Open Access

Spectrally broad laser radiation from continuous wave (cw) lasers can exhibit second-order autocorrelation traces virtually indistinguishable from those of mode-locked lasers. Consequently, based only on autocorrelations, one might erroneously conclude that a cw laser is mode-locked. This pitfall in interpretation can be avoided by carefully characterizing radio frequency transients and spectra. However, optoelectronics are often too slow for lasers with an axial mode spacing in the multi-GHz range. Carefully evaluated autocorrelations then remain the last resort for validating mode locking. We demonstrate in detail what needs to be observed. We compare autocorrelation measurements and calculations of a mode-locked titanium-sapphire (Ti:Sa) laser with 76 MHz repetition rate and a spectrally broad monolithic cw Ti:Sa laser and devise a new, additional measurement to safeguard against misinterpretation of their autocorrelations.

In this paper, the formation of laser-induced periodic surface structures (LIPSS) on atomic-layer deposited MoS 2 layers are studied experimentally. The process parameters (laser fluence and the pulse overlap) corresponding to formation of low- and high-spatial frequency LIPSS as well as ablation and modification of the layers are identified for different pulse durations in the range from 0.2 to 10 ps. The role of the temperature accumulation is evaluated by changing the repetition rate from 0.2 to 2 MHz. The negative accumulation effect, i.e., the ablation of the layers becomes more difficult at higher laser pulse overlaps, is also observed. A simple model explaining the transition between different types of the LIPSS and the decrease of the ablation efficiency with the pulse overlap is suggested.

This study presents a comprehensive evaluation of force sensors manufactured through conventional CNC machining, laser powder bed fusion (LPBF), and material extrusion (MEX) 3D printing methods. The study utilized a combination of finite element method (FEM) simulations, functional testing, durability assessments, and ultimate strength testing in order to assess the viability of additive manufacturing for sensing technology applications. The FEM simulations provided a preliminary framework for predictive analysis, closely aligning with experimental outcomes for LPBF and conventionally manufactured sensors. Nevertheless, discrepancies were observed in the performance of MEX-printed sensors during ultimate strength testing, necessitating the implementation of more comprehensive modeling approaches that take into account the distinctive material characteristics and failure mechanisms. Functional testing confirmed the operational capability of all sensors, thereby demonstrating their suitability for the intended application. Moreover, all sensors exhibited resilience during 50,000 cycles of cyclic testing, indicating reliability, durability, and satisfactory fatigue life performance. Notably, sensors produced via LPBF exhibited a significant increase in strength, nearly three times that of conventionally manufactured sensors. These findings suggest the potential for innovative sensor design and the expansion of their use into higher-loaded applications. Overall, while both LPBF and conventional methods demonstrated reliability and closely matched simulation predictions, further research is necessary to refine modeling approaches for MEX-printed sensors and fully unlock their potential in sensing technology applications. These findings indicate that additive manufacturing of metals may be a viable alternative for the fabrication of biomedical sensors.

The extended quasiparticle picture is adapted to non-Fermi systems by suggesting a Pad´e approximation which interpolates between the known small scattering-rate expansion and the deviation from the Fermi energy. The first two energy-weighted sum rules are shown to be fulfilled independent of the interpolating function for any selfenergy. For various models of one-dimensional Fermions scattering with impurities the quality of the Pad´e approximation for the spectral function is demonstrated and the reduced density matrix or momentum distribution is reproduced not possessing a jump at the Fermi energy. Though the two-fold expansion is necessary to realize the spectral function and reduced density, the extended quasiparticle approximation itself is sufficient for the description of transport properties due to cancellation of divergent terms under integration. The T-matrix approximation leads to the delay time as the time two particles spend in a correlated state. This contributes to the reduced density matrix and to an additional part in the conductivity which is presented at zero and finite temperatures. Besides a localization at certain impurity concentrations, the conductivity shows a maximum at small temperatures interpreted as onset of superconducting behaviour triggered by impurities. The Tan contact reveals the same universal behaviour as known from electron-electron scattering.