Isolated Single-Cycle Attosecond Pulses Sansone, G; Benedetti, E; Calegari, F ...
Science (American Association for the Advancement of Science),
10/2006, Letnik:
314, Številka:
5798
Journal Article
Recenzirano
We generated single-cycle isolated attosecond pulses around ~36 electron volts using phase-stabilized 5-femtosecond driving pulses with a modulated polarization state. Using a complete temporal ...characterization technique, we demonstrated the compression of the generated pulses for as low as 130 attoseconds, corresponding to less than 1.2 optical cycles. Numerical simulations of the generation process show that the carrier-envelope phase of the attosecond pulses is stable. The availability of single-cycle isolated attosecond pulses opens the way to a new regime in ultrafast physics, in which the strong-field electron dynamics in atoms and molecules is driven by the electric field of the attosecond pulses rather than by their intensity profile.
•The variation of the craters generated by fs laser irradiation with repetition rate is investigated.•The influence of the laser pulse repetition rate on removal rate and surface texture on silicon ...is addressed.•Possible effects of plume shielding on crater features and laser surface structuring at high repetition rate is discussed.
The influence of the pulse repetition rate on laser irradiation of silicon, in air, with femtosecond laser pulses is experimentally investigated in the range 10 Hz – 200 kHz. The features of the produced crater and the laser-induced periodic surface structures generated on its surface are characterized by exploiting surface profilometry and scanning electron microscopy. The experimental characterization evidences an interesting influence of the pulse repetition rate on the crater size qualitatively addressing a progressive reduction of the material removal efficiency at higher repetition rates. Moreover, also the surface structures produced by an irradiation sequence with a fixed number of laser pulses (namely N = 100) shows a clear dependence on the repetition rate. The observed effects are rationalized by considering the possible influence of plume shielding and heat accumulation effects typically observed during laser processing with high repetition rate laser systems.
The interaction between proteins and solid surfaces can influence their conformation and therefore also their activity and affinity. These interactions are highly specific for the respective ...combination of proteins and solids. Consequently, it is desirable to investigate the conformation of proteins on technical surfaces, ideally at single molecule level, and to correlate the results with their activity. This is in particular true for biosensors where the conformation-dependent target affinity of an immobilized receptor determines the sensitivity of the sensor. Here, we investigate for the first time the immobilization and orientation of antibodies (Abs) photoactivated by a photonic immobilization technique (PIT), which has previously demonstrated to enhance binding capabilities of antibody receptors. The photoactivated immunoglobulins are immobilized on ultrasmooth template stripped gold films and investigated by atomic force microscopy (AFM) at the level of individual molecules. The observed protein orientations are compared with results of nonactivated antibodies adsorbed on similar gold films and mica reference samples. We find that the behavior of Abs is similar for mica and gold when the protein are not treated (physisorption), whereas smaller contact area and larger heights are measured when Abs are treated (PIT). This is explained by assuming that the activated antibodies tend to be more upright compared with nonirradiated ones, thereby providing a better exposure of the binding sites. This finding matches the observed enhancement of Abs binding efficiency when PIT is used to functionalize gold surface of QCM-based biosensors.
A novel technique was demonstrated that overcomes important drawbacks to crosslink cells by irradiation with ultrashort ultraviolet laser pulses (L-crosslinking). To use this technique coupled to ...Chromatin ImmunoPrecipitation (ChIP) in a high throughput context, a prescreening fast method needs to be implemented to set up suitable irradiation conditions of the cell sample for efficient L-crosslinking with no final and long ChIP analysis. Here a fast method is reported where living human cells have been first transfected with a vector coding for Estrogen Receptor α (ERα), linked to Green Florescent protein (ERα-GFP), so that the well-known interaction between the Estrogen Receptor Elements (ERE) region of the cell DNA and the ERα protein can be detected by studying the fluorometric response of the irradiated cells. The damage induced to cells by ultraviolet irradiation is characterized by looking at the DNA integrity, protein stability, and cellular viability. A second novel approach is presented to analyze or re-visit DNA and RNA sequences and their molecular configurations. This approach is based on methods derived from Chern-Simons super-gravity adapted to describe mutations in DNA/RNA strings, as well as interactions between nucleic acids. As a preliminary case, we analyze the KRAS human gene sequence and some of its mutations. Interestingly, our model shows how the Chern-Simons currents are able to characterize the mutations within a sequence, in particular giving a quantitative indication of the mutation likelihood.
