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A 7.8-GHz linewidth ytterbium-doped fiber (YDF) laser with an output power of 75 W at 1,018 nm is demonstrated based on narrow-bandwidth fiber Bragg gratings. Effective suppression of spectral broadening and amplified spontaneous emission is achieved by optimizing the resonator structure and active fiber parameters. An 1,178-nm diamond Raman output pumped by this narrow-linewidth 1,018 nm source is addressed in this study, which shows a promising application of generating the sodium guide star laser at 589 nm. A single-longitudinal-mode Stokes with an output power of 0.6 W is obtained using this multimode 1,018 nm laser at the pump power of 13 W. The impact of pump spectral linewidth on the effective Raman gain coefficient is analyzed, and the laser threshold of the diamond Stokes resonator increases with the broadening of the pump linewidth.

A high power continuous-wave single-frequency green fiber laser by second-harmonic generation of a Yb-doped fiber amplifier (YDFA) is developed. A linearly polarized single-mode fiber amplifier produces a 60 W infrared laser at 1064 nm with a 103 W incident diode pump laser at 976 nm, corresponding to an optical conversion efficiency of 58%. An external bow-tie enhancement cavity incorporating a noncritically phase-matched lithium triborate crystal is employed for second-harmonic generation. A 33.2 W laser at 532 nm is obtained with a 45 W incident 1064 nm fundamental laser, corresponding to a conversion efficiency of 74%.

A 11.5 W 1152 nm Raman fiber laser with 6 nm spectral width was demonstrated based on the resonator constructed with one fiber loop mirror and one fiber Bragg grating. By mans of experimental measurement and theoretical calculation, the reflectivity of the fiber loop mirror was confirmed as 0.93. The Yb 3+ -doped 1090 nm fiber length was about 5 m. When the maximum pumping power of 976 nm laser was 54.8 W, 32.2 W 1090 nm laser was obtained and the optical to optical conversion efficiency from 1090 nm to 1152 nm light was 48%. Finally, the 1152 nm Raman fiber laser was used for pumping Ho 3+ :LLF crystal, and the 1194 nm fluorescence emission peak was detected for the first time.

A high power, single frequency, quasi-continuous-wave 1336 nm laser is achieved by Raman amplification of an external cavity diode laser in a variably strained polarization maintaining silica fiber. The pump laser is a 1256 nm Ytterbium-Raman integrated fiber amplifier with a maximum output peak power of 235 W. The 1336 nm amplifier produces square-shaped pulses with tunable repetition rate and duration. The peak power is as high as 53 W, which remains constant during the tuning. A polarization extinction ratio of >25 dB is achieved due to the all polarization maintaining fiber configuration. The laser is locked precisely at 1336.63 nm for future application in laser cooling of 27Al+ after 8th harmonic generation.

We demonstrate a 21.2 W continuous-wave single frequency 780 nm laser by efficient single-pass frequency doubling of a 1560 nm fiber amplifier in a periodically-poled magnesium-oxide-doped lithium niobate (MgO:PPLN) crystal.

A narrowband sodium lidar for measuring mesospheric temperature and wind has been established at YangBaJing, Tibet (90°E, 30°N, 4300 m a.s.l), China. The system is designed and optimized based on important upgrades using new technology. In the lidar system, single-mode 589 nm seed laser is produced by frequency doubling of 1178 nm diode laser with a periodically poled lithium niobate (PPLN) waveguide. The output power of 589 nm continuous-wave laser is up to 1.5 W with the help of a seed-injected Raman fiber amplifier. Furthermore, fast three-frequency switcher is designed with a couple of fiber magneto optical switches (FMOS) for measuring wind and temperature, simultaneously, which greatly reduces the system maintenance. These improvements greatly simplify the lidar system, thus, achieve robust operation with minimum maintenance requirements.

