Attosecond Physics
These notes serve as an introduction to the exciting field of attosecond physics, based primarily on foundational texts such as Attosecond and Strong-Field Physics and Attosecond Physics: Attosecond Measurements and Control of Physical Systems. While these comprehensive books offer extensive theoretical and mathematical insights, their depth can make them dense and abstract. In contrast, these notes aim to foster an intuitive understanding of the underlying physics. Key formulas are included, but lengthy derivations are generally omitted for conceptual clarity. However, mathematical details are included where they significantly enhance understanding.
Attosecond science is the art of controlling and measuring phenomena occurring on the timescale of
Since the atomic unit of time is approximately 24 attoseconds, attosecond science naturally plays a crucial role in time-resolved electron dynamics. The properties of matter, in any state, are largely determined by its electronic structure and behaviour. While much of 20th-century physics focused on studying and controlling the structure of matter, a key direction in the 21st century is understanding and manipulating its dynamics at the most fundamental electronic level.
The progress of ultrafast science is intrinsically linked to laser development. The ultrafast revolution began with the invention of Q-switching for nanosecond pulse generation, followed by mode-locking, which enabled the creation of the first sub-picosecond pulses. Further reductions in pulse duration towards the femtosecond regime required additional techniques, including chirped pulse amplification, as the concepts of ultra-intense and ultrashort are strongly connected. Understanding this field benefits from a foundational knowledge of light pulses, as covered in my Ultrafast Laser Physics notes.
Probing and controlling electron dynamics on the attosecond timescale became feasible with the advent of techniques for generating attosecond pulses, typically using few-cycle, intense laser pulses. The observation of second-harmonic generation in 1961 marked the beginning of rapid advancements in nonlinear optics, culminating in the first experimental demonstration of attosecond pulse generation in 2001. It quickly became evident through theoretical work and subsequent experiments that the generated high-order harmonics were phase-locked. In an analogy to how mode-locked lasers enabled femtosecond pulses through the coherent superposition of many frequency modes, these phase-locked high-order harmonics were understood to yield attosecond pulses.
Attosecond pulses promise unprecedented access to observing and influencing electron dynamics at their intrinsic timescale. However, precisely determining and interpreting the key parameters that characterise such dynamics remains a non-trivial experimental and theoretical challenge.
Table of Contents
1 Fundamentals of High-Order Harmonic Generation
2 Generation of Attosecond Pulses
3 Characterisation of Attosecond Pulses