Passive harmonic mode-locking of Er-doped fiber laser using CVD-grown few-layer MoS_2 as a saturable absorber

Passive harmonic mode locking of an erbium-doped fiber laser based on few-layer molybdenum disulfide(MoS2)saturable absorber(SA) is demonstrated. The few-layer MoS2 is prepared by the chemical vapor deposition(CVD) method and then transferred onto the end face of a fiber connector to form a fiber-compatible Mo S2SA. The 20 th harmonic modelocked pulses at 216-MHz repetition rate are stably generated with a pulse duration of 1.42 ps and side-mode suppression ratio(SMSR) of 36.1dB. The results confirm that few-layer MoS2 can serve as an effective SA for mode-locked fiber lasers.     

基于少数层石墨烯可饱和吸收的锁模光纤激光器

本文利用化学气相沉积法高温分解甲烷在铜箔上制得单层石墨烯薄膜, 测量了石墨烯的拉曼光谱. 将石墨烯薄膜逐层转移到光纤跳线的氧化锆插芯端面上做成可饱和吸收材料, 实验研究了环形腔掺铒光纤脉冲激光器的输出特性, 获得了峰值波长为1560.1 nm, 3 dB带宽为0.27 nm, 重复频率为7.69 MHz, 脉冲宽度为58.8 ps 的锁模脉冲序列. 时间带宽积为1.98, 表明脉冲出现了啁啾. 最后, 通过改变两个光纤活动接头之间的空气腔的长度, 激光波长实现了4 nm的调谐. 关键词： 光纤激光器 石墨烯 锁模     

Passive,Stable and Order-Adjustable SBS Q-Switching Fiber Laser

We propose a new method to separate different orders of an all-fiber passive Q-switching stimulated Brillouin scattering(SBS) laser. We use two fiber Bragg gratings connected by two circulators for the filtering. We obtain a stabilized pulse laser and measure the pulse width of different orders. The first order of SBS has a central wavelength of 1549.75 nm, an average output power of 9 mW, and a pulse width of 400 ns. The pulse width of SBS is reduced by the higher-order signals with the larger fluctuations.     

Passively Q-switched fiber laser based on graphene saturable absorber

A passively graphene Q-switched Erbium doped fiber laser around 1.5 μm is demonstrated in this paper. The graphene saturable absorber was fabricated by sandwiching a thin graphene film produced via chemical vapor deposition between two FC fiber connectors. Stable pulse trains were obtained with the pulse repetition rate varying between 34.72 and 53.2 kHz and the average output power ranging from 0.504 mW to 0.926 mW. The achieved shortest pulse duration and highest pulse energy were 3.2 μs and 17.41 nJ, respectively.     

Resonantly pumped 1.645 μm high repetition rate Er:YAG laser Q-switched by a graphene as a saturable absorber

A fiber laser resonantly pumped 1.645 μm passively Q-switched Er:YAG laser is reported. Graphene on a silicon carbide was used as the saturable absorber for the Q-switching. The pulse energy of the 1.645 μm Q-switched Er:YAG laser was 7.05 μJ, with a pulse repetition rate of 35.6 kHz and an average output power of 251 mW.     

KrF准分子激光退火氢化非晶碳化硅薄膜的晶化研究

介绍了利用KrF准分子脉冲激光对氢化非晶碳化硅(a-SiC∶H)薄膜进行激光退火以实现薄膜的结晶化。利用等离子增强化学气相沉积(PECVD)在单晶Si(100)衬底上制备a-SiC∶H薄膜, 再用不同能量密度的激光对薄膜样品进行退火。分析表明, 选用合适能量密度的激光退火能够实现a-SiC∶H薄膜的结晶化, 且结晶颗粒大小随着入射激光能量密度的增加而增大; 显微图表明当入射能量密度超过200 mJ/cm2时, 薄膜表面出现由热弹性波引起的表面波纹现象, a-SiC∶H薄膜结晶过程为液相结晶; 傅里叶红外谱(FTIR)表明随着入射能量密度增加, 薄膜中氢含量降低, Si-C峰增强并且峰位出现蓝移, 薄膜的结晶度提高。     

