Setup of Modulated Temperature FTIR technique to investigate thermal transitions of polymers

Nell'attività di ricerca dottorale è stata sviluppata una nuova tecnica d’indagine spettroscopica (Modulated Temperature Infrared Spectroscopy, MTFTIR) ed applicata allo studio delle transizioni termiche di polimeri. La tecnica permette lo studio delle variazioni conformazionali e strutturali delle singole macromolecole coinvolte nelle transizioni di fase dei materiali, differenziando inoltre transizioni all’equilibrio termodinamico da stati transienti di non-equilibrio. Ad una prima fase di messa a punto dell’apparato sperimentale e delle metodiche sono susseguiti studi su tre polimeri, il polipropilene isotattico, il polietilentereftalato ed il poli(L-lattide). I risultati MTFTIR, accoppiati ad analisi calorimetriche, hanno evidenziato dei comportamenti peculiari delle catene polimeriche nelle fasi vetrose, liquide e cristalline dei materiali, non indagabili o difficilmente distinguibili mediante altre tecniche sperimentali

Time-division multiplexing of the orbital angular momentum of light

We present an optical setup for generating a sequence of light pulses in which the orbital angular momentum (OAM) degree of freedom is correlated with the temporal one. The setup is based on a single $q$-plate within a ring optical resonator. By this approach, we demonstrate the generation of a train of pulses carrying increasing values of OAM, or, alternatively, of a controlled temporal sequence of pulses having prescribed OAM superposition states. Finally, we exhibit an "OAM-to-time conversion" apparatus dividing different input OAM states into different time-bins. The latter application provides a simple approach to digital spiral spectroscopy of pulsed light.Comment: 3 pages and 2 figure

Generation and dynamics of optical beams with polarization singularities

We present a convenient method to generate vector beams of light having polarization singularities on their axis, via partial spin-to-orbital angular momentum conversion in a suitably patterned liquid crystal cell. The resulting polarization patterns exhibit a C-point on the beam axis and an L-line loop around it, and may have different geometrical structures such as \qo{lemon}, \qo{star}, and \qo{spiral}. Our generation method allows us to control the radius of L-line loop around the central C-point. Moreover, we investigate the free-air propagation of these fields across a Rayleigh range.Comment: 6 pages, 4 figures, appears on Optics Express

Violation of Leggett-type inequalities in the spin-orbit degrees of freedom of a single photon

We report the experimental violation of Leggett-type inequalities for a hybrid entangled state of spin and orbital angular momentum of a single photon. These inequalities give a physical criterion to verify the possible validity of a class of hidden-variable theories, originally named "crypto non-local", that are not excluded by the violation of Bell-type inequalities. In our case, the tested theories assume the existence of hidden variables associated with independent degrees of freedom of the same particle, while admitting the possibility of an influence between the two measurements, i.e. the so-called contextuality of observables. We observe a violation the Leggett inequalities for a range of experimental inputs, with a maximum violation of seven standard deviations, thus ruling out this class of hidden variable models with a high confidence.Comment: 5 pages, 4 figure

Alastair Service, The Architects of London and Their Buildings from 1066 to the Present Day

Book review by Roch-Josef di Lisio. Service, Alastair. The architects of London and their buildings from 1066 to the present day. London: Architectural Press; New York: Architectural Book Pub., 1979

Stability of grid amplifiers

We present a stability model for quasi-optical grid amplifiers. This model is useful for predicting and suppressing the common-mode oscillations that often occur in amplifier grids. Three stabilization techniques will be discussed. The first technique uses a capacitor to stabilize the grid. The second approach employs resistance to suppress the oscillations. The final technique stabilizes the grid by reducing the on-chip common-mode resistance, allowing greatly increased amplifier efficiencies. Experimental evidence will be presented to confirm the validity of our stability model

Transmittivity measurements by means of squeezed vacuum light

A method for measuring the transmittivity of optical samples by using squeezed--vacuum radiation is illustrated. A squeezed vacuum field generated by a below--threshold optical parametric oscillator is propagated through a nondispersive medium and detected by a homodyne apparatus. The variance of the detected quadrature is used for measuring the transmittivity. With this method it is drastically reduced the number of photons passing through the sample during the measurement interval. The results of some tests are reported.Comment: 14 pages, 8 figure