Ultrafast

Ultrafast describes processes, techniques, or instruments that operate on extremely short timescales, typically from tens of femtoseconds (10^-15 s) to a few picoseconds (10^-12 s). In practice, it is associated with the use of ultrafast lasers to trigger and observe rapid dynamics, providing a real-time view of phenomena that unfold too quickly for conventional measurements. The term also covers extreme regimes such as attoseconds (10^-18 s) studied in attosecond physics.

Ultrafast lasers, especially mode-locked systems based on titanium-doped sapphire, routinely produce pulses on the order of tens to a few hundred femtoseconds. These pulses enable pump-probe experiments that separate initiation and observation in time, revealing dynamic processes in atoms, molecules, and solids. To characterize and control pulses, researchers use techniques such as autocorrelation, frequency-resolved optical gating (FROG), and spectral phase interferometry for direct electric-field reconstruction (SPIDER). Detectors like streak cameras and fast photodiodes accompany these measurements.

Applications of ultrafast science include studying chemical reaction dynamics, energy and exciton transfer in molecules, carrier relaxation in semiconductors, and phase transitions in solids. In materials processing, ultrafast lasers allow selective ablation with reduced heat affected zones. Ultrafast imaging and microscopy enable visualization of rapid processes in biology and physics, while attosecond techniques probe electron dynamics in atoms and molecules.

Historical development: The capability to generate stable femtosecond laser pulses emerged in the 1980s and spurred a broad range of experimental methods, collectively known as ultrafast spectroscopy. The field continues to evolve with advances in high-harmonic generation, nonlinear optics, and compact sources, expanding access to ultrafast regimes and new measurement modalities.