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Experimental setup: The femtosecond laser pulses from a Ti:sapphire amplifier (fs amp) are spectrally amplitude modulated using a pulse shaper. A lens focuses the beam into a water jet which serves as the transparent sample. The transmitted self-phase modulated beam is collected by an objective and focused into a spectrometer. In the lower row, schematic spectra of the pulses are depicted.
Normalized temporal electric field envelopes of a Gaussian pulse with removed frequencies. (a) Shows the short central part and the ten times magnified wing structure without self-phase modulation, (b) focuses on the central part. In this part, the temporal phase (plotted without carrier) is flat without self-phase modulation (dashed line) and bell shaped with self-phase modulation (dotted line). The intensity corresponds to Fig. 3(d).
Experimental (left) and simulated (right column) normalized power spectral densities and simulated spectral phases (dashed lines). The intensities are shown in the upper left corners (in units of and ). In case (a), the water jet was switched off (no self-phase modulation) while it was turned on in all other cases.
Schematic physical model of spectral hole filling via self-phase modulation using pulses for visualization. In the first column the spectra of the electric fields are depicted. The second column shows the temporal electric fields. In the third column the Fourier decompositions of the pulses into their modes are sketched. The time zeroes are marked by vertical solid lines. The removal of a certain frequency component (mode with solid black line) is interpreted as the interference with a quasi-continuous wave (QCW) [see cases (b)–(e)]. In (c)–(e) the effect of self-phase modulation is shown for increasing intensity (given in units of ).
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