D. Cojoc

Changes in microbubble dynamics near a boundary revealed by combined optical micromanipulation and high-speed imaging

The authors report optical observations of the change in the dynamics of one and the same ultrasound contrast agent microbubble due to the influence of interfaces and neighboring bubbles. The bubble is excited by a 2.25MHz ultrasound burst and its oscillations are recorded with an ultrahigh-speed camera at 15 million frames per second. The position of an individual bubble relative to a rigid wall or second bubble is precisely controlled using optical tweezers based on Laguerre-Gaussian laser beams [P. Prentice et al., Opt. Express 12, 593 (2004); V. Garbin et al., Jpn. J. Appl. Phys. 44, 5773 (2005)]. This allows for repeated experiments on the very same bubble and for a quantitative comparison of the effect of boundaries on bubble behavior.

Three-dimensional digital scanner based on micromachined micromirror for the metrological measurement of the human ear canal

Manufacturers of hearing aids have made initial testing of rapid prototyping of hearing aid shells using laser scans of ear impressions, but they have not performed any actual scans of the human ear canal. We report the direct scanning of the human external auditory canal by using an electromagnetically actuated torsion micromirror fabricated by using a micromachining technique as the scanner. This demonstrates the actual scanning of the human external auditory canal by a single integral microelectro-optical-mechanical system (MEOMS). A prototype three-dimensional (3D) scanning system was developed: It is based on the acquisition of optical range data by a conoscopic holographic laser interferometer using an electromagnetically actuated scanning MEOMS micromirror. A fabrication process, based on a poly(methylmethacrylate) sacrificial layer for the fabrication of a free-standing micromirror was used. Micromirror actuation was achieved by using a magnetic field generated with an electromagnetic coil stick. ...

Multiple optical trapping by means of diffractive optical elements

In this paper, we prove the usefulness of the diffractive optical elements to generate arrays of optical tweezers. A set of micro-particles can be thus trapped in three dimensions and each micro-particle can be then moved independently.

X-ray lithography fabrication of a zone plate for X-rays in the range from 15 to 30 keV

Progress on the fabrication of zone plates for hard X-rays is reported. The issue of achieving a high aspect ratio for lithographic structures has been addressed by developing a specific fabrication protocol based on the combined use of electron beam and proximity X-ray lithography. An example of a 1 mm diameter wide zone plate, optimized for a 23 keV X-ray beam, is presented, showing an aspect ratio of the outermost zone of up to 10. The most critical steps of the fabrication process are discussed on the basis of the results.

X-ray and electron-beam lithography of three-dimensional array structures for photonics

The possibility to realize three-dimensional (3D) photonic crystals and the capability to internally insert a waveguide path poses a big challenge from the fabrication point of view. We present a fabrication method for a 3D lattice with designed linear defects by multitilt x-ray exposures and electron-beam lithography. This combination of different lithographies has been developed to control the design and the realization of the linear defects inside the three-dimensional structure. This method has been applied for the fabrication of Nickel Yablonovite lattices with a lattice parameter of 1.8 μm and a total thickness of 15 μm, a value that allows us to achieve a full three-dimensional optical behavior as confirmed by variable angle reflectance measurements.

Design and Fabrication of Diffractive Optical Element-Microlens with Continuous Relief Fabricated On-Top of Optical Fibre by Focused Ion Beam for Fibre-to-Waveguide Coupling

The purpose of this work is to demonstrate efficient optical coupling between a single mode fibre and a waveguide (LiNbO3-APE) using a diffractive optical elements (DOEs)-microlens with continuous relief fabricated directly on the top of a cleaved fibre using a focused ion beam (FIB) milling process. DOEs with diameters as small as 15 µm were fabricated by means of FIB milling process. A focused Ga + ion beam was used to mill a continuous relief microstructure at a 30 kV acceleration voltage. The design of the DOE-microlens and the calculations related to the optical fibre-to-waveguide coupling was carried with our own developed code. The profile of the fabricated DOE-microlens was very well reproduced in nine annulus each of 100 nm thick. The focusing performance of DOE-microlens with nine annulus was investigated. This fabricated DOE-microlens was able to focalize the Gaussian beam leaving the fibre, into a wave guide plane at a distance of 28 µm from the DOE-microlens surface. The fundamental mode size of the beam leaving the fibre was of about 10.5 µm while the size of the focused waist was 5.2 µm. This has led to an efficient matching the fundamental mode of the fibre vis-a-vis that of waveguide. Coupling efficiency test were carried using a laser beam λ=1550-nm wavelength. The optical coupling using the DOE-microlens on-top-of the fibre-to-waveguide is 67% more efficient than the direct coupling between the fibre and the waveguide. This shows that the design meets the applications requirement for fibre-waveguide coupling, and that DOE-microlens fabricated by FIB technology are practicable.

1F-2 Optical Trapping of Ultrasound Contrast Agent Microbubbles: Study of the Bubble-Wall and Bubble-Bubble Interaction in Ultrasound

Here we present optical tweezers as a micromanipulation tool for the study of ultrasound contrast agent (UCA) microbubbles. Optical trapping and the resulting manipulation of individual and multiple microbubbles enables the study of their dynamics with controlled boundary conditions. The bubble response to ultrasound is recorded optically using the ultra high-speed Brandaris 128 camera. In our experiments, the amplitude of bubble oscillations was found to be strongly influenced by the vicinity of the sample chamber wall. Experiments with two trapped bubbles also showed a considerable influence of the neighboring bubble on the amplitude of oscillations of the other one

Design and fabrication of lenses on the top of an optical fiber for efficient fiber-to-waveguide coupling by means of Focus Ion Beam (FIB) lithography

In this paper, efficient optical coupling between a single mode fiber and a LiNbO/sub 3/-APE waveguide using a lens fabricated on the top of the fiber was demonstrated.

X-ray lithography patterning of magnetic material and their characterization

Patterned arrays of magnetic wires, dots and anti-dots have attracted a lot of interest both for their potential applications in magnetic data-storage devices and for the investigation of magnetic phenomena in low-dimensional systems. However the employment of micro- and nano-structures in magnetic high density recording media and non-volatile RAM is not trivial: compared to the case of a continuous film, the small size of the islands increases the effects of the demagnetizing field, affecting the static and dynamic magnetic properties. Moreover, some new effects arise due to the lateral confinement of the structures, e.g.: quantized spin-wave modes. These latter effects are of great interest also from a fundamental point of view.

Phase diffractive elements for three dimensional spot arrays generation

We propose a combined analytical-iterative optimization approach to design phase diffractive elements that generate three-dimensional array of light spots The validity of this method is demonstrated by computer simulations for an array of eight spots positioned in two planes separated by 500 /spl mu/m along the optical axis.