Selective growth of ZnO nanowires on substrates patterned by photolithography and inkjet printing

Zinc oxide nanowires (ZnO NWs) were grown by a two-step growth method, involving the deposition of a patterned ZnO thin seeding layer and the chemical vapor deposition (CVD) of ZnO NWs. Two ways of patterning the seed layer were performed. The seeding solution containing ZnO precursors was deposited by sol–gel/spin-coating technique and patterned by photolithography. In the other case, the seeding solution was directly printed by inkjet printing only on selected portion of the substrate areas. In both cases, crystallization of the seed layer was achieved by thermal annealing in ambient air. Vertically aligned ZnO NWs were then grown by CVD on patterned, seeded substrates. The structure and morphology of ZnO NWs was analyzed by means of X-ray diffraction and field emission scanning electron microscopy measurements, respectively, while the vibrational properties were evaluated through Raman spectroscopy. Results showed that less-defective, vertically aligned, c-axis oriented ZnO NWs were grown on substrates patterned by photolithography while more defective nanostructures were grown on printed seed layer. A feature size of 30 µm was transferred into the patterned seed layer, and a good selectivity in growing ZnO NWs was obtained.     

基于光纤拉曼放大的级联式全光纤1020nm光源

设计并制作了输出功率为196 mW的级联式全光纤1020 nm光源.该光源采用光纤拉曼放大器与掺镜光纤放大器级联的放大方案,实现了对低功率1020 nm种子光的放大.在光纤拉曼放大级,采用了3段不同长度的拉曼增益光纤进行了对比实验,比较了一定信号光功率和抽运光功率下拉曼增益光纤长度对光纤拉曼放大级输出功率的影响;测量了...     

Comparison of Brillouin-Raman comb fiber laser in two different configurations

The properties of a Brillouin-Raman comb fiber laser are compared for two different configurations: co-propagating and counter-propagating Raman pump. The optical spectrum is compared for changing the Raman pump power and the power or the wavelength of seed laser. A Brillouin-Raman comb with 400 linewidth lasers in a flat-amplitude bandwidth of 32 nm between 1538 and 1570 nm, with an average optical power 20 dB above the nearby frequencies was generated. The lasers in the comb had an OSNR of 20 dB and a wavelength spacing of 0.08 nm. The results for the counter-propagating configuration were observed to have better quality.     

Dependency of injection seeding and spectral purity of a single resonant KTP optical parametric oscillator on the phase matching condition

For spectroscopic and remote sensing applications injection seeded optical parametric oscillators (OPOs) are well established. In this paper we study the dependencies of signal resonant injection seeding of an OPO on its resonator length, phase matching angle and pump power in detail. The quality of the seeding process is assessed by stabilising the seed laser on a molecular absorption line of water vapour and using a water vapour absorption cell as a narrow bandwidth filter for the injection seeded radiation. A reduction of the acceptance of injection seeding is observed with increasing pump power. For small phase mismatch injection seeding with a spectral purity of 99.7% was observed at 13-fold OPO threshold. A signal pulse energy of 38 mJ with 50% pump depletion was achieved with a beam parameter M² of about 6. PACS 42.65.Yj; 42.79.Nv; 42.79.Qx     

Cascaded four-wave mixing generation in photonic crystal fibers

We investigate the efficient generation of broadband cascaded four-wave mixing products seeded at different wavelengths in photonic crystal fibers, with a high-peak power picosecond pulse pumping in the anomalous dispersion region as well as the normal dispersion regime. Multiple four-wave mixing products with different frequency intervals have been experimentally achieved when pumping in the anomalous dispersion region. Measured results present bandwidths of over 500 nm. We have also experimentally demonstrated that only seeding at the Stokes or anti-Stokes peaks can we get the efficient generation of cascaded four-wave mixing or cascaded stimulated Raman scattering when pumping in the normal dispersion regime.     

