Attosecond transient absorption experiments in poly(3-hexylthiophene) targets

Abstract

In this thesis I present the development of a new type of experiment that extends the avenues of common time resolved measurements in the attosecond science field. The work presented here brings the tools of attosecond science to study electron dynamics in the systems that are the central topic in plastic electronics. A new experimental scheme is designed to study exciton formation and evolution in organic semiconductor Poly(3-HexylThiophene) (P3HT) that is used in organic solar cells. A variation of attosecond transient absorption spectroscopy was proposed to study the dynamics. The challenges of this experimental arrangement were to prepare the correct laser targets and both pump and probe pulses. Here I present the development of solid state polymer targets that were used for the transient absorption experiments. These targets have been succesfully prepared as free standing films in the range of 50 nm - 200 nm thickness and their X-ray absorption spectra were measured. Carrier envelope phase stable laser pulses centered at 1750 nm were achieved in a few optical cycle regime via Hollow Core Fiber (HCF) compression scheme developed in house. These pulses were used to drive High Harmonic Generation (HHG) beyond the 160 eV energy range in a differentially pumped Ne gas target. Strong CEP dependent half cycle cutoofs were observed in the HHG spectra confirming isolated attosecond pulses. X-ray absorption spectrum in P3HT targets was measured using this new source. Two routes for the optical pump generation have been explored. 17 fs, 2 mJ pulse was obtained from the 1750 nm driver via the cascaded third harmonic generation process in a non linear crystal and characterised using the SHG-FROG technique. This pulse was implemented as an optical pump in the transient absorption experiment. An interferometric optical setup was constructed that combines both the pump and the probe generation and the delay control between them. The setup was used to obtain the initial transient absorption experiment data.