  Uncertainties of refractive and group index in dispersion measurement by
spectrally resolved white light interferometry are deeply analyzed. First, the
contribution to uncertainty of the different parameters affecting both indices
is identified. Afterwards, results are presented for a 1.5 mm thick fused
silica sample over a broad spectral range, from 400 to 1000 nm, and the effects
that mostly deteriorate the measurement accuracy are established. Finally, the
different contributions are quadratically combined to determine the total
uncertainty of the two indices.
