Periodic Reporting for period 1 - UniLase (Second-modelocking for a universal material-processing laser)
Periodo di rendicontazione: 2022-12-01 al 2025-05-31
Lasers are among the most versatile technologies ever invented. Within just a few years of their discovery, they were already being used in applications as diverse as machining metals and performing eye surgery. Since then, lasers have become central to modern life. From shipbuilding to the production of computer chips, many technologies today would be impossible without specialised lasers.
The type of laser required for a task is determined above all by the time structure of its light. At one extreme, continuous-wave (cw) lasers emit a steady beam that can reach very high powers but offer only limited precision. At the other, ultrafast lasers produce extremely short flashes, so fast that they are over before atoms in the target material can move. This enables unmatched precision, though at much lower processing speeds and higher cost.
The Unilase project explores a bold new possibility: that a rapid train of ultrafast pulses, arriving faster than atoms can recover from the effect of the previous pulse, could act collectively on materials. This approach could greatly increase processing speed and even unlock physical effects that cannot be achieved with isolated pulses.
To realise this, Unilase pursues a new laser concept called second mode-locking. Conventional ultrafast lasers rely on mode-locking, where many colour components of the light combine to form pulses. Second mode-locking takes this further: creating many such pulses inside the laser and locking them to each other in time and phase. The name reflects both this “second level” of locking and an analogy to second quantisation in physics, where particles can be created or annihilated. Similarly, the laser must be able to create or remove pulses to sustain a coherent population of many locked pulses.
In parallel, Unilase investigates how such collective pulse trains, repeated at nearly one trillion per second (1 THz), interact with materials. The aim ranges from fundamental questions, such as whether supersonic material removal is possible, to applied goals like damage-free medical treatments or faster, more precise industrial processing.
The type of laser required for a task is determined above all by the time structure of its light. At one extreme, continuous-wave (cw) lasers emit a steady beam that can reach very high powers but offer only limited precision. At the other, ultrafast lasers produce extremely short flashes, so fast that they are over before atoms in the target material can move. This enables unmatched precision, though at much lower processing speeds and higher cost.
The Unilase project explores a bold new possibility: that a rapid train of ultrafast pulses, arriving faster than atoms can recover from the effect of the previous pulse, could act collectively on materials. This approach could greatly increase processing speed and even unlock physical effects that cannot be achieved with isolated pulses.
To realise this, Unilase pursues a new laser concept called second mode-locking. Conventional ultrafast lasers rely on mode-locking, where many colour components of the light combine to form pulses. Second mode-locking takes this further: creating many such pulses inside the laser and locking them to each other in time and phase. The name reflects both this “second level” of locking and an analogy to second quantisation in physics, where particles can be created or annihilated. Similarly, the laser must be able to create or remove pulses to sustain a coherent population of many locked pulses.
In parallel, Unilase investigates how such collective pulse trains, repeated at nearly one trillion per second (1 THz), interact with materials. The aim ranges from fundamental questions, such as whether supersonic material removal is possible, to applied goals like damage-free medical treatments or faster, more precise industrial processing.
Although still in its build-up phase, the Unilase project has already produced results that are attracting strong attention, including more than ten invited talks at leading scientific conferences and several publications. The progress so far includes two fundamental advances on the path to second mode-locking, as well as two practical demonstrations of the power of collective interactions between many ultrafast pulses.
As a first conceptual step, we addressed a long-standing puzzle: why do lasers with multiple pulses inside their cavities tend to be unstable? We discovered that their relative positions shift randomly, much like the jittery motion of pollen grains suspended in water, known as Brownian motion. In that case, the grains move because of collisions with atoms; in lasers, the pulses move because of randomly emitted photons dictated by the laws of quantum physics. With this new understanding, we were able to stabilise such lasers and bring their performance close to that of conventional mode-locked systems.
A second breakthrough followed from tackling the question of how pulses can be created and organised into a coherent population. Here we drew inspiration from biology, where living organisms achieve order through hierarchical self-organisation—structures built within structures. By applying this principle across time, we showed how to organise many pulses in a controlled and stable way.
With these foundations in place, we are now constructing a new laser system to attempt the first demonstration of second mode-locking. The outcome will reveal whether this bold concept can be realised in practice.
In parallel, we have also explored the collective effects of high-repetition-rate pulses. Preliminary experiments show supersonic material removal for the first time. In addition, in collaboration with other researchers, we demonstrated a tiny ultrafast chemical reactor, created momentarily within a liquid by focusing laser pulses. The reactor drives fluid motion that circulates the entire container, which is about a billion times larger than the reactor itself, so that every portion of the liquid briefly reaches thousands of degrees for just a millionth of a second. This enables unique chemical pathways, and using this approach we succeeded in synthesising previously unattainable types of zeolites, an important class of catalysts.
As a first conceptual step, we addressed a long-standing puzzle: why do lasers with multiple pulses inside their cavities tend to be unstable? We discovered that their relative positions shift randomly, much like the jittery motion of pollen grains suspended in water, known as Brownian motion. In that case, the grains move because of collisions with atoms; in lasers, the pulses move because of randomly emitted photons dictated by the laws of quantum physics. With this new understanding, we were able to stabilise such lasers and bring their performance close to that of conventional mode-locked systems.
A second breakthrough followed from tackling the question of how pulses can be created and organised into a coherent population. Here we drew inspiration from biology, where living organisms achieve order through hierarchical self-organisation—structures built within structures. By applying this principle across time, we showed how to organise many pulses in a controlled and stable way.
With these foundations in place, we are now constructing a new laser system to attempt the first demonstration of second mode-locking. The outcome will reveal whether this bold concept can be realised in practice.
In parallel, we have also explored the collective effects of high-repetition-rate pulses. Preliminary experiments show supersonic material removal for the first time. In addition, in collaboration with other researchers, we demonstrated a tiny ultrafast chemical reactor, created momentarily within a liquid by focusing laser pulses. The reactor drives fluid motion that circulates the entire container, which is about a billion times larger than the reactor itself, so that every portion of the liquid briefly reaches thousands of degrees for just a millionth of a second. This enables unique chemical pathways, and using this approach we succeeded in synthesising previously unattainable types of zeolites, an important class of catalysts.
Unilase is already pushing beyond the state of the art on several fronts. Conceptually, we have provided the first clear explanation of why lasers with multiple pulses have historically been unstable, and developed a new strategy for stabilising them. We also introduced a novel framework for systematically creating and organising many pulses through hierarchical self-organisation, laying the foundation for second mode-locking as a fundamentally new class of lasers.
On the experimental side, we have demonstrated material ablation at supersonic speeds, far faster than previously thought possible, and realised an ultrafast micro-reactor within liquids, where extreme temperatures are reached for only millionths of a second to drive unique chemical processes. These breakthroughs show that collective ultrafast interactions can achieve effects qualitatively beyond what is possible with existing laser technologies.
On the experimental side, we have demonstrated material ablation at supersonic speeds, far faster than previously thought possible, and realised an ultrafast micro-reactor within liquids, where extreme temperatures are reached for only millionths of a second to drive unique chemical processes. These breakthroughs show that collective ultrafast interactions can achieve effects qualitatively beyond what is possible with existing laser technologies.