Up to now it has not been possible to look inside a laser, but now research has shown how an ultrafast measurement technique allows for a clearer understanding of how laser pulses emerge out of nowhere.
Lasers that emit ultrashort pulses of light are essential for technologies such as communications and industrial processing and have been central to fundamental to research. While lasers were first invented in the 1960s, the exact instrument whereby lasers produce such bright lights has remained unknown, however researchers have developed an ultrafast measurement technique that could change this.
Recently, research performed in collaboration between the FEMTO-ST Institute in France (CNRS and the University of Bourgogne-Franche-Comté) and the Laboratory of Photonics at Tampere University of Technology (TUT), published in Nature Photonics has demonstrated for the first time how laser pulses emerge out of nowhere from noise and then display complex collapse and oscillation dynamics before stabling into a regular operation.
Professor Goëry Genty, who supervised the research in the Laboratory of Photonics at TUT said: “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 stabilises has been beyond the capability of optical measurement techniques.”
The new advancement has led to findings in the real-time measurement of the laser temporal intensity with sub-picosecond resolution, as well as its optical spectrum with sub-nanometre resolution. By recording both the temporal and spectral properties simultaneously, an advanced computer algorithm can retrieve the complete characteristics of the underlying electromagnetic field.
These results have important interdisciplinary applications, and Professor John M. Dudley, who led the research at the University of Bourgogne-Franche-Comté, explained: “The results provide a very convenient laboratory example of what is known as a ‘dissipative solution 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 science.”
The team have also observed several interaction scenarios between dissipative soliton emerging from noise, whilst reconstructing the evolution of the electromagnetic field.
Genty said: “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.”
The researchers believe that their results will allow improved design and performance of ultrafast pulsed lasers.