Founding Team

For more than twenty years, the Nelson Lab (academic setting) has been exploring how materials behave under extreme conditions. The story begins in the 2000s, when graduate students and postdocs started building laser-driven instruments that could launch pressure waves into materials, to investigate the responses.

One of the earliest surprises came from a deceptively simple optical trick. The lab was experimenting with a conical lens called an axicon. When a laser beam passes through it, the beam transforms into a thin ring of light. A student directed this laser ring onto a piece of polymer, expecting nothing unusual. But at the very center of the ring - where no laser light actually touched - something curious appeared. The effect wasn’t caused by the light itself, but by the pressure wave it launched. As that wave converged inward, it amplified, eventually becoming so strong that the material behaved in unexpected, nonlinear ways. Cranking up the laser energy pushed the effect further: the pressure wave turned into a shock wave. That was the moment the 2D focusing shock method was born. Over the years, the lab showed that these concentrated shocks could do remarkable things: turn graphite into diamond-like sp³ bonds, toughen glass, or even transform an insulator into a metal.

But the lab’s curiosity didn’t stop there. If focusing could make waves stronger, could there be another way to push pressures higher? Inspiration came from a very different corner of Nelson Lab research - THz spectroscopy. In that field, the team had mastered a technique called tilted pulse front. It’s a geometric trick that lets an ultrafast laser efficiently generate powerful THz pulses inside a crystal by keeping the optical and THz waves in sync. Each step of the laser pulse adds more strength to the THz wave as it travels.

That begged new questions: Could we pump a pressure wave the same way - additively, step by step, until they reached new extremes? And how can we engineer it?

The additive aspect itself was straightforward - it could be confirmed with simple acoustic simulations. But turning the idea into a working instrument was another matter. The engineering proved challenging.

Then, an unexpected inspiration came from outside. At the University of Hong Kong, a research group had been experimenting with two tilted mirrors that formed a free-space optical cavity named FACED. Their goal was not high-pressure physics at all, but fast imaging: the setup split an incoming laser pulse into multiple sub-pulses with tunable spacing in space and time, which they used as scanning probes for biological samples.

That raised a provocative question: what if we flipped the idea around? Instead of using the split pulses as probes, why not use them as pumps?

This thought became the seed of what we now call Zebra. With two tilted mirrors, a single laser line is broken into a train of weaker sub-lines, each arriving slightly out of step with the next. When these laser lines strike the surface of a solid, they act together - like overlapping ripples in water - to additively build up a stronger surface acoustic wave.

Still, the lab wanted faster, higher, and stronger waves.

What if we combined the best of both worlds - focusing and additive pumping?

That challenge led to the multi-ring method. By arranging several axicon telescopes, we created concentric laser rings of different diameters, each arriving at a sample just a few nanoseconds apart. The timing is tuned so that the laser rings and the focusing shock achieve a speed-matching condition and converge at the geometric center of the sample.

With the multi-ring method, the Nelson Lab recently crossed a remarkable threshold: achieving megabar-level pressures in tiny volumes of water. What started as a curious observation of “something funny in the center of a ring” has now grown into a powerful toolkit for shaping matter under some of the most extreme conditions possible on a benchtop.