High-resolution Interferometric Diagnostics for Ultrashort Pulses

AbstractI present several new methods for the characterisation of ultrashort pulses using interferometry.A generalisation of the concatenation algorithm for spectral shearing interferometryenables interferograms taken at multiple shears to be combined. This improves theprecision of the reconstructed phase in the presence of detector noise, and enablesthe relative phase between disjoint spectral components to be obtained without decreasingthe spectral resolution. The algorithm is applied to experimental data fromtwo different implementations of spectral shearing interferometry for ultrashort opticalpulses. In one, the shears are acquired sequentially, and in the other they areacquired simultaneously.I develop a form of spatio-temporal ultrashort pulse characterisation which performsboth spatial and spectral shearing interferometry simultaneously. It requires a similargeometrical setup to common implementations of spectral phase interferometryfor direct electric-field reconstruction, but provides complete amplitude and phasecharacterisation in time and one spatial dimension.I develop the theory of lateral shearing interferometry for spectrally resolved wavefrontsensing of extended ultraviolet and soft x-ray pulses generated using high-harmonicgeneration. A comprehensive set of wavefront measurements of harmonics 13–25 inKrypton show good agreement with theory, validating the technique.I propose and numerically demonstrate quantum-path interferometry mediated bya weak control field for high harmonic generation. This is a general technique formeasuring the amplitude and relative phases of each contributing quantum path. Thecontrol field perturbatively modulates the phase of each path. The differing sensitivityof each path to the parameters of the control field allows their contributions to bedistinguished from one another.ii