Femtosecond fiber Bragg grating fabrication with adaptive optics aberration compensation.

We present fiber Bragg gratings (FBGs) fabricated using adaptive optics aberration compensation for the first time to the best of our knowledge. The FBGs are fabricated with a femtosecond laser by the point-by-point method using an air-based objective lens, removing the requirement for immersion oil or ferrules. We demonstrate a general phase correction strategy that can be used for accurate fabrication at any point in the fiber cross-section. We also demonstrate a beam-shaping approach that nullifies the aberration when focused inside a central fiber core. Both strategies give results which are in excellent agreement with coupled-mode theory. An extremely low wavelength polarization sensitivity of 4 pm is reported.

Nitrogen adduction by three coordinate group 10 organometallic cations: platinum is favoured over nickel and palladium.

Previous studies have shown that highly reactive product ions formed by collision-induced dissociation (CID) of precursor ions generated via electrospray can readily react with residual solvent or drying gases, especially in ion trap mass spectrometers. Here we report on the rapid addition of nitrogen to the coordinatively unsaturated organoplatinum cation, [(phen)Pt(CH(3))](+) (phen=1,10-phenanthroline) formed via decarboxylation of the acetate complex [(phen)Pt(O(2) CCH(3))](+). This contrasts with the related coordinatively unsaturated group 10 cations: addition of nitrogen to [(phen)Pd(CH(3))](+) occurs at longer reaction times, whereas addition of nitrogen to [(phen)Ni(CH(3))](+) is virtually non-existent. To better understand these reactions, density functional theory (DFT) calculations were carried out at the B3LYP/SDD6-31+G(d) level of theory to determine the N(2)-binding energies of [(phen)M(CH(3))](+). [(phen)Pt(CH(3))](+) has a higher binding energy to N(2) (1.06 eV) than either [(phen)Ni(CH(3))](+) (0.61 eV) or [(phen)Pd(CH(3))](+) (0.66 eV), consistent with the experimental ease of addition of nitrogen to the coordinatively unsaturated organometallic complexes, [(phen)M(CH(3))](+). Finally, [(phen)M(CH(3))](+) are reactive to other background gases, forming [(phen)M(O(2))](.+) (for M=Ni) in reactions with oxygen and undergoing water addition (for M=Ni, Pd and Pt) and water addition/CH(4) elimination reactions to yield [(phen)M(OH)](+) (for M=Ni and Pt).

Quantum mechanics-free subsystem with mechanical oscillators.

Quantum mechanics sets a limit for the precision of continuous measurement of the position of an oscillator. We show how it is possible to measure an oscillator without quantum back-action of the measurement by constructing one effective oscillator from two physical oscillators. We realize such a quantum mechanics-free subsystem using two micromechanical oscillators, and show the measurements of two collective quadratures while evading the quantum back-action by 8 decibels on both of them, obtaining a total noise within a factor of 2 of the full quantum limit. This facilitates the detection of weak forces and the generation and measurement of nonclassical motional states of the oscillators. Moreover, we directly verify the quantum entanglement of the two oscillators by measuring the Duan quantity 1.4 decibels below the separability bound.