Quasi-phase-matched self-pumped optical parametric oscillation in a micro-resonator.

At Olkaria II power plant located in Kenya, the brine from the separator is re-injected back into the ground. This study analyzes a flash geothermal-solar hybrid cycle using the working fluids n-butane, n-pentane, cyclopentane, hexamethyldisiloxane and toluene in order to utilize the brine. The studied working fluids have no potential to deplete the ozone or cause global warming. The working fluids were analyzed in terms of net power output and pump power required. This was done by heating Therminol VP-1 fluid to a maximum temperature of 400 °C using the parabolic trough solar collector and varying the working fluids mass flow rate, Therminol VP-1 flow rate and pressure, and the brine pressure and flow rate. They were varied to investigate their effect on the power output of the Organic Rankine Cycle. The working fluid with higher net power output was selected as a suitable working fluid for the hybrid cycle. The selected working fluid was used to determine the average hourly power output in each month of the hybrid system using the irradiance of Olkaria II power station. N-butane showed the best results in net power output hence it was selected as a suitable working fluid as compared to the other working fluids. When the hybrid system was analyzed using n-butane to obtain the hourly average power output in each month, the results revealed that the month of February has the highest hourly average power output where the Steam Turbine has an average hourly power output of 10.48 MW and Binary Turbine net power output of 18.56 MW. The minimum average hourly power output was obtained in the month of June where the Steam Turbine has an average hourly power output of 9.08 MW and Binary Turbine net power output of 16.88 MW.

Researchers at the University of Queensland, Australia, have developed and refined an optical feedback technique for measuring surface roughness. We spoke to one of the authors, Jeremy Herbert, to find out more. Optical feedback interferometry is a non-contact sensing technique that uses a laser as not only a coherent light source, but also as a receiver of information. The beam from the laser is reflected off a target where it is modulated by some property of the material. This light is then reinjected back into the laser cavity where it mixes with the standing wave and disturbs the normal operation of the laser. By monitoring this disturbance through either the output power or the terminal voltage of the laser, information about the target can be determined. Schematic of the roughness measurement experiment showing the direction of translation as parallel to the lasing axis The primary advantage of optical feedback is that a sensor can detect changes in optical path length on the order of nanometres, and/or minute changes in target reflectivity using compact and low cost components; in some configurations, a laser diode is the only optical component. This allows extremely sensitive measurement of quantities such as displacement, velocity and refractive index of transparent media. Another more recent application is the imaging of targets using exotic wavelengths (such as terahertz radiation) for which simple detectors are not widely available. The sensitivity of instrumentation based on optical feedback is a double-edged sword. While this type of sensor can measure minute changes in the properties of the target, it is also very sensitive to changes in environmental parameters such as temperature and vibration. A common approach to minimise the effects of these unwanted influences on the output signal is to perform repeated measurements and average them. Unfortunately in some circumstances, such as the one outlined in the article, it is not possible to perform repeated measurements, and so an alternative strategy is required. Roughness target locations where a focused translating beam would experience higher (green) and lower reflectivity (red). The black arrow shows the direction of scanning. In the article, a method of determining information about the roughness of a surface using optical feedback was described and demonstrated. The method does not rely on repeated measurement, but instead uses the windowed standard deviation of the optical feedback signal to track the effective reflectivity of the surface as it moves. A method to compute the windowed standard deviation in a real-time manner was presented in an earlier article also published in Electronics Letters (Herbert, J, Wilson, S, Rakic, A and Taimre, T, ‘FPGA implementation of a high-speed, real-time, windowed standard deviation filter’, Electronics Letters, 2016, 52, (1), pp. 22–23). This work is significant because it demonstrates a viable method for the use of optical feedback signals to measure surface roughness without necessitating repeated measurements of the target. It provides evidence for the idea that an online surface roughness sensor could be developed, with the small size and low cost advantages of laser feedback, for use in the manufacturing process of objects with specific roughness tolerances. More broadly, this approach could be applicable to other scenarios in which repeating a measurement is impossible, such as in determining information about a particle randomly passing through the beam. Possible applications of this work in the short term could be in the area of tribology, the measurement of mechanical wear, and in manufacturing processes that require tight control of surface roughness. Longer-term applications are also possible in areas where the measurement quantity of interest can be modelled as the problem of surface roughness, such as in the measurement of particle size. Since this work was completed, further efforts have been directed toward applying the methods in the article to other scenarios in which repeated measurements are not possible. Examples of these situations include the characterisation of uniquely shaped particles passing through the beam, and in the online control of manufacturing processes such as polishing. Optical feedback sensors are unusual in that they are able to measure nanometre-sized changes in optical path length, and yet can be constructed using a small number of compact and relatively inexpensive components. As manufacturers compete to have the most effective quality control and manufacturing processes, sensing techniques such as the one outlined in this article become more and more relevant. Over the coming years, further work in this area could result in low cost sensors that could improve the yield of manufacturing processes through the increased availability of information about process parameters.

