Integrated waveguides and deterministically positioned nitrogen vacancy centers in diamond created by femtosecond laser writing.

Diamond's nitrogen vacancy (NV) center is an optically active defect with long spin coherence times, showing great potential for both efficient nanoscale magnetometry and quantum information processing schemes. Recently, both the formation of buried 3D optical waveguides and high-quality single NVs in diamond were demonstrated using the versatile femtosecond laser-writing technique. However, until now, combining these technologies has been an outstanding challenge. In this Letter, we fabricate laser-written photonic waveguides in quantum grade diamond which are aligned to within micron resolution to single laser-written NVs, enabling an integrated platform providing deterministically positioned waveguide-coupled NVs. This fabrication technology opens the way toward on-chip optical routing of single photons between NVs and optically integrated spin-based sensing.

Femtosecond laser inscription of Bragg grating waveguides in bulk diamond.

Femtosecond laser writing is applied to form Bragg grating waveguides in the diamond bulk. Type II waveguides are integrated with a single pulse point-by-point periodic laser modification positioned toward the edge of the waveguide core. These photonic devices, operating in the telecommunications band, allow for simultaneous optical waveguiding and narrowband reflection from a fourth-order grating. This fabrication technology opens the way toward advanced 3D photonic networks in diamond for a range of applications.

[Assessment of the risk of occupation-related stress in the bakery industry at the ASPAN of Bergamo]. / Valutazione del rischio stress lavoro-correlato nelle imprese panificatrici afferenti all'ASPAN di Bergamo.

The attention to developing the subjective dimensions and environmental policies to promote health in the contexts of work is established with the development of "model of organizational health." This model explains the concepts of stress and health in the workplace as phenomena not reducible to the individual dimension, going to intercept the styles of living that characterize organizational practices, significant in the process of health promotion (Avallone and Paplomatas, 2005). The aim of this work consists in the recognition of risk factors and protective measures which characterize the context of the bakery, investigating the size of individual, relational, organizational and socio-economic conditions. The methodology included a phase of analysis of the context, a collection of the principal objective data and a reinterpretation of them inside a narrative and autobiographcial prospective, offered by the subjects interested in the evaluation.

Background-free broadband CARS spectroscopy from a 1-MHz ytterbium laser.

We introduce a novel configuration for broadband, time-resolved CARS spectroscopy/microscopy in which pump, Stokes and probe pulses are all derived from a single femtosecond Yb:KYW laser. The 1-MHz repetition rate of the system allows very intense CARS signals to be obtained over short acquisition times, while a delayed probe pulse ensures an efficient non-resonant background suppression.

Femtosecond laser fabricated monolithic chip for optical trapping and stretching of single cells.

We report on the fabrication by a femtosecond laser of an optofluidic device for optical trapping and stretching of single cells. Versatility and three-dimensional capabilities of this fabrication technology provide straightforward and extremely accurate alignment between the optical and fluidic components. Optical trapping and stretching of single red blood cells are demonstrated, thus proving the effectiveness of the proposed device as a monolithic optical stretcher. Our results pave the way for a new class of optofluidic devices for single cell analysis, in which, taking advantage of the flexibility of femtosecond laser micromachining, it is possible to further integrate sensing and sorting functions.

Sub-100 fs pump-probe spectroscopy of Single Wall Carbon Nanotubes with a 100 MHz Er-fiber laser system.

An extremely compact and versatile near-infrared two-color femtosecond pump-probe spectroscopy apparatus based on an amplified Erfiber laser system is presented and applied to the characterization of the relaxation dynamics of single-wall carbon nanotubes with fundamental absorption in the 2 microm spectral region. By implementing a fast-scan technique, dynamics as long as 3 ps are acquired in 5 s with a relative sensitivity of 10(-4) and a temporal resolution below 100 fs at 2 microm.

Fabrication of photonic devices in nanostructured glasses by femtosecond laser pulses.

