Contrast improvement by using tailored laser pulses to circumvent undesired excitations

We report on fluorescence contrast improvement by using phase, amplitude, and polarization shaped laser pulses. The measurements were conducted by applying phase functions at different spectral amplitudes for excitations of dyes and agree very well with calculations. In particular, undesired one-photon excitations are circumvented with phase and amplitude tailored pulses for two-photon transition. This is realized by cutting out the laser spectrum at the wavelength of the one-photon process while utilizing an antisymmetric phase function that allows for constructive interference of the remaining outer spectral contributions for two-photon absorption. Moreover, polarization enhanced contrast between dyes is demonstrated where the two-photon dye is predominantly excited in one polarization direction and simultaneously the one-photon dye in the other polarization direction. The presented methods of shaping ultrashort laser pulses have a high potential for imaging applications.