Council’s Centre of Excellence for Transformative Meta-Optical Systems (TMOS) have recently taken steps toward a more portable way to generate one in real life.
The Melbourne-based research team suggests that this could lead to better, less invasive technology capable of performing biopsies without the cell trauma caused even by the smallest handheld tweezers or needles. The team’s paper is published in the peer-reviewed journal ACS Photonics from the American Chemical Society.
While the term “tractor beam” conjures images of science fiction and intergalactic tow trucks, the most realistic application of a near-future tractor beam is in healthcare. Currently, people who need biopsies are subjected to needles wide enough to take a sample of cells, or even more involved procedures using handheld forceps, which can cause significant tissue damage. Although these procedures are generally safe and essential, medical care with less or no cutting is almost always safer and less painful.
The secret of this new technology lies in the triple helix solenoid beam—a twist of three “strands” of light that form an overall tunnel or tube shape. These beams are generated by passing a normal beam of light (also known as a Gaussian beam) through a specially created metasurface, which functions like a pasta extruder or light stencil. The metasurface is composed of whisper-thin nanopatterned silicon on a panel of glass. Metasurfaces, in general, use micro-etched or prepared surfaces to change the form of electromagnetic waves, similar to a variety pack of pasta-shaping plates.
In a statement, TMOS explained that the beam draws particles up similarly to how a drill bit pulls sawdust. The three strands of the triple helix end up cradling a particle, which is something simple optical (laser) tweezers can also do. However, the new part is the traction, or ‘tractor-ing,’ created by the twisting motion of the solenoid beam. These unusual beams were developed beginning in the late 2000s and publicized by NASA research in 2011. The idea quickly gained traction.
This new paper follows conference presentations in 2020 and 2021 by three of the same researchers. Once the basic premise of the solenoid beam was established, with its ability to draw in particles rather than push them away, researchers shifted to optimizing the setup and fine-tuning details to create the most coherent beam. This beam improves both the amount of light energy retained in the conversion from Gaussian beam to solenoid beam and the coherence of the beam itself. Previously, solenoid tractor beams used spatial light modulators (SLMs), which are effective but large and bulky, making them unsuitable for handheld applications. It’s akin to bringing an overhead projector into a dark hallway instead of a flashlight. By using a much smaller setup with a prepared silicon microwafer, the researchers have maintained high efficiency while reducing bulk and equipment costs.
To clarify, this paper focuses on the new metasurface—the “plate” that transforms regular light into a spiraling tractor beam. It does not address the beam’s ability to draw in particles, which is already well established. The team discusses the recent history of that research in their introduction, highlighting the significant progress made since they first began presenting these ideas in 2020. They conclude that their new metasurface could be crucial in enhancing tractor beams further.
“Various innovative methods have been explored. However, these pioneering works have confronted challenges related to beam quality, efficiency, and the need for modulation of the beam in time,” the team wrote. “Our device has a transmission efficiency of ∼76% that, along with the small size, weight, and cost of the metasurface approach, renders it as a promising alternative to SLM-based systems for a range of applications.”
By Impact Lab
