Researchers manage to generate attosecond pulses at 100 kHz repetition rate

Max Born is the director of the Institute for Nonlinear Optics and Short pulse Spectroscopy.

The observation and control of electron dynamics in atoms, molecule, and solids can be achieved with attosecond laser pulse in the extreme ultraviolet. Most attosecond laser sources operate at a pulse repetition rate of 1 kHz, which limits their usefulness in complex experiments. We have been using a high power laser system developed at MBI. There are new types of experiments that can be done in attosecond science.

Scientists can study ultrafast dynamics of electrons in atoms, Molecules and Solids with the help of lightpulses in the extreme ultraviolet region. Experiments are usually performed using a sequence of two laserpulses with a time delay between them. The first pulse sucks in air and the second pulse takes a snapshot of the evolving system. The XUV pulse's absorption spectrum is usually measured as a function of delay between the twopulses. A movie of the dynamics under study can be created if the experiment is repeated for different times.

To get the most detailed insights into the dynamics of the system under investigation, it is important to measure the available information. It is possible to measure the three-dimensional momenta of charged particles in atomic and molecular targets. The REMI apparatus can be used to achieve this. The scheme works by detecting ion and electron events at the same time. The detection rate is limited to a fraction of the laser pulse repetition rate. REMI experiments with 1 kHz class attosecond pulse sources are not possible.

MBI has developed a laser system that uses optical chirped amplification pulse. The amplification medium has very little heat generated because no energy is stored inside. The Ti:Sapphire laser, which is most often used in attosecond laboratories around the world, is amplification to much higher average powers. The ability to amplify very broad spectrum is a second advantage of the technology. The average power of the system is 20 W and the pulse energy is 200 UJ. We have previously generated attosecond pulse trains with this laser system.

In many attosecond experiments it is beneficial to have isolated attosecond pulse instead of a train of multiple attosecond pulse. To enable the efficient generation of isolated attosecondpulses, the laser pulse durations should be close to a single cycle of light. The isolated attosecond pulse is confined to one point in time. The hollow fiber pulse compression technique is used to achieve near- single-cycle laser pulse. The 7 fs pulse is sent through a 1m long hollow waveguide filled with neon gas. The chirped mirrors can be used to compressed the pulse durations. These are only 1.3 optical cycles.

The 1.3 cycle pulse is sent into a beamline. The main part of the energy is used to make XUV waves. Experiments can be done after removal of the high power NIR beam, and with a photon flux of 10 11 photons per second.

We performed an attosecond streaking experiment in order to understand the generated attosecond XUV pulse. The XUV pulse is used to ionize an atomic gas medium, while a strong NIR pulse is used to modify the XUV generated photoelectron wave packets. The photoelectrons are accelerated or decelerated depending on the exact timing of the XUV and NIR pulse. The attosecond pulse shapes have been retrieved using a global optimization algorithm. Our analysis shows that the main attosecond pulse has a duration. The main pulse is accompanied by two satellites. Before and after the main attosecond pulse generation, these stem from half an NIR cycle. The pre- and post-pulse satellites have different intensities.

The isolated attosecond pulse opens the door for pump-probe studies at a repetition rate of 1 or 2 orders of magnitude above current implementations. We are using a reaction microscope to conduct experiments.

The research is in a magazine.

More information: Tobias Witting et al, Generation and characterization of isolated attosecond pulses at 100 kHz repetition rate, Optica (2021). DOI: 10.1364/OPTICA.443521 Journal information: Optica Provided by Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy (MBI) Citation: Researchers manage to generate attosecond pulses at 100 kHz repetition rate (2022, March 22) retrieved 22 March 2022 from https://phys.org/news/2022-03-attosecond-pulses-khz-repetition.html This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.