Alkali—SCl2 chemiluminescence: Vibrational population inversion in the B state of S2

S₂(B-X) chemiluminescence, primarily from ν′ = 0 and 1, has been observed in alkali atom—SCl₂ reactions. The addition of He or Ar buffer gas to the reaction chamber alters the reaction dynamics, and at certain buffer gas pressures the S₂ emission originates exclusively from the ν′ = 6–9 vibrational levels of the B(³Σ_u^?) state.     

Optimizing the efficiency of femtosecond-laser-written holograms

Computer-generated binary holograms are written on a polished copper surface using single 800-nm, 120-fs pulses from a 1-kHz-repetition-rate laser system. The hologram efficiency (i.e. the power in the holographic reconstructed image relative to the incoming laser power) is investigated for different laser-structuring parameters. Theoretical diffraction grating efficiencies for a binary amplitude grating show good agreement with the experimental measurements for diameters of the laser-formed holes below the pitch. Modelling based on straightforward geometrical arguments is used to find the optimal hole size. For a coverage (i.e. relative laser-structured area) of ～43 %, the efficiency reaches ～10 %, which corresponds to a relative power transferred to one reconstructed image of ～20 %. The efficiency as a function of pitch (for fixed coverage) is fairly constant from 2 to 6 μm.     

DOUBLESLICING: a non-iterative single profile multi-exponential curve resolution procedure. Application to time-domain NMR transverse relaxation data

A new non-iterative curve resolution technique for resolving single decay profiles is proposed. The new technique, called DoubleSlicing, is based on the Decra (Direct Exponential Curve Resolution Algorithm) principle. While the original Decra was designed to resolve several decay curves simultaneously and thus fitting common pure exponentials, DoubleSlicing can resolve single decay profiles by a simple double data transformation followed by an analytical and unique three-way decomposition. The new approach is successfully demonstrated on experimental NMR CPMG relaxation data, measured on combinations of unmixed paramagnetic CuSO(4) solutions. Decay signals of the water component were acquired following an innovative experimental design that ensured no interaction between the components present in each sample under observation. DoubleSlicing proved to be accurate in estimating relaxation times differing in one order of magnitude (range: 19.6-159.4ms). Its performance was comparable to discrete exponential fitting with the advantage of being much faster - in terms of computation time, DoubleSlicing outperformed exponential fitting by a factor of four.     

Ultra-short pulse laser ablation of copper, silver and tungsten: experimental data and two-temperature model simulations

Experimental results of femtosecond laser ablation of the metals copper, silver and tungsten are compared to simulations based on the two-temperature model. The comparison provides new information about the laser-heating process: For the noble metals (Cu, Ag), the energy transport via ballistic electrons must be included, while this effect is negligible for a transition metal (W). The comparison provides values for the range of ballistic electrons in the noble metals. The model calculation is also employed to investigate the dependence of the threshold fluence and melting depth on pulse duration. It is observed that for pulses shorter than approximately 1 ps the threshold fluence and melting depth are independent of the pulse duration, while they increase as τ ^0.47 and τ ^0.51, respectively, for pulses longer than ∼40 ps, in good agreement with approximate analytical expressions predicting a ?{t}\sqrt{\tau} dependence.     

Femtosecond laser excitation of dielectric materials: experiments and modeling of optical properties and ablation depths

Modeling of the interaction between a dielectric material and ultrashort laser pulses provides the temporal evolution of the electronic excitation and the optical properties of the dielectric. Experimentally determined reflectances and ablation depths for sapphire are compared to the calculations. A decrease in reflectance at high fluences is observed experimentally, which demonstrates the necessity of a temperature-dependent electron scattering rate in the model. The comparison thus provides new constraints on the optical parameters of the model.     

Ultra-short pulse laser ablation of metals: threshold fluence, incubation coefficient and ablation rates

In this paper we present femtosecond laser ablation studies of the metals copper, silver and tungsten. Measurements of the threshold fluence determined from the hole diameters versus fluence provide incubation coefficients of the three materials, which are found to be equal within one standard deviation. Furthermore, we have determined the single-shot threshold fluences to be 1.7±0.3 J/cm², 1.5±0.4 J/cm² and 0.44±0.02 J/cm² for copper, silver and tungsten, respectively. These are in good agreement with theoretical values calculated neglecting heat diffusion.