Pairs of light pulses controllable from a single fiber laser

In an innovative approach to controlling ultrashort laser flashes, researchers at the Universities of Bayreuth and Konstanz are using soliton physics and two pulse combs in a single laser. The method has the potential to significantly accelerate and simplify laser applications.

Traditionally, the pulse spacing of lasers is defined by dividing each pulse into two pulses and delaying them by different mechanically adjustable distances. Alternatively, two laser sources with slightly different orbital periods (“dual combs”) are used to generate fast motion delays from the superposition of the two pulse combs.

The purely optical method demonstrated by Professor Georg Herink, head of the group “Experimental Physics VIII – Ultrafast Dynamics” at the University of Bayreuth and his doctoral student Julia A. Lang in cooperation with Professor Alfred Leitenstorfer and Sarah R. Hutter of the University of Konstanz relies on two pulse combs within a single laser. It enables extremely fast and flexibly adjustable pulse sequences.

At the same time, this can be implemented in very compact light sources based on fiberglass. By temporally merging the two pulse combs outside the laser, researchers obtain pulse patterns that can be set with arbitrary delays as needed.

The researchers use a trick: instead of the usual single pulse of light, two pulses circulate through the laser. “There is just enough time between the two pulses to apply a single ‘perturbation’ using a fast optical switch inside the laser,” says Lang, first author of the study. “Using laser physics, this ‘intracavity modulation’ causes the pulse speed to change and thus shifts the two pulses relative to each other in time.”

The fiberglass-based laser source was built by Hutter and Leitenstorfer from the University of Konstanz. Thanks to a special real-time measurement method, Bayreuth researchers can now precisely observe how short pulses of light, called solitons, move when external influences act on them. This real-time spectral interferometry makes it possible to precisely measure the distance between each pair of pulses, more than 10 million times per second.

“We show that we can adjust the timing extremely quickly over a wide range and achieve freely programmable movement shapes,” says Herink. The research now presented in Scientists progress presents an innovative approach to the control of solitons and, in addition to new insights into soliton physics, opens possibilities for particularly fast and efficient applications of ultrashort laser pulses.