Taming ultrafast laser filaments for optimized semiconductor–metal welding

Ultrafast laser welding is a fast, clean, and contactless technique for joining a broad range of materials. Nevertheless, this technique cannot be applied for bonding semiconductors and metals. By investigating the nonlinear propagation of picosecond laser pulses in silicon, it is elucidated how the evolution of filaments during propagation prevents the energy deposition at the semiconductor–metal interface. While the restrictions imposed by nonlinear propagation effects in semiconductors usually inhibit countless applications, the possibility to perform semiconductor–metal ultrafast laser welding is demonstrated. This technique relies on the determination and the precompensation of the nonlinear focal shift for relocating filaments and thus optimizing the energy deposition at the interface between the materials. The resulting welds show remarkable shear joining strengths (up to 2.2 MPa) compatible with applications in microelectronics. Material analyses shed light on the physical mechanisms involved during the interaction

Cascaded four-wave mixing in liquid-core optical fibers

Ultrafast nonlinear interactions in optical fibers are commonly employed for generating light with tailored properties, with four-wave mixing (FWM) being a widely used mechanism. Existing systems mainly rely on fibers with solid glass cores, facing limitations due to a lack of tunability and susceptibility to noise. Here, fibers with fluidic cores emerge as a promising alternative for efficient FWM, offering novel functionalities and expanded parameter ranges. In this study, we investigate single and cascaded FWM in liquid-core fibers regarding spectral tunability and interplay with the Raman effect. The study relies on binary liquids used as core materials in combination with ultrashort ps-pulses and seeding. Strong side bands were observed whose spectral position could be adjusted by the liquid composition and the seed wavelength. Seeding additionally leads to higher-order side bands, which we assign to cascaded FWM. Furthermore, we explore the interaction between FWM and stimulated Raman scattering by adjusting the FWM peaks to overlap or deviate from the Raman bands through variations of the core liquid and the seed wavelength. The presented results shed light on the unique characteristics of the liquid-core fiber platform in the context of parametric nonlinear interactions, particularly regarding tunability and interaction with Raman scattering. These findings offer new possibilities for the development of light sources capable of Raman-free photon pair generation for quantum technology or for creating tunable narrowband spectra for imaging applications in life sciences

Taming Ultrafast Laser Filaments for Optimized Semiconductor–Metal Welding

Ultrafast laser welding is a fast, clean, and contactless technique for joining a broad range of materials. Nevertheless, this technique cannot be applied for bonding semiconductors and metals. By investigating the nonlinear propagation of picosecond laser pulses in silicon, it is elucidated how the evolution of filaments during propagation prevents the energy deposition at the semiconductor–metal interface. While the restrictions imposed by nonlinear propagation effects in semiconductors usually inhibit countless applications, the possibility to perform semiconductor–metal ultrafast laser welding is demonstrated. This technique relies on the determination and the precompensation of the nonlinear focal shift for relocating filaments and thus optimizing the energy deposition at the interface between the materials. The resulting welds show remarkable shear joining strengths (up to 2.2 MPa) compatible with applications in microelectronics. Material analyses shed light on the physical mechanisms involved during the interaction. © 2020 The Authors. Laser & Photonics Reviews published by Wiley-VCH Gmb