No abstract

Ultrafast photonics has become an interdisciplinary topic of great consequence due to the spectacular progress of compact and efficient ultrafast pulse generation. Wide spectrum bandwidth is the key element for ultrafast pulse generation due to the Fourier transform limitation. Herein, monoclinic Nb 2 GeTe 4 , an emerging class of ternary narrow-gap semiconductors, was used as a real saturable absorber (SA), which manifests superior wide-range optical absorption. The crystallization form and growth mechanism of Nb 2 GeTe 4 were revealed by a thermodynamic phase diagram. Furthermore, the Nb 2 GeTe 4 −SA showed reliable saturation intensity and larger modulation depth, ascribed to a built-in electric field driven by the asymmetric crystal architecture confirmed via X-ray diffraction, polarized Raman spectra, and scanning transmission electron microscopy. Based on the Nb 2 GeTe 4 −SA, femtosecond mode-locked operation with good overall performance was achieved by a properly designed ring cavity. These results suggest that Nb 2 GeTe 4 shows great promise for ultrafast photonic applications and arouse interests in exploring the intriguing properties of the ternary van der Waals material family.

Tantalum disulfide (TaS2), an emerging group VB transition metal dichalcogenide, is emerging as a prototype for revealing basic physical phenomena and developing practical applications.

No abstract

By using the dispersive temporal holography technology, we observe the real-time dynamics of period-doubling bifurcation evolution in an ultrafast fiber laser. The pulse properties including the phase, polarization state, chirp, pulse width, and pulse energy are fully bifurcated, which embody the bifurcation induced “phase transition.” There are two types of bifurcation in the laser buildup: one to many bifurcation towards the chaos and the multiple bifurcated pulses back to the stationary state along the reversed trajectory. Both of them can be explained by the rule of the same phase transition. We conclude and illustrate the differences and connections to another common pulsation, the Hopf bifurcation. The findings can promote an understanding of the bifurcations in ultrafast lasers, and are beneficial for an improvement of laser stability.