Dual-wavelength Bi_2Se_3-based passively Q-switching Nd~(3+)-doped glass all-fiber laser

We demonstrate a dual-wavelength passively Q-switched Nd~(3+)-doped glass fiber laser using a few-layer topological insulator Bi_2Se_3 as a saturable absorber(SA) for the first time, to the best of our knowledge. The laser resonator is a simple and compact linear cavity using two fiber end-facet mirrors. The SA is fabricated by Bi_2Se_3/polyvinyl alcohol composite film. By inserting the SA into the laser cavity, a stable Q-switching operation is achieved with the shortest pulse width and maximum pulse repetition rate of 601 ns and 205.2 kHz,respectively. The maximum average output power and maximum pulse energy obtained are about 6.6 mW and 38.8 nJ, respectively.     

Graphene oxide-COOH as a new saturable absorber for both Q-switching and mode-locking fiber lasers

Graphene oxide carboxylic acid(COOH), a novel two-dimensional(2D) layered material with its unique optical and electronic properties, is discovered to exhibit the saturation of optical absorption under laser illumination.Applying the liquid-phase exfoliation method, we prepare graphene oxide-COOH dispersions with deionized water and fabricate graphene oxide-COOH polyvinyl alcohol polymer composite film. We further obtain stable Q-switching pulse and mode-locked laser operation with a 22.7 MHz repetition rate and a 1.5 ps pulse duration by incorporating the graphene oxide-COOH-based saturable absorbers into the all-fiber erbium-doped fiber laser cavity. The experimental results show that the proposed graphene oxide-COOH material can act as an effective absorber for pulsed fiber lasers, which demonstrate potential applications in the area of ultrafast optics.     

电光调Q脉冲Ho:YLF激光器实验研究

2μm低重复频率高峰值功率高光束质量激光在中长波光参量非线性频率变换等领域具有较为广阔的应用前景。采用L型谐振腔结构,使用42 W的掺Tm光纤激光器泵浦Ho:YLF晶体。基于磷酸钛氧铷（RTP）电光调Q技术,实现了重复频率50 Hz、脉冲宽度18 ns、脉冲能量13.5 mJ、峰值功率0.75 MW的2.05μm Ho:YLF固体激光输出。光束的水平方向和竖直方向M2因子分别为1.4和1.1。该Ho:YLF固体激光器采用光纤激光器泵浦,具有结构紧凑的特点,为更高能量的Ho激光输出奠定了基础。     

High-peak-power operation of a Q-switched Tm3+-doped silica fiber laser operating near 2 microm

A peak output power of greater than 4.1 kW and a pulse duration at FWHM of 150 ns have been obtained in a Q-switched Tm3+-doped silica fiber laser in the wavelength region near 2 microm when the laser was pumped with a Nd:YAG laser operating at 1.319 microm. An acousto-optic modulator was used as a Q-switching element and operated at repetition rates of as much as 30 kHz. A core diameter of 17 microm was used to increase the laser gain volume, permitting high-pump-power absorption and an output of high pulse energy and peak power. Stimulated Brillouin scattering was directly observed in the output pulse, and as much as 10 orders of stimulated Brillouin scattering was recorded. This is the first report to the authors' knowledge of high-peak-power operation of a Tm3+-fiber laser.     

Picosecond pulse generation in a mono-layer MoS_2 mode-locked Ytterbium-doped thin disk laser

A mode-locked(ML)picosecond ytterbium-doped thin disk laser using a monolayer Mo S2as the saturable absorber(SA)is demonstrated.The monolayer MoS_2 is fabricated through the method of low-pressure chemical vapor deposition.The laser directly produces stable ML picosecond pulses at a slope efficiency of 9.71%.The maximum output power is approximately 890 mW,while the corresponding repetition,pulse energy,and pulse duration are 48.6 MHz,18.3 nJ,and 13.1 ps,respectively.Results suggest that the monolayer MoS_2 is a promising SA for ultrafast lasers system.     

