Optimum peak pulse investigation for OTDR instrumentation

This work presents an experimental study of the optimal peak-power pulse for testing telecommunications fibers. Using a Q-switched fiber laser at 1060 nm, we obtained 100-ns pulses at a 10-kHz repetition rate with an average power of 60 mW corresponding to a 60-W peak power. With these pulses, we generated up to fifth-order Stokes within the fiber, with wavelengths on the third window of telecommunications. We demonstrate that the power exceeding the optimum peak power does not increase the penetration length of OTDR systems because of the pump depletion. The shape of the Stokes-shifted pulses attained at the end of the test fiber is similar to the pulse shape from a Q-switched fiber laser, also showing the possibility to produce suitable peak powers and pulse shapes for OTDR applications at different wavelengths.     

全光纤高功率被动锁模掺铥光纤激光器

利用非线性光环形镜(NOLM)的可饱和吸收特性实现了可自启动的2μm全光纤高能量被动锁模掺铥光纤激光器。当泵浦功率大于3W时,激光器工作在连续或不稳定脉冲运转状态;泵浦功率达到4.69W后,输出为自启动锁模脉冲,重复频率4.26MHz,中心波长2 061.5nm,光谱半极大宽度18.1nm,平均输出功率8.8mW;继续增加泵浦功率到最大值7.56W,可以得到中心波长2 062.2nm、光谱半极大宽度17.1nm、斜率效率为6.2%、脉冲宽度和能量分别为424fs和65.6nJ的稳定锁模脉冲。这是目前已报道的在未经放大情况下脉冲能量最高的2μm锁模脉冲光纤激光器。     

超宽带近红外和蓝光飞秒激光脉冲产生的实验研究

增益介质中泵浦光束提供的软光阑效应对于实现克尔透镜稳定锁模及其超宽带光谱脉冲的产生具有非常重要的作用.实验上首先对半导体泵浦全固化钛宝石飞秒激光器的锁模动态特性进行了研究,在4 W绿光泵浦状态下获得了平均输出功率为570 mW、中心波长在794 nm～835 nm范围内调谐、光谱带宽最大可达135 nm的近红外光脉冲输出,其相应的时域变换极限脉冲宽度均小于10 fs.另外,将光束聚焦在超薄BBO晶体上,获得了中心波长在418 nm～429 nm之间调谐、光谱宽带时域变换极限小于15 fs的蓝光飞秒脉冲.     

Optimization of laser propagation in optical-field-ionization plasmas for X-ray laser generation

Optical-field-ionization X-ray lasers are investigated numerically with a three-dimensional wave propagation code considering the effects of photoionization, energy depletion due to ionization, and refraction on pump laser pulses in spatially and temporally varied plasmas. By focusing the pump laser with small f-number optics at the optimal position, simulations show that diffraction and ionization-induced refraction in plasmas are compensated to keep the pump beam propagating at the optimal size for a longer distance. An amplification length as long as 5 mm can be achieved in Pd-like xenon and Ni-like krypton X-ray lasers at a pump energy of 160 mJ in 50-fs and 30-fs pulses, respectively. The significant reduction of the pump energy is a desirable step toward low-threshold and practical high-repetition-rate operations. PACS 42.55.Vc; 52.50.Jm     

Compact laser source for high-power white-light and widely tunable sub 65 fs laser pulses

We demonstrate an Yb:KGW femtosecond solitary mode-locked laser oscillator, which is used as a pump source for tapered fibers to generate white-light laser pulses with an average output power of up to 2.5 W and a spectral bandwidth of over 1000 nm. By spectrally filtering these pulses and subsequent compression of the filtered pulses with a prism sequence, we are able to generate ultrashort laser pulses with durations between 26 and 65 fs that are tunable from 600 to 1450 nm and with tens to several hundreds of milliwatts of average power.     

低阈值锁模状态可转换的全保偏光纤激光器

报道了一种可实现低阈值自启动的全保偏九字腔光纤激光器。谐振腔结构中使用相移器降低锁模阈值,当泵浦功率达到120 mW时,便可实现自启动的传统孤子锁模,中心波长为1530 nm,脉冲宽度为614.6 fs。随后泵浦功率逐渐增大到470 mW,实现了从孤子脉冲到类噪声脉冲的转换,在该锁模状态下的激光器输出功率为63.2 mW,对应的类噪声脉冲能量为5.69 nJ。所搭建的激光器具有低锁模阈值、自启动的优势,并且仅通过调节泵浦功率就能够实现超快脉冲和高能量脉冲间的转换,具有广泛的应用价值。     

Theoretical and experimental studies of combined self-phase modulation and stimulated Raman-scattering in single-mode fibres

A theoretical model of pulse propagation through single-mode fibres is presented taking into account the combined action of self-phase modulation, stimulated Raman-scattering and the group velocity mismatch between pump and Stokes pulses. Due to the walk-off of Stokes and laser light an asymmetric pump pulse depletion resulting in considerable reshaping of laser pulses and an asymmetric self-phase modulation spectrum can be calculated and experimentally verified. A maximum laser power is found to be transferable through the fibre.     

