Assessing the effect of the matrix in resonant infrared MAPLE

The ablation yield of polyethylene glycol is measured as a function of laser pulse energy and polymer molecular weight for both free running and Q-switched Er:YAG lasers. The results show that the deposition rate is dependent on the absorption coefficient in a way that is consistent with the blow-off ablation model but that the linear dependence of the efficiency on laser pulse energy is also consistent with a steady-state ablation model. The results for both lasers are remarkably similar given that the pulse durations are 350 μs and 85 ns, respectively. Furthermore, polystyrene thin films are deposited as well and it is found that the morphology depends on the THF/MeOH ratios in the matrices. The significance of these results is discussed as well as future directions for this research.     

Multiple beam atom interferometer: theory and experiment

Received: 30 May 1997/ 27 August 1997     

Nonlinear optical properties of a new two-photon-absorption organic dye: HEASPS

Trans-4-[p-(N-hydroxyethyl-N-ethylamino)styryl]-N-methylpyridinium p-toluene sulfonate (abbreviated as HEASPS) is a two-photon-absorption (TPA) dye newly synthesized by our research group. It possesses a much larger TPA cross-section and much stronger upconversion fluorescence emission than those of common organic dyes (such as rhodamine) when excited with near-infrared (IR) radiation. TPA spectrum and upconversion efficiency spectrum of HEASPS solution at different wavelengths have been measured. The largest molecular TPA cross-section σ₂ ^′ is measured to be 2.06×10^-47 cm⁴ s/photon at 930 nm. At 1064 nm, σ₂ ^′ is 2.71×10^-48 cm⁴ s/photon, which is only one-ninth of that at 930 nm. The upconverted lasing efficiency spectrum has been measured at different wavelengths. The highest efficiency is 5.1% at 1020 nm, whereas it is 3.5% at 1064 nm. Its optical-power-limiting properties at 930 nm have also been illustrated. Received: 30 November 2000 / Published online: 27 April 2001     

Preparation of Aligned Polymer Micro/Nanofibres by Electrospinning

Polymer micro/nanofibres are prepared by typical and modified methods of electrospinning. The morphologies and microstructures of the electrospun micro/nanofibres are characterized by a scanning electron microscope （SEM）. The micro/nanofibres prepared by the typical electrospinning are usually collected in the form of nonwoven mats lacking of structural orientation, However, by modifying collector（s） of the electrospinning setup, the resulting polymer fibres show aligned structures to some extent. We analyse all the forces that the fibres experienced during electrospinning and find that the electrostatic force originating from the splitting electric field plays a key role in the alignment of the micro/nanofibres.     

Chiral Invariant Phase Space model

The CHIPS (CHiral Invariant Phase Space) model is used for approximation of the Drell-Yan process in hadron-nucleon interactions. It is proved that the Drell-Yan cross-section at low p _T ² is a function of only x₁ and x₂ and does not evolve as a function of the squared mass of the lepton pair M². The CHIPS model predicts that the Drell-Yan structure functions evolve as a function of p _T ² . This p _T ² evolution can be measured in experiments at RHIC and LHC.     

Topography and friction properties of macromolecular thin films using atomic-force-microscopy technology

Applied Physics A - The research work in this letter is on the microtribological properties of poly(ether ketone ketone) (PEKK) and sulfonated PEKK (S-PEKK) thin films. Polystyrene (PS) was used as...     

Dielectric breakdown of rubber materials by femtosecond irradiation

We report the reversible micro-structuring of a synthetic rubber polymer (cis1,4-polybutadiene (PB)) by femtosecond laser illumination. Visco-elastic relaxation of the optically damaged region was observed. The recovery time, typically 10²–10⁴ ms, can be varied by changing the irradiation pulse energy. Multi-shot-induced damage recovers on the much longer scale of 10¹–10² s. It was found that the doping of PB by 4 wt. % of pentazadiene ([4-NO₂]–phenyl–N=N–N(C₃H₇)–N=N–phenyl–[4-NO₂]) reduces the threshold of light-induced photo-modification by 20%. This is explained by photo-induced (homolytic) cleavage of the pentazadiene bonds and formation of gaseous N₂, which facilitates material failure at the irradiated spot. The recovery of optical transmission can be applied to optical memory, optical and micro-mechanical applications. The underlying mechanism of the phenomenon is discussed in terms of anelastic α- and β-relaxation (polymer backbone and chains/coils relaxation, respectively). Received: 11 October 2001 / Accepted: 9 July 2002 / Published online: 25 October 2002 RID="*" ID="*"Corresponding author. Fax: +81-88/656-7598, E-mail: misawa@eco.tokushima-u.ac.jp     

Coexistence of color superconductivity and chiral symmetry breaking within the NJL model

The phase diagram for quark matter is investigated within a simple Nambu-Jona-Lasinio model without vector correlations. It is found that the phase structure in the temperature-density plane depends sensitively on the parametrization of the model. We present two schemes of parametrization of the model where, within the first one, a first-order phase transition from a phase with broken chiral symmetry to a color superconducting phase for temperatures below the triple point at T _t = 55 MeV occurs, whereas for the second one a second-order phase transition for temperatures below T _t = 7 MeV is found. In the latter case, there is also a coexistence phase of broken chiral symmetry with color superconductivity, which is a new finding within this class of models. Possible consequences for the phenomenology of the QCD phase transition at high baryon densities are discussed. Received: 3 January 2003 / Accepted: 21 February 2003 / Published online: 24 April 2003     

Effect of neutrino trapping on the three flavor FFLO phase of QCD

We compute the effect of a non-zero lepton chemical potential on the structure of the three flavor Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) phase of QCD at finite temperature. We show that, as in the BCS case, the lepton chemical potential favors two-species color superconductivity and disfavors the three species pairing. We stress that this study could be relevant for the cooling of a proto-neutron star with a FFLO core, if the temperatures are higher than the un-trapping temperature.     

Steady-state mechanism for polymer ablation by a free-running Er:YAG laser

A free-running Er:YAG laser is used to ablate polyethylene glycol and the ablation yield is studied as a function of molecular weight (1000-10,000 g/mol) and laser fluence (8-25 J/cm²). A steady-state ablation mechanism is proposed which includes recoil-induced expulsion as the primary contributor to the ablation yield. It is also proposed that the formation of a molten layer is a necessary part of the ablation mechanism because the calculated tensile strengths for the solid polymer are too large to permit fracture of the target due to the laser-induced stress transient. The ablation yield is found to depend in a sigmoidal fashion upon laser fluence, thus implying a variable ablation enthalpy. Finally, the current results are compared with that obtained previously with a free electron laser.