High-brightness tapered lasers and amplifiers at 670 nm with output powers up to 1 W and nearly diffraction limited beam quality were realised. The devices consist of a 750 &mgr;m long straight section and a 1250 &mgr;m long tapered section. Devices with a taper angle of 2°, 3° and 4° were manufactured. The material quality was studied in a long-term test for ridge-waveguide lasers. Devices with 7.5 &mgr;m ridge width show reliable operation at 100 mW output power over more than 10000 h. At a temperature of 15°C a tapered lasers with an angle of 4° reached an output power of 1 W at a current of 2.1 A. The highest conversion efficiency for this device was 24%, the peak wavelength of the emission was 668 nm and the spectral width was smaller than 0.2 nm. The beam propagation factor was M² = 1.7 (1/e²) and M² = 3.0 (second moments). At 500 mW output power, master-oscillator power-amplifier (MOPA) devices showed also a nearly diffraction limited beam quality with M² < 1.5 and reliable operation with degradation rates as low as 7x10^-6 h^-1 over 1200 h. The spectral line-width in this arrangement is determined by the master oscillator and is suitable for high-resolution spectroscopy.

Summary form only given. A 95 GHz gyrotron capable of generating CW power levels in excess of 2 MW is currently under development at CPI. The gyrotron makes use of a single-anode electron gun that produces a 90-kV, 75-A electron beam for interaction with the TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">22</sub> , <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> , <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> cavity mode. Microwave power produced in the interaction cavity is transformed into a fundamental Gaussian beam using an internal waveguide launcher and three focusing and phase-correcting mirrors. The Gaussian beam exits the tube through an edge-cooled chemical-vapor-deposition (CVD) diamond window. The spent electron beam is dissipated in a 40.6-cm diameter collector fabricated from a strengthened copper alloy. The collector nominally operates at a depressed voltage 61 kV above the cathode potential to minimize the amount of power absorbed and improve efficiency.In the first series of experiments, a maximum output power level of 1.45 MW was obtained using a 61 kV cathode voltage, 90 kV total accelerating voltage, and 75 A beam current. Interaction and total output efficiencies were 21% and 32%, respectively. At a beam current of 40 A and the same voltage settings, an output power of 1.08 MW was measured for an interaction efficiency of 30% and a total output efficiency of 44%. Experimental evidence indicated that an oscillation in the beam tunnel region just prior to the interaction cavity was a likely cause of the lower than expected efficiency and output power at higher beam currents. In an attempt to alleviate the detrimental effects of the oscillation, a new beam tunnel was installed on the gyrotron. No other major changes to the gyrotron were made. In a second series of tests, a maximum, output power of 1.72 MW was obtained with a cathode voltage of 70 kV, an accelerating voltage of 93 kV and a beam current of 75 A. The interaction efficiency at this point was 25% and the total output efficiency was 33%. At 45 Abeam current, an accelerating voltage of 90 kV, and a collector voltage of 61 kV, an output power of 1.40 MW was obtained with an interaction efficiency of 35% and a total output efficiency of 51%. It appears that the presence of beam tunnel power still degrades the interaction efficiency at higher values of beam current, but there has been a marked improvement between the first and second series of tests, where the maximum achievable power has increased from 1.45 MW to 1.72. The operation at 1.4 MW output power with over 50% efficiency is also an important achievement.

A midinfrared vertical external cavity surface emitting laser with 4.5 μm emission wavelength and operating above room temperature has been realized. The active part consists of a single 850 nm thick epitaxial PbSe gain layer. It is followed by a 2 1/2 pair Pb1−yEuyTe/BaF2 Bragg mirror. No microstructural processing is needed. Excitation is done optically with a 1.5 μm wavelength laser. The device operates up to 45 °C with 100 ns pulses and delivers 6 mW output power at 27 °C heat-sink temperature.

High-efficiency and high-power operation have been demonstrated for blue GaN-based vertical-cavity surface-emitting lasers (VCSELs) with AlInN/GaN distributed Bragg reflectors. The high-efficiency performance was achieved by introducing a novel SiO2-buried lateral index guide and adjusting the front mirror reflectivity. Lateral optical confinement has been shown to greatly lower the otherwise significant loss of transverse radiation exhibited by typical VCSELs based on GaN. Employing a long (10λ) cavity can also enhance the output power, by lowering the thermal resistance of the VCSEL and increasing the operating current associated with thermal rollover. This modification, in conjunction with optimized front mirror reflectivity and a buried SiO2 lateral index guide, results in a blue VCSEL (in the continuous wave mode with an 8 μm aperture at 20 °C) having a superior differential quantum efficiency value of 31% and an enhanced 15.7 mW output power. This unit also exhibits a relatively high output power of 2.7 mW at temperatures as high as 110 °C. Finally, a 5.5 μm aperture VCSEL was found to generate a narrow divergence (5.1°) single-lobe far field pattern when operating at an output power of approximately 5 mW.

