Guenter Steinmeyer

Fabrication and characterization of single-walled carbon nanotube saturable absorbers for solid-state laser mode-locking near 1 μm

Ultrafast single-walled carbon nanotube saturable absorbers were fabricated and optimized for mode-locking solid-state lasers near 1 mum. Their typical modulation depth and recovery time were measured to be Gt 0.3% and ~ 750 fs, respectively.

Carbon-nanotube mode-locked Cr:YAG laser

Transmissive single-walled carbon nanotube saturable absorbers were used for passive mode-locking of a Cr:YAG laser, delivering tunable sub-100-fs pulses around 1.5 µm with output powers up to 110mW at 84.6 MHz.

Second harmonic characteristics of photonic composite glass layers with ZnO nanocrystallites for ultrafast applications

ZnO nanocrystalline thin layers are of growing interest for ultrafast optical applications. Previous investigations delivered different values of second order susceptibilities. The quantitative contribution of grain structure - depending on fabrication procedure - is not well understood. For our investigations, pure and doped polycrystalline and amorphous ZnO thin filmes of 0.1 to 1.5 μm thickness have been prepared by spray pyrolysis and alternative techniques. Texture, thickness and further structural properties of the layer have been characterized by SEM, AFM, XRD, and optical spectroscopy. Using 20-fs Ti:Sa laser pulses centered at 800 nm, we measured the angular dependence of SHG intensity and determined second order susceptibilities. For a small range of crystallinity parameters, pronouced SHG efficiencies appear. From our experiments, design parameters for ZnO nanolayers can be derived which enable a tailoring of sandwich structures for advanced non-linear processing and femtosecond laser autocorrelation.

On the pulse width of synchronously pumped lasers

The pulse width of a synchronously pumped laser chiefly depends on the available cavity bandwidth and the pump-pulse duration. A functional form of this dependence was suggested in the literature. We present an alternate relation which is supported by analytical and numerical results, as well as by experimental results, obtained by us and by others.

Rogue waves in the beam profiles of multifilaments

Here we discuss a second optical system that clearly features rogue waves, namely the spatial fluence distribution in multifilament beam profiles. Given the formal analogy between one-dimensional fiber solitons and the spatial two-dimensional filament strings, the appearance of rogue waves may not appear overly surprising at first sight. We will show, however, that there are marked differences in the driver mechanism between both optical systems. In particular, while shot-to-shot energy fluctuations on the input beam are considered the driver for rogue wave dynamics in fibers, the formal equivalent of shot-to-shot beam profile variations does not seem to play any role in our system. Instead, mechanical turbulence inside the filament cell appears to act as the trigger mechanism. Refractive index fluctuations inside the cell then act to steer individual filaments into each other, which gives rise to short lived mergers. These filament mergers constitute the rogue waves in our two-dimensional system.

Non-instantaneity of χ (3) nonlinear optical effects

We present direct experimental evidence for a non-instantaneous nonlinear response in TiO2. An asymmetry in interferometric FROG measurements indicates a relaxation time constant of about 5 fs.

Characterization of ultrashort pulses with spatio-temporal and angular resolution

Recent progress in wavefront autocorrelation of ultrashort pulses is reported. The Shack-Hartmann wavefront sensor concept is extended to spatially resolved autocorrelation. Specific advantages and limitations of system design, dynamic range, and optical components are discussed.