•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.
We report on fs laser structuring and graphitization of diamond and experimental characterization of its THz response. A full characterization of graphitized, conductive layer generated by laser ...irradiation is carried out by performing scanning-electron microscopy, Raman spectroscopy and electrical measurements. The transmittance of the laser textured diamond samples, both with the graphitic overlayer and after selective oxidizing etching, is analyzed in the (0.25 ÷ 6.0) THz spectral range. A significant selective absorption of the graphitized overlayer towards polarized THz radiation is demonstrated, which is associated to the formation of graphitic laser induced periodic surface structures. This anisotropy allows conceiving compact passive metasurfaces based on conductive/dielectric patterns on the diamond plate surface for the development of robust, lightweight and broadband THz optical components.
In this work we present the results of the fabrication and characterization of a large area Superconducting Nanowire Single Photon Detector (SNSPD). A particular geometry was adopted to enhance the ...coupling with the Lidar system MALIA (Multiwavelength Lidar Apparatus), a setup used for atmospheric aerosols observations from ultraviolet to infrared. The devices realized are very promising as they exhibit a very low dead time despite the large sensitive area.
•fs- and ns-laser (266 and 532nm) processing of PDMS-elastomer, in air, is studied.•High definition tracks (on the PDMS-elastomer surface) for electrodes are produced.•Selective Pt or Ni ...metallization of the tracks is produced via electroless plating.•Irradiated and metallized tracks are characterized by μ-Raman spectrometry and SEM.•DC resistance of Pt and Ni tracks is always between 0.5 and 15Ω/mm.
Medical grade polydimethylsiloxane (PDMS) elastomer is a widely used biomaterial as encapsulation and/or as substrate insulator carrier for long term neural implants because of its remarkable properties. Femtosecond (λ=263 and 527nm) and nanosecond (266 and 532nm) laser processing of PDMS-elastomer surface, in air, is investigated. The influence of different processing parameters, including laser wavelength, pulse duration, fluence, scanning speed and overlapping of the subsequent pulses, on the surface activation and the surface morphology are studied. High definition tracks and electrodes are produced. Remarkable alterations of the chemical composition and structural morphology of the ablated traces are observed in comparison with the native material. Raman spectra illustrate well-defined dependence of the chemical composition on the laser fluence, pulse duration, number of pulses and wavelength. An extra peak about ∼512–518cm−1, assigned to crystalline silicon, is observed after ns- or visible fs-laser processing of the surface. In all cases, the intensities of SiOSi symmetric stretching at 488cm−1, SiCH3 symmetric rocking at 685cm−1, SiC symmetric stretching at 709cm−1, CH3 asymmetric rocking+SiC asymmetric stretching at 787cm−1, and CH3 symmetric rocking at 859cm−1, modes strongly decrease. The laser processed areas are also analyzed by SEM and optical microscopy. Selective Pt or Ni metallization of the laser processed traces is produced successfully via electroless plating. The metallization process is not sensitive with respect to the time interval after the laser treatment. DC resistance is measured to be as low as 0.5Ωmm−1. Our results show promising prospects with respect to use such a laser-based method for micro- or nano-fabrication of PDMS devices for MEMS and NEMS.
Titanium dioxide (TiO2) is at the basis of many important applications which are decisively controlled by its photophysical characteristics. Photoluminescence (PL) analysis provides important ...information on these latter, while also representing a less explored and possibly multi-parametric route to chemical sensing. In the present work we show that oxygen exposure produces opposite responses in the PL activity of the two most common TiO2 polymorphs (rutile and anatase) and discuss the origin of such a phenomenon, focusing in particular on the near-infrared PL characteristic for rutile TiO2. We propose an interpretation of the experimental findings in terms of two possible O2/TiO2 interaction routes, namely: (a) molecular chemisorption of oxygen and consequent dynamics of self-trapped hole states close to the sample surface and (b) dissociative chemisorption of oxygen, affecting the density of oxygen vacancies at (or close to) the surface. The remarkable result of an individual analyte producing different detectable effects on a same sensing material epitomizes the potentialities offered by an optical PL-based approaches toward multi-parametric chemical sensing, encouraging the exploration beyond the established chemoresistive approaches which are based on a single parameter. Moreover, it highlights interesting prospects for TiO2-based optical sensing.
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