Laser pulse shaping is reported for applications on multiphoton processes in dye molecules. Particularly phase-tailored pulse shapes are employed for two-photon excited fluorescence of dyes in a liquid environment, also at the distal end of an optical fiber, in order to improve the contrast between dye markers having similar excitation spectra. Precompensation of the optical fiber properties is utilized by analytical pulse shaping in order to receive specific parametric pulse forms after the fiber. This will lead to new endoscopic imaging applications with an increased fluorescence contrast. Moreover, selective excitation is also demonstrated for three-photon transitions of the two dyes, p-Terphenyl (PTP) and BM-Terphenyl (BMT), in solution by using shaped pulses without a fiber. A good agreement between experiment and theoretical simulation is obtained. With this approach it is possible to achieve a considerable change of the fluorescence contrast between the two dyes which is relevant for imaging applications of biological molecules.
We have performed transient multi-photon ionization experiments on small alkali clusters of different size in order to probe their wave packet dynamics, structural reorientations, charge transfers and dissociative events in different vibrationally excited electronic states including their ground state. The observed processes were highly dependent on the irradiated pulse parameters like wavelength range or its phase and amplitude; an emphasis to employ a feedback control system for generating the optimum pulse shapes. Their spectral and temporal behavior reflects interesting properties about the investigated system and the irradiated photo-chemical process. First, we present the vibrational dynamics of bound electronically excited states of alkali dimers and trimers. The scheme for observing the wave packet dynamics in the electronic ground state using stimulated Raman-pumping is shown. Since the employed pulse parameters significantly influence the efficiency of the irradiated dynamic pathways photo-induced ioniziation experiments were carried out. The controllability of 3-photon ionization pathways is investigated on the model-like systems NaK and K2. A closed learning loop for adaptive feedback control is used to find the optimal fs pulse shape. Sinusoidal parameterizations of the spectral phase modulation are investigated in regard to the obtained optimal field. By reducing the number of parameters and thereby the complexity of the phase moduation, optimal pulse shapes can be generated that carry fingerprints of the molecule's dynamical properties. This enables to find "understandable" optimal pulse forms and offers the possiblity to gain insight into the photo-induced control process. Characteristic motions of the involved wave packets are proposed to explain the optimized dynamic dissociation pathways.