When a short pulse passes through dispersive material, its different wavelengths travel at different group velocities and the pulse stretches, with red leading blue in normally dispersive glass, called positive chirp. Chirp also arises from self-phase modulation and from directly modulated diode lasers. It can be removed with prisms, gratings or chirped mirrors, and it is deliberately added to stretch pulses before amplification.
Those two lenses and the AOM put a lot of positive chirp on it, pre-compensate with the prism pair or the pulse is 300 fs at the sample.
Also heard as
- frequency chirp
Related terms
GVD
Group Velocity Dispersion: how strongly a material's group velocity changes with wavelength, which stretches short pulses.
CPA
Chirped Pulse Amplification: stretching a short pulse before amplifying it, then recompressing it afterwards.
Transform-limited
Describes a pulse that is as short as its spectral bandwidth allows, with no leftover chirp.
Self-phase modulation
Spectral broadening of an intense pulse caused by its own intensity changing the refractive index it travels through.
Pulse duration
How long a laser pulse lasts, normally given as the full width at half maximum of its intensity.