The paper reports on controlled formation of microscale wrinkles and ridges on the surface of a bioelectrode via mechanical stretching to tune and optimize the electrochemical sensing performances of graphene oxide (GO) based nitrate ion sensors. The bioelectrode consists of GO nanosheets drop-coated on a gold (Au) layer with a pre-stretched elastomer substrate. Enzyme nitrate reductase is used for covalent immobilization on the wrinkled-ridged GO surface. Upon relaxation from the pre-stretch, wrinkles or ridges are formed in the GO layer. As the pre-stretch increases, the sinusoidal wrinkles transform to localized ridges on the surface of bioelectrodes. Such morphological transitions, realized by simple mechanical stretching and relaxing, allow optimizing of the electrochemical current and sensing characteristics of the nitrate sensor. The sensing performances of the bioelectrodes at different pre-stretches are investigated. In addition to an increased electroactive surface area, the predominant localized ridges with small sinusoidal wrinkles formed on the GO surface provide a favorable spatial feature, enabling efficient radial diffusion of nitrate ions from surrounding analyte solutions onto the surface of the textured bioelectrode. At the pre-stretch of 8%, the nitrate sensor using the wrinkled-ridged bioelectrode exhibits a considerably high sensitivity of 0.224 μA L mol−1 cm−2 in response to nitrate ions, which is five times higher than that provided by the planar counterpart. Also, the textured bioelectrode shows high selectivity even in the presence of other inferring ions. The present nitrate sensor has potential applications in nitrate detection in sustainable agriculture, environmental monitoring, food analysis, and pharmaceutical industries.

We report on the development of an enhanced and robust microfluidic plant chip-based growth and monitoring system for high-throughput phenotyping of Arabidopsis thaliana. The system consists of multiple vertical plant chips, a microfluidic hormone concentration gradient generator, multiple simple gravity pumps, and a robotic arm with a stereoscope for plant imaging. We validate this system by phenotyping the growth of Arabidopsis plants in medium containing different hormone concentrations, in a real-time manner. Our results show that Arabidopsis growth and hormone response in this system closely replicates growth on standard laboratory petri plates.

The wavelength tunability of conventional fiber lasers are limited by the bandwidth of gain spectrum and the tunability of feedback mechanism. Here a fiber laser which is continuously tunable from 1 to 1.9 μm is reported. It is a random distributed feedback Raman fiber laser, pumped by a tunable Yb doped fiber laser. The ultra-wide wavelength tunability is enabled by the unique property of random distributed feedback Raman fiber laser that both stimulated Raman scattering gain and Rayleigh scattering feedback are available at any wavelength. The dispersion property of the gain fiber is used to control the spectral purity of the laser output.

Robust high-power narrow-linewidth lasers at 589 nm are required for sodium laser guide star adaptive optics in astronomy. A high-power 589 nm laser based on Raman fiber amplifier is reported here, which works in both continuous-wave and pulsed formats. In the continuous-wave case, the laser produces more than 50 W output. In the pulsed case, the same laser produces square-shaped pulses with tunable repetition rate (500 Hz to 10 kHz) and duration (1 ms to 30 μs). The peak power is as high as 84 W and remains constant during the tuning. The laser also emits an adjustable sideband at 1.71 GHz away from the main laser frequency for better sodium excitation. The versatility of the laser offers much flexibility in laser guide star application.

It is challenging to integrate porous graphene foam (GF) and GF-based nanocomposites into microfluidic channels and even create microfluidic structures within these materials. This is because their irregular interior pore shape and geometry, rough exterior surface, and relatively large material thickness make it difficult to perform conventional photolithography and etching. This challenge has largely hindered the potential of using GF-based materials in microfluidics-based sensors. Here we present a simple approach to create well-defined flow-through channels within or across the GF-based materials, using a liquid-phase photopolymerization method. This method allows embedding of a nanocomposite-based scaffold of GF and titanium nitride nanofibers (GF–TiN NFs) into a channel structure, to realize flow-through microfluidic electrochemical sensors for detecting nitrate ions in agricultural soils. The unique GF–TiN nanocomposite provides high electrochemical reactivity, high electron transfer rate, improved loading capacity of receptor biomolecules, and large surface area, serving as an efficient electrochemical sensing interface with the help of immobilized specific enzyme molecules. The microfluidic sensor provides an ultralow limit of detection of 0.01 mg L−1, a wide dynamic range from 0.01 to 442 mg L−1, and a high sensitivity of 683.3 μA mg−1 L cm−2 for nitrate ions in real soil solution samples. The advantageous features of the GF–TiN nanocomposite, in conjunction with the in situ integration approach, will enable a promising microfluidic sensor platform to monitor soil ions for nutrient management towards sustainable agriculture.

