A saturable absorber (SA) based on niobium diselenide (NbSe₂), which is a layered transition metal dichalcogenide (TMD) in the VB group, is fabricated by the optically driven deposition method, and the related nonlinear optical properties are characterized. The modulation depth, saturable intensity, and nonsaturable loss of the as-prepared NbSe₂ nanosheet-based SA are measured to be 16.2%, 0.76 MW/cm², and 14%, respectively. By using the as-fabricated NbSe₂ SA, a highly stable, passively Q-switched, erbium-doped, all-fiber laser is realized. The obtained shortest pulse width is 1.49 μs, with a pulse energy of 48.33 nJ at a center wavelength of 1560.38 nm. As far as we know, this is the shortest pulse duration ever obtained by an NbSe₂ SA in a Q-switched fiber laser.

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.

In this letter, indium phosphide (InP) nanowires (NWs) are fabricated by Au-nanoparticle assisted vapor-liquid-solid method and applied as a saturable absorber (SA) for continuous-wave (CW) mode-locked femtosecond Yb:KYW bulk laser. I-scan method was used to characterize the saturable absorption properties of the prepared InP NWs SA. Pulses as short as 394 fs with the repetition rate of 41.5 MHz and maximum average output power of 315 mW are achieved. To the best of our knowledge, this is the first demonstration of InP NWs working as SA for the fs-pulse generation in the solid-state bulk laser. The results indicate that InP NWs are a promising SA candidate for applications in ultrafast photonic devices.

In this paper, a high-power and high-efficiency 4.3µm mid-infrared (MIR) optical parametric oscillator (OPO) based on ZnGeP2 (ZGP) crystal is demonstrated. An acousto-optically Q-switched Ho:Y3Al5O12 laser operating at 2.1µm with a maximum average output power of 35 W and pulse width of 38 ns at a repetition rate of 15 kHz is established and employed as the pump source. A doubly resonant OPO is designed and realized with the total MIR output power of 13.27 W, including the signal and idler output power of 2.65 W at 4.07µm and 10.62 W at 4.3µm. The corresponding total optical-to-optical and slope efficiencies are 37.9% and 67.1%, respectively. The shortest pulse width, beam quality factor, and output power instability are measured to be 36 ns, Mx2=1.8, My2=2.0, and RMS<1.9% at 8 h, respectively. Our results pave a way for designing high-power and high-efficiency 4–5µm MIR laser sources.

A high-energy picosecond 355 nm ultraviolet (UV) laser operating at 100 Hz was demonstrated. A 352 mJ, 69 ps, 1064 nm laser at 100 Hz was realized firstly by cascaded regenerative, laser diode end-pumped single-pass and side-pumped main amplifiers. The stimulated Raman scattering-based beam shaping technique, thermally induced birefringence compensation and 4f spatial filter-image relaying systems were used to maintain a relatively homogeneous beam intensity distribution during the amplification process. By using lithium triborate crystals for second- and third-harmonic generation (THG), a 172 mJ, approximately 56 ps, 355 nm UV laser was achieved with a THG conversion efficiency of 49%. To the best of our knowledge, it is the highest pulse energy of a picosecond 355 nm UV laser so far. The beam quality factor ${M}^2$ and pulse energy stability were ${M}_x^2$ =3.92, ${M}_y^2$ =3.71 and root mean square of 1.48%@3 hours. This laser system could play significant roles in applications including photoconductive switch excitation, laser drilling and laser micro-fabrication.

In this paper, two-dimensional (2D) few-layer Ta₂CT_x nanosheets are fabricated by liquid phase exfoliation (LPE) method. The nonlinear optical absorption properties are studied by Z-scan and I-scan techniques, revealing excellent saturable absorption response with an effective nonlinear absorption coefficient of -92.2 cm/MW@1064 nm. The saturation intensity and modulation depth for 1064 nm and 1550 nm are determined to be 79 and 51 MW/cm², 9.9% and 4.5%, respectively. Furthermore, by decorating few-layer Ta₂CT_x nanosheets onto microfiber, few-layer Ta₂CT_x saturable absorber (SA) is fabricated and applied in Yb-doped and Er-doped fiber lasers (YDFLs and EDFLs). Not only a normal mode-locked operation but also square-wave pulse (SWP) are realized by increasing the length of the laser cavity at 1.5 µm, highlighting the great potential of few-layer Ta₂CT_x nanosheets as an optical modulator. The maximum pulse duration of 5.56 ns is also the widest SWP width that can be realized with 2D materials without filtering device in the cavity. Our work provides a platform for exploring novel SAs materials and nonlinear phenomena in mode-locked fiber lasers.