Sensing the quantum behaviour of magnetic nanoparticles by electron magnetic resonance.

We have investigated Magnetic Nanoparticles (MNPs) of spinel type iron oxide (of approximately 8 nm) mineralized in the internal cavity of the bioreactor ferritin nanocage. In particular, we have used Electron Magnetic Resonance, EMR, spectroscopy and taken advantage of the capacity of the protein shells to control the size of the MNPs. EMR measurements in perpendicular and parallel configurations have been recorded at various temperatures. A model based on the giant spin is used to interpret the experimental results. The analysis indicates that the observed quantum behaviour has to be ascribed to the whole MNP and that the thermal population of excited spin states has a strong influence in the EMR behaviour of MNPs.

The ß-subunit of cholera toxin has a high affinity for ganglioside GM1 embedded into solid supported lipid membranes with a lipid raft-like composition.

In this communication, we report on the fabrication of GM1-rich solid-supported bilayer lipid membranes (ssBLM) made of sphingomyelin and cholesterol, the main components of lipid rafts,which are the physiological hosting microenvironment of GM1 on the cell membrane. The functionality of the ganglioside has been checked by measuring the apparent dissociation constant K(D) of the complex formed by the ß-subunit of the cholera toxin and GM1. The value found deviates less than one order of magnitude from that measured for in vivo cells, indicating the potential of these ssBLM as optimized in vitro biomimetic platforms.

All optical switches based on the coupling of surface plasmon polaritons.

We studied the potentials of All Optical Switches (AOS) based on the intensity-dependent coupling and decoupling of light into the SPP modes (Surface Plasmon Polaritons) of a sinusoidally corrugated thin metal film (TMF), due to Kerr induced refractive index changes of the surrounding dielectrics. The ideal device has two spatially separated outputs, collecting the reflected and transmitted light and the active volume can be as small as 10(-2) mm(3). Gold and PTS (poly-(2,4-hexadiyne-1,6-diol bis(p-toluene sulfonate) are the materials considered. Losses are limited to 1.5 dB,while a 20 dB extinction ratio per gate has been theoretically demonstrated with signal pulsewidths of 5-10 ps , using a maximum optical switching peak power of 11 kW.

Photobleaching of polydiacetylene waveguides: a characterization of the process and patterning of optical elements.

The photobleaching process of poly-3butoxyl-carbonyl-methyl-urethane (poly-3BCMU) waveguides by means of an UV lamp and the 488-nm line of an Ar laser is characterized and modeled. The limits of the theory are discussed in light of experimental results, and we stress the role of the oxygen diffusion rate on the process. Finally, we adopt the photobleaching method to pattern a guided-wave micro-optic device and holographic diffraction gratings on spun poly-3BCMU films.

Thermal annealing of K(+)-Na(+) ion-exchanged waveguides.

The process of thermal annealing of K(+)(-)Na(+) ion-exchanged waveguides in soda lime glass is characterized and compared with a simple theoretical model. The discrepancies between theory and experiments in the case of initially thick guides disappear if the existence of a stress-induced contribution to the refractive index is assumed that is not proportional to the concentration of the doping ions. The results obtained for initially thin guides are exploited for the design of annealed single-mode channel waveguides: 0.4-dB coupling losses with commercial single-mode fibers at lambda = 1.321 microm were measured.

Optical fiber monitored by a directional coupler for delivering laser radiation in medical treatments.

The safety of therapeutic laser treatments could be strongly improved by introducing real-time monitoring to the fiber delivery system. Since any fiber damage leads to a significant variation of the backscatter, its detection could be exploited to monitor the system, in particular the fiber trip. To assess this potential, the backscattered modal power distribution (BMPD) from flat, bulb, and damaged fiber tips were investigated. The BMPD detection was accomplished by using a conventional beam-splitter method and two directional couplers: a prism-fiber and a fiber-fiber lapped coupler. Unlike the conventional method, use of the couplers allows for the separate detection of backscattered and forward transmitted signals. Therefore variations in the backscatter that are due to only a change in the laser pulse can be determined. Moreover, the directional couplers, because of the amplification of high-index modes, allow for an increase in sensitivity of the method. This was particularly evident in our tests on fiber tips that had been dipped into water to obtain a better simulation of the real working conditions. Finally, the influence of the target on the BMPD was investigated as a function of its distance from the fiber tip. All the tests confirm that the target must be taken into account if the distance is <1 mm, but the monitoring system can also be used when the fiber tip works in contact with the tissue wall provided that one can ensure contact by pushing the tip against the target wall.

Probe for laser angioplasty radiating a corolla shaped beam.

Laser angioplasty is a rapidly widening field. However, at present, the experimental research on human patients is limited by severe technical problems, particularly in the case of coronary arteries. The risk of mechanical or laser-induced perforations is likely the most serious. To get rid of this drawback here a new fiber-optic probe is described, characterized by a corolla shaped output beam and by no axial radiation. The probe consists of a conical fiber tip inserted in a particular quartz microcapsule. Its optical behavior has been studied both experimentally and theoretically, using a ray tracing method. Some preliminary tests carried out on the aorta wall from a cadaver are also described. The results seem to confirm that the new probe minimizes the risk of vessel perforation, while its diameter is suitable even for coronary applications.

Reflection holographic filters for compacting optical processors.

Character recognition experiments, carried out with reflection matched filters, are described. The reflection filters are obtained by means of volume holograms, recorded in photographic emulsion and suitably processed. These filters allow a good discrimination among similar characters and exhibit large positioning tolerances. They turn out to be well comparable with transmission hologram filters. An advantage of reflection filters is that the filtering operation can be performed with one-lens processor, thus reducing by one-half the size and the cost of the processor.

Geodesic lenses for guided optical waves.

Two-dimensional lenses are essential elements in integrated optics. As an alternative to the techniques already suggested and tested to obtain such optical systems, a different method is reported that consists of extending to thin film optics the principle of configuration lenses already studied for application to microwave antennas. The working principle of such lenses is that the propagation occurs along a curved surface in a two-dimensional Riemann space. The rays are the geodesics of the surface. Two optical geodesic lenses having planar input and output have been constructed and tested. They can be easily inserted in planar film circuits. The advantage of these optical systems is that the substrate can be prepared in advance with the accuracy of glass optics. Then the dielectric film can be deposited with the same method used for planar components.