Non-thermal ablation of expanded polytetrafluoroethylene with an intense femtosecond-pulse laser

Ablation of expanded polytetrafluoroethylene without disruption of the fine porous structure is demonstrated using an intense femtosecond-pulse laser. As a result of laser-matter interactions near ablation threshold fluence, high-energy ions are emitted, which cannot be produced by thermal dissociation of the molecules. The ion energy is produced by Coulomb explosion of the elements of (-CF_{2}-CF_{2-})n and the energy spectra of the ions show contributions from the Coulomb explosions of the ions rather than those of thermal expansion to generate high-energy ions. The dependence of ion energy on the laser fluence of a 180-fs pulse, compared with that of a 400-ps pulse, also suggests that the high-energy ions are accelerated by Coulomb explosio

Variations of the cephalic vein anterior to the clavicle in humans

Background: Clinicians should understand that jugulocephalic vein (JCV) variants may be occasionally found. This study aims to classify JCV variants and obtain their frequency.   Materials and methods: We investigated anatomical variants of the cephalic vein in 55 human cadavers during a gross anatomy course at our medical school.   Results: The percentage of JCVs that pass through the anterior part of the clavicle and anastomose to the jugular vein as per previous studies and our study was 2–5%. Five cases with anastomosis between the cephalic and external jugular veins that pass through the anterior part of the clavicle were found. The courses were classified into 1A, 1B, 2A, and 2B. Type 1 extends beyond the clavicle and anastomoses with the external jugular vein. Type 2 follows the same course as type 1, but anastomoses with the subclavian vein. Subtype A does not have a branch that anastomoses with the axillary vein, whereas subtype B does. We encountered two cases of type 1A and three of type 1B.   Conclusions: Four anatomical variants of the cephalic vein around the clavicle were identified. Clinicians’ knowledge of these variants is expected to decrease possible complications if venous access via the cephalic vein is needed

Mechanism of femtosecond laser nano-ablation for metals

Metals have three ablation threshold fluences (high,middle and low-threshold fluence, here called) forfemtosecond laser pulses. In order to investigatethe physics of metal ablation under an intenseoptical field, the ions emitted from a laserirradiatedcopper surface were studied by time-offlightenergy spectroscopy. The low laser fluenceat which ions are emitted, Fth,L is 0.028 J/cm2, andtwo higher emission thresholds were identified atfluences of Fth,M =0.195 J/cm2 and Fth,H =0.470J/cm2. The relation between the number of emittedions per pulse Ni and laser fluence F was in goodagreement with Ni ∝F4 for Fth,L - Fth,M, Ni ∝F3 forFth,M - Fth,H, and Ni ∝F2 for ≥ Fth,H. Thedependence of ion production on laser energyfluence is explained well by multiphotonabsorption and optical field ionization.For fluence levels near the middle to high ablationthreshold, the formation of grating structures onmetal surfaces has been observed. The interspacesof grating structures were shorter than the laserwavelength, and the interspaces depend on fluencefor Mo and W with a 160 fs laser pulse. Thisphenomenon is well explained by the parametricdecay model proposed by Sakabe et al

Path Integral Approach to the Non-Relativistic Electron Charge Transfer

A path integral approach has been generalized for the non-relativistic electron charge transfer processes. The charge transfer - the capture of an electron by an ion passing another atom or more generally the problem of rearrangement collisions is formulated in terms of influence functionals. It has been shown that the electron charge transfer process can be treated either as electron transition problem or as elastic scattering of ion and atom in the some effective potential field. The first-order Born approximation for the electron charge transfer cross section has been reproduced to prove the adequacy of the path integral approach for this problem.Comment: 19 pages, 1 figure, to appear in Journal of Physics B: Atomic, Molecular & Optical, vol.34, 200