Search Results (3)

Aside from the industry-standard Gaussian intensity profile, top hat and non-conventional laser beam shapes, such as doughnut-shaped profile, are ever more required. The top hat laser beam profile is well-known for uniformly irradiating the target material, significantly reducing the heat-affected zones, typical of Gaussian laser irradiation, whereas the doughnut-shaped laser beam has attracted much interest for its use in trapping particles at the nanoscale and improving mechanical performance during laser-based 3D metal printing. Solar-pumped lasers can be a cost-effective and more sustainable alternative to accomplish these useful laser beam distributions. The sunlight was collected and concentrated by six primary Fresnel lenses, six folding mirror collectors, further compressed with six secondary fused silica concentrators, and symmetrically distributed by six twisted light guides around a 5.5 mm diameter, 35 mm length Nd:YAG rod inside a cylindrical cavity. A top hat laser beam profile (M_x² = 1.25, M_y² = 1.00) was computed through both ZEMAX^® and LASCAD^® analysis, with 9.4 W/m² TEM₀₀ mode laser power collection and 0.99% solar-to-TEM₀₀ mode power conversion efficiencies. By using a 5.8 mm laser rod diameter, a doughnut-shaped solar laser beam profile (M_x² = 1.90, M_y² = 1.00) was observed. The 9.8 W/m² TEM₀₀ mode laser power collection and 1.03% solar-to-TEM₀₀ mode power conversion efficiencies were also attained, corresponding to an increase of 2.2 and 1.9 times, respectively, compared to the state-of-the-art experimental records. As far as we know, the first numerical simulation of doughnut-shaped and top hat solar laser beam profiles is reported here, significantly contributing to the understanding of the formation of such beam profiles. Full article

A single-longitudinal-mode (SLM) Neodymiun-doped Yttrium Aluminium Garnet (Nd:YAG) laser at 1123 nm was first demonstrated with a twisted-mode (TM) cavity. By eliminating the spatial hole burning phenomenon, a stable SLM 1123 nm laser output was obtained. An efficient TM cavity was designed based on the Brewster plate with high reflection under s-polarization radiation. At an incident pump power of 7.65 W, the maximum output power of 689 mW was obtained. The corresponding optical conversion efficiency was about 9%. The center wavelength was 1122.58 nm and the line-width was <140 MHz. Full article

A well-defined condition-monitoring for power transformers is key to implementing a correct condition-based maintenance (CBM). In this regard, partial discharges (PD) measurement and its analysis allows to carry out on-line maintenance following the standards IEC-60270 and IEC-60076. However, new PD measurements techniques, such as acoustics or electromagnetic (EM) acquisitions using ultra-high-frequency (UHF) sensors are being taken into account, IEC-62478. PD measurements with antennas and the effect of their EM propagation in power transformer tanks is an open research topic that is considered in this paper. In this sense, an empty tank model is studied as a rectangular cavity and their resonances are calculated and compared with their measurement with a network analyser. Besides, two low cost improved monopole antennas deployed inside and outside of the tank model capture background noise and PD pulses in three different test objects (Nomex, twisted pair and insulator). The average spectrum of them are compared and can be found that mainly, the antenna frequency response, the frequency content distribution depending on the PD source and the enclosure resonances modes are the main factors to be considered in PD acquisitions with these sensors. Finally, with this set-up, it is possible to measure PD activity inside the tank from outside. Full article