Matrix-assisted laser desorption mass spectrometry of gas-phase peptide–metal complexes

Cation attachment to a model peptide has been investigated in matrix-assisted laser desorption experiments. Angiotensin I (Asp–Arg–Val–Tyr–Ile–His–Pro–Phe–His–Leu) is chosen as a system for study, and Cu²⁺ and K⁺ salts are used as cationizing agents. Three fundamentally different types of samples are investigated: (1) a crystalline sample of Ang I, metal salt and MALDI matrix, prepared with the conventional dried droplet method; (2) a solvent-free fine powder mixture of the same three compounds, and (3) a solution of the angiotensin and the metal salt in an ionic liquid matrix (a molten organic salt that acts as a MALDI active solvent). Effective protonation and cationization of the peptide are achieved with the three methods. The transition metal systematically provides more efficient cationization than the alkali metal. At sufficiently high concentration of the salt, the attachment of up to four copper cations to the angiotensin is observed in the MALDI spectrum. In contrast, only one K⁺ cation is efficiently bound to the peptide. For a given salt concentration, the highest degree of cationization is obtained in the laser desorption from the ionic liquid matrix. This is attributed to the efficient transfer of free metal cations to the desorption plume, where the complexation takes place.     

Chaos in an Ar+ Composite Resonator Laser Using KNSBN;Cu Crystal Self-Pumped Phase-Conjugator

Observation of the dynamics in a single-mode Ar⁺ composite resonator laser using KNSBN;Cu crystal self-pumped phase-conjugator is reported. The sequence of instabilities occurring on gain change corresponds to the transition the chaos of the logistic equation. Period-doubling route to chaos, and period-5, -3,-3×2, and -2 together with -3 windows in the chaotic range were observed. The strange attractor which is similar to that of the forced Duffing equation is obtained by reconstructing phase-space pictures of the system.     

Coupling of desorption and photoionization processes in two-step laser mass spectrometry of polycyclic aromatic hydrocarbons

The response of polycyclic aromatic hydrocarbons (PAHs) to different desorption and ionization fluences has been investigated in a laser desorption/multiphoton ionization/time-of-flight mass spectrometry scheme. The results evidence an intricate relationship between the desorption and ionization steps, tentatively attributed to the amount of internal energy acquired by the desorbed molecules. Different behaviors have been found for the various PAHs considered, leading to a parametric “signature” for each species. Moreover, some insights on the fragmentation mechanism of the desorbed PAHs have been obtained, with possible interpretation in the frame of a “ladder-switching” model.     

Light-induced sodium desorption from paraffin film

Sodium photoejection from a paraffin coated cell has been observed and analyzed in detail. The effect has been detected by observing the fluorescence induced by a cw dye laser. A maximum Na density of about 2.9 ×10⁸ atoms/cm³ was obtained by shining the cell with 1.05 W Ar⁺ laser green light. A progressive slowing of the dynamics of the process is reported, probably due to a change in the chemical rearrangement of the Na atoms in the coating under intense light exposure. This aging effect represents a limitation in the practical application of this kind of materials.     

Time reversal and non-linear elastic wave spectroscopy (TR NEWS) techniques

Non-linear elastic wave spectroscopy (NEWS) has been shown to exhibit a high degree of sensitivity to both distributed and isolated non-linear scatterers in solids. In the case of an isolated non-linear scatterer such as a crack, by combining the elastic energy localization of time reversal (TR) with NEWS, it is shown that one can isolate non-linear scatterers in solids. The experiments reviewed here present two distinct methods of combining TR and NEWS for this purpose. The techniques each have there own advantages and disadvantages, with respect to each other and other non-linear methods, which are discussed.     

Ultrafast emission of ions during laser ablation of metal for 3D atom probe

The 3D atom probe(3DAP) is an imaging instrument based on the controlled field evaporation of single atoms from a sample having a tip shape with an end radius of 50 nm. In the fs laser assisted 3DAP the evaporation is induced by the laser pulses so that the physical process involved in this 3DAP analysis might correspond to the very early stages of the ablation process. In this paper we present the principle of the 3DAP and we discuss the existing models of the fs assisted evaporation. At last, we test the relevance of these models with pump-probe experiments on tungsten tips in the tomographic atom probe.     

Non-linear based time reversal acoustic applied to crack detection: Simulations and experiments

In non-destructive evaluation, non-linear elastic wave spectroscopy (NEWS) methods represent powerful tools to explore damaged zones in a sample. The combination of these methods with time reversal (TR) process can be used to either increase the stress on the retrofocusing position or to retrofocuse elastic waves on the defect, when only the non-linear components of the received signal are time reversed. In this paper, we propose two different approaches to detect cracks in metallic samples in coupling NEWS methods and TR process. The first one, NEWS-TR, is defined by sending back only the non-linear components which are preliminary time reversed. Two different techniques to filter non-linear components have been numerically studied: classical harmonic filter and pulse inversion. In these two cases, performances of retrofocusing on different defect positions are analyzed and compared. The second approach, TR-NEWS, consists in measuring the non-linear signature on the focal spot. An experimental study of parametric interaction between two reversed signals (f₁ and f₂) is led. Measurements of components at f₂-f₁ and f₂+f₁ around a crack are performed and discussed.     

Improved frequency stability of the ammonia laser

A sodium-filled Fabry-Perot resonator shows many different types of irregular behavior. A sophisticated experimental apparatus allows reproducible measurements of oscillation scenarios leading to chaos and thus permits a detailed classification of the different phenomena. A quantitative explanation — featuring a new mechanism — for the best reproducible class of chaotic oscillations is given.     

Laser-induced thermal desorption mass spectrometry of functionalized silicon surfaces

Functionalization of materials and laser patterning of chemisorbed layers play an increasing role in tailoring and structuring surface properties on the nanoscale. An attractive method of investigating organic functionalizations is laser-induced thermal desorption (LITD). The analysis of well-defined H- and D-terminated Si(1 1 1)-(1 × 1):H(D) surfaces was used to quantify the LITD technique. Moreover, oxidized silicon surfaces were functionalized with trimethylsilyl (TMS) and (3,3,3-trifluoropropyl)-dimethylsilyl (TFP) hydrophobic end groups. The samples were irradiated normal to the surface with focused XeCl laser pulses. The desorbed species were monitored at an oblique angle and their time-of-flight (TOF) distributions were measured with a quadrupole mass analyzer. The TOF temperatures of silicon were calibrated for different laser pulse energies by desorption of H₂ and D₂. In the LITD experiments, the desorption of trimethylsilanol groups was observed for TMS terminations, indicating that essentially the whole molecule desorbs from the surface. The TOF data could be fitted to Maxwellian distributions, providing the desorption yield of the emitted species, their mass, and temperature. On the other hand, several characteristic fragments were found for the TFP-terminated surface. The TOF distributions indicate that the fragments detected with the analyzer derived from different desorbed species.     

Optimization of Directivity of Point Source Array by Using Pseudostochastic Sequences

We investigate the methods to optimize the directivity of point source array by using pseudostochastic sequences. Maximum-length sequence （MLS） array and Quadratic-residue sequence （QRS） array are theoretically analysed, and their simulated responses are shown. The results indicate that pseudostochastic sequences can be used to optimize the directivity of point source array.