Researchers have demonstrated how laser pulses emerge from noise, then collapse and oscillate before stabilizing. The discovery was made possible by real-time measurement of the laser’s temporal intensity with subpicosecond resolution and the laser’s optical spectrum with subnanometer resolution. By recording both the temporal and spectral properties of the pulses simultaneously, researchers were able to create an algorithm to retrieve the complete characteristics of the laser’s underlying electromagnetic field. Professor Goëry Genty works in the Laboratory of Photonics at Tampere University of Technology. Courtesy of Tampere University of Technology. Researchers from Tampere University of Technology (TUT) and FEMTO-ST Institute used simultaneous dispersive Fourier transform and time-lens measurements to characterize the spectral and temporal evolution of ultrashort solitons as their dynamics passed through a transient, unstable regime with complex break-up and collisions before stabilization. They reconstructed the soliton amplitude and phase and calculated the corresponding complex-valued eigenvalue spectrum. While reconstructing the evolution of the electromagnetic field, the team observed a wide range of interactions between dissipative soliton structures emerging from noise. “The results provide a completely new window on previously unseen interactions between emerging dissipative solitons in form of collisions, merging or collapse,” said professor Goëry Genty of TUT. The findings show how real-time measurements can provide fresh insights into ultrafast transient dynamics in optics. The researchers believe that their results could be used to improve 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,” said professor John M. Dudley of FEMTO-ST. The research was published in Nature Photonics (doi:10.1038/s41566-018-0106-7).