Loading...
Electric field sensing through second harmonic generation of ultrafast laser pulses
Schrama, Claudia
Schrama, Claudia
Citations
Altmetric:
Advisor
Editor
Date
Date Issued
2018
Date Submitted
Collections
Research Projects
Organizational Units
Journal Issue
Embargo Expires
Abstract
In dynamic processes such as spark discharges, it is impossible to insert field probes to measure rapidly varying and localized electric fields. In this thesis, we investigate the use of second harmonic generation of an ultrafast laser pulse as a probe for an electric field. In an centrosymmetric medium, second harmonic generation is not allowed in the electric dipole approximation. However, breaking the symmetry of air with an applied electric field allows for the second harmonic generation to occur. The second harmonic signal holds information about the applied electric field and can be used to provide information on the vector structure of the electric field. Here we show that second harmonic generation can be used as a noninvasive field probe for the vector electric field applied over an air gap. We find that there is a significant background second harmonic signal without an applied field that results from a quadrupole nonlinear response of the air. When characterizing this background we find that the polarization purity is crucial to minimizing the quadrupole signal. Subtracting this background, taking two polarization directions, and scanning the beam spatially around a blade electrode, we show that we can make a field map of the electric field that is consistent with an electrostatic calculation. Analyzing the results from this work, we propose two methods for using this probe. The first is to use a pulse sequence and observe the second harmonics with a photomultiplier tube to see the voltage response over time. The pulse sequence will capture the electric field at each pulse and show the variations in the field over time. The second method is to use a beam that is simultaneously focused in space and in time. This will give a shorter depth of focus and should minimize the background second harmonic signal. The imaging is a possible probe for fields changing on the order of seconds. The efficiencies that need to be reached to image single shots are currently not available.
Associated Publications
Rights
Copyright of the original work is retained by the author.