Laser operation near 1.06 μm by diode-pumped Nd:(Lu x Gd 1-x ) 3 Ga 5 O 12 (Nd:LGGG, with x = 0.1) and Gd 3 Al x Ga 5-x O 12 (GAGG, with x = 1) disordered crystals has been investigated. Cw oscillation with a slope efficiency as high as 61 % and 230 mW output power was achieved with 400 mW absorbed power from a 1-W laser diode in Nd:LGGG. Under the same pumping conditions cw oscillation with a slope efficiency as high as 55% and 255 mW output power was achieved with 500 mW absorbed power in Nd:GAGG. Stable passive mode-locking with single- or multi-wavelength spectrum was obtained with a semiconductor saturable absorber mirror (SAM) and a single-prism, dispersion-compensated cavity with both the samples. Fourier-limited pulses with duration = 4 - 9 ps and output power ≈ 40 mW were generated at three well-defined laser transitions in the range 1062-1067 nm with ND:GLGG. Two-color mode-locking regime well described by Fourier-limited synchronized pulses with duration = 3.7 and 5.9 ps and output power ≈ 65 mW, with wavelength separation of 1.3 nm around 1062 nm was obtained with Nd:GAGG.

Organic materials are becoming widely used in optical fields due to their many advantageous properties such as flexibility, ruggedness, and low cost. In particular, application of organic polymer to an optical amplifier and/or a laser oscillator has attracted much attention recently. In these circumstances, we have demonstrated a novel solid-state dye-laser by using organic thin film made of Rhodamine B (Rh-B)-doped UV-cured polymer as gain medium, in which distributed feedback operation has been achieved by inducing a periodic gain structure onto the gain medium. However, the characteristics of the lasing output of such a laser oscillator have still not been examined. In this paper we shall thus present a numerical analysis of lasing output of the solid-state dye laser with a photo-induced periodic-gain. Since in the photo-induced DFB operation an interference fringe of lightwave is used for pumping a periodic-gain stucture onto the gain medium, the output power strongly depends on the shape of the interference pattern. Using several parameters obtained in the experiments, dependences of output power on the visibility and average power of the pumping interference pattern are numerically calculated. In addition, the effects of gain saturation against the pump energy are also discussed from the viewpoint of practical applications.

Experimental operation of a high power microwave source with a metamaterial (MTM) structure is reported at power levels to 2.9 MW at 2.4 GHz in full 1 μs pulses. The MTM structure is formed by a waveguide that is below cutoff for TM modes. The waveguide is loaded by two axial copper plates machined with complementary split ring resonators, allowing two backward wave modes to propagate in the S-Band. A pulsed electron beam of up to 490 kV, 84 A travels down the center of the waveguide, midway between the plates. The electron beam is generated by a Pierce gun and is focused by a lens into a solenoidal magnetic field. The MTM plates are mechanically identical but are placed in the waveguide with reverse symmetry. Theory indicates that both Cherenkov and Cherenkov-cyclotron beam-wave interactions can occur. High power microwave generation was studied by varying the operating parameters over a wide range, including the electron beam voltage, the lens magnetic field, and the solenoidal field. Frequency tuning with a magnetic field and beam voltage was studied to discriminate between operation in the Cherenkov mode and the Cherenkov-cyclotron mode. Both modes were observed, but pulses above 1 MW of output power were only seen in the Cherenkov-cyclotron mode. A pair of steering coils was installed prior to the interaction space to initiate the cyclotron motion of the electron beam and thus encourage the Cherenkov-cyclotron high power mode. This successfully increased the output power from 2.5 MW to 2.9 MW (450 kV, 74 A, 9% efficiency).

The Recirculating Planar Crossed-Field Amplifier (RPCFA) has demonstrated amplification in excess of 10 dB of a ~30 kW RF signal, with 15% bandwidth. The RPCFA is the amplifying adaptation of the Recirculating Planar Magnetron (RPM) also developed at the University of Michigan. Ansys HFSS and the particle-in-cell code MAGIC were used to design a prototype. The prototype RPCFA was constructed and demonstrated transmission characteristics similar to those predicted by simulation. Sustained amplification for pulses 100's of nanoseconds in length have been observed with peak amplification as high as 16dB and greater than 1 MW of output power. The RPCFA is shown to be unsaturated at the 10's of kW RF drive at which it has been tested, suggesting higher input drive power may lead to even greater output power. The range of amplifiable frequencies implied by the transmission band is verified experimentally. The lower limit for RF drive power that can be amplified is found to be approximately 100 W. Sources of irreproducibility of microwave gain are being investigated. Injection of higher drive power up to 1 MW is planned.

