ChirpedPulse

A chirped pulse is an electromagnetic pulse in which the instantaneous frequency changes over time. The frequency can either increase or decrease during the duration of the pulse, and it is often described by a chirp rate. Linear chirp means the frequency varies linearly with time, while more complex chirps exhibit higher-order variations.

In ultrafast optics, chirped pulses are central to chirped-pulse amplification (CPA), a technique for delivering extremely high peak powers without damaging the amplifying medium. The pulse is first stretched in time to reduce peak power, then amplified, and finally compressed back to a short duration. This approach, developed in the 1980s by Mourou and Strickland, enabled major advances in high-intensity lasers; they were awarded the Nobel Prize in Physics in 2018 for related work.

Chirped pulses are also widely used in radar, sonar, and communications. Linear frequency modulated (LFM) chirps are transmitted and later compressed with a matched filter, providing high range resolution and robustness to noise.

Generation and control of chirped pulses rely on dispersion management. Devices such as grating or prism pairs, chirped fiber Bragg gratings, and tailored optical fibers introduce known amounts of group delay dispersion to impose or compensate chirp. Modern systems may also employ nonlinear optical processes to shape the chirp for specific applications.

Measurement and characterization of chirped pulses employ techniques such as frequency-resolved optical gating (FROG) and spectral phase interferometry for direct electric-field reconstruction (SPIDER). These methods assess pulse duration, spectral content, and phase to verify pulse quality.