Experimental acoustic modal analysis of a tenor saxophone.

This paper presents an application of the Experimental Acoustic Modal Analysis (AMA) on a vintage 10 M Conn tenor saxophone. This technique originates from the traditional Modal Analysis which is commonly adopted to determine the dynamic behaviour of solid structures. The methodology is based on the measurement of Frequency Response Functions (FRFs) as a ratio of the acoustic pressure, measured by means of a set of microphones positioned along the saxophone body, and the volume velocity produced by an acoustic source and measured at the instrument input. The microphones are housed on the stripped saxophone keys by means of tailored three-dimensional printed adapters. The AMA makes use of the FRFs to extract modal parameters, such as resonance frequencies, loss factors, and mode shapes. These parameters pertain to the cavity modes of the saxophone passive resonator. The analysis has been performed for three different notes (B ♭, B, and C) and for two registers of the instrument in order to show the potential of the technique. Moreover, the influence of the mouthpiece volume on the cavity modes has been shown. The information obtained by AMA can find useful application in the validation of analytical or numerical models of this kind of musical instruments.

Low threshold Fabry-Perot optofluidic resonator fabricated by femtosecond laser micromachining.

We report the realization and characterization of an optofluidic microlaser based on a Fabry-Perot resonator fabricated by exploiting two direct writing fabrication techniques: the femtosecond laser micromachining and the inkjet printing technology. In this way a standard Fabry-Perot cavity has been integrated into an optofluidic chip. When using rhodamine 6G dissolved in ethanol at concentration of 5∙10-3 mol/l, laser emission was detected at a threshold energy density of 1.8 µJ/mm2 at least one order of magnitude lower than state-of-the-art optofluidic lasers. Linewidth below ~0.6 nm was measured under these conditions with a quality factor Q~103. These performances and robustness of the device makes it an excellent candidate for biosensing, security and environment monitoring applications.

Structured beam diffraction.

We report on the observation of a modulated pattern induced by a single laser beam in a polymeric film. In spite of the simple geometrical configuration, the analysis of the far field diffraction pattern allows a sensitive retrieving of the wavelength of the recording beam and of its incidence angle, pointing out the high information content of the recorded spot. A theoretical model is presented which satisfactorily explains the observed behavior. It takes into account the interaction of structured light with structured matter with the same symmetries and spatial modulation frequencies close to each other. This result shows a feature of the interaction between structured light and structured matter which has not been explored yet.

First-order optical Freedericksz transition in a dye-doped nematic liquid crystal.

A first-order optical Freedericksz transition in a nematic liquid crystal doped by a small quantity of a dichroic dye with negative dichroism is observed. The initial homeotropic state corresponds to maximum absorption for the linearly polarized incident beam, while reorientation reduces absorption increasing the optical torque: this process produces the positive feedback leading to the observed bistable behavior.

Turbulence to turbulence transition in homeotropically aligned nematic liquid crystals.

In this paper, a study of the electrically driven turbulent-turbulent transition in a homeotropically oriented nematic sample is reported. The transition has the characteristics of a nucleation process, and its threshold has been experimentally determined. The nucleation rate and the growth velocity of the new turbulent nuclei are also reported.

Determination of small anisotropy of holographic phase gratings.

We show the possibility of detecting small anisotropies in holographic polymer dispersed liquid-crystal samples, using a simple experimental setup that allows us to determine the behavior of the diffraction efficiency versus incident angle for two reading polarizations. This analysis is extremely sensitive to small changes in the parameters that define the grating anisotropy, giving us a way to determine with great accuracy the components of the modulated part of the dielectric tensor.

Photopolarimetric characterization of the transition between two turbulent states in a nematic liquid crystal film.

This work was aimed at the photopolarimetric characterization of the transition between two dynamic scattering modes that take place in a planarly aligned nematic liquid crystal sample, under the effect of an external low-frequency electric field. The time evolution of the degree of polarization and the behavior of the radiation entropy of the transmitted light allow us to interpret the transition between two turbulent states, or dynamic scattering modes, as a decay from a two-dimensional (2D) to a (3D) turbulence.