Cnoidal waves are a type of nonlinear periodic wave solutions of the nonlinear dynamic equations. They are well known in fluid dynamics, but it is not the case in optics. In this paper we show both experimentally and numerically that cnoidal waves could be formed in a fiber laser either in the net normal or net anomalous cavity dispersion regime, especially because, as the pump power is increased, the formed cnoidal waves could eventually evolve into a train of bright (in the net anomalous cavity dispersion regime) or dark (in the net normal cavity dispersion regime) solitons. Numerical simulations of the laser operation based on the extended nonlinear Schrödinger equation (NLSE) have well reproduced the experimental observations. The result not only explains why solitons can still be formed in a fiber laser even without mode locking but also suggests a new effective way of automatic stable periodic pulse train generation in lasers with a nonlinear cavity.

报道了采用真空烧结法结合热等静压技术制备的Nd:Y₂O₃透明陶瓷的荧光光谱特性及相关激光输出。通过与Nd:YAG透明陶瓷的荧光光谱对比，表明Nd:Y₂O₃透明陶瓷的⁴F_3/2-⁴I_11/2跃迁光谱存在着多个增益相当的谱线，这更有利于实现同时双波长段激光振荡；不同斯塔克子跃迁光谱的离散特性有利于通过腔镜镀膜控制不同波长损耗，获得丰富的1.0~1.1 μm波段激光。利用简单的平平两镜腔结构完成进一步的实验，通过选择的输出镜片镀膜获得了输出功率3.62 W、转换效率40.4%的1074.6 nm和1078.8 nm的双波长输出和输出功率1.7 W、转换效率19.4%的1130.3 nm波长输出。

We experimentally demonstrated a type of tunable and switchable harmonic h-shaped pulse generation in a thulium-doped fiber (TDF) laser passively mode locked by using an ultralong nonlinear optical loop mirror. The total cavity length was ～3.03 km, the longest ever built for a TDF laser to our best knowledge, which resulted in an ultralarge anomalous dispersion over 200 ps2 around the emission wavelength. The produced h-shaped pulse can operate either in a fundamental or in a high-order harmonic mode-locking (HML) state depending on pump power and intra-cavity polarization state (PS). The pulse duration, no matter of the operation state, was tunable with pump power. However, pulse breaking and self-organizing occurred, resulting in high-order HML, when the pump power increased above a threshold. At a fixed pump power, the order of HML was switchable from one to another by manipulating the PS. Switching from the 8th up to the 48th order of HML was achieved with a fixed pump power of ～4.15 W. Our results revealed the detailed evolution and switching characteristics of the HML and individual pulse envelope with respect to both the pump power and PS. We have also discussed in detail the mechanisms of both the h-shaped pulse generation and the switching of its HML. This contribution would be helpful for further in-depth study on the underlying dynamics of long-duration particular-envelope pulses with ultralarge anomalous dispersion and ultralong roundtrip time.

We experimentally demonstrate the generation of sub-100-fs pulses from a diode-pumped passively mode-locked Yb:Y3ScAl4O12 (Yb:YSAG) ceramic laser. Stable mode-locked pulses as short as 96 fs at the central wavelength of 1052 nm with a repetition rate of ～102 MHz are obtained. The laser has a maximum average output power of 51 mW. To the best of our knowledge, these are so far the shortest pulses and the first demonstration of sub-100-fs pulses obtained from the mode-locked Yb:YSAG ceramic lasers.

We report on broadly wavelength-tunable passive mode-locking with high power operating at the 2 μm water absorption band in a Tm:CYA crystal laser. With a simple quartz plate, stable mode-locking wavelengths can be tuned from 1874 to 1973 nm, with a tunable wavelength range up to ～100 nm and maximum output power up to 1.35 W. The bandwidth is narrow as ～6 GHz, corresponding to a high coherence. To our knowledge, this is the first demonstration of wavelength-tunable mode-locking with watt-level in the 2 μm water absorption band. The high temporal coherent laser can be further applied in spectroscopy, the efficient excitation of molecules, sensing, and quantum optics.

We report on a widely tunable, narrow linewidth operation of a Tm:YAG ceramic laser. A volume Bragg grating is used in the cavity as a folding mirror for wavelength selection. The wavelength is tuned from 1956.2 to 1995 nm, leading to a total tuning range of 38.7 nm. The linewidth is around 0.1 nm over the whole tuning range. A maximum output power of 1.51 W at 1990.5 nm is achieved at 37.8 W absorbed pump power. Different saturation behaviors are observed in the laser performances at different wavelengths.