In this study, we fabricated a flexible 3D mesh structure with periodic voids by using a 3D lithography method and applying it to a vibration energy harvester to lower resonance frequency and increase output power. The fabrication process is mainly divided into two parts: three-dimensional photolithography for processing a 3D mesh structure, and a bonding process of piezoelectric films and the mesh structure. With the fabricated flexible mesh structure, we achieved the reduction of resonance frequency and improvement of output power, simultaneously. From the results of the vibration tests, the meshed-core-type vibration energy harvester (VEH) exhibited 42.6% higher output voltage than the solid-core-type VEH. In addition, the meshed-core-type VEH yielded 18.7 Hz of resonance frequency, 15.8% lower than the solid-core-type VEH, and 24.6 μW of output power, 68.5% higher than the solid-core-type VEH. The advantage of the proposed method is that a complex and flexible structure with voids in three dimensions can be relatively easily fabricated in a short time by the inclined exposure method. As it is possible to lower the resonance frequency of the VEH by the mesh structure, use in low-frequency applications, such as wearable devices and house appliances, can be expected in the future.

The choice of mechanical and electrical topologies can affect piezoelectric energy harvesting efficiency, but the problem of achieving high‐efficiency energy conversion in energy harvesters stacked as cantilevers has not been perfectly solved. This study focuses on the topology of piezoelectric elements in a stacked vehicle suspension vibration energy harvesting device. Through theoretical analysis, the stress expressions of the excited and driven elements are derived. The stress of the piezoelectric elements is affected by the positions of the connection and excitation points. A stress model was established for a four‐piece piezoelectric element connected by a thin light rod in ANASYS. The simulation results show that the average stress in the piezoelectric bending element model is maximum when the excitation and connection points are located at both ends of the free end. Compared with the middle position of the free end of the piezoelectric element, the average stress of the model is increased by 92.904%. Considering the difference in voltage generated by piezoelectric elements, four kinds of electrical topology are designed and analyzed experimentally. When the driven elements are connected in parallel and then connected in series with the excited element, the output power varied the least with the change of load resistance. The system produces a high power and offers a wide selection of load resistors. When the load is 26 kΩ, a single set of four piezoelectric elements produces 86.407 mW of output power.

The Varian EIMAC X2242 utilizes pyrolytic graphite screen and control grids and a high-density mesh cathode in a new multimegawatt tetrode. It is capable of delivery 3 MW of output power. The first tests of the device performed in a modified, well-instrumented, JAERI (Japan Atomic Energy Research Institute) Tokamak-60 (JT-60) ICRH (ion cyclotron range of frequencies) amplifier, are described. The tests were run at 110 and 131 MHz at pulse widths to 10 s. Output power to 1.5 MW at 110 MHz and 1.6 MW at 131 MHz was observed. The amplifier was stable with significant reverse screen grid current. Internal examination of the tube after its return showed it to be undamaged, illustrating the high-temperature capabilities of pyrolytic graphite. Means of increasing tube power output at these frequencies are being developed. >

The paper ports on the study of photoluminescence and nonlinear optical processes from a nanoobject in the shape of a single nanohole and nanoslit. It has been shown that a strong surface plasmon resonance in the nanoopenings allows to realize: (1) an extremely broad photoluminescence band with a considerable quantum yield and (2) an effective generation of harmonics radiation. The combination of these two physical effects and using a microcavity based on a photonic crystal opens up the possibility of constructing of a nano spatially and femto temporally broadband and wavelength tunable light source.

CVBs (cylindrical vector beams) are widely used in optical imaging, optical trapping, material processing, etc. In this study, based on mode-selective couplers and passive mode-locking fiber technology, a cylindrical vector fiber amplifier with an MOPA (master oscillator power amplifier) structure was developed. In the experiment, the pre-amp stage reached 19.87 mW output power and a CVB output with a mode purity greater than 97%. The measured beam quality factor was M2 = 2.1. The CVB output power obtained by the first-amp stage was 152.4 mW, and the mode purity was greater than 92%. The measured beam quality factor was M2 = 1.99. The internal inhomogeneity and external effects of the isotropic LMA (large-mode-area) fiber led to a decrease in beam quality and mode purity. After amplification, the gain of the fundamental mode was higher and the power was greater, resulting in a greatly reduced mode purity. This CVB fiber amplifier yielded important research value in expanding the applications of high-power fiber lasers.