New ultrafast measurement technique shows how lasers start from chaos

"The reason why understanding these lasers has been so difficult is because the pulses they produce are typically of picosecond duration or shorter. Following the complex build-up dynamics of such short pulses for the hundreds, sometimes thousands of bursts before the laser actually stabilizes has been beyond the capability of optical measurement techniques," says Professor Goëry Genty, who supervised the research in the Laboratory of Photonics at Tampere University of Technology (TUT).

This research was performed in collaboration between the FEMTO-ST Institute in France (CNRS and the University of Bourgogne-Franche-Comté) and the Laboratory of Photonics at TUT. The particular scientific advance that led to the novel findings is the real-time measurement of the laser temporal intensity with sub-picosecond resolution, as well as its optical spectrum with sub-nanometer resolution. By recording both these temporal and spectral properties simultaneously, an advanced computational algorithm can retrieve the complete characteristics of the underlying electromagnetic field.

Aside from providing new insights into how pulsed lasers operate, the research results have important interdisciplinary applications.

"The results provide a very convenient laboratory example of what is known as a "dissipative soliton system" which is a central concept in nonlinear science and also relevant to studies in other fields, such as biology, medicine and possibly even social sciences," says Professor John. M. Dudley, who led the research at the University of Bourgogne-Franche-Comté.

While reconstructing the evolution of the electromagnetic field, the team observed a wide range of interaction scenarios between dissipative soliton structures emerging from noise.

"The approach we have implemented can operate at low input power levels and high speeds. The results provide a completely new window on previously unseen interactions between emerging dissipative solitons in form of collisions, merging or collapse," Genty says.

The researchers believe that their results will allow improved design and performance of ultrafast pulsed lasers.

"This is a truly fascinating area of research where studies motivated by questions in fundamental science have the potential to have real practical impact in future photonic technology," concludes Dudley.