Overview

An attosecond (abbreviated as as) is a unit of time equal to one quintillionth of a second (10⁻¹⁸ s). Because this interval is far shorter than everyday experience can convey, attoseconds are primarily used to describe and measure the motion and dynamics of electrons inside atoms, molecules and solids. For a concise definition see definition resources.

Scale and characteristics

Thinking in attoseconds requires comparing vastly different scales. An attosecond is a thousand times shorter than a femtosecond (10⁻¹⁵ s) and a million times shorter than a picosecond (10⁻¹² s). Electron orbital and transition times in many atoms and simple molecules often fall in the tens to hundreds of attoseconds, so attosecond resolution is necessary to observe those processes directly.

  • Value: 1 as = 10⁻¹⁸ seconds = 0.000000000000000001 s.
  • Context: atomic electron dynamics, inner-shell ionization, and sub-femtosecond charge migration.
  • Analogy: it is many orders of magnitude shorter than the intervals relevant to chemical reactions or biological processes.

Generation and measurement

Attosecond pulses of light are produced by converting intense, ultrashort infrared or visible laser pulses into high-order harmonics in gases or other media. This high-harmonic generation process concentrates energy into extreme ultraviolet or soft X-ray bursts lasting only a few hundred or fewer attoseconds. Experimental techniques to characterize and time-resolve these pulses include streaking and interferometric methods tailored to attosecond timing; for technical introductions see experimental methods.

Applications and examples

Attosecond science enables time-resolved studies of electronic motion that underlie chemical bond formation and breaking, ultrafast charge transfer in materials, and responses of solids to strong fields. Examples include tracking how an electron departs an atom after photoionization or observing charge migration across a molecule on sub-femtosecond timescales. Researchers also use attosecond pulses to probe transient electronic states in condensed matter systems.

History and notable facts

The development of attosecond techniques arose from advances in femtosecond lasers and nonlinear optics in the late 20th and early 21st centuries. Recognition of the field's impact on experimental physics and chemistry has increased, and overviews of its milestones are collected in specialist reviews and summaries review articles. The ability to make and measure attosecond pulses transformed experimental access to electron dynamics.

Attoseconds belong to a family of submultiples of the second used in ultrafast science. Common related units are the femtosecond (10⁻¹⁵ s) and the zeptosecond (10⁻²¹ s). For broader comparisons and educational resources consult general time-scale summaries time-scale references. Understanding these relationships helps place attosecond phenomena within the continuum from atomic to macroscopic processes.