MIT researchers found that chaotic laser light can transform into a precise, stable beam. This breakthrough enables much faster, high-resolution imaging of how drugs move into the brain.
Researchers at MIT have identified an unexpected effect in optical physics that could lead to a new kind of bioimaging technology with both higher speed and strong resolution. Under specific conditions, a disordered beam of laser light can reorganize itself into a narrow, sharply focused “pencil beam.”
Using this effect, the team captured 3D images of the human blood-brain barrier about 25 times faster than the current gold-standard approach, while maintaining similar image quality. The method also allows scientists to observe individual cells taking in drugs in real time. This capability could help researchers determine whether treatments for neurodegenerative diseases such as Alzheimer’s or ALS successfully reach the brain.
“The common belief in the field is that if you crank up the power in this type of laser, the light will inevitably become chaotic. But we proved that this is not the case. We followed the evidence, embraced the uncertainty, and found a way to let the light organize itself into a novel solution for bioimaging,” says Sixian You, assistant professor in the MIT Department of Electrical Engineering and Computer Science (EECS), a member of the Research Laboratory for Electronics, and senior author of a paper on this imaging technique.
She is joined on the paper by lead author Honghao Cao, an EECS graduate student; EECS graduate students Li-Yu Yu and Kunzan Liu; postdocs Sarah Spitz, Francesca Michela Pramotton, and Federico Presutti; Zhengyu Zhang PhD ’24; Subhash Kulkarni, an assistant professor at Harvard University and the Beth Israel Deaconess Medical Center; and Roger Kamm, the Cecil and Ida Green Distinguished Professor of Biological and Mechanical Engineering at MIT. The paper was published on April 27 in Nature Methods.
Unexpected Laser Behavior Challenges Assumptions
The discovery began with an observation that initially puzzled the team.
The researchers had previously developed a precise fiber shaper, which allows them to carefully control how laser light travels through a multimode optical fiber. This type of fiber can handle high levels of power.
Cao increased the laser power step by step to test how much the fiber could withstand.
Normally, higher power leads to more scattering because of imperfections inside the fiber, causing the beam to become increasingly disordered. Instead, as the power approached the point where the fiber might be damaged, the light suddenly concentrated into a single, extremely sharp beam.
“Disorder is intrinsic to these fibers. The light engineering you typically need to do to overcome that disorder, especially at high power, is a longstanding hassle. But with this self-organization, you can get a stable, ultrafast pencil beam without the need for custom beam-shaping components,” You says.
Key Conditions for Self-Organizing Light
To reproduce this effect, the researchers identified two important requirements.
First, the laser must enter the fiber at a perfectly aligned, zero-degree angle, which is more precise than typical setups. Second, the power must be increased to a level where the light begins interacting directly with the glass of the fiber.
“At this critical power, the nonlinearity can counter the intrinsic disorder, creating a balance that transforms the input beam into a self-organized pencil beam,” Cao explains.
These conditions are not commonly explored. Researchers often avoid high power levels to prevent damage to the fiber, and such precise alignment is usually unnecessary since multimode fibers already carry large amounts of energy.
When combined, however, these factors allow the system to produce a stable beam without complex optical adjustments.
“That is the charm of this method — you could do this with a normal, optical setup and without much domain expertise,” You says.
Cleaner Beam Improves Image Quality
Further testing showed that the pencil beam is both stable and capable of high resolution compared to similar beams. Many traditional beams produce “sidelobes” — blurred halos that can interfere with image clarity.
In contrast, this beam remains clean and tightly focused.
The researchers then applied it to biomedical imaging of the human blood-brain barrier.
Faster 3D Imaging of the Blood-Brain Barrier
The blood-brain barrier is a dense layer of cells that protects the brain from harmful substances while also blocking many medications. Scientists often want to track how drugs move through this barrier and whether they reach their targets in brain tissue.
With conventional optical techniques, researchers typically capture one 2D slice at a time and repeat the process multiple times to build a complete image, You explains.
Using the new approach, the team generated ultrafast, high-precision images while also tracking how cells absorb proteins in real time.
“The pharmaceutical industry is especially interested in using human-based models to screen for drugs that effectively cross the barrier, as animal models often fail to predict what happens in humans. That this new method doesn’t require the cells to have a fluorescent tag is a game-changer. For the first time, we can now visualize the time-dependent entry of drugs into the brain and even identify the rate at which specific cell types internalize the drug,” says Kamm.
“Importantly, however, this approach is not limited to the blood-brain barrier but enables time-resolved tracking of diverse compounds and molecular targets across engineered tissue models, providing a powerful tool for biological engineering,” Spitz adds.
The researchers produced cellular-level 3D images with higher quality than other methods and achieved speeds roughly 25 times faster.
“Usually, you have a tradeoff between image resolution and depth of focus — you can only probe so far at a time. But with our method, we can overcome this tradeoff by creating a pencil-beam with both high resolution and a large depth of focus,” You says.
Future Research and Applications
The team plans to further investigate the underlying physics behind this self-organizing beam and better understand how it forms. They also aim to apply the technique to other uses, such as imaging neurons in the brain, and to explore opportunities for commercialization.
Reference: “Self-localized ultrafast pencil beam for volumetric multiphoton imaging” by Honghao Cao, Sarah Spitz, Li-Yu Yu, Kunzan Liu, Zhengyu Zhang, Federico Presutti, Francesca Michela Pramotton, Subhash Kulkarni, Roger D. Kamm and Sixian You, 27 April 2026, Nature Methods.
DOI: 10.1038/s41592-026-03067-0
This work was funded, in part, by MIT startup funds, the National Science Foundation (NSF), the Silicon Valley Community Foundation, Diacomp Foundation, the Harvard Digestive Disease Core, a MathWorks Fellowship, and the Claude E. Shannon Award.
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