Group Velocity Dispersion, the frequency derivative of the inverse group velocity, usually given in fs squared per mm or ps squared per km. Fused silica has about 36 fs squared per mm at 800 nm, normal dispersion, where red travels faster than blue. A 20 fs pulse through 1 cm of silica comes out near 50 fs, so ultrafast setups count every lens and add negative dispersion with prisms, gratings or chirped mirrors.
Total GVD from the objective and AOM is about 8,000 fs squared, set the prism compressor for that before measuring at the sample.
Also heard as
- group velocity dispersion
- beta2
Do not mix it up with
- Chromatic dispersion: Chromatic dispersion is the general wavelength dependence of index; GVD is its second-order effect on pulse group delay.
Related terms
Chromatic dispersion
The change of refractive index with wavelength, which separates colors in prisms and spreads pulses in time.
Chirp
A change in instantaneous frequency across a pulse, so its colors arrive spread out in time.
CPA
Chirped Pulse Amplification: stretching a short pulse before amplifying it, then recompressing it afterwards.
Walk-off
The drifting apart of interacting beams in a crystal, either sideways from birefringence or in time from velocity mismatch.
Supercontinuum
Extremely broad, spatially coherent white-light spectrum created by sending intense pulses through a nonlinear fiber.