The shape of the capillary produced during the welding of 1.4301 (X5CrNi18-10, AISI 304) stainless steel at a welding speed of 12 m/min using core-ring-shaped beams delivered through a multi-waveguide fiber was examined by means of synchrotron X-ray imaging. The results show that, under the range of process parameters covered here, ring beams create a temperature field which includes two hot spots which lag behind the center of the beam and are equidistant from the center line of the weld. In the case of small ring diameters these two hot spots can be close enough to the core beam that they can combine with it to create a wide capillary, the shape of which inhibits the formation of pores. When larger diameters are employed, the ring beam hot spots create a separate, secondary capillary (or capillaries) which may sporadically coalesce with the core beam capillary due to surface tension effects. When the capillaries merge, the depth of penetration of the combined capillary is reduced compared with the one created by the core alone. If the coalescence of the capillaries is sporadic then the weld stability is poor from both a porosity and a depth of penetration point of view.
Pt thin films with thicknesses of 5, 10, 20, and 50 nm on fused silica substrates, and 50 nm films on sapphire substrates, were processed by a single shot of a four-beam femtosecond laser interference pattern with a squarelattice period of 2.25 & micro;m. The formation route branched drastically with the film thickness under the same interference pattern: nanobumps in the 50 nm films, openings with lifted edges in the 20 nm films, closed annular walls - wall-like rims - in the 10 nm films, and film removal with central substrate holes in the 5 nm films. The wall-like rim, approximately 80 nm high and much taller than the 10 nm film thickness, is the delaminated film itself standing on the substrate. Nanowhiskers with tip radii of approximately 10 nm or less were formed on the delaminated film edges. The structure diameters increased with fluence following a threshold-type behavior, and forming a nanobump of the same size on sapphire required an approximately 1.6 times higher fluence than on fused silica, consistent with the substrate thermal transport properties. The thickness dependence is explained by the absorptance-to-thickness ratio calculated by the transfer-matrix method.
We developed an NH3 gas visualization system using a DFB laser and an NIR camera. The DFB laser was modulated between wavelengths within and outside of the NH3 gas absorption spectrum. The NH3 gas region appeared as a blinking region in NIR camera images, enabling the visualization of the spatial extent of the NH3 gas. Additionally, by evaluating the absorption On/Off ratio, it was possible to determine the NH3 concentration and the detection limit of the NH3 gas visualization system.
Optical vortex arrays (OVAs) are a promising platform for massively parallel photonics, but existing generation methods are limited by low power capacity, restricted scalability, or high complexity. We demonstrate a simple and robust method that overcomes these limitations by combining a reformulation of Hermite-Gaussian to Laguerre-Gaussian mode conversion representation with multibeam interference. Using a compact diffractive optical element (DOE)-spiral phase plate (SPP)- 4 f Fourier optical system, we experimentally generated a triangular lattice of 3070 coherent vortices with a peak power of 58 megawatts (MW). This result demonstrates more than three orders of magnitude improvement in both the vortex number and peak power compared with those of spatial light modulator (SLM)-, metasurface-, and conventional DOE-based OVA systems, establishing a new benchmark for large-scale, high-power vortex array generation. Moreover, our method provides OVA generation with high peak and average power while remaining inherently scalable in the vortex number, wavelength, and input laser power owing to the interference-based DOE-SPP design. This capability not only advances fundamental optical vortex science but also provides a powerful route for applications in parallel laser processing, broadband chiral photonics, massively parallel biophotonics, and future explorations in quantum and nonlinear photonics.
