Bernhard Kohler

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We use the algorithmic method of generalized projections (GP's) to retrieve the intensity and phase of an ultrashort laser pulse from the experimental trace in frequency-resolved optical gating (FROG). Using simulations, we show that the use of GP's improves significantly the convergence properties of the algorithm over the basic FROG algorithm. In(More)
To better understand DNA photodamage, several nucleosides were studied by femtosecond transient absorption spectroscopy. A 263-nm, 150-fs ultraviolet pump pulse excited each nucleoside in aqueous solution, and the subsequent dynamics were followed by transient absorption of a femtosecond continuum pulse at wavelengths between 270 and 700 nm. A transient(More)
Frequency-resolved optical gating (FROG) measurements were made to characterize pulses from a Ti:sapphire chirped-pulse amplified laser system. By characterizing both the pulse intensity and the phase, the FROG data provided the first direct observation to our knowledge of residual phase distortion in a chirped-pulse amplifier. The FROG technique was also(More)
Ultrashort-pulse-characterization techniques generally require instantaneously responding media. We show that this is not the case for frequency-resolved optical gating (FROG). We include, as an example, the noninstantaneous Raman response of fused silica, which can cause errors in the retrieved pulse width of as much as 8% for a 25-fs pulse in(More)
The one-dimensional vibration mode of a piezoelectric layer under different load conditions has been reconsidered. Derived analytical expressions for admittance and impedance at special frequencies are listed. Based on the expressions derived, two applications are proposed involving electrical measurements on a piezoelectric plate. Concerned are first the(More)
The challenge of nano packaging requires new non-destructive evaluation (NDE) techniques to detect and characterize very small defects like Kirkendall voids or micro cracks. Imaging technologies with resolutions in the sub-micron range are desired. Possible evaluation methods are for example x-ray microscopy, x-ray tomography, ultrasonic microscopy and(More)
Advanced scanning probe microscopy techniques combine atomic force microscopy (AFM) with ultrasound. Atomic force acoustic microscopy (AFAM) and ultrasonic force microscopy (UFM) become increasingly powerful tools for the determination of material properties on nanoscale. AFAM is mainly applied to the analysis of materials with elastic properties locally(More)
A series of organic- and water-soluble distyrylbenzene-based two-photon absorption (TPA) fluorophores containing dialkylamino donor groups at the termini was designed, synthesized, and characterized. The central core was systematically substituted to modulate intramolecular charge transfer (ICT). These molecules allow an examination of solvent effects on(More)
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