High-resolution Interferometric Diagnostics for Ultrashort Pulses

7. LATERAL SHEARING INTERFEROMETRY FOR HIGH-HARMONIC GENERATION10255Pressure (atm)Response (atm)0.10.0500.10.05(a)(b)25kz (rad/mm)010501051913013−1 0 1z (mm)0−5 0 5z (mm)Figure 7.19: (a) Gas pressure. (b) Amplitudeof gas jet response (product of gas pressureand transmission to z = ∞) for harmonics13–25.Figure 7.20: Components of the longitudinalphase mismatch from the refractive indexat the laser wavelength (cyan solid), refractiveindex of the harmonics (magentasolid), Gouy phase (black solid), intensitydependenceof short and long (blue andgreen solid) trajectories below cutoff, andthe dominant trajectory (red solid) abovecutoff. The total phase mismatch is alsoshown (blue, green and red dashed).One may now interpret the simulated far-field macroscopic profiles which were used for thecomparison in Fig. 7.12. These are shown in Fig. 7.21. They are in fact very similar to the singleatomresponse (Fig. 7.18), the main differences being a small increase (decrease) in the apparentamplitude of the off-axis components for z < 0(z > 0) due to the phase matching, and a movementof 1–2 mm of the entire response to negative z . The latter effect is caused by the shifted peaks ofthe gas jet response, shown in Fig. 7.19, and is greater for the lower harmonics.180