High-resolution Interferometric Diagnostics for Ultrashort Pulses

2. BACKGROUNDtion to produce a spatially uniform reference pulse which must contain all frequencies present inthe test pulse.2.5 Outline of this dissertationThe work presented in chapters 3–5 can now be placed in context.All forms of shearing interferometry (sections 2.3.6 and 2.4.1.3) suffer from relative phase ambiguitiesacross spectral nulls — regions of zero intensity. In chapter 3, I present a means of overcomingthis ambiguity: an algorithm for combining interferograms taken at different shears. Asmall shear may sample fine spectral details, achieving high resolution, simultaneously with alarge shear which obtains the phase difference across regions of zero intensity. I also show that theuse of multiple shears improves the precision even if spectral nulls are absent.Chapter 4 presents two experimental implementations of multiple spectral shearing interferometry.The first uses a SEA-SPIDER to acquire multiple shears in sequence. The second uses anewly developed implementation of CAR-SPIDER to acquire a range of shears simultaneously.Section 2.4 showed that only a few methods for complete spatio-temporal characterisation exist.Of these, most rely on the production of a reference pulse with properties that may not beachieveable in practice. Most approaches are also the combination of two separate instruments— one for the spatial and one for the temporal characterisation, with an associated increase incomplexity and number of components. In chapter 5, I present a method for two-dimensionalspatio-temporal pulse measurement which addresses both of these concerns. It is based on combinedlateral and spectral shearing interferometry but performs both of these using a single interferometer.62