Cemal Esen

Analysis of the particle stability in a new designed ultrasonic levitation device

The use of acoustic levitation in the fields of analytical chemistry and in the containerless processing of materials requires a good stability of the levitated particle. However, spontaneous oscillations and rotation of the levitated particle have been reported in literature, which can reduce the applicability of the acoustic levitation technique. Aiming to reduce the particle oscillations, this paper presents the analysis of the particle stability in a new acoustic levitator device. The new acoustic levitator consists of a piezoelectric transducer with a concave radiating surface and a concave reflector. The analysis is conducted by determining numerically the axial and lateral forces that act on the levitated object and by measuring the oscillations of a sphere particle by a laser Doppler vibrometer. It is shown that the new levitator design allows to increase the lateral forces and reduce significantly the lateral oscillations of the levitated object.

Microassembly of complex and three-dimensional microstructures using holographic optical tweezers

In this paper we investigate a flexible method for the fabrication of complex microstructures using binding microparticles. Utilizing optical forces, micro-objects are caught, positioned and used as building blocks to form defined structures, analogous to assembling processes in the macroscopic world. Durable linkage between the individual particles is realized using biomolecules with high affinities applied as particle coatings. Planar structures can be assembled employing optical manipulation as well as three-dimensional patterns by stacking the generated layers. Even the properties of the generated structures can be locally designed as desired by using building blocks from diverse materials exhibiting different properties. This method benefits from its simplicity and the potential extensibility of the fabricated structure at any time of the experiment.

Using Laser Microfabrication to Write Conductive Polymer/SWNTs Nanocomposites

We present a novel laser microfabrication method to generate structures on the basis of a new class of functional photosensitive composites. particular, the focus lies Inon the development of conductive composites by incorporatingSWNTs into the matrix of polymers thus forming highly conductive nanocomposites. Conductive microstructures have been produced with the ultra-high resolution technology based on laser direct writing (e.g. single-, two-photon polymerization) using polymer/SWNTs nanocomposites. This technology opens new prospects for the realization of novel MEMS and MOEMS with increased functionality, integration, and higher level of miniaturization.

Pollen characterization and identification by elastically scattered light

The authors recorded the elastic light-scattering pattern of pollen over a large spatial angle range to investigate the potential light scattering for pollen identification. The scattering from elm, hazel, birch, chestnut, willow, sunflower, ragweed and pine was measured. The scattering patterns show distinct differences that can be used for the classification of pollen with simple algorithms.

Elastic Light Scattering on Single Pollen: Scattering in a Large Space Angle

We investigated the elastically scattered light of single pollen in a large space angle. Scattering pattern of birch, elm, hazel, sunflower, pine, ragweed, chestnut, and willow pollen were recorded in the backward and sideward hemisphere. Characteristic features could be detected, that may help identify the pollen by light scattering. We also show scattering pattern of a willow pollen rotated relative to the laser beam, and the relations between the sideward and backward scattering hemispheres.

Development of a single-axis ultrasonic levitator and the study of the radial particle oscillations

This work describes the development and analysis of a new single-axis acoustic levitator, which consists of a 38 kHz Langevin-type piezoelectric transducer with a concave radiating surface and a concave reflector. The new levitator design allows to significantly reducing the electric power necessary to levitate particles and to stabilize the levitated sample in both radial and axial directions. In this investigation the lateral oscillations of a levitated particle were measured with a single point Laser Doppler Vibrometer (LDV) and an image evaluation technique. The lateral oscillations were measured for different values of particle diameter, particle density and applied electrical power.

Enhancement of Raman scattering by deformation of microparticles.

Raman scattering on deformed droplets levitated in an acoustic levitator and produced by a vibrating-orifice aerosol generator were investigated. Our samples experiments were diethyl hexyl sebecate (DEHS) droplets in the millimeter-size range and ethanol droplets in the size range 50-100 microm. The C-H stretching region from 2800 to 3100 cm(-1) was investigated. We found that the Raman intensity measured by a scattering angle of 90 degrees depended on the shape of the droplets. Raman scattering on spherical droplets was smaller than scattering on spheroidal droplets with the same volume. Similar results were observed for the fluorescence signal of Rhodamine 6G-doped DEHS droplets.

Whispering gallery mode pressure sensing

Optical resonances of microresonators, also known as whispering gallery modes, are attracting considerable interest as highly sensitive measuring devices with a variety of applications. Such resonators can be used for pressure, force or strain measurement. Droplets, embedded in an appropriate substrate, form perfect spheres due to their surface tension and can be used as optical resonators with high quality factors. The resonance frequencies of these droplets depend sensitively on their size and shape. Pressure changes affect the droplet shape. Therefore, pressure change can be measured with high sensitivity. In the work presented here, ethanol droplets embedded in a silicone matrix are considered. The shift of the resonance frequencies of microdroplets embedded in silicone as function of the applied pressure is investigated.

Generation of bioinspired structural colors via two-photon polymerization

Colors of crystals, pigments, metals, salt solutions and bioluminescence occur in nature due to the optical properties of electrons in atoms and molecules. However, colors can also result from interference effects on nanostructures. In contrast to artificial coloration, which are caused by well-defined regular structures, the structural colors of living organisms are often more intense and almost angle-independent. In this paper, we report the successful manufacturing of a lamellar nanostructure that mimics the ridge shape of the Morpho butterfly using a 3d-direct laser writing technique. The viewing angle dependency of the color was analyzed via a spectrometer and the structure was visualized using a scanning electron microscope. The generated nano- and micro-structures and their optical properties were comparable to those observed in the Morpho butterfly.

Laser direct writing of high refractive index polymer/TiO2 nanocomposites

This work reports the preparation of polymer/TiO2 nanocomposite by adding TiO2 nanoparticles to the polymer matrices. TiO2 nanoparticles can be effectively dispersed into the polymer. The refractive index of the nanocomposites can be tuned by increasing the concentration of TiO2 nanoparticles. The prepared samples exhibit excellent optical transparency in the Vis-NIR region, i.e. at two-photon polymerization (TPP) processing wavelength, and can be used to write threedimensional structures by means of TPP. Structures with high refractive index have been produced with the novel ultrahigh resolution technology based on TPP processing of polymer/TiO2 nanocomposites.