In this paper, two-dimensional material Sb₂Te₃ nanosheets are fabricated and the optical nonlinear response is investigated. A laser diode (LD) end-pumped doubly Q-switched Tm:YAP laser with electro-optic modulator (EOM) and Sb₂Te₃ nanosheets based saturable absorber (SA) is presented. The shortest pulse duration of 38 ns is achieved at the pulse repetition frequency of 100 Hz, corresponding to the highest peak power of 111.8 kW. The double Q-switching technique shows the advantages of pulse duration compression and peak power improvement. The coupled rate equations for the doubly Q-switched laser are developed and the corresponding numerical simulation agrees with the experimental results. We believe that the Sb₂Te₃ is a potential nanomaterial for the application in optoelectronic field.

In the current study, layered metallic vanadium disulfide (VS₂) is fabricated by a liquid-phase exfoliation method, and its microstructures as well as optical characteristics are investigated. Based on first-principles calculations, the band structure and density of the states of both bulk T-VS₂ and monolayer H-VS₂ are illustrated, showing the metallic behavior with a zero band gap. By using VS₂ as the saturable absorber in a doubly Q-switched Tm:YAP laser with an EOM, the Q-switching laser pulses at 2 μm with 22 ns and 200 Hz are generated, corresponding to the single pulse energy of 755 μJ and the peak power of 34.3 kW. The coupled rate equations of the doubly Q-switched laser are given, and the numerical simulations agree with the experimental results. The results indicate that VS₂ is a promising nanomaterial due to its nonlinear optical property. The doubly Q-switched laser demonstrates a high level of performance in reducing pulse width and enhancing pulse peak power.

We propose a high-power, noise-like pulse (NLP), Tm-doped fiber oscillator applying the nonlinear polarization rotation method. The repetition rate is 12.94 MHz resulting in a pulse energy of 75.7 nJ. The emitted mode-locking spectrum can be tuned from 1885 nm to 1949 nm in a 64 nm spectral range. A theoretical model is built to illustrate the NLP dynamics and its boundary conditions with a soliton pulse inside the 2 μm fiber ring cavity. The corresponding simulation results match well with our experimental results.

A >600 MHz harmonic mode-locked femtosecond holmium-doped (Ho-doped) fiber laser is presented by using the nonlinear polarization rotation (NPR) method. When the fiber laser works in fundamental mode-locking (FML) regime at 2063.1 nm, a pulse repetition rate of 20.8 MHz is obtained with a corresponding pulse duration of 983 fs. By increasing the pump power, 29th-order harmonic mode-locking (HML) operation of the Ho-doped fiber laser is realized for the first time, to the best of our knowledge. The maximum pulse repetition rate of 603 MHz at 2063.7 nm is achieved with a harmonic pulse duration of 996 fs, corresponding to a super-mode suppression radio (SMSR) of as high as 33 dB.

Abstract We firstly propose a roadmap for the design of high repetition rate (~100 MHz) Tm-doped ultrafast fiber laser with an emission wavelength above 2000 nm. This roadmap is confirmed by both theoretical simulation and experimental verification. The designed Tm-doped fiber oscillator not only operates in continuous wave regime with a broad tunable wavelength range of ~ 100 nm, but also in mode-locking regime with an emission wavelength > 2000 nm (up to 2020 nm). A 470-fs laser pulse with a pulse repetition rate of ~96 MHz and the maximum average power of 50 mW are achieved at the output wavelength of 2007 nm, matching well with the theoretical prediction. In a further step, the seed laser pulse is amplified to 3.3 W, accompanied by a Raman frequency shift of the output wavelength to 2346 nm. The homogeneous intense broadband spectrum with a bandwidth of 240-nm centered at 2200 nm is also observed.

We report the surface morphology and the nonlinear absorption characteristics of MXene VCrC nanosheets prepared by the liquid-phase exfoliation method. The self-made MXene VCrC was applied as a saturable absorber in the Tm:YAP laser experiments, performing excellent Q-switching optical modulation characteristics in infrared range. With this absorber, a stable passively Q-switched 2 μm laser was achieved. Under an incident pump power of 3.52 W, a maximum output power of 280 mW was obtained with a T = 3% output coupler at a repetition frequency of 49 kHz. The corresponding pulse energy and peak power were 5.7 μJ and 6.6 W, respectively. The shortest pulse duration was 658 ns at the repetition rate of 63 kHz with a T = 1% output coupler.