Focused femtosecond laser pulses have been used to modify the optical properties of glass doped with CdSxSe1-x nanocrystals. Large positive refractive index changes have been observed and exploited for the fabrication of photonic devices. In particular, we report on highly confining optical waveguides and single and multi-layer volume diffraction gratings.

High quality buried waveguides in stoichiometric LiTaO3 for nonlinear frequency conversion.

High-quality buried optical-waveguides were fabricated by reverse-proton-exchange in periodically-poled stoichiometric lithium tantalate. Experimental results show excellent fiber-mode matching, losses below 0.3 dB/cm and almost non-critical conditions for a quasi-phase-matched second-harmonic generation process from telecom wavelengths. The interaction length of 2.5 cm is the highest so far reported for lithium tantalate waveguides.

Spectral shift of femtosecond pulses in nonlinear quadratic PPSLT Crystals.

Spectral blue- and red-shifts in a range of 100 nm are achieved by propagating 40 fs pulses with a 70 nm spectrum centered at 1450 nm in a 25-mm-long periodically poled stoichiometric lithium tantalate crystal. We show experimentally that these shifts, originating from a phase-mismatched second harmonic generation process under conditions of strong group velocity mismatch, can be efficiently controlled by acting on pulse intensity and phase-mismatch.

Beam dynamics and wave packet splitting in a periodically curved optical waveguide: multimode effects.

A theoretical and experimental analysis of beam dynamics and wave packet splitting of light in a periodically bent optical waveguide, a phenomenon recently observed [Phys. Rev. Lett. 94, 073002 (2005)] which is the optical equivalent of adiabatic stabilization of atoms in intense and high-frequency laser fields, is presented in the multimode operational regime. Inhibition of wave packet splitting is theoretically predicted and experimentally observed for higher-order mode excitation.

Comparative study of the therapeutic effect of photoactivated hematoporphyrin derivative and aluminum disulfonated phthalocyanines on tumor bearing mice.

Although the hematoporphyrin derivative (Hpd) is one of the most studied photosensitisers for photodynamic therapy (PDT), it is far from ideal. Therefore, many laboratories have been investigating a new group of sensitisers, the phthalocyanines. Particularly, in our laboratory we decided to study the aluminum disulfonated phthalocyanines (AlS2PC). They are chemically stable, readily soluble in water and have a strong absorption in the red part of the spectrum at 675 nm. Mice bearing the MS-2 fibrosarcoma treated with 5 mg/kg of AlS2PC survived indefinitely also using a low laser power of 100 mW/cm2 X 10' of exposure time, in contrast to experiments carried out with Hpd where the optical therapeutic laser power was 400 mW/cm2 X 10' and the dose of Hpd was 25 mg/kg. Furthermore, treatment of mice bearing the highly metastatic tumor, B16 melanoma, with 5 mg/kg of AlS2PC and laser light (100 mW/cm2 X 10'), significantly prolonged the survival time in respect to mice treated with 25 mg/kg of Hpd and laser light (400 mW/cm2 X 10').

Second harmonic generation from radiation to guided modes for the characterization of reverse-proton-exchanged waveguides.

By prism-coupling an ordinary radiation mode into a lithium niobate planar waveguide, a second harmonic extraordinary guided mode can be generated if the proper coupling angle is chosen. By measuring this angle, the effective index of the radiation mode and thus of the interacting guided mode can be determined. This fact is exploited for the characterization of reverse-proton-exchanged waveguides, whose lowest order modes cannot be efficiently prism-coupled due to their confinement inside the sample.

Reverse-proton-exchange in stoichiometric lithium tantalate.

Buried waveguides with nearly symmetrical refractive index profile and high homogeneity were obtained by applying the reverse-proton-exchange technique to MgO doped stoichiometric lithium tantalate, a promising nonlinear material due to its low coercive field and high damage threshold. By characterizing several samples fabricated under different experimental conditions, we identified a fabrication procedure in which the annealing and the reverse-exchange processes are performed at the same temperature, and the diffusion of hydrogen ions towards the substrate is negligible during the burial step. These fabrication conditions are simpler than the conventional ones used for lithium niobate. Accurate empirical laws were found, relating the fabrication conditions to the optical parameters.

