Group delay dispersion (GDD) and group velocity dispersion (GVD)

Group delay dispersion (GDD) and group velocity dispersion (GVD) are critical parameters for understanding how the propagation time and speed of light pulses change with frequency or wavelength as they travel through transmitting media, such as glass optics, or interact within the layers of thin-film coatings.

Group delay refers to the time delay experienced by light of various frequencies, while group velocity is the speed at which the envelope of a pulse propagates through a medium. GDD and GVD characterize the rate at which group delay and group velocity, respectively, vary with the frequency or wavelength of light.

GDD and GVD are expressed in units of time squared, typically in femtoseconds squared (fs²). Both can be measured using a white light interferometer.

The measurement conditions for which we can perform the test are outlined below.

For a 1" sample

• Reflection optics AOI: 0° & 5-70°

• Transmission AOI: 0-70°

For a 2" sample

• Reflection optics AOI: 5-70° (0° could be possible, discuss with expert)

• Transmission AOI: 0-70°

Spectral coverage:

• 400-1060 nm (VIS/NIR basic version)

• 250-1060 nm (UV/VIS/NIR version)

• 900-2400 nm (IR version)

To carry out the testing, the following measurement details and sample information should be available:

• Sample matrix: Substrates, coating, etc.

• Reflection/transmission angle of incidence: Reflection AOI of 45°, Transmission AOI of 45°, etc.

• Polarization: p, s, N/A

• Working wavelength range

• Measurement points: How many and where in the sample?

• Expected GDD/GVD