Alessandra Rocco

The aim of this paper is to investigate the ability of different NDT techniques to detect and evaluate barely visible and non-visible impact damage on composite laminates. Firstly, a conventional ultrasound technique was adopted to investigate the delamination in carbon fibre laminates after low velocity impact s. Then the results were compared with a thermographic and holographic analysis, as well as a theoretical simulation of the expected delamination. The results were compared and discussed. Overall a good agreement was found between the data obtained by the different techniques. Furthermore, the true values of the damage parameters were confirmed by DT performed on the samples.

In this work, the application of Electronic Speckle Pattern Interferometry (ESPI) is employed for inspecting composite materials subject to thermal load. The composite samples are of interest in the aerospace industry. Through realtime surface illumination by visible laser (i.e. 532 nm), the ESPI technique allows the non-contact, non-destructive, full frame and real time detection of micro-deformations, micro-cracks, residual stress and delamination. The evaluation of the effective delaminated area of damaged polymer/Carbon Nanotubes fiber reinforced composites after flexural tests is presented.

We present a narrow-linewidth, singly-resonant cw optical parametric oscillator, emitting more than 1 W in the 2.7–4.2 µm range. The OPO is pumped by a narrow linewidth (40 kHz) fibre-laser system and the signal frequency is locked to a high-finesse Fabry–Pérot cavity in order to increase the spectral resolution, thus obtaining a residual linewidth of 70 kHz for the signal. We tested the spectral performance of our OPO on several transitions in the ν₁ rovibrational band of CH₃I, measuring line intensities and showing sub-Doppler dip detection.

We present a widely-tunable, singly-resonant optical parametric oscillator, emitting more than 1 W in the region between 2.7 and 4.2 μm. Two configurations have been studied in order to improve the frequency stability and the linewidth of the OPO emission. First, we stabilized the signal frequency to a high-finesse Fabry-Perot cavity. Then, we locked both pump and signal frequency to the frequency comb generated by a NIR fs mode-locked fibre laser, linked to the caesium primary standard. With this last configuration we carried out saturation spectroscopy of several transitions belonging to the ν₁ rovibrational band of CH₃I, resolving their electronic quadrupole hyperfine structure, and determining the absolute frequency of the hyperfine components with a 50-kHz-uncertainty. An upper limit for the idler linewidth has been estimated as 200 kHz FWHM.

We present a widely-tunable, singly-resonant optical parametric oscillator, emitting more than 1 W between 2.7 and 4.2 μm, which is phase locked to a self-referenced frequency comb. Both pump and signal frequencies are directly phase-locked to the frequency comb of a NIR-emitting fs mode-locked fibre laser, linked, in turn, to the caesium primary standard. We estimate for the idler frequency a fractional Allan deviation of ∼ 3 × 10⁻¹²τ^−1/2 between 1 and 200 s. To test the spectroscopic performance of the OPO, we carried out saturation spectroscopy of several transitions belonging to the ν₁ rovibrational band of CH₃I, resolving their electronic quadrupole hyperfine structure, estimating a linewidth better than 200 kHz FWHM for the idler, and determining the absolute frequency of the hyperfine components with a 50-kHz-uncertainty.

We report on efficient cw high-power second harmonic generation in a periodically poled LiTaO₃ crystal placed in a resonant enhancement cavity. We tested three configurations, differing in the coupling mirror reflectivity, and a maximum conversion efficiency of about 76%, corresponding to 6.1 W of green light with 8.0 W of fundamental power, was achieved. This is, to the best of our knowledge, the highest cw power ever reported using a periodically-poled crystal in an external cavity. We observed photo-thermal effect induced by photon absorption at the mirrors and in the crystal, which however does not affect stable operation of the cavity. A further effect arises for two out of the three configurations, at higher values of the input power, which degrades the performance of the locked cavity. We suggest this effect is due to the onset of competing nonlinearities in the same crystal.

This study compares the experimental results of absorption and refractive index of a probe laser measured in a strongly driven two-level atom with the results measured in a degenerate two-level system using pump-probe spectroscopy. This work demonstrates the possibility of realization an anomalous dispersive transparent medium using the strongly driven 4s^{2 1}S₀ - 4s4p ¹P₁ Ca transition. Absorption and phase shift profiles are measured as function of the driving field intensity using a Ca atomic beam. With increasing driving field intensities absorption and phase shift decrease, but the absorption decreases stronger than the dispersion. Results show that the resonant absorption and the anomalous dispersion are reduced with respect to the non-driving case by a factor 490 and 47, respectively. This means that a ~ 10-fold enhancement of the amount of dispersion provided per amount of absorption is attained.