Parametrically polarization shaped pulses guided via a hollow core photonic crystal fiber for coherent control

We present ultrafast polarization pulse shaping through a micro structured hollow core photonic crystal fiber. The pulses are shaped in pulse sequences in which the energy, distance, phases, and chirps as well as the state of polarization of each individual sub-pulse can be independently controlled. The application of these pulses for coherent control is demonstrated for feedback loop optimization of the multi-photon ionization of potassium dimers. In a second experiment, this process is investigated by shaper-assisted pump–probe spectroscopy which is likewise performed with pulses that are transmitted through the fiber. Both techniques reveal the excitation pathway including the dynamics in the participating electronic states and expose the relevance of the polarization. These methods will be valuable for endoscopic applications

Phase sensitive pulse shaping for molecule selective three-photon excitation

In this paper we present a method for selective three-photon excitation of the two dyes, p-Terphenyl (PTP) and BM-Terphenyl (BMT), in solution by using shaped pulses. A good agreement between experiment and theoretical simulation is obtained. With this method 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

Epimerization of trans-Cycloalkenes with the X–C=C–SeR*-Unit – The Steric Demand of X = H, F, Cl, Br, I, Me, Et and CF3

Trans-cycloalkenes with the X–C=C–SeR*-unit and ring sizes from 9 to 20 have been synthesized. Bond the selenium atom is the chiral (S)-o-(1-Methoxypropyl)phenyl-residue R*, and X = H, F, Cl, Br, I, Me, Et and CF3. The planar-chiral trans-cycloalkenes in combination with the chiral residue R* exist as two diastereomers. These can be distinguished in principle by NMR spectroscopy. We have studied the epimerization of the trans-cycloalkenes, i.e., the 180° rotation of the X–C=C-unit through the cavity of the ring. The measurements were done with variable temperature 13C NMR spectroscopy in the range from –110 to 140°C. The obtained values of the Gibbs energy of activation ΔG‡C depend strongly on the ring size. Furthermore, the ΔG‡C values show dramatic steric effects due to the groups X. The steric requirement of X increases in the series H << F << Cl < Me < Br < I < Et < CF3. Here, F is significantly larger than H, and CF3 is larger than Et. The corresponding iPr-compounds could not be synthesized. The transition state structures of the ring inversion for ring sizes 8–20 were calculated at the DFT level of theory

Parametrically shaped femtosecond pulses in the nonlinear regime obtained by reverse propagation in an optical fiber

We present the experimental realization of a method to generate predetermined, arbitrary pulse shapes after transmission through an optical fiber in the nonlinear regime. The method is based on simulating the reverse propagation of the desired pulse shape in the fiber. First, linear and nonlinear parameters of a single-mode step-index fiber required for the simulation are determined. The calculated pulse shapes are then generated in a pulse shaper

Influence of nonlinear effects on the three-photon excitation of L-Tryptophan in water using phase-shaped pulses

In its geometric form, the Maupertuis Principle states that the movement of a classical particle in an external potential V(x) can be understood as a free movement in a curved space with the metric gμν(x) = 2M[V(x) - E]δμν. We extend this principle to the quantum regime by showing that the wavefunction of the particle is governed by a Schrödinger equation of a free particle moving through curved space. The kinetic operator is the Weyl-invariant Laplace–Beltrami operator. On the basis of this observation, we calculate the semiclassical expansion of the particle density

Contrast optimization of two-photon processes after a microstructured hollow- core fiber demonstrated for dye molecules

We demonstrate selective excitation of dyes with overlapping absorption spectra in solution with pulses transmitted through a hollow-core ber. Thereto we show ects occurring in the ber can be compensated and what the limiting pulse energies are. Furthermore, an overview over various phase parametrizations is given and we examine which are best used when optimizing a two-photon fluorescence contrast of two dyes in a sample. This could be relevant for future endoscopic applications as well as state of the art two- photon microscopy

Hydration effects turn a highly stretched polymer from an entropic into an energetic spring

Polyethylene glycol (PEG) is a structurally simple and nontoxic water-soluble polymer that is widely used in medical and pharmaceutical applications as molecular linker and spacer. In such applications, PEG’s elastic response against conformational deformations is key to its function. According to text-book knowledge, a polymer reacts to the stretching of its end-to-end separation by a decrease in entropy that is due to the reduction of available conformations, which is why polymers are commonly called entropic springs. By a combination of single-molecule force spectroscopy experiments with molecular dynamics simulations in explicit water, we show that entropic hydration effects almost exactly compensate the chain conformational entropy loss at high stretching. Our simulations reveal that this entropic compensation is due to the stretching-induced release of water molecules that in the relaxed state form double hydrogen bonds with PEG. As a consequence, the stretching response of PEG is predominantly of energetic, not of entropic, origin at high forces and caused by hydration effects, while PEG backbone deformations only play a minor role. These findings demonstrate the importance of hydration for the mechanics of macromolecules and constitute a case example that sheds light on the antagonistic interplay of conformational and hydration degrees of freedom

Synthesis, self-assembly, and photocrosslinking of fullerene-polyglycerol amphiphiles as nanocarriers with controlled transport properties

In this work, we report a new, simple, gram-scale method for synthesizing water-soluble fullerene-polyglycerol amphiphiles (FPAs) that self-assemble into partially and fully crosslinked nanoclusters with the ability to controllably transport hydrophobic and hydrophilic agents

Selective excitation with shaped pulses transported through a fiber using reverse propagation

Reverse propagation is a numeric technique that makes it possible to obtain arbitrarily shaped pulses after propagation through a fiber in the nonlinear regime. We apply it to achieve selective two-photon excitation of dyes that have overlapping absorption spectra with pulses transported through the fiber. By comparing both contrast and signal level it is shown that phase and amplitude shaped pulses generated using reverse propagation are superior to pulses with antisymmetric phase despite loss caused by amplitude shaping

Supramolecular hydrophobic guest transport system based on pillar[5]arene

A pillar[5]arene-based bioactive guest loading system has been developed, which can increase the solubility of the drug norharmane in aqueous medium, and also enable its pH-stimulated release. Furthermore, this supramolecular transport system reduces the toxicity of loaded gues