We report a correlative imaging analysis of a crystalline silicon target after irradiation with a low number of 1055 nm, ~ 850 fs laser pulses with several microscopy techniques (e.g., scanning ...electron microscopy, atomic force microscopy, Raman micro-imaging and confocal optical microscopy). The analysis is carried out on samples irradiated both in high vacuum and at atmospheric pressure conditions, evidencing interesting differences induced by the ambient environment. In high-vacuum conditions, the results evidence the formation of a halo, which is constituted by alternate stripes of amorphous and crystalline silicon, around the nascent ablation crater. In air, such an effect is drastically reduced, due to the significant back-deposition of nanoparticulate material induced by the larger ambient pressure.
High harmonic generation provides a means of producing attosecond pulses of light which are the shortest, controllable probes available to science for time-resolving ultrafast dynamics. We review ...techniques based on high harmonic generation for generating single attosecond pulses using high-power, multi-cycle laser sources, including optical-, polarisation-, and ionisation-gating schemes as well as techniques based on field synthesis. By significantly reducing the technical demands placed on the driving laser, these techniques have the potential to greatly broaden the application base for attosecond pulses.
•The effect of the LIPSS process on the surface chemical properties and consequently on SEY is investigated.•Femtosecond Laser-Induced Periodic Surface Structures (LIPSS) are used to reduce SEY in ...copper.•Copper treated with LIPSS shows a low surface debris density and is therefore less critical for ultra-high vacuum applications in particle accelerators.
The electron-cloud phenomenon is one cause of beam instabilities in high intensity positive particle accelerators. Among the proposed techniques to mitigate or control this detrimental effect, micro-/nano-geometrical modifications of vacuum chamber surfaces are promising to reduce the number of emitted secondary electrons. Femtosecond laser surface structuring readily allows the fabrication of Laser Induced Periodic Surface Structures (LIPSS) and is utilized in several fields, but has not yet been tested for secondary electron emission reduction. In this study, such treatment is carried out on copper samples using linearly and circularly polarized femtosecond laser pulses. The influence of the formed surface textures on the secondary electron yield (SEY) is studied. We investigate the morphological properties as well as the chemical composition by means of SEM, AFM, Raman and XPS analyses. Surface modification with linearly polarized light is more effective than using circularly polarized light, leading to a significant SEY reduction. Even though the SEY maximum is only reduced to a value of ~1.7 compared to standard laser-induced surface roughening approaches, the femtosecond-LIPSS process enables to limit material ablation as well as the production of undesired dust, and drastically reduces the number of redeposited nanoparticles at the surface, which are detrimental for applications in particle accelerators. Moreover, conditioning tests reveal that LIPSS processed Cu can reach SEY values below unity at electron irradiation doses above 10−3 C/mm2.
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•Vmh2 hydrophobin self-assembles into multi-layers on gold surface.•The bio-functionalized surface is able to entrap free glucose molecules and swell.•The Vmh2 functionalized gold surface lends ...itself as a smart delivery systems.
Hydrophobins (HFBs) are peculiar proteins which self-assemble at hydrophilic-hydrophobic interfaces into amphipathic membranes, and some of them (class I HFB) are able to form much more stable amyloid-like layers. This feature makes them suitable for many purposes, particularly when stable surface functionalization is required, also in view of their versatility in binding different kinds of molecules. For instance, it has been shown that Vmh2 from Pleurotus ostreatus (a class I HFB) is able to bind molecules like glucose, thus offering the perspective of using Vmh2 as a surface functionalization tool in bio-hybrid devices. In this paper a quantitative analysis of glucose interaction with the Vmh2 layer is reported; in particular, it is shown that Vmh2 layer swells by almost doubling its thickness as a result of glucose diffusion and each Vmh2 monomer is able to bind approximately 30 glucose molecules. These results have been achieved by self-assembling multi-layers of Vmh2 on a gold substrate and, subsequently, measuring both the mass of the bound glucose and the thickness of the resulting layer through two different and complementary techniques: quartz crystal-microbalance and ellipsometry. The data provided by the two techniques are in a satisfactory agreement and offer a plausible description of the mechanisms underlying the interaction of glucose with Vmh2 layer. This facile and versatile coating is of interest for biomedical applications of gold surfaces and particles.
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