Abstract
The response of solids to electromagnetic fields is of crucial importance in many areas of science and technology. Many fundamental questions remain to be answered about the dynamics of the photoexcited electrons that underpin this response, which can evolve on timescales of tens to hundreds of attoseconds. How, for example, is the photoexcited electron affected by the periodic potential as it travels in the solid, and how do the other electrons respond in these strongly correlated systems? Furthermore, control of electronic motion in solids with attosecond precision would pave the way for the development of ultrafast optoelectronics. Attosecond electron dynamics can be traced using streaking, a technique in which a strong near-infrared laser field accelerates an attosecond electron wavepacket photoemitted by an extreme ultraviolet light pulse, imprinting timing information onto it. We present attosecond streaking measurements on the wide-bandgap semiconductor tungsten trioxide, and on gold, a metal used in many nanoplasmonic devices. Information about electronic motion in the solid is encoded on the temporal properties of the photoemitted electron wavepackets, which are consistent with a spread of electron transport times to the surface following photoexcitation.
Highlights
Attosecond streaking of photoelectrons emitted by extreme ultraviolet light has begun to reveal how electrons behave during their transport within simple crystalline solids
Measuring these dynamics using attosecond streaking will enable such systems to be specially tailored for applications in areas such as ultrafast opto-electronics
We show that streaking can be extended to this very general type of sample by presenting streaking measurements on an amorphous film of the wide-bandgap semiconductor tungsten trioxide, and on polycrystalline gold, a material that forms the basis of many nanoplasmonic devices
Summary
We show that robust attosecond-resolved measurements can be performed using streaking on this very general type of sample by fully reconstructing the streaking field at the sample surface with attosecond precision, and by confirming the photoemission of attosecond photoelectron wavepackets The durations of these wavepackets are consistent with the spread of electron propagation times to the surface associated with a range of emission depths. The dispersion at 84 eV (the typical photoelectron energy in our experiments) is −72 as[2] A −1, which is small over a sub-nanometre mean free path for an excitation pulse lasting several hundred attoseconds These simple considerations indicate that even for disordered samples without any surface preparation, it should be possible to photoemit a sub-cycle photoelectron wavepacket using an extreme ultraviolet isolated attosecond pulse lasting several hundred attoseconds.
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