单频光纤拉曼放大器的实验研究

本文进行了1031 nm抽运光对1080 nm单频信号光的拉曼放大实验,详细研究了单频信号光种子功率、拉曼增益光纤长度、抽运方式等因素对 单频光纤拉曼放大器(SF-FRA)输出特性的影响.结果表明,在未受受激布里渊散射(SBS)因素限制时,相同抽运功率条件下,单频信号光种子功率越高,SF-FRA的效率越高;拉曼增益光纤越长,SF-FRA的效率越高;前向抽运时,SF-FRA的效率较高.实验中发现SF-FRA的拉曼放大过程对单频信号光的线宽有较小的展宽.此外,单频信号光远场干涉短曝光图像的对比度为0.814,单频信号光与SF-FRA放大光远场干涉短曝光图像可见度为0.719,表明SF-FRA对单频信号光的相干性有一定影响.实验结论可为其他特殊波长SF-FRA的设计提供一定的参考.     

An analysis of undulator optimization in self-seeding free electron lasers

A simple analysis is given for the optimum length of undulator in a self-seeding free electron laser(FEL).The obtained relations show the correlation between the undulator length and the system parameters.The power required for the seeding in the second part of the undulator and the overall efficiency of monochromatizating the seeding determine the length of the first part of the undulator;the magnitude of seeding power dominates the length of the second part of the undulator;the whole length of the undulator in a self-seeding FEL is determined by the overall efficiency for getting coherent seed,and is about half as long again as that of SASE,not including the dispersion section.The requirement of the dispersion section strength is also analyzed.     

Analysis and simulation of single-frequency Raman fiber amplifiers

High power operation of single-frequency Raman fiber amplifiers is usually limited by the onset of stimulated Brillouin scattering. A theoretical investigation on single-frequency Raman fiber amplifier limited by stimulated Brillouin scattering is presented in this paper, based on the intensity equations combining stimulated Brillouin scattering and stimulated Raman scattering. A combination of methods is proposed to increase the output power of single-frequency Raman fiber amplifier. These methods include applying a suitable pump scheme according to the fiber length and seed signal power, using short gain fibers, utilizing a multiple-stage scheme and providing suppression of stimulated Brillouin scattering.     

Over 200 W average power tunable Raman amplifier based on fused silica step index fiber

A high-power tunable Raman Amplifier is presented. The seed signal (varying from 1118 nm to 1130 nm in wavelength) was generated in a tunable Raman oscillator and fed into the Raman amplification stage. A conversion efficiency of up to 86 % was achieved and a maximum output power of over 200 W was measured. The Raman gain coefficient for the amplifier fiber was measured to be 0.76×10^?14 m/W. Furthermore, the measured output power was compared with values obtained from simple mathematical model and a good agreement up to the highest output power of amplified signal was achieved.     

受激布里渊散射光限幅输出波形控制研究

数值模拟了种子场诱导受激布里渊散射光限幅过程的限幅输出波形特性.得到利用种子场控制限幅脉冲波形的规律：选取种子场脉冲宽度为抽运脉冲宽度的五倍，抽运脉冲相对于种子脉冲的延迟时间控制在与抽运脉冲宽度相当时，限幅输出波形最佳.限幅输出波形同时受抽运光功率影响，随抽运能量的增加，限幅脉冲功率不断下降，直至趋于0. 关键词： 受激布里渊散射 限幅输出波形 注入种子     

High-power supercontinuum generation in highly nonlinear, dispersion-shifted fibers by use of a continuous-wave Raman fiber laser

High-power supercontinua are demonstrated in highly nonlinear, dispersion-shifted fibers with a continuous-wave Raman fiber laser. Supercontinuum growth is experimentally studied under different combinations of fiber length and launch power to show output powers as high as 3.2 W and bandwidths greater than 544 nm. Modulation instability (MI) is observed to seed spectral broadening at low launch powers, and the interplay between MI and stimulated Raman scattering plays an important role in the growth of the continuum at high launch powers. The effect on continuum generation of parametric four-wave mixing coupled with the higher-order dispersion properties of the fiber is investigated.     

