Zumbusch, Andreas
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Lehre in Zeiten digitalen Wandels : Das ADILT Programm der Universität Konstanz
Als eine Reaktion auf den digitalen Wandel hat die Universität Konstanz das Programm „Advanced Data and Information Literacy Track (ADILT)“ initiiert. Ziel des ADILT ist die studienbegleitende Vermittlung von Daten- und Informationskompetenz in einem interdisziplinären Ansatz. Im vorliegenden Artikel wird sowohl das Programm selbst als auch beispielhaft die Umsetzung des Programms in den Fachbereichen Chemie und Physik beschrieben.
Boxcar detection for high-frequency modulation in stimulated Raman scattering microscopy
Stimulated Raman scattering (SRS) microscopy is an important non-linear optical technique for the investigation of unlabeled samples. The SRS signal manifests itself as a small intensity exchange between the laser pulses involved in coherent excitation of Raman modes. Usually, high-frequency modulation is applied in one pulse train, and the signal is then detected on the other pulse train via lock-in amplification. While allowing shot-noise limited detection sensitivity, lock-in detection, which corresponds to filtering the signal in the frequency domain, is not the most efficient way of using the excitation light. In this manuscript, we show that boxcar averaging, which is equivalent to temporal filtering, is better suited for the detection of low-duty-cycle signals as encountered in SRS microscopy. We demonstrate that by employing suitable gating windows, the signal-to-noise ratios achievable with lock-in detection can be realized in shorter time with boxcar averaging. Therefore, high-quality images are recorded at a faster rate and lower irradiance which is an important factor, e.g., for minimizing degradation of biological samples.
Simultaneous second-harmonic generation, third-harmonic generation, and four-wave mixing microscopy with single sub-8 fs laser pulses
We demonstrate a compact pulse compression scheme that offers flexible chirp control for improved conversion efficiencies in high resolution nonlinear optical microscopy. An Er:fiber laser combined with a highly nonlinear optical fiber yields pulses centered at 1100 nm with a bandwidth of 500 nm. The compressed pulses with a duration of 7.6 fs enable simultaneous second-harmonic generation, third-harmonic generation, and four-wave mixing microscopy. The spectrum is tailored for an ideal compromise between conversion efficiency and spectral discrimination between the three types of broadband nonlinear signals. Distinct differences in structural contrast obtained from the simultaneous read-out of the three nonlinear signals are demonstrated in a biological sample.
Observation of liquid glass in suspensions of ellipsoidal colloids
Despite the omnipresence of colloidal suspensions, little is known about the influence of colloid shape on phase transformations, especially in nonequilibrium. To date, real-space imaging results at high concentrations have been limited to systems composed of spherical colloids. In most natural and technical systems, however, particles are nonspherical, and their structural dynamics are determined by translational and rotational degrees of freedom. Using confocal microscopy of fluorescently labeled core-shell particles, we reveal that suspensions of ellipsoidal colloids form an unexpected state of matter, a liquid glass in which rotations are frozen while translations remain fluid. Image analysis unveils hitherto unknown nematic precursors as characteristic structural elements of this state. The mutual obstruction of these ramified clusters prevents liquid crystalline order. Our results give insight into the interplay between local structures and phase transformations. This helps to guide applications such as self-assembly of colloidal superstructures and also gives evidence of the importance of shape on the glass transition in general.
Advancing with pyrrolopyrrole cyanines: a next generation class of near-infrared fluorophores
Fluorescent dyes are the basis for a broad range of modern techniques in life and material sciences. Consequently, there is a pressing need for the development of new classes of NIR fluorophores in recent years. Pyrrolopyrrole Cyanines (PPCys) are a novel class of NIR chromophores that were first presented in 2007 by Fischer and coworkers.[1] Their optical properties are marked by strong and narrowband NIR absorptions, strong NIR fluorescence and hardly any absorption in the visible range. The absorption maxima can be tuned over a broad range while high fluorescence quantum yields are maintained. PPCys are attractive candidates for labelling applications or as selective NIR absorbers. Moreover, PPCys exhibit very high photostability. Due to these outstanding photophysical properties, PPCys are heading into a promising future as NIR dyes.
Detection and tracking of anisotropic core-shell colloids
Optical microscopy techniques with three dimensional (3D) resolution are powerful tools for the real-space imaging of the structure and dynamics of colloidal systems. While real-space imaging of spherical particles is well established, the observation of shape anisotropic particles has only recently met a lot of interest. Apart from translation, shape anisotropic particles also possess additional rotational degrees of freedom. In this manuscript, we introduce a novel technique to find the position and the orientation of anisotropic particles in 3D. It is based on an algorithm which is applicable to core-shell particles consisting of a spherical core and a shell with arbitrary shape. We demonstrate the performance of this algorithm using PMMA/PMMA (polymethyl methacrylate) core-shell ellipsoids. The algorithm is tested on artificial images and on experimental data. The correct identification of particle positions with subpixel accuracy and of their orientations with high angular precision in dilute and dense systems is shown. In addition, we developed an advanced particle tracking algorithm that takes both translational and rotational movements of the anisotropic particles into account. We show that our 3D detection and tracking technique is suitable for the accurate and reliable detection of large and dense colloidal systems containing several thousands of particles.
Coherent anti-Stokes Raman scattering microspectroscopy based on a compact Er:fiber laser
A two branch Er:fiber laser was developed for coherent anti-Stokes Raman scattering (CARS) microspectroscopy. The compact and highly stable light source allows for fast single-frequency CARS microspectroscopy with a wide tuning range from 1150 cm-1 up to 3800 cm-1. Single-pass frequency conversion enables easy tunability. The spectral selectivity of the system is shown using polymer beads. Imaging of biological samples is demonstrated on C. elegans and yeast cells. Modification of the light source allows for broadband background-free CARS microspectroscopy. Impulsive excitation of molecular resonances is achieved using an 11 fs pulse at 1210 nm. Broadband excitation gives access to molecular resonances from 0 cm-1 up to 4000 cm-1. Time-delayed narrowband probing at 775 nm enables sensitive and high-speed spectral detection of the CARS signal, free of nonresonant background with a resolution of 10 cm-1.