High-resolution Interferometric Diagnostics for Ultrashort Pulses

7. LATERAL SHEARING INTERFEROMETRY FOR HIGH-HARMONIC GENERATION13800015Harmonic order17192123Intensity60004000200025−2 0 20−2 0 2x (mm)x (mm)Figure 7.10: A typical raw intensity image.Figure 7.11: Shot-averaged spatial intensityprofiles at different shears at a single gas jetz position. The uncertainty, taken as thestandard error, is indicated by the shadederror.be emphasized that this factor did not vary with the gas jet z position, meaning that any agreementbetween the measured and theoretical values in the z -dependence of the intensity is genuine.Figure 7.13 shows the amplitude and phase profiles for harmonics 13, 19, and 25 at gas jet positions−4mm, −1mm and 2mm. For harmonic 25, the agreement is good: the beam profile isclose to Gaussian and experiment and theory agree in terms of the peak intensity, beam width,and phase curvature. For harmonic 19, the phase agreement is poor at −4mm but reasonable atthe other values, whilst the intensity agrees reasonably. For harmonic 13, there is some disagreementin the beam width, but overall the measured intensity profiles are in reasonable agreementwith the simulation. For the phase, the agreement is once again poor at −4mm. At −1mm, thesimulated phase differs greatly from quadratic, being largely flat across the majority of the beamand then flipping by ≈ π in the wings. The flat central phase is captured by the measurements,along with a phase flip on one side. Finally at 2mm, the agreement is good for the phase.These observations are consistent with three general trends in the agreement between theory172