Stimulated Raman spectra generated by ps-pulses in a single-mode fiber

Efficient frequency conversion of 5 ps-pulses from a cavity dumped Rh6G-dye laser by stimulated-Raman-scattering (SRS) into the first and second Stokes order has been achieved. The simulateneously produced asymmetric spectrical broadening of the pump pulses leads to double peaks in the Raman spectrum. By means of spectrally resolved cross-correlation measurements with 2 ps pulses from a second synchronized dye laser, the relative arrival time of the various spectral components is measured. Furthermore it is shown that the effect of a reduction of the pump peak power by SPM is partially compensated by the temporal broadening of the pump pulses leading to a longer interaction length for SRS.     

大模面积掺Yb3+双包层光纤激光器的实验研究

本文研究了在连续泵浦和脉冲泵浦两种情况下, 大模面积（LMA）掺Yb³⁺双包层光纤激光器的输出特性. 采用连续泵浦, 在最大泵浦功率为10.4 W时, 得到了平均功率4.6 W、中心波长1.09 μm的准连续激光输出. 采用脉冲泵浦, 得到了脉宽小于50 ns、峰值功率为5.3 kW、重复频率为5 kHz、单脉冲能量为0.26 mJ的稳定的调Q脉冲输出.     

孤子分子/类噪声脉冲可切换的混合锁模光纤激光器

不同类型脉冲之间的演化是被动锁模光纤激光器丰富动力学的体现。报道了一种可实现多种脉冲切换的混合锁模光纤激光器,当泵浦功率为400 mW时实现了孤子分子、谐波锁模、孤子簇之间的相互切换。增加泵浦功率至600 mW时获得了类噪声脉冲输出,对应的输出功率和单脉冲能量分别为15.2 mW和0.86 nJ。通过调节偏振控制器实现了类噪声脉冲中心波长从1 895 nm到1 930 nm可调谐。所搭建的激光器具有锁模脉冲可切换,波长可调谐,能自启动等优点。     

Conical Emission Patterns by Femtosecond Pulses with Different Spectral Bandwidths

Different conical emission （CE） patterns are obtained experimentally at various incident powers and beam sizes of pump laser pulses with pulse durations of 7fs, 44fs and 100fs. The results show that it is the incident power but not the incident power density that determines a certain CE pattern. In addition, the critical powers for similar CE patterns are nearly the same for the laser pulses with the same spectral bandwidth. Furthermore, as far as a certain CE pattern is concerned, the wider the spectral bandwidth of pump laser pulse is, the higher the critical power is. This will hopefully provide new insights for the generation of CE pattern in optical medium.     

Er3+-Yb3+共掺杂光纤环型腔被动谐波锁模激光器

 报道了Er³⁺-Yb³⁺共掺杂光纤作为增益介质的环型腔光纤激光器。利用光纤的非线性偏振旋转效应产生可饱和吸收体的锁模机制,通过调整泵浦功率,调节偏振控制器的状态,实现了连续基波锁模和高阶谐波锁模两种稳定的锁模运转状态。其中连续基波锁模重复频率15.89 MHz,中心波长为1.557 nm,光谱宽度为9.9 nm。二阶谐波锁模重复率为31.79 MHz,三阶谐波锁模脉冲重复率为46.99 MHz。观察到了调Q锁模和调Q脉冲序列,给出了各种运转状态的实验结果并对多种锁模机理作了简要的分析。     

High-conversion-efficiency and tunable phase-stabilized infrared parametric laser source

High-conversion-efficiency and tunable self-phase-stabilized infrared laser pulses have been generated from a two-stage optical parametric amplifier. With a 1 kHz repetition rate 800 nm pump source, the output idler pulses are tunable from 1.2 to 2.4 μm, and the maximum output average power of the idler pulses is >2 W with the total 7.4 W pump power, and the maximum parametric conversion efficiency in the final optical parametric amplifier is near 60%. Due to the differential frequency process, the output idler pulses is self-phase-stabilized, the phase fluctuation can reach 0.374 rad (rms).     

LD抽运Nd∶YVO4自喇曼倍频黄光激光器

报道了LD抽运的自喇曼c切Nd∶YVO4调Q腔内倍频黄光激光器.Nd∶YVO4晶体同时作为激光介质和喇曼晶体，通过声光调Q技术，产生了1 178.7 nm的喇曼激光，经过KTP腔内倍频，输出589.4 nm黄光.测量了平均输出功率随抽运功率和脉冲重复率的变化.典型的1 066.7 nm基频光、1 178.7 nm喇曼光和589.4 nm倍频光的脉冲宽度分别为24.9 ns、11.2 ns和6.8 ns.在脉冲重复率为15 kHz，抽运功率为7.56W时，产生了平均功率为151 mW的589.4 nm光的输出.     

