Laserspektroskopische Untersuchungen mit Femtosekunden-Zeitauflösung an Oligothiophenen unter besonderer Berücksichtigung der Triplettzustände

Laserspektroskopie an Thiophenoligomeren. Schnelle Relaxationen nach Anregung mit Femtosekunden Laserimpulsen wurden untersucht. Es wurde eine ultraschnelle Triplettbildung (Intersystem Crossing) innerhalb von 2 ps gefunden

Verbundprojekt 1:Technologiebaukasten, Teilprojekt 1.5 - Institut für Photonische Technologien e.V. (IPHT): Methodenentwicklung für Prozessdiagnostik und prozessvorbereitende Maßnahmen für ausgewählte Beschichtungsverfahren : Wachstumskern "J-1013" - Surface Technologies Net ; Abschlussbericht

[no abstract available

Amorphous Silicon Thin-Film Solar Cells on Fabrics as Large-Scale Detectors for Textile Personal Protective Equipment in Active Laser Safety †

Laser safety is starting to play an increasingly important role, especially when the laser is used as a tool. Passive laser safety systems quickly reach their limits and, in some cases, provide inadequate protection. To counteract this, various active systems have been developed. Flexible and especially textile-protective materials pose a special challenge. The market still lacks personal protective equipment (PPE) for active laser safety. Covering these materials with solar cells as large-area optical detectors offers a promising possibility. In this work, an active laser protection fabric with amorphous silicon solar cells is presented as a large-scale sensor for continuous wave and pulsed lasers (down to ns). First, the fabric and the solar cells were examined separately for irradiation behavior and damage. Laser irradiation was performed at wavelengths of 245, 355, 532, and 808 nm. The solar cell sensors were then applied directly to the laser protection fabric. The damage and destruction behavior of the active laser protection system was investigated. The results show that the basic safety function of the solar cell is still preserved when the locally damaged or destroyed area is irradiated again. A simple automatic shutdown system was used to demonstrate active laser protection within 50 ms

Excitation Energy Dependent Ultrafast Luminescence Behavior of CdS Nanostructures

Selected semiconductor nanostructures provide extremely localized coherent light sources. Here an ensemble of CdS nanostructures was excited by UV/vis femtosecond laser pulses and their ultrafast luminescence characteristics were investigated as functions of the pulse energy fluence and the photon quantum energy. All optical Kerr gating enabled studies of the emission dynamics with a time resolution of 150 fs avoiding any influence on the CdS emission. The initially observed emission built up after a delay of 0.1–3 ps and decayed rapidly in a biexponential way, strongly dependent on both the laser energy fluence and the quantum energy. The central wavelength of the emission spectrum revealed a significant blue-shift within the first few ps followed by a transient red-shift relative to spontaneous excitonic emission of CdS. All findings are mainly attributed to stimulated radiative carrier recombination in the laser excited electron–hole plasma after its thermalization with the CdS lattice

Plasmonic Coupling and Long-Range Transfer of an Excitation along a DNA Nanowire

We demonstrate an excitation transfer along a fluorescently labeled dsDNA nanowire over a length of several micrometers. Launching of the excitation is done by exciting a localized surface plasmon mode of a 40 nm silver nanoparticle by 800 nm femtosecond laser pulses <i>via</i> two-photon absorption. The plasmonic mode is subsequently coupled or transformed to excitation in the nanowire in contact with the particle and propagated along it, inducing bleaching of the dyes on its way. <i>In situ</i> as well as <i>ex situ</i> fluorescence microscopy is utilized to observe the phenomenon. In addition, transfer of the excitation along the nanowire to another nanoparticle over a separation of 5.7 μm was clearly observed. The nature of the excitation coupling and transfer could not be fully resolved here, but injection of an electron into the DNA from the excited nanoparticle and subsequent coupled transfer of charge (Dexter) and delocalized exciton (Frenkel) is the most probable mechanism. However, a direct plasmonic or optical coupling and energy transfer along the nanowire cannot be totally ruled out either. By further studies the observed phenomenon could be utilized in novel molecular systems, providing a long-needed communication method between molecular devices

Notes on thermometric artefacts by Er3+ luminescence band interference

Optical thermometry based on the intensity ratio of the 2H11/2 → 4I15/2 (525 nm) and 4S3/2 → 4I15/2 (545 nm) emission of Er3+ provides a powerful tool for microscale temperature sensing. Crystalline β-NaYF4:Er,Yb is an excellent thermometry material for green upconversion emission upon NIR laser excitation. However, interfering 2H9/2 → 4I13/2 emission is observed around 555 nm for continuous-wave laser excitation intensities above 10 W/cm2. In this study, the green Er3+ emission bands are characterized and it is demonstrated how the true sample temperature is determined circumventing possible artefacts