Wissenschaftliche Gesellschaft für Lasertechnik e.V.

By propagating beamlets from a periodically placed array of single-mode fiber amplifiers in a large mode-are (LMA) fiber, we find that a self-image of the initial beamlets is formed at certain distances in the LMA fiber. A Talbot mirror fiber device (TMFD) based on this property is proposed for phase-locking of a multi-fiber laser. For this laser system, we investigate how the LMA fiber length variation; the fiber amplifier phase variation, amplitude variation, and displacement affect the self-image qualities and the coupling efficiency.

The generation and characterization of the Four-Wave-Mixing (FWM) effect in an Erbium Doped Zirconia-Yttria-Alumino Silicate Fiber (EDZF) is described. The EZDF is fabricated from a conventional silica preform by Modified Chemical Vapour Deposition (MCVD) and also solution doping to add glass modifiers and nucleating agents, with the resulting preform annealed and drawn into a fiber strand with a 125 ± 0.5 µm diameter. A 4 m long EZDF with a propagation loss of 0.68 dB/m and an erbium concentration of 3000 ppm is used to investigate the FWM effect. The FWM power levels are measured to be approximately - 45 dBm at a region of 1565 nm and show good agreement with the theoretical predicted values. A non-linear coefficient of 14 W-1km-1 is also measured, along with chromatic and slope dispersion values of 28.45 ps/nm.km and 3.63 ps/nm2.km, which agree with the predicted values. The fabricated EZDF has many potential applications utilizing the FWM effect, including the generation of multi-wavelength outputs.

We present our study regarding a compact system design for cell counting and simultaneous 3D imaging, based on digital in-line holographic microscopy configuration. The system is built around the known experimental configuration which includes a pinhole but we also investigate the configuration with a monomode fiber as a light source. Considered samples consist of a very low concentration of cells in flow in a microchannel. The main challenge in our design is to obtain the digital hologram of one cell on a regular video camera sensor in proper resolution conditions, as opposed to the usual configurations where the aim is to visualize a large area. This fact is possible with shorter distances between pinhole and sample and with pinholes with diameters slightly larger than 1micron. These can now be realized by considering the microtechnological processes for microchannel and pinhole fabrication on the same substrate with high refractive index - to increase the numerical aperture of the system The geometrical parameters are established after the numerical analysis of the diffracted field from a single cell and of the entire system numerical aperture values.

Arrays of highly localized wavepackets enable for an efficient multichannel processing of optical data because of their undistorted propagation in space and time domain. Reconfigurable arrangements of supercollimated and temporally nondiffracting few-cycle pulses were generated by microaxicons programmed into the phase map of a liquid-crystal-on-silicon spatial light modulator. As an example, the transfer of quick response code data with few-femtosecond pulses of a Ti:sapphire laser oscillator is reported. Data encoding in beam arrays via maps of temporal and spectral moments is proposed.

Broadband antireflection layer have been fabricated by two dimensional (2D) photonic crystals (PCs) with tapered pillars on Si substrate. These PCs have been produced by interference lithography and reactive ion etching (RIE) techniques. The effect of depth and filling factor (FF) of the PCs on the reflectance magnitude and bandwidth has been investigated. The obtained reflectance was less than 1% in the broad spectral range from 400 to 2100 nm. Our numerically simulation shows the PC pillars slope has essential effect in the reduction of the reflection. However, our results show that the existence of RIE grasses in the PCs which are created in the RIE process have not been influenced in the performance of the antireflection layer which leads to simpler fabrication process.

The fabrication of arrays consisting of densely ordered circular convex microlenses with diameters of 126 $\mu$m made of quartz glass in a photoresist reflow and dry etch structure transition process is demonstrated. The rectangular lens arrays with dimensions of 6 mm x 9 mm were designed for focussing collimated light on the pixel center regions of a translucent interference display, which also was produced in microtechnological process steps. The lenses focus light on pixel centers and thus serve for increasing display brightness and contrast since incoming collimated light is partially blocked by opaque metallic ring contacts at the display pixel edges. The focal lengths of the lenses lie between 0.46 mm and 2.53 mm and were adjusted by varying ratio of the selective dry etch rate of photoresist and quartz glass. Due to volume shrinking and edge line pinning of the photoresist structures the lenses curvatures emerge hyperbolic, leading to improved focussing performance.

