Photoelectron Spectroscopy using high repetition rate attosecond pulses

Abstract

In attosecond physics, pump-probe experiments have been a promising tool to study the fundamental light-matter interaction process of photoionization. In this context, photoelectron spectroscopy is used to spatially and temporally characterize the ejected photoelecron. Low repetition rates can be limited in resolution by space-charge effects \cite{spacecharge} and measurement statistics which can be reduced by high repetition rate measurement of photoelectron spectra.

This thesis presents how a high speed digital signal processing card is implemented together with a programmed application software to measure high repetition rate photoelectron spectroscopy. In order to analyze the acquisition conditions and the spectrum generation, the card is tested with a $1kHz$ laser system. We measure the travel time (time-of-flight) of photoelectrons from the moment of ionization until the moment of detection and further convert this quantity to kinetic energy. The results show that both time-of-flight and kinetic energy photoelectron spectra can be measured with the established setup. We corrected a trigger offset to better resolve sidebands created during the pump-probe experiments. We understood that the peak detection function provided by the graphical programming software Labview requires specific input parameters to better resolve the photoelectron time-of-flights and that the current duty cycle needs to be adjusted for high repetition rate measurements. The implementation of the acquisition cards Zero-Suppress mode remains an important feature to reduce the amount of data flow.

Popular Abstract

Light might appear invisible if we look outside the window or yellow if we look at the sun, but in reality one can say that light is made out of small particles named photons and each of these photons carries a package of energy with it.

All materials surrounding us are also made out of small entities named atoms which contain even smaller subparts named electrons. Those electrons are responsible for the currents which feed all our electrical everyday devices. This can happen because the electrons are electrically charged.
When a photon travels through air and collides with an atom, an electron is released from the atom and because of their charges, the current they produce can be measured.

Imagine yourself back when you were a small child and your mom had to put in a lot of effort to get you out of your bed in the morning. She had to shout loud enough, turn on a number of lamps in your room, in other words, she had to expend some minimum amount of energy to eventually wake you up. The electron is just in the same position as you are. It is comfortably lying in its bed inside its room – the atom – and an external effort – the energy of the photon – brings it out of its room.
Now, if your mom increased the amount of effort by rising her volume and opening all windows to let the cold air in, she managed to wake up your siblings during the same time. In case you have one sibling and both of you get out of your room simultaneously, your mom is still able to distinguish who is coming from which room and who is fastest down in the kitchen. The electron, however, has several siblings, for instance 10, and some of them share the same room. When all of them leave their room at the same time, they run into each other and take more time to go to the kitchen. It becomes harder to distinguish which electron came first out of the same room and which exact room they all came from.
In this thesis, we look at exactly those electrons that leave their atom and we collect information about how much time they take out of their room until a specific point in time where we can detect them. The problem of electrons that run into each other on that way can be solved by using less energy each time a photon collides with the atom. A tool called high repetition rate can be employed to do so and the motivation of this thesis is to examine this tool.

• author: Rämisch, Lisa
• supervisor: Miguel Miranda; Mathieu Gisselbrecht
• organization: Atomic Physics; Department of Physics
• course: FYSK02 20171
• year: 2017
• type: M2 - Bachelor Degree
• subject: Physics and Astronomy
• language: English
• id: 8917433
• date added to LUP: 2017-06-20 12:58:14
• date last changed: 2018-02-13 10:39:12