Age-related changes in the fluorescence of melanin and lipofuscin granules of the retinal pigment epithelium: a time-resolved fluorescence spectroscopy study.

The photophysical properties of purified populations of melanin and lipofuscin granules from human retinal pigment epithelium, and their changes with donor age, have been investigated using high-sensitivity time-resolved fluorescence spectroscopy techniques with picosecond gating capabilities. The overall fluorescence intensity of both melanin and lipofuscin granules clearly increased with increasing donor age, the increase being most marked for melanin. In all granule populations the fluorescence decays were multiexponential with subnanosecond and nanosecond decay components. The resultant time-integrated and time-gated spectra also exhibited marked age-variations for each type of granule. Young melanin showed spectral patterns similar to those of bovine melanin, while a yellow-orange fluorescence band appeared in melanin samples from older age groups. Lipofuscin granules exhibited a blue, a yellow and an orange band whose relative amounts were age-related. The results demonstrate the potential of time-resolved techniques for discriminating fluorophores in vitro and in situ, and have confirmed results previously obtained using extraction techniques. Furthermore, the ability of this technique to identify and quantify individual fluorophores within granules may provide an important insight into the origin and development of lipofuscin within the retinal pigment epithelium and ultimately into the mechanisms of age-related retinal diseases.

Time-gated fluorescence spectroscopy of the tumor localizing fraction of HpD in the presence of cationic surfactant.

Time-gated fluorescence spectroscopy was performed on the tumor localizing fraction (TLF) of HpD in buffer at different concentrations of cationic surfactant. This technique obtains emission spectra with programmable delay relative to the excitation pulse. According to the measured fluorescence decay-time constants (approximately 0.7, approximately 3 and approximately 15 ns) three gates were considered, delayed by 0, 5 and 18 ns, respectively, to evaluate the contribution of the emitting molecular species to the spectra. Simultaneous to these measurements, fluorescence decay waveforms and time-integrated spectra were also detected. In buffer and in detergent micelles the fluorescence spectra are given by the superposition of the emission of the different molecular species present in the solution, and no appreciable interaction among the chromophores is observed. On the contrary, in the pre-micellar range of the surfactant, evidence for the existence of an energy transfer mechanism was found. This effect seems to be related to the configurational state of the TLF polymeric chains and depends on the relative TLF/surfactant concentration.

Distribution of di-sulfonated aluminum phthalocyanine and Photofrin II in living cells: a comparative fluorometric study.

Microspectrofluorometric and fluorescence imaging techniques have been employed to study the internalization and intracellular distribution of both Photofrin II, an experimental drug used in photodynamic therapy, and di-sulfonated aluminum phthalocyanine, a very promising photosensitizer. The results obtained by microscopic techniques in living cells have been compared with those obtained in solution on cell extracts. Experimental results indicated that the complexity of the drug-cell interaction can be explained according to the chemico-physical nature of the drugs. In particular, the presence of both monomeric and aggregated fractions, which are supposed to be internalized through different mechanisms, accounts for the intracellular distributions observed for both drugs, depending on the treatment conditions. Equilibria among the drug fractions take place within the cells, resulting in the persistence of the intracellular fluorescence. On the whole, the behavior of the two drugs appears very similar, except for some aspects related to the intracellular distribution, which can be explained in terms of different degree of lipophilicity of the drugs.

Age-related changes in the morphology, absorption and fluorescence of melanosomes and lipofuscin granules of the retinal pigment epithelium.

