The interaction of intense femtosecond laser pulses with solid targets is a topic that has attracted a large amount of interest in science and applications. For many of the related experiments a large energy deposition or absorption as well as an efficient coupling to extreme ultraviolet (XUV), X-ray photon generation, and/or high energy particles is important. Here, much progress has been made in laser development and in experimental schemes, etc. However, regarding the improvement of the target itself, namely its geometry and surface, only limited improvements have been reported. The present paper investigates the formation of laser-induced periodic surface structures (LIPSS or ripples) on polished thick copper targets by femtosecond Ti:sapphire laser pulses. In particular, the dependence of the ripple period and ripple height has been investigated for different fluences and as a function of the number of laser shots on the same surface position. The experimental results and the formation of ripple mechanisms on metal surfaces in vacuum by femtosecond laser pulses have been analysed and the parameters of the experimentally observed “gratings” interpreted on base of theoretical models. The results have been specifically related to improve high-intensity femtosecond-laser matter interaction experiments with the goal of an enhanced particle emission (photons and high energy electrons and protons, respectively). In those experiments the presently investigated nanostructures could be generated easily in situ by multiple pre-pulses irradiated prior to a subsequent much more intense main laser pulse.
The initial nucleation and coalescence of Cu by supercritical fluid deposition (SCFD) were monitored by measuring the surface reflectivity of visible white light. The reflectivity at 770 nm is sensitive to initial nucleation, thus, the nucleation and coalescence temperatures of Cu-SCFD can be easily monitored by this in situ technique. The nucleation temperature of Cu-SCFD was found to be independent of the precursor concentration, which suggests a strong adsorption and surface saturation of the source precursor at high concentration. A high H 2 concentration up to 0.39 mol/L with Cu(tmhd) 2 as a precursor can decrease the nucleation temperature from 215 to 180 C. A high H 2 concentration is also effective for realizing a smooth surface morphology of the deposited Cu film and for making the film thin at the coalescence stage probably because of the initial nucleation with a high number density. The fabrication of a 10-nm-thick continuous Cu film, which is required as a seed layer in ultralarge scale integration (ULSI), was successfully demonstrated with a high H 2 concentration of 0.39 mol/L.
Optical fibers play an important role in general, and in particular in the field of sensors. As part of a sensor system quite often fibers are coupled by a ball lens. For efficient usage, the fiber ball lens systems (FBLS) have to be optimized. The present work presents analytic expressions for design parameters of such systems. FBLS comprise sections of a single-mode optical fiber, a coreless fiber (CLF) and a ball lens. Their geometric dimensions have to be optimized for their use in different application in optical metrology. The derived expressions facilitate the optimum parameter choice which usually is done by expensive numerical simulations. For comparison and validation of the results by experiments, FBLS with different ball lens radii and CLF sections have been prepared by a fusion splicer technique. Their characteristics were investigated in the optical spectral ranges at 630nm and 1550nm. Experimental methods comprising far-field, near-field, reflection /transmission measurements with optical fibers validate the theoretical considerations. To our knowledge this is the first time that simple analytic approaches have been applied to the fabrication of FBLS. This facilitates and quickens their general design for different applications in optical metrology significantly.
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