Ultrafast laser spectroscopy

Ultrafast laser spectroscopy uses ultrashort light pulses to track changes in molecules, atoms, and materials on femtosecond-to-picosecond timescales.

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Femtochemistry: The study of chemical reactions as they unfold on femtosecond timescales. It applies ultrashort-pulse measurements to follow bond rearrangements during reactions.
Femtosecond: A unit of time equal to 10⁻¹⁵ seconds. Many ultrafast experiments resolve molecular motion over femtosecond intervals.
Excited-state dynamics: The time-dependent evolution of a system after it enters an electronically or vibrationally excited state. Ultrafast spectra measure how excited populations form, move, and decay.
Ahmed Zewail: An Egyptian-American chemist who pioneered femtochemistry using femtosecond laser pulses. His reaction studies established ultrafast spectroscopy as a way to observe transition dynamics.
Time-resolved spectroscopy: Spectroscopy that measures how a sample’s response changes over time after a defined event. Ultrafast laser spectroscopy is its subset for dynamics too rapid for longer pulses.
Pump–probe spectroscopy: A method that excites a sample with one pulse and probes it after a controlled delay. Changing the pulse delay samples successive stages of ultrafast evolution.
Ultrashort pulse: A brief burst of light whose duration is typically measured in femtoseconds or picoseconds. Its duration sets the basic temporal window available for observing dynamics.
Vibrational wavepacket: A coherent quantum superposition of vibrational states that evolves as molecular motion. Time-resolved signals can track its motion through a molecular potential-energy surface.
Femtosecond laser: A laser that produces optical pulses lasting on the order of femtoseconds. Reliable femtosecond sources supplied the brief excitation and probe pulses the methods require.
Steady-state spectroscopy: Spectroscopy that measures a sample under constant illumination or in an unchanging state. It gives spectral averages without the time sequence central to ultrafast measurements.