多源共蒸发制备高性能REBa2Cu3O7-x涂层导体的进展与展望

REBa2Cu3O7-x (RE：钇、钆等稀土元素,REBCO）高温超导体因其具备较高的不可逆场和上临界场等优越性能,一经发现就备受关注。但由于材料本身固有的陶瓷性及弱连接等属性,导致其实际应用起来难度较大。目前,人们已经发展了诸多制备工艺来克服这些困难,实现了REBCO超导体的实际应用。按照前驱膜沉积方法可将REBCO超导薄膜的制备分为物理法和化学法。本文综述了物理气相沉积（PVD-Physical Vapor Deposition）法中多源共蒸发法制备REBCO超导薄膜的技术起源及演变历程,并与金属有机沉积、金属有机化学气相沉积、脉冲激光沉积等不同方法生产的REBCO超导带材进行对比,突出多源共蒸发法制备的REBCO薄膜性能优异、在商业化生产效率上具有更大的优势。最后对多源共蒸发法制备REBCO超导薄膜进行总结及展望,解决多源共蒸发沉积制备REBCO薄膜的成相机理、提高薄膜的钉扎中心等问题对未来第二代高温超导带材的大规模应用具有重要意义。     

Effects of irradiation conditions on the lateral grain growth during laser crystallization of amorphous silicon films on borosilicate glass substrates

The effects of preheating laser power and pulse laser energy on the size and crystallinity of laterally grown grains by dual-laser crystallization of amorphous silicon (a-Si) films on borosilicate glass substrates were investigated. Plasma-enhanced chemical vapor deposition was adopted for the deposition of the a-Si films in order to reduce the process temperature and thus the diffusion of metal impurities from the glass substrate to the deposited a-Si films. It was found that the preheating laser power is critical in enhancing grain size, whereas the pulse laser energy is closely related to crystal quality. It is demonstrated that by properly adjusting the process conditions, laterally grown grains of 50-μm size could be obtained.     

低温GaAs被动调Q锁模Nd:Gd0.42 Y0.58VO4 混晶激光器特性研究

采用低温生长GaAs晶体作为被动饱和吸收体兼输出镜,实现了Nd:Gd0.42Y0.58VO4混晶激光器的调Q锁模运转.研究了Nd:Gd0.42Y0.588VO4激光器的基频运转特性.在输出镜透射率T=10%、腔长L=40 mm的情况下,当抽运功率为8.6 W时,获得激光输出功率3.78 W,光-光转换效率为43.9%.并测量了Nd:Gd0.42Y0.58VO4混晶被动调Q激光器的输出特性.实验结果表明激光器调Q运转阈值为2 W,当抽运功率为3.7 W时,激光器出现调Q锁模行为;当抽运功率为8.6 W时,激光器调Q锁模深度达70%以上,对应的脉冲包络重复频率为670 kHz,半峰全宽为180 ns,平均输出功率为1.35 W,光-光转换效率为15.7%.     

Film growth and mechanism of LICVD of chromium films from Cr(CO)6 at 248 nm

The probe-beam transmission method was used to study the chemical vapor deposition of chromium films due to photodecomposition of Cr(CO)₆ by pulsed excimer laser radiation at 248 nm in a reversed-substrate configuration, where the film forms on the quartz entrance window of the deposition cell. The dependence of the deposition rate and the film formation time on the laser pulse intensity and repetition rate as well as on the Ar buffer gas pressure was determined for different stages of the deposition process. The experiments were performed at room temperature, on a deposition area of about 0.15 cm², with laser fluences up to 100mJ cm^–2, pulse repetition rates between 5 and 80 pps and buffer gas pressures between 10 and 700 mbar. The results are discussed within the framework of a simple model for LICVD. They reveal the dominant role of gas-phase photodissociation and diffusion in chromium film deposition under the conditions employed. Some results concerning the morphology and the depth distribution of Cr, O, and C in films deposited in the reversed-substrate configuration are also presented.     

