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.
Supercontinuum generation is a key process for nonlinear tailored light generation and strongly depends on the dispersion of the underlying waveguide. Here we reveal the nonlinear dynamics of soliton-based supercontinuum generation in case the waveguide includes a strongly dispersive resonance. Assuming a gas-filled hollow core fiber that includes a Lorentzian-type dispersion term, effects such as multi-color dispersive wave emission and cascaded four-wave mixing have been identified to be the origin of the observed spectral broadening, greatly exceeding the bandwidths of corresponding non-resonant fibers. Moreover, we obtain large spectral bandwidth at low soliton numbers, yielding broadband spectra within the coherence limit. Due to the mentioned advantages, we believe the concept of resonance-enhanced supercontinuum generation to be highly relevant for future nonlinear light sources.
Supercontinuum generation enabled a series of key technologies such as frequency comb sources, ultrashort pulse sources in the ultraviolet or the mid-infrared, as well as broadband light sources for spectroscopic methods in biophotonics. Recent advances utilizing higher-order modes have shown the potential to boost both bandwidth and modal output distribution of supercontinuum sources. However, the strive towards a breakthrough technology is hampered by the limited control over the intra- and intermodal nonlinear processes in the highly multi-modal silica fibers commonly used. Here, we investigate the ultrafast nonlinear dynamics of soliton-based supercontinuum generation and the associated mode coupling within the first three lowest-order modes of accurately dispersion-engineered liquid-core fibers. By measuring the energy-spectral evolutions and the spatial distributions of the various generated spectral features polarization-resolved, soliton fission and dispersive wave formation are identified as the origins of the nonlinear broadening. Measured results are confirmed by nonlinear simulations taking advantage of the accurate modeling capabilities of the ideal step-index geometry of our liquid-core platform. While operating in the telecommunications domain, our study allows further advances in nonlinear switching in emerging higher-order mode fiber networks as well as novel insights into the sophisticated nonlinear dynamics and broadband light generation in pre-selected polarization states.
Due to their unique properties such as transparency, tunability, nonlinearity and dispersion flexibility, liquidcore fibers represent an important approach for future coherent mid-infrared light sources. However, the damage thresholds of those fibers are largely unexplored. Here, we report on the generation of solitonbased supercontinuum in carbon disulfide (CS2) liquidcore fibers at average power levels as high as 0.5 W operating stable for a long term (>70 hours) without any kind of degradation or damage. Additionally, we also show stable high power pulse transmission through liquid-core fibers exceeding 1 W of output average power for both CS2 and tetrachloroethylene (C2Cl4) as core materials.
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