Passive harmonic mode locked all-normal-dispersion Yb-doped fibre lasers

Passive harmonic mode-locking of dissipative solitons is demonstrated in all-normal dispersion Yb-doped fibre lasers.A difference equation model of the mode-locked fibre lasers is adopted to simulate the intra-cavity nonlinear dynamics.Hysteresis phenomena around the mode-locking threshold,and the effect of introducing linear phase bias are discussed.The passive harmonic mode-locking as one kind of multipulsing operations is revealed.Moreover,the simulation shows the bistability between multipulsing and single-pulse or period multiplication.     

爆轰合成氧化亚铁掺杂的二氧化硅包覆铁纳米颗粒

用一定比例的硝酸铁盐、硅酸钠盐、无水乙醇与黑索金混合制成塑性炸药。在密闭容器中以氩气为保护气,通过爆轰合成氧化亚铁掺杂的二氧化硅包覆铁纳米颗粒。采用X射线衍射(XRD)、透射电镜(TEM)及振动样品磁强计(VSM)对爆轰产物的组成成分、形态结构以及磁性进行测试。实验结果表明,爆轰产物以金属颗粒为核、二氧化硅为包覆层的壳/核结构形式出现,颗粒尺寸在60nm左右。通过分析爆轰产物的磁性曲线可知,在室温下爆轰产物具有较高的剩磁比和矫顽力,表现出弱的铁磁性,是优良的储磁材料。     

重金属Zn、Pb在铜锈环棱螺体内的积累

研究了环境中常见的两种重金属污染物锌(Zn)、铅(Pb)在铜锈环棱螺体内的积累。结果表明:铜锈环棱螺的腹足和内脏团是Pb的主要积累部位,肝脏为Zn的主要积累部位。随着时间变化,进入铜锈环棱螺体内的Pb和Zn可在组织间转移和重新分布。铜锈环棱螺对Zn的富集能力强,实验条件下,肝脏中Zn的含量能随暴露液中Zn浓度、时间等外界条件的变化而变化;在0～10.0mL.L-1的浓度范围,肝脏中Zn浓度与暴露液中Zn浓度呈线形关系。     

Artificial spectral filtering in dissipative soliton fiber lasers with invisible bandpass filters

We numerically study the artificial spectral-filtering effect in dissipative soliton fiber lasers without intracavity spectral filters. It is found that in dissipative soliton lasers with real saturable absorbers (SAs), the dynamic spectral filtering of the real SAs serves as an artificial spectral filter and contributes to the pulse shaping. While in the dissi- pative soliton lasers with artificial SAs, such as nonlinear polarization rotation, the spectral filtering introduced by the intracavity polarization-dependent components acts as an artificial spectral filter and shapes the pulses to obtain mode-locking. An investigation of the artificial spectral-filtering effect reveals the operating mechanisms of the dissipative soliton fiber lasers without visible bandpass filters.     

始兴石斛的无菌播种及快速繁殖

以始兴石斛种子为外植体,研究了NAA、6-BA、IBA、蔗糖以及活性炭(AC)等对种子无菌萌发及快速繁殖的影响。结果表明:适合种子萌发的培养基是MS+6-BA1.5mg.L-1+NAA 0.6mg.L-1+AC0.1%,萌发率可达100%;适合原球茎增殖的培养基是MS+6-BA0.8mg.L-1+NAA0.3mg.L-1+蔗糖4.5%,增殖系数为7.75倍;适合分化的培养基是MS+6-BA2.5mg.L-1+NAA0.5mg.L-1+AC0.03%,分化率为92%;适合生根的培养基是1/2MS+IBA0.5mg.L-1+AC0.05%,生根率为95.3%;以苔藓和树皮作为基质,试管苗移栽成活率可达93%以上。     

Enhancement of multiple four-wave mixing via cascaded fibers with discrete dispersion decreasing

Cascaded fiber geometry with the dispersion of each fiber decreasing is proposed to enhance the multiple four-wave mixing(FWM) generation. The first fiber with relatively large dispersion initiates and accelerates the expansion of multiple FWM, and the second fiber with small dispersion would allow the phase-matching process(thus the spectrum broadening)to keep going. Numerical and experimental results show that with this geometry not only multiple FWM expansion can be accelerated, but also the efficiency of multiple FWM products can be effectively improved with shorter fibers.     

All-normal-dispersion Yb-doped mode-locked fibre laser and its stability analysis

We experimentally demonstrate an all-normal-dispersion Yb-doped mode-locked fibre laser with no intentional spectral filter inserted.Pulses with 1.1 nJ pulse energy at a repetition rate of 20.4 MHz are achieved.A theoretical model of the fibre laser is derived,whose coefficients are explicitly dependent on the orientations of the wave plates and the polarizer.Based on the model,stability diagrams of both the mode-locking and the continuous wave regimes of the laser are presented.The influence of group-velocity dispersion (GVD) and cavity length on the stability of mode-locking is also discussed.