脉冲激光沉积法制备的ZnO薄膜的低阈值电抽运紫外随机激射

分别采用直流反应溅射法和脉冲激光沉积法在硅衬底上沉积ZnO薄膜, 用X射线衍射、扫描电镜、光致发光谱等手段对两种方法沉积的ZnO薄膜的结晶状态、 表面形貌和光致发光等进行了表征. 进一步对比研究了以上述两种方法制备的ZnO薄膜作为发光层的金属-绝缘体-半导体结构器件的电抽运紫外随机激射. 结果表明, 与以溅射法制备的ZnO薄膜作为发光层的器件相比, 以脉冲激光沉积法制备的ZnO薄膜为发光层的器件具有更低的紫外光随机激射阈值电流和更高的输出光功率. 这是由于脉冲激光沉积法制备的ZnO薄膜中的缺陷更少, 从而显著地减少了紫外光在光散射过程中的光损耗. 关键词： 随机激射 ZnO薄膜 脉冲激光沉积 溅射     

Graphene-based passively Q-switched dual-wavelength erbium-doped fiber laser

We demonstrate a compact Q-switched dual-wavelength erbium-doped fiber (EDF) laser based on graphene as a saturable absorber (SA). By optically driven deposition of graphene on a fiber core, the SA is constructed and inserted into a diode-pumped EDF laser cavity. Also benefiting from the strong third-order optical nonlinearity of graphene to suppress the mode competition of EDF, a stable dual-wavelength Q-switching operation has been achieved using a two-reflection peak fiber Bragg grating as the external cavity mirror. The Q-switched EDF laser has a low pump threshold of 6.5 mW at 974 nm and a wide range of pulse-repetition rate from 3.3 to 65.9 kHz. The pulse duration and the pulse energy have been characterized. This is, to the best of our knowledge, the first demonstration of a graphene-based Q-switched laser.     

Q-switched fiber laser by all-fiber piezoelectric modulation and pulsed pump

We have demonstrated a Q-switched fiber laser based on a mechanical all-fiber Q-switching module and pulsed-pump configuration. A piezoelectric actuator was utilized in the module to change the round-trip loss of the fiber laser cavity, and exploited the pulsed pump to prevent the multiple pulsing phenomena. Q-switching pulses were successfully achieved at the repetition rates from 1 Hz to 2 kHz, and the average output power was 11 mW. The peak power in excess of 114 W with associated pulse width of 193 ns was obtained at the repetition rate of 500 Hz. Besides preventing multiple pulsing phenomena, pulsed-pump configuration can also suppress amplified spontaneous emission and increase pulse stability and peak power simultaneously.     

Fabrication of hollow thin films of yttria-stabilized zirconia by chemical vapor infiltration using NiO as oxygen source

Deposition of yttria-stabilized zirconia films on surface oxidized Ni wire substrate by chemical vapor infiltration (CVI) using ZrCl₄ and YCl₃ as metal sources and NiO as oxygen source were studied. The resultant films were cubic crystals of YSZ with a Y₂O₃ content of 1.0–3.7 mol%. The growth rate is larger than that obtained by conventional method of chemical vapor deposition (CVD), increased with the flow rate and decreased with diameter of NiO fiber. The growth rate above its thickness of 4 μm decreased with an increase in the oxidation temperature since the porosity of NiO wire might decrease with an increase in the oxidation temperature. Growth of YSZ films with the CVI method simultaneously involved CVD and electrochemical vapor deposition (EVD).     

Furnace chemical vapor deposition bismuth-doped silica-core holey fiber

A bismuth-doped-pure-silica holey fiber is fabricated using a fiber preform made by the furnace chemical vapor deposition method. The spectroscopic properties of the fiber are studied, and laser action at λ=1450 nm with an efficiency of 12% is demonstrated.