The paper gives an overview of the applications of digital holography based on the one hand on CCD-recording, computer storage, and numerical reconstruction of the wave fields, and on the other hand on numerical calculation of computer generated holograms (CGH) and the transfer of these CGHs to spatial light modulators (SLM) for optical reconstruction of the wave fields. The first mentioned type of digital holography finds applications in digital holographic microscopy, particle analysis, and interferometric form and deformation measurement, while the second type constitutes the basis for holographic 3D TV. The space-bandwidth-problem occuring in this context is addressed and first partial solutions are presented.

In this numerical study, the influence of the choice of metal (and hence of the conductivity) used for the fabrication of THz fishnet metamaterials is investigated. We explore an exemplary structure for which surface-plasmon-polaritons offer – assuming sufficiently good conductivity – pronounced extraordinary transmission and strong multiple magnetic resonances with negative permeability. We analyze the dependence of these signatures on the type of metallization. Studying five different metals, we find that the metallization is important for achieving the multiple resonances. A reduction of the conductivity can lead to a dramatic weakening and even a near-disappearance of magnetic resonances if they lose their diamagnetic character.

Complex polarisation sensitive systems such as imaging Mueller matrix polarimeters are commonly calibrated using the eigenvalue calibration method. In this paper we present an extensive review of the method and an existing variant. We also introduce two more variants of the method to calibrate imaging polarimeters that use high numerical aperture optics. The calibration methods are tested using a Mueller matrix confocal microscope of high numerical aperture, and the effect of the pinhole size on the polarisation is also assessed experimentally.

An experimental study was carried out, aimed at optimizing the optical/geometrical configuration for measuring the concentration of biological cells by means of static light scattering measurements. A LED-based optoelectronic setup making use of optical fibers was experimented, as the precursor of a low-cost device to be integrated in instrumentation for cytometry. Two biological sample types were considered as test samples of the most popular analyses – cervical cells and urine, respectively. The most suitable wavelengths and detecting angles were identified, and calibration curves were calculated.

An ultra violet (UV) -cured glassy material with less than 30% organic residues was fabricated by the fast sol-gel method. The material presents high thermal stability, good optical quality and high adhesive strength. It is suitable for optical bonding and, for manufacture of optical elements and micro-structured optical devices. Either soft-lithography or photo-lithography may be used for manufacture of the material while its curing can be thermal (few hours) or UV (few seconds). In this work we present the technology to fabricate optical elements at scales spanning the sub-micron to centimeter range. This technology enables mass-production of optical elements at low cost.

The interaction of distilled water microdroplets (volumes of 3-4μl) with pulsed laser beams emitted at 532nm is described. At 532nm the distilled water absorption is very low and the interaction of a water bead with the laser radiation is dominated by unresonant phenomena. Following the collision of the laser beam with a microdroplet in suspended/ hanging/pendant position in air, deformations and mechanical vibrations of the droplets are produced. The conditions in which the droplets lose material as a consequence of the impact with laser beams are also explored. The effects produced on the droplet were studied pulse by pulse and depend on: droplet’s content, beam wavelength, power and focusing conditions, irradiation geometry and adhesion of the bead to the capillary on which it is suspended. The laser pulses energies were varied in four steps: 0.25mJ, 0.4mJ, 0.7mJ and 1mJ. The pulse full time width was 5ns and the typical focus diameter on the droplet was 90μm; the beam had a relatively low divergence around the focus point. The microdroplets and the modification/evolution of their shapes are visualised by recordings performed at 10kframes/second. Following a microdroplet interaction with the laser beam one may also produce at a controlled moment in time nanodroplets propagating at high (probably supersonic) speeds and microdroplets propagating at slower speeds. One may also produce pendant droplets of smaller dimensions than the initial one as well as micro/nano gas bubbles in the pendant droplet’s material/volume. In a second set of experiment was recorded at high speed the behaviour of the microdroplets of Rhodamine 6G in distilled water at resonant interaction with similar laser pulses, at the same power levels. The optical phenomena considering that the microdroplets contents are Newtonian liquids which dominate the beads behaviour at interaction with the laser beams, are discussed.