All-fiber source at 2.2 μm is investigated with amplified spontaneous Raman scattering process in highly Ge-doped silica fiber. By optimizing the gain fiber length, the second-order Raman Stokes light at 2.43 μm is suppressed and 3 W first-order Raman Stokes light at 2.2 μm is obtained with a homemade 2-μm Q-switched Tm3+-doped fiber laser as pump source. The conversion efficiency is 35.9 % from 2.0 to 2.2 μm, and the peak power of the 2.2-μm laser is about 400 W.

The CICC (cable-in-conduit conductor) in ITER (International Thermal-nuclear Experimental Reactor) will run in high-current, fast transient magnet field and complex environment. In response to the impact of magnet fields above 10 T, the Nb3Sn conductor has been introduced. However, the AC (alternating current) loss mechanism of Nb3Sn conductor on strain has not been explored. So, it is necessary to study the AC loss calculation method with transient electromagnetic field and wide range of strain, the coupling current in complex field and current signal of field is simplified to the spectrum effects of coil excitation, and calculation technology of AC loss, which contains the frequency, magnet field, coil characteristics and other parameters, is constructed to meet the discrete Fourier transform (DFT). By comparative analysis of simulation, it is found that the AC loss calculation of the conductor with spectrum algorithm is closer to the actual project value than the traditional algorithm. For the rapid excitation, in particular plasma discharge and burst, spectrum algorithm and the traditional algorithm are consistent. For the relative error calculation of hysteresis loss and coupling loss, it is found that the coupling loss is cumulative linearly, where the hysteresis loss is not so. As a function of the amplitude, frequency and phase angle, the relative error is less than 40%. The results showed that the method of Fourier restructuring is satisfactory.

A single-frequency low-noise green laser at 509 nm is developed for the study of cesium Rydberg atoms. The laser is generated by single-pass second-harmonic generation of a Yb fiber amplifier seeded with an external cavity diode laser (ECDL) at 1018 nm in a periodically poled MgO-doped lithium-niobate crystal. An up to 2.03 W, 509 nm laser is obtained from a 10.04 W incident 1018 nm laser with a conversion efficiency of 20.2%. The linewidth of the 509 nm laser is estimated to be 40 kHz according to the measured linewidth of 20 kHz of the 1018 nm fundamental laser. The relative intensity noise is 0.038% rms integrated from 10 Hz to 10 MHz.

Efficient generation of watt-level laser source at wavelength between 2.1 and 2.5 μm is analyzed and experimentally demonstrated with cascaded Raman scattering process in highly Ge-doped silica fibers.

The conversion efficiency of double-clad Raman fiber laser is limited by the cladding-to-core area ratio. To get high conversion efficiency, the inner-cladding-to-core area ratio has to be less than about 8, which limits the brightness enhancement. To overcome the problem, a cascaded-cladding-pumped cascaded Raman fiber laser with multiple-clad fiber as the Raman gain medium is proposed. A theoretical model of Raman fiber amplifier with multiple-clad fiber is developed, and numerical simulation proves that the proposed scheme can improve the conversion efficiency and brightness enhancement of cladding pumped Raman fiber laser.

Raman fiber laser is an efficient way to expand the spectral coverage of fiber lasers. In recent years, output power of Raman fiber laser has been scaled quickly. There is a great potential in further power scaling, technical innovations, and scientific applications. An integrated ytterbium-Raman fiber amplifier architecture was proposed, which allows power scaling of Raman fiber laser to over kilowatt and more. Hundred watt level single frequency Raman fiber amplifier was achieved, which allows the generation of high power sodium guide star laser. New scheme of cladding pumped Raman fiber laser is studied in order to improve the brightness enhancement. Furthermore, possible application in spectral beam combing is discussed.

