Ultrafast measurements in condensed matter

• Main Author: Okell, William
• Other Authors: Tisch, John; Marangos, Jon
• Published: Imperial College London 2014
• Subjects: 530
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.656617

In this thesis I describe the development of an apparatus for performing attosecond photoelectron measurements in condensed matter, and the completion of attosecond streaking measurements on metal films using the apparatus. A commercial Ti:sapphire chirped pulse amplification laser system was used to generate 28fs, 2.5mJ pulses with a central wavelength of 790nm and a 1kHz repetition rate. These pulses were post-compressed using a hollow fibre system. The resulting few-cycle pulses had sub-4fs duration, and 0.4mJ energy. Diagnostics performed on the hollow fibre system revealed ionisation induced carrier-envelope phase fluctuations at input pulse energies in excess of 1mJ. These fluctuations were avoided for attosecond experiments by careful choice of the experimental parameters. The few-cycle pulses were used to generate isolated attosecond pulses through high-harmonic generation, in an amplitude-gating scheme. An ultra-high vacuum compatible two-part extreme-ultraviolet multilayer mirror setup was developed for attosecond streaking measurements on surfaces. The base pressure in the experimental chamber is 3 x 10^-9 mbar. Attosecond streaking measurements were performed on amorphous WO3 and polycrystalline Au, without any prior surface cleaning. The results indicate the applicability of attosecond streaking to a very general class of solid state samples. In WO3 the 4f photoemission precedes the valence photoemission by 140 ± 190as. In gold, possible signatures of plasmon dynamics were detected.