Picosecond and subpicosecon pulse generation in synchronously pumped mode-locked cw dye lasers

Generation of tunable near-infrared picosecond and subpicosecond pulses in a synchronously pumped cw mode-locked Oxazine-1-perchlorate dye laser has been investigated for different values of the important system parameters. The experimental results confirm the predictions of a simple theoretical model which describes the steady-state pulse duration in terms of gain modulation strength, pump power, intracavity bandwidth, pump pulse length and cavity detuning. For a pump-pulse length of 100 ps and a bandwidth of more than 500 Å for the intracavity tuning element dye-laser pulses as short as 0.35 ps have been obtained. Under these conditions up to 100 mW of average output power were provided. In addition, mode-locking of an Oxazine 750 dye laser by synchronous pumping with the cw train of pulses obtained from the Oxazine-1-Perchlorate laser is reported.     

Diode-Pumped Passively Mode-Locked 1079 nm Nd:CaGdAlO_4 Laser

We demonstrate a diode-pumped passively cw mode-locked NdiCaGdAlO_4 laser operating at 1079 nm with a semiconductor saturable absorber mirror for the first time to the best of our knowledge.The threshold pump power of the laser is 180 mW.A maximum average output power of 93 mW is obtained under the pump power of1.94 W.The pulse duration of the mode-locked pulses is 3.1 ps and the repetition rate is 157 MHz.     

光子晶体光纤飞秒激光非线性放大系统的耦合动力学过程研究

构建了掺镱大模场面积单偏振光子晶体光纤飞秒激光非线性放大系统. 讨论了腔内净色散量和抽运功率对振荡级输出参数的影响和振荡级参数对放大级输出参数的影响. 在本实验条件下, 当腔内净色散量取较大负色散时, 振荡级直接输出的脉冲更宽, 且携带更少的啁啾. 当振荡级抽运4.53 W时, 选择最接近变换极限的脉冲作为种子脉冲, 放大级在60 W抽运时输出压缩后无基底的短脉冲, 宽度为45.7 fs, 平均功率28 W. 振荡级抽运功率增加到5.08 W, 放大级抽运70 W时, 获得最高输出功率34.5 W, 对应脉宽53.5 fs.     

Yb-doped strictly all-fiber laser actively Q-switched by intermodal acousto-optic modulation

We show an actively Q-switched ytterbium-doped strictly all-fiber laser. Cavity loss modulation is achieved in a tapered optical fiber by core-to-cladding mode-coupling induced by travelling flexural acoustic waves. When the acoustical signal is switched-off, the optical power losses within the cavity are reduced, and then a laser pulse is emitted. Trains of Q-switched pulses were successfully obtained at repetition rates in the range 1–10 kHz, with pump powers between 59 and 88 mW, at the optical wavelength of 1064.1 nm. Best results were for laser pulses of 118 mW peak power, 1.8 μs of time width, with a pump power of 79 mW, at 7 kHz repetition rate.     

抽运能量对受激布里渊散射光限幅特性的影响

采用布里渊噪声起源模型,数值模拟了受激布里渊散射介质CCl4对波长1064nm的Nd：YAG纳秒激光脉冲的传输特性及光限幅特性。入射抽运脉冲能量较低时,非线性介质对纳秒激光脉冲呈光学透明。入射抽运脉冲能量高于受激布里渊散射产生阈值后,透射脉冲峰值受限,脉宽压缩,能量趋于饱和,说明该光学系统同时具有光功率限幅和能量限幅的光限幅特性。利用理论模型模拟了如下光限幅参量：透射脉冲峰值功率、透射能量、能量透射率、脉宽压缩率依赖抽运光能量的变化关系。相应的理论模拟计算结果由实验进行验证,实验结果与理论模拟相符合。     

Concept study of a 100-PW femtosecond laser based on laser ceramics doped with chromium ions

A new concept of a superpowerful femtosecond laser based on CPA in polycrystalline chromium doped ceramics (Cr:YAG, Cr:YSGG, etc.) pumped by a Nd:glass laser is proposed. In contrast to amplifiers in available petawatt laser systems (neodymium glass, titanium-doped sapphire, and parametric amplifiers with a DKDP crystal), these ceramics combine three key favorable properties: a large gain bandwidth to amplify chirped pulses with less than 20-fs durations, a wide aperture to amplify chirped pulses to the multikilojoule level, and a high conversion efficiency of narrowband Nd:glass laser pulses into chirped pulses. These properties open up the opportunity to create a unique laser with a peak power of 100 PW at a 10-kJ pump power.