双纵模窄线宽光纤拉曼放大器

 报道了一台实现了双纵模窄线宽激光输出的光纤拉曼放大器。利用中心波长1 079.7 nm的双纵模窄线宽种子激光器获得了频率间隔1.4 GHz、功率比约3∶1的双纵模输出,各纵模的线宽约为10 MHz;再利用1 031 nm泵浦光对双纵模种子光进行拉曼放大,实现了1.07 W双纵模激光输出。拉曼放大过程中,两个纵模的线宽、频率间隔及功率比保持得很好。     

Two-frequency amplification in a semiconductor tapered amplifier for cold atom experiments

Simultaneous two-frequency amplification is highly desirable in cold atom experiments. The nonlinear response would appear in the two-frequency amplification with a semiconductor tapered amplifier(TA) and has a direct influence on the experimental result. We investigated in detail the effects of frequency difference, total power, and power ratio of two seeding lasers on the output components based on a simplified theoretical model. The simulation results showed that the multiple sideband generation in the amplifier due to self-phase and amplitude modulation could be suppressed and the TA tended to linearly amplify the power ratio between two-frequency components, when the two seeding lasers had a large frequency difference. This was verified experimentally in the output power ratio measurement via a calibrated Fabry-Perot interferometer method with a good linearity and an uncertainty of 1%. We also discussed the consequences of power ratio responses in the amplification in light of cold atom experiments, especially in the ac Stark shift related phase error of Raman-type atom interferometers(AIs). It was shown that the fluctuation of intensity ratio of Raman beams may induce significant systematic errors for an AI gyroscope.     

Optically controlled seeding of Raman forward scattering and injection of electrons in a self-modulated laser-wakefield accelerator

Optical seeding of plasma waves and the injection of electrons are key issues in self-modulated laser-wakefield accelerators. By implementing a copropagating laser prepulse with proper timing, we are able to control the growth of Raman forward scattering and the production of accelerated electrons. The dependence of the Raman intensity on prepulse timing indicates that the seeding of Raman forward scattering is dominated by the ionization-induced wakefield, and the dependence of the divergence and number of accelerated electrons further reveals that the stimulated Raman backward scattering of the prepulse plays the essential role of injecting hot electrons into the fast plasma wave driven by the main pulse.     

Optical and structural properties of polycrystalline CVD diamond films grown on fused silica optical fibres pre-treated by high-power sonication seeding

In this paper, the growth of polycrystalline chemical vapour deposition (CVD) diamond thin films on fused silica optical fibres has been investigated. The research results show that the effective substrate seeding process can lower defect nucleation, and it simultaneously increases surface encapsulation. However, the growth process on glass requires high seeding density. The effects of suspension type and ultrasonic power were the specific objects of investigation. In order to increase the diamond density, glass substrates were seeded using a high-power sonication process. The highest applied power of sonotrode reached 72 W during the performed experiments. The two, most common diamond seeding suspensions were used, i.e. detonation nanodiamond dispersed in (a) dimethyl sulfoxide and (b) deionised water. The CVD diamond nucleation and growth processes were performed using microwave plasma assisted chemical vapour deposition system. Next, the seeding efficiency was determined and compared using the numerical analysis of scanning electron microscopy images. The molecular composition of nucleated diamond was examined with micro-Raman spectroscopy. The sp³/sp² band ratio was calculated using Raman spectra deconvolution method. Thickness, roughness, and optical properties of the nanodiamond films in UV–vis wavelength range were investigated by means of spectroscopic ellipsometry. It has been demonstrated that the high-power sonication process can improve the seeding efficiency on glass substrates. However, it can also cause significant erosion defects at the fibre surface. We believe that the proposed growth method can be effectively applied to manufacture the novel optical fibre sensors. Due to high chemical and mechanical resistance of CVD diamond films, deposition of such films on the sensors is highly desirable. This method enables omitting the deposition of an additional adhesion interlayer at the glass–nanocrystalline interface, and thus potentially increases transmittance of the optical system.     

Experimental investigation of the spectro-temporal dynamics of the light pulses of Q-switched Nd:YAG lasers and nanosecond optical parametric oscillators

