High-resolution Interferometric Diagnostics for Ultrashort Pulses

4.2 Simultaneous acquisition of shearsSEA-CAR-SPIDERImagingspectrometerFigure 4.8: Experiment for demonstrating and verifying measurement of shaped pulses with SEA-CAR-SPIDER. The dashed lines represent the beams used for spectral interferometry.λ (nm)I (t )420820800780ky (rad/pix)−202-1-2-3log 10 |B|−500 0 500t (fs)0 10 20Ĩ (λ)−2 0 2k x (rad/pix)Figure 4.9: Temporal intensity, spectrum andspectrogram of the bichromatic double pulse,as reconstructed using SEA-CAR-SPIDER.Figure 4.10: Amplitude of Fourier transformof AB interferogram, log 10 color scale. Theboxes show the filters used for the interferogram(red) and noise estimation (green).spectral lobes. The fringes are therefore largely flat, with small modulations caused by high-orderphase distortions present in our laser system. The triangular fringe-covered area at the bottom ofFig. 4.11(c) represents cross-term interference between the upper and lower lobes. The fringe tiltis due to the group-delay difference between the lobes, whilst their phase offset (with respect tothe self-overlap fringes) encodes the relative phase of the lobes.I extracted the fringe phase using Fourier filtering and applied the multiple-shear algorithmusing the 6 shears indicated by the dashed lines in Fig. 4.11(c). I verified the accuracy of the measurementusing spectral interferometry (SI), shown by the dashed lines in Fig. 4.8. I first characterizedan unshaped pulse, produced with no mask in the pulse shaper, using a single shear with theSEA-CAR-SPIDER. I then obtained the phase of the reference arm by interferometry with the characterizedunshaped pulse. The phase of any shaped pulses could then be simply and accurately101