The morphological and spectral characteristics of purified populations of melanosomes and lipofuscin granules from the human retinal pigment epithelium (RPE) were studied with respect to donor age. All melanosome and lipofuscin fractions exhibited the typical ultrastructural appearance associated with these granules. Absorption profiles of both melanin and lipofuscin granules demonstrated an increased optical density of the granules with increasing age. The former was associated with an overall increase of melanin within the granules. Melanosomes were weakly fluorescent; emission in the blue decreased with increasing age while emission in the red increased. The fluorescent intensity of lipofuscin granules increased with age. These results provide support for the concept that melanogenesis is occurring within the human RPE throughout life and that pigment granules within the RPE undergo age-related modifications during life.

Effects of hematoporphyrin-derivative on mouse erythroleukemia cells in the absence of light irradiation.

This paper concerns a general study on the effects of hematoporphyrin-derivative (HpD) on mouse erythroleukemia (MEL) cells, in the absence of light irradiation. In particular, HpD intrinsic cytotoxicity was evaluated at different doses and the results correlated with those referring to membrane functional and morphological changes. HpD uptake and release processes were also studied and compared with the above-mentioned results. In order to have an overall picture of HpD-cell interactions, time-resolved fluorescence measurements were performed on both undifferentiated and differentiated MEL cells. The results obtained indicate that, even at HpD doses exhibiting neither any cytotoxicity nor any morphological damage (1-10 micrograms/ml), membrane permeability alterations are observed. Thirty minutes of treatment are sufficient for HpD to develop its toxic effect: indeed, no differences in HpD influence on cell viability can be observed after 30 min, 60 min or 5 days of treatment. HpD cytotoxicity is reduced by high protein content in the incubation culture medium. The presence of both monomeric species and 580 nm emitting species was observed at cellular level. The latter is likelier in undifferentiated MEL cells, which also exhibit higher overall HpD uptake, as compared with differentiated MEL cells.

The time-dependent behaviour of hematoporphyrin-derivative in saline: a study of spectral modifications.

Hematoporphyrin-Derivative (HpD), a widely-used tumor-specific photosensitizer, is a complex mixture of porphyrins whose composition has yet to be clarified. This paper reports on the behaviour of HpD in saline. From a spectroscopic point of view, the fresh solution is characterized by two main absorption peaks, attributable to monomeric and dimeric forms. With aging, a new porphyrin species (NPS) appears. To define the NPS, absorption, excitation and emission spectra were measured in different conditions and time-resolved fluorescence measurements were also performed. This species exhibits an absorption/excitation peak at 405 nm, an emission peak at 575 nm and a fluorescence decay time of approximately 3.5 ns. Its formation is strongly influenced by many environmental factors: in particular, gases diluted in the solution, temperature, pH and concentration. The presence of Oxygen and a pH value outside the 6-8 range may be considered inhibiting factors. The NPS seems to be quite important in the understanding of HpD tumor-specificity, since the presence of an emission band similar to the NPS one seems to be favoured in tumor cells as compared with normal cells.

Time-resolved fluorescence spectroscopy of hematoporphyrin-derivative in human lymphocytes.

This paper reports on time-resolved microfluorimetric measurements on hematoporphyrin-derivative (HpD)-treated lymphocytes. HpD is at present widely used as a tumor-locating and photosensitizing drug. It is therefore of great importance to study the extent to which the HpD uptake process depends on cell functional and structural properties. Time-resolved fluorescence measurements in single cells are very useful in this respect, since they give information on the content of fluorescent molecules through fluorescence peak-intensity, and, indirectly, on the binding properties through the fluorescence decay times. In particular, we studied the dependence of HpD fluorescence on the cellular functional state. To this end, we performed in-cell fluorescence measurements on human lymphocytes, both in quiescent conditions and in the pre-replicative phase, after stimulation with phytohemagglutinin (PHA). We found a higher HpD content in stimulated lymphocytes. Moreover, we found a spectral band around 575 nm, corresponding to a particular porphyrin species, in which the differences between normal and stimulated lymphocytes are more striking. The porphyrin species emitting in this band seems to play a role in the specific interaction of HpD with tumors, since a similar emission band has also been found in tumor cells containing HpD.