We discover that the spatially coherent radiation within a certain frequency range can be obtained without a common nonlinear optical process. Conventionally, the emission spectra were obtained by de-exciting excited centers from real excited energy levels to the ground state. Our findings are achieved by deploying a high-entropy glass system (HEGS) doped with neodymium ions. The HEGS exhibits a much broader infrared absorption than common glass systems, which can be attributed to be high-frequency optical branch phonons or allowable multi-phonon processes caused by phonon broadening in the system. A broadened phonon-assisted wideband radiation (BPAWR) is induced if the pump laser is absorbed by the system. The subsequent low-threshold self-absorption coherence modulation (SACM) can be controlled by changing excitation wavelengths, sample size, and doping concentrations. The SACM can be red-shifted through the emission of phonons of the excited species and be blue-shifted by absorbing phonons before they are de-excited. There is a time delay up to 1.66 ns between the pump pulse and the BPAWR when measured after traveling through a 35 mm long sample, which is much longer than the Raman process. The BPAWR-SACM can amplify the centered non-absorption band with a gain up to 26.02 dB. These results reveal that the shift of the novel radiation is determined by the frequency of the non-absorption band near the absorption region, and therefore the emission shifts can be modulated by changing the absorption spectrum. When used in fiber lasers, the BPAWR-SACM process may help to achieve tunability.

Multi-pulse oscillations are prevalent phenomena observed in mode-locked lasers and nonlinear microresonators, where the short- and long-range interactions between nonlinear wavepackets give rise to diverse pulse patterns such as soliton molecules, soliton crystals, and soliton bursts. However, these intricate nonlinear interactions are highly sensitive to the parameters of dissipative systems, leaving the properties of multiple pulses far from being controlled, which hampers their applications such as high-speed optical communication and material processing. In this study, we propose a universal approach for quantitatively tailoring multiple solitons in mode-locked fibre lasers through spectral phase programming, enabling the on-demand generation of soliton patterns with separations that follow from constant, geometric, or arithmetic sequences. By combining with spectral filtering, we demonstrate dual-colour soliton patterns in the same cavity, further highlighting the adaptability of soliton structures. Numerical simulations validate the experimental observations, demonstrating that the spectral phase modulates solitons to emit sub-pulses, which interact with other solitons to generate trapping potentials, thereby giving rise to diverse soliton patterns.

This article presents a high-precision obstacle detection algorithm using 3D mechanical LiDAR to meet railway safety requirements. To address the potential errors in the point cloud, we propose a calibration method based on projection and a novel rail extraction algorithm that effectively handles terrain variations and preserves the point cloud characteristics of the track area. We address the limitations of the traditional process involving fixed Euclidean thresholds by proposing a modulation function based on directional density variations to adjust the threshold dynamically. Finally, using PCA and local-ICP, we conduct feature analysis and classification of the clustered data to obtain the obstacle clusters. We conducted continuous experiments on the testing site, and the results showed that our system and algorithm achieved an STDR (stable detection rate) of over 95% for obstacles with a size of 15 cm × 15 cm × 15 cm in the range of ±25 m; at the same time, for obstacles of 10 cm × 10 cm × 10 cm, an STDR of over 80% was achieved within a range of ±20 m. This research provides a possible solution and approach for railway security via obstacle detection.

Monolayer MoS ₂ film on quartz was fabricated by a home-made three-temperature zone chemical vapor deposition method. The photo, AFM image, Raman spectroscopy and HRTEM image showed that high quality as-grown MoS ₂ film completely covered the whole quartz substrate of a few cm ² . A Nd:YVO ₄ laser with mode-locking operation was obtained by using the monolayer MoS ₂ on quartz as the saturable absorber (SA). To the best of our knowledge, this is the first report on large-area growth of high quality monolayer MoS ₂ film on transparent quartz substrate, and the first time that the CVD MoS ₂ SA was used in mode-locked solid state lasers. Because of the large area, high transmission, low non-saturable loss and high optical damage threshold of this material, it is very suitable for application in mode-locked solid state lasers.