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High-resolution Interferometric Diagnostics for Ultrashort Pulses

High-resolution Interferometric Diagnostics for Ultrashort Pulses

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8.6 Simulated experiment20.1(a)50.1(b)0.0540.05θ Q3000−0.0521−0.05-2−0.1−0.1−0.1 −0.05 0 0.05 0.1−0.1 −0.05 0 0.05 0.1θI|D|θIθ QargDFigure 8.10: (a) Amplitude and (b) phase of the computed dipole response (ω;θ Q ,θ I ) at the 49 thharmonic.Whilst the eye can discern some regular patterns in both, a normal fringe pattern is not observedbecause there are many Fourier components present. Around (θ Q ,θ I )=(−0.1,0), an enhancementof the amplitude over many periods of the pattern shows that control field is starting to distort theamplitude of the quantum paths, rather than just their phases.The results are best interpreted in control-field sensitivity space, found by taking discreteFourier trans<strong>for</strong>ms along both control field amplitude co-ordinates yielding ˜(ω;ᾱ). This is plotted<strong>for</strong> four harmonics in Fig. 8.11, along with the control-field sensitivities ¯S (j )ω,Cexpected fromthe perturbative analysis. The αβm labelling system <strong>for</strong> the orbits has been extended slightly:above cutoff, α = C refers to “coalesced” long and short trajectories. For the 30 th harmonic, thereare many peaks and it is difficult to assign the orbits. However, <strong>for</strong> the higher harmonics, almostall of the strong peaks can be assigned to an orbit, showing that the quantum-path analysis hassucceeded.The next section addresses some technical issues which arise during the discrete Fourier trans<strong>for</strong>mto control-field sensitivity space. These do not affect the physics and it is possible to skip tosection 8.8 without losing much understanding.205

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