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We introduce a noninterferometric single beam method to characterize and compensate the spectral phase of ultrashort femtosecond pulses accurately. The method uses a pulse shaper that scans calibrated phase functions to determine the unknown spectral phase of a pulse. The pulse shaper can then be used to synthesize arbitrary phase femtosecond pulses or it can introduce a compensating spectral phase to obtain transform-limited pulses. This method is ideally suited for the generation of tailored spectral phase functions required for coherent control experiments.

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We explore and demonstrate the use of phase-modulated ultrafast laser pulses for controlling nonlinear optical processes in large molecules, proteins, and solid materials. Our experiments illustrate that in condensed phases, when spectra are broad, the spectrum of the nth-order electric field, determined by multiphoton intrapulse interference, plays a major role in controlling multiphoton excitation. These findings determine key parameters (amplitude, period, and symmetry of the phase function) for coherent femtosecond laser control in condensed phases.

Nonlinear optical processes are controlled by modulating the phase of ultrafast laser pulses taking advantage of multiphoton intrapulse interference. Experimental results show orders of magnitude control over two-and three-photon excitation of large organic molecules in solution using specific phase functions. We show simulations on the effect of phase modulation on the second-and third-order amplitude of the electric field spectrum, and demonstrate that the observed control is not caused by simple changes in peak intensity.