We report an experimental investigation of the spectro-temporal dynamics of the pulse formation in Q-switched Nd:YAG lasers and in nanosecond optical parametric oscillators (OPOs). The temporal evolution of the spectral intensity distribution of the light pulses was measured with a 1-m Czerny–Turner spectrometer in combination with a fast streak camera. This detection system allows the analysis of temporal changes in the spectrum of single nanosecond pulses. The measurements were performed for a flashlamp-pumped, Q-switched Nd:YAG laser and for an unseeded as well as for a seeded singly-resonant nanosecond OPO. The laser output spectrum varies strongly from pulse to pulse and even within a single pulse due to mode beating. In an unseeded OPO, individual spectral modes start to oscillate statistically from the parametric noise for pump powers close to the OPO threshold. With increasing pump power a strong modulation in the spectral formation of the pulse is observed, resulting from a strong interaction of parametric conversion and back conversion of signal and idler radiation into pump radiation. By means of injection seeding, the starting condition was controlled for a single mode. Due to the seed radiation, the seeded mode starts sooner than the unseeded modes. These are suppressed completely in the case of sufficient seed power and moderate pump power. The observations are in good agreement with results of corresponding numerical simulations. PACS 42.65.Sf, 42.65.Yj     

Surface potential driven dissolution phenomena of [0 0 0 1]-oriented ZnO nanorods grown from ZnO and Pt seed layers

Highly oriented ZnO nanorods are synthesized hydrothermally on ZnO and Pt seed layers, and they are dissolved in KOH solution. The rods grown on ZnO seed layer show uniform dissolution, but those grown on Pt seed layer are rod-selectively dissolved. The ZnO nanorods from both seed layers show the same crystalline structure through XRD and Raman spectrometer data. However, the surface potential analysis reveals big difference for ZnO and Pt seed cases. The surface potential distribution is very uniform for the ZnO seed case, but it is much fluctuated on the Pt seed case. It suggests that the rod-selective dissolution phenomena on Pt seed case are likely due to the surface energy difference.     

Facilitative effect of graphene quantum dots in MoS_2 growth process by chemical vapor deposition

The substrate treatment with seeding promoter can promote the two-dimensional material lateral growth in chemical vapor deposition(CVD) process. Herein, graphene quantum dots(GQDs) as a novel seeding promoter were used to obtain uniform large-area MoS_2 monolayer. The obtained monolayer MoS_2 films were confirmed by optical microscope,scanning electron microscope, Raman and photoluminescence spectra. Raman mapping revealed that the MoS_2 monolayer was largely homogeneous.     

Study of multiple impurity seeding effect using SONIC integrated divertor code for JT-60SA plasma prediction

In order to study the potential impurity seeding operation regime of the future fusion devices, the first application of the integrated divertor code SONIC to the Ar + Ne mixed-impurity seeding operation of JT-60SA steady-state high-β plasma has been carried out. In the case, Ne is added to Ar-only seeding, the separatrix electron density has fell into the desired low separatrix electron density of the scenario. This is mainly because the D⁺ flow velocity towards the inner divertor has been increased by the Ne seeding. The resultant friction force transports Ar impurities towards the inner divertor region, while impurities are stagnated in the top of scrape-off layer (SOL) in the Ar-only seeding case. The higher impurity radiation power in the divertor regions and lower one in the SOL region above the X point have been obtained in mixed-impurity seeding cases, which show similar tendency as the Ar + Ne mixed-impurity seeding experiment in JT-60 U. At the core edge, Z_eff has been slightly increased and the radiation power has been decreased as the Ne seeding rate increases. The core plasma/impurity transport has been also evaluated by the TOPICS code using the impurity density at the core edge computed by the SONIC as a boundary parameter. The results show lower Z_eff and radiation power, and higher electron temperature in the core in the mixed-impurity seeding cases. Above possible contributors to the better energy confinement indicate that the mixed-impurity seeding operation might be more effective than Ar-only seeding operation.     

Influencing factors of external fluorescence seeding enhancing stimulated Raman scattering in liquid‐core optical fiber

This paper reports an external fluorescence seeding technology enhancing the stimulated Raman scattering (SRS) in liquid‐core optical fiber (LCOF). By surrounding a small section of LCOF with a glass capillary and a solution of Rhodamine 6G filled between them to separate fluorescent dye and Raman medium, the initial intensity of SRS is linearly amplified by external fluorescence seeding, and then the SRS of LCOF can be enhanced effectively. Experimental results show that both the concentration of fluorescent dye and the seeding position have an influence on enhancement of SRS. The maximum enhancement of Stokes lines is obtained when the concentration of dye solution is optimized at ~10⁻⁶ mol/l and seeding position is located at the input end. Copyright © 2013 John Wiley & Sons, Ltd.