Spatio-temporal characterization of intense ultrashort laser pulses

Abstract

When ultrashort pulses pass through common optical elements such as gratings and thick lenses, they can pick up spatio-temporal couplings (STCs) - nonseparable chromatic aberrations. The main cause of this phenomenon is the inherent feature of ultrashort pulses—their broadband spectrum. STCs increase pulse duration and reduce the intensity at the focus, which will be detrimental for many applications, for example, in high-harmonic generation (HHG). This project identifies and visualizes the STCs of ultrashort laser pulses used for HHG and laser-driven acceleration by removing aberrations shared by all wavelengths. Spatially resolved Fourier Transform spectrometry is the main method for our STC characterization. Improvement of the existing data analysis code, including the shared aberration removal and comprehensive STC analysis documentation, are included in this work.

Popular Abstract

Lasers have unique properties that distinguish them from ordinary sunlight or light from our homes' lamps. That property is known as spatial and temporal coherence. Thanks to those properties, pulses with very short duration, i.e., in the femtosecond range, can be generated. A femtosecond is the millions of billions of a second. But why do we need such a short pulse? There are two answers: first, using the short pulse, we can take a “movie” of fast events, and second, achieving high intensity is feasible with short pulses. By saying “fast event,” we mean ultrafast events like electron motion around nuclei in the atom and chemical reactions that unfold on the femtosecond (fs) time scale.

Relatively recently, the process called high-order harmonic generation allowed to achieve pulses on the attosecond time scale. It is an extremely short duration. Accessing such an ultrashort duration provides us with advanced insights into the dynamics of electrons in atoms, molecules, and solids. This knowledge can be applied to achieve real-time control of electron motion in matter, with practical applications such as the transition from THz-to-PHz electronics, probing the molecular composition of biological systems for health monitoring, and disease detection. Reaching high intensity with ultrashort pulses has important applications in particle acceleration. Since at such high intensity, particles can accelerate close to the speed of light in less than a meter. This allows us to drastically reduce the size of conventional particle accelerators. High-speed protons can kill cancer cells, which has an important application in medicine.

When generating and manipulating ultrashort pulses, their field can be distorted by common optical elements, like lenses, gratings, etc. These distortions are usually called spatio-temporal couplings (STC). To put it in the simplest terms, STC means that the pulse properties cannot be written separately as a space and a temporal component. These distortions can be beneficial or harmful to the system. In both cases, it becomes important to characterize them. During this project, STC characterization is done for the two laser systems used for high-order harmonic generation (AttoLab) and particle acceleration (Multi-pass cell MPC system at DESY). In the AttoLab, significant STCs are observed. STCs are also present in the source of the MPC system but these do not transfer to the compressed output pulses.

• author: Merdanov, Mekan
• supervisor: Cord Arnold
• organization: Atomic Physics; Department of Physics
• course: PHYM03 20241
• year: 2024
• type: H2 - Master's Degree (Two Years)
• subject: Physics and Astronomy
• keywords: Ultrafast optics, Spatio-temporal couplings (STC), Spatially resolved Fourier Transform spectrometry
• publication/series: Lund Reports in Atomic Physics (LRAP)
• report number: LRAP 599
• language: English
• id: 9169591
• date added to LUP: 2024-08-13 08:13:23
• date last changed: 2024-08-13 08:13:23