Second-modelocking for a universal material-processing laser

Lasers are ubiquitously used to cut, drill, mark, texture, 3D print materials.

Material-processing lasers remain divided into CW, nanosecond- and ultrafast-pulsed, each excelling and falling short differently.

CW lasers reach the highest powers, cost the least, and are far more common but cause heat damage, and their utility is material-specific. Ultrafast lasers achieve supreme precision on any material but remain niche as they are inefficient and expensive. Nanosecond lasers fall in between.

We propose to overcome this categorisation by inventing a universal laser that can process any material, from metals to living tissue, exceed the efficiency limit of equilibrium thermodynamics, approach the quantum mechanical limit and surpass the speed of industrial CW lasers.

It will do so by taking our invention of ablation-cooled laser-material removal (Nature 2016) to uncharted territory where electrons and atoms will be kept perpetually far from mutual equilibrium even between successive pulses. The same laser will perform 3D printing or tissue welding by switching to quasi-CW operation.

To this end, we need the unprecedented combination of 30-fs pulses at 1-kW average power and on-the-fly tunable repetition rates of 0.1-1 THz. The latter implies an impossibly short laser cavity.

The alternative is to support multiple pulses in the same cavity but this has long suffered from poor performance due to fundamental reasons.

Regular modelocking generates ultrashort pulses by locking cavity modes via nonlinear feedback but it has no mechanism to mutually lock multiple pulses. We fill this conceptual gap by introducing a nonlinear time filter.

This innovation underlies the new laser concept of second modelocking, which will create thousands of ultrafast pulses in perfect periodic arrangement to reach extreme repetition rates with a disruptive potential for not only material processing and laser surgery, but also microwave, THz generation, beyond-5G communications, laser ranging.