Efficient procedure for the measurement of preresonant excitation profiles in UV Raman spectroscopy

Resonance Raman spectroscopy (RRS) is a promising technique for investigating samples with low concentrations of single constituents or many different constituents. The wavelength dependent resonance enhancement (resonance profile) of the respective molecule yields information about the targeted species and reveals the optimal wavelength for high resolution RRS. A significant increase of the Raman scattered intensity can already be achieved in the vicinity of the molecules' absorption band (preresonance). Measuring such preresonance and resonance profiles requires precise control of excitation conditions and careful assessment of the spectral accuracy of the setup. We present a comprehensive procedure for the acquisition of preresonance profiles in Raman spectroscopy. An experimental setup for recording the single spectra is combined with an efficient algorithm for data postprocessing. The procedure is demonstrated on amino acids measured in the UV and can be applied to any molecule and wavelength range. © 2017 Author(s)

UV-resonance Raman spectroscopy of amino acids

Resonant enhancement of Raman signals is a useful method to increase sensitivity in samples with low concentration such as biological tissue. The investigation of resonance profiles shows the optimal excitation wavelength and yields valuable information about the molecules themselves. However careful characterization and calibration of all experimental parameters affecting quantum yield is required in order to achieve comparability of the single spectra recorded. We present an experimental technique for measuring the resonance profiles of different amino acids. The absorption lines of these molecules are located in the ultraviolet (UV) wavelength range. One limitation for broadband measurement of resonance profiles is the limited availability of Raman filters in certain regions of the UV for blocking the Rayleigh scattered light. Here, a wavelength range from 244.8 nm to 266.0 nm was chosen. The profiles reveal the optimal wavelength for recording the Raman spectra of amino acids in aqueous solutions in this range. This study provides the basis for measurements on more complex molecules such as proteins in the human perilymph. The composition of this liquid in the inner ear is essential for hearing and cannot be analyzed non-invasively so far. The long term aim is to implement this technique as a fiber based endoscope for non-invasive measurements during surgeries (e. g. cochlear implants) making it available as a diagnostic tool for physicians. This project is embedded in the interdisciplinary cluster of excellence "Hearing for all" (H4A). © 2016 SPIE

Impact of spatial inhomogeneities on on-axis pulse reconstruction in femtosecond filaments

We demonstrate a strong influence of the spatial beam profile on the vacuum-propagated on-axis pulse shapes for a femtosecond filament in argon. The effects can be minimized by transmitting the filament into the far-field by a laser-drilled pinhole setup. Using this method, we can monitor the pulse compression dynamics along the entire longitudinal extension of the filament, including the ionization-induced plasma channel

Spatial contributions of electron trajectories to high-order-harmonic radiation originating from a semi-infinite gas cell

We report on the analysis of the spatial beam profile of high-order harmonic radiation originating from a semi-infinite gas cell (SIGC). We experimentally assign contributions of electron trajectories to different spatial regions of the harmonic radiation beam. The angular divergence of the harmonic radiation is studied for the first time in a SIGC as a function of different phase-matching parameters. We relate the ratio of the dipole phase coefficients to the coherence time and divergence angle measurements. Simulations, including high-order-harmonic propagation, give further insight into the generation process and the influence of phase matching. The analysis reveals that the SIGC enables tuning of the cutoff frequency by altering the absorption of the generating medium.The authors thank Vasily V. Strelkov and Pascal Salie`res for valuable discussions and the Deutsche Forschungsge- meinschaft DFG and the Cluster of Excellence QUEST for financial support of this work. Carlos Hernández-García and Luis Plaja acknowledge support from Junta de Castilla y León (Consejería de Educación and Fondo Social Europeo) and Spanish MINECO (FIS2009-09522)

Carrier-envelope phase sensitive inversion in two-level systems

We theoretically study the carrier-envelope phase dependent inversion generated in a two-level system by excitation with a few-cycle pulse. Based on the invariance of the inversion under time reversal of the exciting field, parameters are introduced to characterize the phase sensitivity of the induced inversion. Linear and nonlinear phase effects are numerically studied for rectangular and sinc-shaped pulses. Furthermore, analytical results are obtained in the limits of weak fields as well as strong dephasing, and by nearly degenerate perturbation theory for sinusoidal excitation. The results show that the phase sensitive inversion in the ideal two-level system is a promising route for constructing carrier-envelope phase detectors

High-order harmonic spectroscopy in an ionized high-density target

We use high-order harmonic spectroscopy to study ionization dynamics in a macroscopic target with tunable density, spanning over six orders of magnitude. In an in situ pump-probe experiment, the target is prepared at different densities with varying degrees of laser-induced ionization. High-order harmonic radiation is generated in the pre-ionized target, and a steepening in the decrease of the harmonic yield is observed for increasing pre-ionization, allowing not only to identify the contributing quantum paths during high-order harmonic generation but also in determining the amount of ionization within the target. The measurements allow probing of ionization dynamics in laser-induced plasma with high spatio-temporal resolution and are specifically of interest for the optimization of the harmonic generation process in high-density targets with number densities of up to 1022 cm−3

Fruchtfolge-Planer

Die Fruchtfolge spiegelt den ganzen Landwirtschaftsbetrieb wider. Wenn ein flächenrelevanter Betriebszweig geändert wird, hat das in der Regel Einfluss auf die ganze Fruchtfolge. Das Aufstellen einer Fruchtfolge ist somit eine sehr komplexe Angelegenheit. Der Fruchtfolgeplaner hilft dabei