Albrecht Lindinger

High resolution vibronic spectra of the amino acids tryptophan and tyrosine in 0.38 K cold helium droplets

High resolution vibronic absorption spectra are reported for the amino acids tryptophan and tyrosine embedded in large (N≃103–104) helium droplets. The spectra exhibit a large number of sharp (δν≈0.5 cm−1) 000 band origins which are attributed to different conformers. The significant differences to previous spectra of the isolated molecules from seeded beam expansions are interpreted in terms of the lower temperatures and the suppression of certain conformers in the liquid helium environment.High resolution vibronic absorption spectra are reported for the amino acids tryptophan and tyrosine embedded in large (N≃103–104) helium droplets. The spectra exhibit a large number of sharp (δν≈0.5 cm−1) 000 band origins which are attributed to different conformers. The significant differences to previous spectra of the isolated molecules from seeded beam expansions are interpreted in terms of the lower temperatures and the suppression of certain conformers in the liquid helium environment.

Laser-induced fluorescence spectroscopy of van der Waals complexes of tetracene–ArN (N⩽5) and pentacene–Ar within ultracold liquid He droplets

Abstract Van der Waals complexes of tetracene and pentacene with several Ar atoms have been assembled within cold (0.38 K) liquid 4 He droplets (≈6000 atoms) and then studied spectroscopically via laser-induced fluorescence (LIF). The spectra reveal a series of well-resolved sharp peaks (linewidth δν 4 He droplets were apparently suppressed in the earlier seeded beam experiments presumably because of the much higher internal temperatures.

Coherent control with shaped femtosecond laser pulses applied to ultracold molecules

We report on coherent control of excitation processes of translationally ultracold rubidium dimers in a magneto-optical trap by using shaped femtosecond laser pulses. Evolution strategies are applied in a feedback loop in order to optimize the photoexcitation of the Rb{sub 2} molecules, which subsequently undergo ionization or fragmentation. A superior performance of the resulting pulses compared to unshaped pulses of the same pulse energy is obtained by distributing the energy among specific spectral components. The demonstration of coherent control to ultracold ensembles opens a path to actively influence fundamental photoinduced processes in molecular quantum gases.

The phonon wings in the (S1 ← S0) spectra of tetracene, pentacene, porphin and phthalocyanine in liquid helium droplets

The vibronic spectra of the large organic molecules tetracene (C18H12), pentacene (C24H14), base-free porphin (C20H14N4) and base-free phthalocyanine (C32H18N8) have been investigated in large (N ≈ 103–104) 4He droplets using laser induced fluorescence. The spectra show sharp zero phonon lines (Δν ⩽ 0.2 cm−1), accompanied by weaker phonon wings on the blue side. The very small inhomogeneous broadening of the zero phonon lines supports the unique properties of liquid He as an extremely gentle ultra-cold matrix for high resolution spectroscopy of larger molecules. Pronounced structures in the phonon wings, which are characteristic for each molecule, are attributed to the excitation of vibrational modes of the helium atoms located in shells surrounding the molecule.

Phase, amplitude, and polarization shaping with a pulse shaper in a Mach-Zehnder interferometer

We present a shaper scheme that fully controls the spectral phase, amplitude, and polarization of femtosecond laser pulses. In particular, it enables independent manipulation over the major axis orientation and the axis ratio of the polarization ellipse. This is accomplished by integrating a 4f-shaper setup in both arms of a Mach-Zehnder interferometer and rotating the polarization by 90 degrees in one of the arms before overlaying the beams. The generated pulses are resolved in a simple and intuitive detection scheme.

Optimal control of filamentation in air

The authors demonstrate optimal control of the propagation of ultrashort, ultraintense (multiterawatt) laser pulses in air over distances up to 36m in a closed-loop scheme. They optimized three spectral ranges within the white-light continuum as well as the ionization efficiency. Optimization results in signal enhancements by typical factors of 2 and 1.4 for the target parameters. The optimization results in shorter pulses by reducing their chirp in the case of white-light continuum generation, while they correct the pulse from its defects and set the filamentation onset near the detector as far as air ionization is concerned.

Time-resolved explosion dynamics of H 2 O droplets induced by femtosecond laser pulses

Series of time-resolved still images of the explosion dynamics of micrometer-sized water droplets after femtosecond laser-pulse irradiation were obtained for different laser-pulse intensities. Amplified pulses centered around a wavelength of 805 nm with 1-mJ energy and 60-fs duration were focused onto the droplet to initiate the dynamics. Several effects, such as forward and backward plumes, jets, water films, and shock waves, were investigated. Additionally, the influence of different pulse durations produced by chirping the laser pulses was observed.

Full control over the electric field using four liquid crystal arrays

We present a femtosecond pulse shaper setup that is capable of shaping the phase, amplitude, and polarization simultaneously and independently. The modulator utilizes four liquid crystal arrays, a pair of half-wave plates, and a polarizer to gain full control of the electrical field. This is done in a common-path common-optic scheme without using interferometry. The functionality of the setup is demonstrated by using systematic parameter scans and example pulses.

Splitting of the Zero Phonon Lines of Indole, 3-Methyl Indole, Tryptamine and N-Acetyl Tryptophan Amide in Helium Droplets

The high resolution vibronic spectra of the S1←S0 transition (ν≈34900 - 35300 cm-1) of indole and its derivatives 3-methyl indole, tryptamine and N-acetyl tryptophan amide (NATA) embedded in large (N∼103-104) helium droplets exhibit an unexpected splitting of the zero phonon lines. Up to four components are observed, also for the different conformers in tryptamine, with spacings of about Δν≈1-2 cm-1 not seen in previous studies of the embedded amino acids tryptophan and tyrosine and other organic molecules. The split levels are attributed to different arrangements of two He atoms from the bath which are localized at the two different sites on the two sides of the indole chromophore. The relative intensities of the different components depend on the particular “side chain” attached to a common indole chromophore.

One parameter fs-pulse form control on NaK and Na2K

One parameter control experiments are carried out on two simple model systems with different complexities, the dimer NaK and the trimer Na2K. The influence of the most important pulse features in formally found optimal control results are investigated independently for both molecules: the chirp and the separation of subpulses in pulse trains. For both molecules, the photoinduced processes under control are the transient three photon ionizations. Studies are presented that reveal the dependence of the measured ion yield on the applied chirps and the pulse separations. The pulse trains consisting of several subpulses are created by applying a sinusoidal spectral phase modulation. These studies may as well aid the interpretation of generated complex pulse shapes obtained in optimal control experiments.