300 W CW linearly-polarized 1120 nm laser is achieved with an integrated Yb-Raman fiber amplifier. 86 W 1178 nm single frequency Raman fiber amplifier is generated and frequency doubled to 589 nm with power up to 52.7 W.

We will review the development of high power Raman fiber laser and report our recent works on power scaling, including the demonstration of a 1.3 kW all-fiber Raman amplifier.

A high power 589 nm laser based on Raman fiber amplifier is reported here, which could work in both continuous wave and pulsed format for the laser guide star system.

Analysis of pressure fluctuation signals measured from wind caps which was a new method was proposed to realize the condition monitoring of gas-solid flow in fluidized bed. Pressure fluctuation signals measured from a wind cap in a cold bubbling fluidized bed setup at different superficial gas velocities, static bed heights and bed material particle sizes, were analyzed with wavelet analysis method. After wavelet analysis, the energy of reconstructed signals at different levels and the ratios of energy at different levels to total energy were calculated. Finally, the influence of operating conditions changes on the characteristic pressure fluctuations of the wind cap in bubbling fluidized bed was analyzed. It is found that the variations of low-frequency reconstructed signals are related with the variations of gas-solid flow state at different operating conditions. So the proposed method in the paper is proved to be practical.

Raman laser generation at the long wavelength transmission edge of silica fiber is explored. Numerical simulation reveals that high efficiency 2nd Stokes Raman laser operation around 2.5 μm is feasible with highly Ge-doped silica fiber as the gain medium and pulsed 2-μm fiber laser as the pump source. Based on the spontaneous cascaded Raman amplification process, 0.30-W laser at 2.43 μm is obtained with an optical efficiency of 16.5% pumped at 2008 nm. And 0.15-W laser at 2.48 μm is achieved with an optical efficiency of 7.9% pumped at 2040 nm. To the best of our knowledge, the results represent the longest wavelength operation of silica-based fiber laser.

A kilowatt-level Raman fiber laser is demonstrated with an integrated Ytterbium-Raman fiber amplifier architecture. A high power Ytterbium-doped fiber master oscillator power amplifier at 1080 nm is seeded with a 1120 nm fiber laser at the same time. By this way, a kilowatt-level Raman pump laser at 1080 nm and signal laser at 1120 nm is combined in the fiber core. The subsequent power conversion from 1080 nm to 1120 nm is accomplished in a 70 m long passive fiber. A 1.28 kW all-fiber Raman amplifier at 1120 nm with an optical efficiency of 70% is demonstrated, limited only by the available pump power. To the best of our knowledge, this is the first report of Raman fiber laser with over one kilowatt output.

An integrated ytterbium-Raman fiber amplifier architecture is proposed for power scaling of a Raman fiber laser. It is an ytterbium (Yb) fiber amplifier seeded with a double or multiple wavelength laser and followed by a passive Raman fiber. The bluest wavelength light gets amplified in the Yb fiber and the power is transferred to redder wavelengths in the following Raman fiber. A proof of principle experiment demonstrates a 300 W all-fiber linearly polarized single mode amplifier at 1120 nm with an optical efficiency of 70%, limited only by available pump power. The amplifier consists of 4 m of Yb-doped fiber and 20 m of germanium-doped fiber, and seeded with a laser emitting at 1070 and 1120 nm. The power evolution of the 1070 and 1120 nm light inside the amplifier is investigated, both numerically and experimentally. The possibility of power scaling to over kilowatt levels is discussed.

We demonstrated lasing at ~2075 nm in a 42cm long Ho3+-doped fluorotellurite microstructured fiber pumped by a 2008 nm fiber laser. The obtained maximum output was ~1038 mW for a pump power of 3755 mW.