In this thesis, I present several new technologies aimed at improving ultrafast spectroscopy at attosecond timescales. The focus of the work was on femtosecond field synthesis, but work on attosecond streaking spectroscopy is also presented.

We used CEP few-cycle near-infrared laser pulses to generate XUV isolated attosecond pulses for attosecond streaking spectroscopy on solid surfaces. We characterised the few-cycle pulses using a SEA-F-SPIDER and constructed a combined Second Harmonic/Transient Grating FROG to permit the characterisation of pulses from the UV to the short wavelength infrared. The isolated attosecond pulses were applied, with the few-cycle pulses, to the measurement of the photoemission time delay from gold and silver surfaces. We studied the effect of the few-cycle pulse's Gouy phase on streaking measurements and found that, for our system, the effect was larger than previous reports suggested. We then developed and implemented a bi-material target for surface streaking. This system minimised the systematic error resulting from Gouy phase shifts. We then used the system to measure the photoemission delay between the two materials, finding that gold valence photoelectrons were delayed by 171 ± 49 as relative to silver valence photoelectrons.

We constructed a three-colour field synthesizer. The purpose of this system was to generate sub-cycle shaped pulses that could optimise attosecond pulse generation. The output of a CEP stable NIR amplifier was split with one channel being the CEP-stable few-cycle NIR pulse. The other two channels were a 40 fs duration, short wavelength infrared pulse centred at 1300 nm, generated using a commercial OPA system, and a 46 fs duration UV pulse centred at 405 nm generated by second-harmonic generation. The relative stability of each channel and was measured to be 0.179 rad for the second harmonic relative to the few-cycle pulse. For the infrared pulse relative to the few-cycle pulse, the stability was 13.2 rad, which was larger due to the phase instability in commercial OPA. The spatial quality of the beams was measured and found to be suitable for the driving HHG.

Two of the three pulses in the synthesizer were used to generate attosecond pulses at 90 eV photon energy with a two-fold increase in flux compared to the single colour case. Synthesized-field waveform-dependent shifts in the cutoff were observed in the HHG spectrum. The resulting attosecond pulses were characterised using gas-phase attosecond streaking, showing that their duration was minimally affected by the presence of the weaker field due to spectral filtering by a multilayer mirror. From the streaking trace, we were able to accurately retrieve the spectrum of the multi-cycle pulse.