1,720,985 research outputs found
Modification of glasses and optical waveguides using high electric fields
No full textThis thesis describes work done towards establishing efficient and reproducible second harmonic generation in thermally poled novel high-index bismuth-borate glass structures. According to the rectification model, glass with higher χ(3) values than silica would permit χ(2) to scale up proportionally, for a given frozen-in electric field strength. The fundamental research on poling induced nonlinearity has been extended to investigate several compositions of Bi2O3ZnOB2O3 glass systems, whose refractive index is measured to increase with the Bi2O3 content. Intrinsic third-order optical nonlinearity χ(3) up to thirty times higher than silica have been measured in bismuth-based compounds, and even larger values are potentially achievable.In this thesis, a reliable procedure to induce large and stable second order nonlinear coefficient χ(2) in bismuthate glasses has been established along with the understanding towards efficient generation of second harmonic power in waveguiding layers. Characterization methods to determine the nonlinear formation dynamics and resolve nonlinear thickness and profile has been optimized to quantify the magnitude and distribution of second order nonlinearities in thermally poled bismuthate glasses. The development of a new poling procedure, where the applied voltage is varied during the cooling phase, instead of being kept constant, has allowed a record value of χ(2) = 2.3 pm/V in 12.5% Bi2O3 bulk samples to be achieved. The control of nonlinear region evolution gained by establishing the innovative time-varying voltage poling procedure has led to the first demonstration of second-order nonlinearity value as high as 2 pm/V induced by thermal poling in bismuthate sputtered slab waveguides.These achievements opened new investigations towards realizing efficient monolithic structures leading to high performance active devices based on poled bismuth-based glass waveguides. In particular, an all-glass electro-optic modulator and a frequency doubler have been targeted, based on sputtering and femtosecond laser direct writing, respectively
Photo-generated metamaterials induce modulation of CW terahertz quantum cascade lasers
Full text linkPeriodic patterns of photo-excited carriers on a semiconductor surface profoundly modifies its effective permittivity, creating a stationary all-optical quasi-metallic metamaterial. Intriguingly, one can tailor its artificial birefringence to modulate with unprecedented degrees of freedom both the amplitude and phase of a quantum cascade laser (QCL) subject to optical feedback from such an anisotropic reflector. Here, we conceive and devise a reconfigurable photo-designed Terahertz (THz) modulator and exploit it in a proof-of-concept experiment to control the emission properties of THz QCLs. Photo-exciting sub-wavelength metastructures on silicon, we induce polarization-dependent changes in the intra-cavity THz field, that can be probed by monitoring the voltage across the QCL terminals. This inherently flexible approach promises groundbreaking impact on THz photonics applications, including THz phase modulators, fast switches, and active hyperbolic media
Tailoring the Coefficient of Friction by Direct Laser Writing Surface Texturing
Full text linkThe modification of the surface topography at the micro- and nanoscale is a widely established as one of the best ways to engineering the surface of materials, to improve the tribological performances of materials in terms of load capacity and friction. The present paper reviews the state of the art on laser surface texturing by exploiting the technique of direct laser writing for tailoring the coefficient of friction, highlighting the effect of the textures' arrangement on the lubricated conformal and non-conformal contact behavior
LINEWIDTH MEASUREMENT OF MID INFRARED QUANTUM CASCADE LASER BY OPTICAL FEEDBACK INTERFEROMETRY
No full textVoltage-assisted cooling: a new route to enhance χ(2) during thermal poling
No full textModifying the standard constant-voltage poling procedure significantly enhances the in-built electric field strength (and consequently χ) and leads to control of the nonlinear region evolution, both crucial parameters to integrate nonlinearity in waveguiding regions
Synergizing health: combined gynecological and bariatric robotic surgery for endometrial cancer in obese women
Full text linkEndometrial cancer is the most common gynecological tumor, with approximately 10 200 new
cases in 2022 in Italy.
Its incidence is on the rise,
possibly linked to undefined factors, with many
attributing it to the increasing rates of obesity
in high-income countries. This is not an unreasonable assumption, considering the correlation
between obesity and the general risk of cancer,
as well as the effects of unopposed hyperestrogenism due to inadequate progesterone production from adipose tissue.
Strong evidence from the literature underscores the health benefits of weight reduction.
It is particularly noteworthy for women with precancerous lesions and early-stage tumors who
wish to conceive.
Rapid and significant weight
loss can be achieved through bariatric surgery,
and the combination of minimally invasive robotic
surgery with sleeve gastrectomy seems to be a
promising option for severely obese women (body mass index (BMI) >35 kg/m2
) (Figure 1). This
choice is supported by the minimally invasive
approach recommended for endometrial cancer
and the surgeon’s comfort with the robotic technique in severely obese patient
Bacterial adhesion eradication and biofilm inhibition through laser surface texturing
No full textThe growing problem of bacterial and microbial resistance to antibiotics is closely tied to the ability of such microorganisms to form biofilms, composed of complex microbial communities embedded in an extracellular matrix (EPS). In fact, quorum sensing enables bacteria to coordinate their behaviors within biofilms, further increasing their resistance to external threats compared to free-floating forms, thus complicating the treatment with conventional antibiotics. Therefore, biofilm formation is closely linked to antimicrobial resistance (AMR), which significantly increases health threats and the costs for the healthcare public system. Traditional antibacterial agents, such as silver ion coatings, photocatalytic materials, leaching biocides, and polymer chains, have shown some limitations, such as pathogen resistance, durability issues, and potential health risks. In response to these challenges, laser surface texturing (LST) has emerged as a promising and sustainable antibacterial alternative which consists in modifying the surfaces at the micro- and nanometric scales to inhibit bacterial colonization or destroy bacterial membranes. LST can prevent bacterial adhesion and biofouling or, on the other hand, promote biocidal action after bacterial adhesion. This review examines how laser-treated surfaces influence the behavior of key bacterial strains, such as Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa, exploring the mechanisms by which LST affects bacterial adhesion, morphology, and biofilm formation. The effectiveness of these mechanisms will be assessed both individually and in combination based on the characteristics of each bacterial strain
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Bleaching of sol-gel glass film with embedded gold nanoparticles by thermal poling
Full text linkGold clusters embedded in glass are expected to be hard to dissolve in the form of ions since gold is essentially a nonreactive metal. In spite of that, bleaching of Au-doped nanocomposite sol-gel glass film on a soda-lime glass substrate is demonstrated in which electric-field thermal poling is employed to effectively dissolve randomly distributed gold nanoparticles (15 nm in diameter) embedded in a low conductivity sol-gel glass film with a volume filling factor as small as 2.3%. The surface plasmon absorption band at 520 nm is suppressed in the region covered by the anodic electrode. The phenomenon is explained by the ionization of the gold nanoparticles and the redistribution of gold ions in the glass matrix due to the action of the extremely high electrostatic field locally developed during poling
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