Biomedical subjects

Stephan Malkmus

Publications and source records attributed to Stephan Malkmus.

4 recordsLinked to original sources

PubMed2006

Ultrafast structural dynamics of photochromic indolylfulgimides studied by vibrational spectroscopy and DFT calculations.

The structural dynamics of the ring-opening reaction in a photochromic indolylfulgimide, a reversible, ultrafast photoswitch, is investigated by ultra-broadband time-resolved vibrational spectroscopy. The experimentally observed vibrational modes of the indolylfulgimide photoisomers C and E are assigned to normal modes with the help of DFT calculations. A complete evaluation of the observed vibrational dynamics including excited-state vibrational modes is used to characterize the reaction path and the cooling behavior of the photoswitch.

Algorithms↗

PubMed2006

Electron-hole dynamics in CdTe tetrapods.

We present transient absorption studies with femtosecond time resolution on the electron-hole dynamics in CdTe tetrapod nanostructures. Electron-hole pairs are generated by optical excitation in the visible spectral range, and an immediate bleach and induced absorption signal are observed. The relaxation dynamics to the lowest excitonic state is completed in about 6 ps. Experiments with polarized excitation pulses give information about the localization of the excited-state wave functions. The influence of the nanocrystal shape on the optical properties of CdTe nanoparticles is discussed.

Anisotropy↗

PubMed2006

Analysis of wave packet motion in frequency and time domain: oxazine 1.

Wave packet motion in the laser dye oxazine 1 in methanol is investigated by spectrally resolved transient absorption spectroscopy. The spectral range of 600-690 nm was accessible by amplified broadband probe pulses covering the overlap region of ground-state bleach and stimulated emission signal. The influence of vibrational wave packets on the optical signal is analyzed in the frequency domain and the time domain. For the analysis in the frequency domain an algorithm is presented that accounts for interference effects of neighbored vibrational modes. By this method amplitude, phase and decay time of vibrational modes are retrieved as a function of probe wavelength and distortions due to neighbored modes are reduced. The analysis of the data in the time domain yields complementary information on the intensity, central wavelength, and spectral width of the optical bleach spectrum due to wave packet motion.

Algorithms↗

PubMed2005

Chirp dependence of wave packet motion in oxazine 1.

The motion of vibrational wave packets in the system oxazine 1 in methanol is investigated by spectrally resolved transient absorption spectroscopy. The spectral properties of the probe pulse from 600 to 700 nm were chosen to cover the overlap region where ground-state bleach and stimulated emission signals are detected. The spectral phase of the pump pulse was manipulated by a liquid crystal display based pulse-shaping setup. Chirped excitation pulses of negative and positive chirp can be used to excite vibrational modes predominantly in the ground or excited state, respectively. To distinguish the observed wave packets in oxazine 1 moving in the ground or excited state, spectrally resolved transient absorption experiments are performed for various values of the linear chirp of the pump pulses. The amplitudes of the wave packet motion show an asymmetric behavior with an optimum signal for a negative chirp of -0.75 +/- 0.2 fs/nm, which indicates that predominantly ground-state wave packets are observed.

Journal Article↗