Monolithic high-average-power linearly polarized nanosecond pulsed fiber laser with near-diffraction-limited beam quality

An all-fiberized high-average-power narrow linewidth ns pulsed laser with linear polarization is demonstrated. The laser system utilizes a typical master oscillator power amplifier (MOPA) configuration. The stimulated Brillouin scattering (SBS) is effectively suppressed due to the short fiber length and large mode area in the main amplifier, combined with the narrow pulse duration smaller than the phonon lifetime of SBS effect. A maximal output power of 466 W is obtained with a narrow linewidth of ${\sim}$203.6 MHz, and the corresponding slope efficiency is ${\sim}$80.3%. The pulse duration is condensed to be ${\sim}$4 ns after the amplification, corresponding to the peak power of 8.8 kW and the pulse energy of $46.6~\unicode[STIX]{x03BC}\text{J}$. Near-diffraction-limited beam quality with an $M^{2}$ factor of 1.32 is obtained at the output power of 442 W and the mode instability (MI) is observed at the maximal output power. To the best of our knowledge, this is the highest average output power of the all-fiberized narrow linewidth ns pulsed fiber laser with linear polarization and high beam quality, which is a promising source for the nonlinear frequency conversion, laser lidar, and so on.

High power all-fiberized and narrow-bandwidth MOPA system by tandem pumping strategy for thermally induced mode instability suppression

An all-fiberized and narrow-bandwidth master oscillator power amplification (MOPA) system with record output power of 4 kW level and slope efficiency of 78% is demonstrated. Tandem pumping strategy is tentatively introduced into the narrow-bandwidth MOPA system for thermally induced mode instability (TMI) suppression. The stimulated Brillouin scattering (SBS) effect is balanced by simply using one-stage phase modulation technique. With different phase modulation signals, SBS limited output powers of 336 W, 1.2 kW and 3.94 kW are respectively achieved with spectral bandwidths accounting for 90% power of ${\sim}$0.025, 0.17 and ${\sim}$0.89 nm. Compared with our previous 976 nm pumping system, TMI threshold is overall boosted to be ${>}$5 times in which tandem pumping increases the TMI threshold of ${>}$3 times. The beam quality ($M^{2}$ factor) of the output laser is well within 1.5 below the TMI threshold while it is ultimately saturated to be 1.86 with the influence of TMI at maximal output power. Except for SBS and TMI, stimulated Raman scattering (SRS) effect will be another challenge for further power scaling. In such a high power MOPA system, multi-detrimental effects (SBS, SRS and TMI) will coexist and may be mutual-coupled, which could provide a well platform for further comprehensively investigating and optimizing the high power, narrow-bandwidth fiber amplifiers.

Investigation of Flyback Transformer Flux Leakage Reduction Ways

Results of experimental investigation and design optimization of flyback transformer are presented. Aim of the work is to investigate experimentally the impact of the flyback transformer design on the flux leakage and maximal output power. It is difficult to evaluate the effect of the leakage flux mathematically because it depends on various factors: the position of the windings relative to each other; the position of the windings in the transformer; the distance between the winding. A multi-winding flyback transformer was used for experiments. Using the results of the experiments optimal design of the investigated flyback transformer was defined.

Numerical investigation of an impact of a top gold metallization on output power of a p-up III-N-based blue-violet edge-emitting laser diode

The effect of modifications in epi-side (top) gold metallization on a thermal performance and on power roll-over of blue-vio- let III-N-based p-up edge-emitting ridge-waveguide laser diode (RW EEL) was explored in this paper. The calculations were carried out using a two-dimensional self-consistent electrical-thermal model combined with a simplified optical model tuned to a RW EEL fabricated in the Institute of High Pressure Physics (Unipress). Our results suggest that with proper modifica- tions in the III-N-based RW EEL, excluding modifications in its inner structure, it is possible to considerably improve the thermal performance and, thus, increase the maximal output power.

An Integrated Numerical Model for a PEM Fuel Cell System

PEM Fuel Cell (PEMFC) system plays an important role in a future hydrogen economy. Numerical modeling is useful to evaluate and optimize PEM fuel cell system. Therefore, this paper developed an integrated numerical model for predicting the power output of PEMFC system and optimizing system operation parameters to achieve the maximal output power. The developed numerical model integrated the models of fuel cell stack itself and its auxiliary systems, which were quantitatively described and analyzed with calculation equations. Furthermore, the newly developed numerical model was applied to a PEMFC powered scooter to estimate the output power a PEMFC system and optimize the operation conditions parameters of its auxiliary systems based on optimization algorithm. This validates that the developed integrated numerical model is useful and reliable for predicting the net output power and achieving maximal net output power through optimizing the operating parameters of a PEMFC system.

Design and implementation of a measurement system for automatically measurement of electrical parameters of thermoelectric generators

ABSTRACTThe continues development of thermoelectric generators causes a permanent improvement of their characteristics. New types of thermoelectric generators can work at temperatures up to 1000 K. With this, special measurement equipment is needed to control the electrical parameters of the new developed specimens. The devices must be tested over the whole range of operating temperatures. For each temperature value a series of electrical measurements has to be performed. To establish the maximal output power of the thermoelectric generators, a load resistor with variable resistance has to be connected to the output of thermoelectric generator. The measurement system should measure the electrical current through the load resistor and the voltage over this resistor to determine the device parameters. A large amount of measurement data have to be collected and processed to evaluate the electrical characteristics of the specimen and to present them in graphical form, suitable for the comparison with others specimens.

EFFICIENT ULTRAVIOLET LIGHT FREQUENCY DOWN-SHIFTING BY A THIN FILM OF ZnO NANOPARTICLES

The maximal efficiency of a single junction solar cell (SC) is defined as the Shockley–Queisser limit, which determines the maximal output power which can be furnished by a SC as a function of the bandgap of the semiconductor constituting the cell. The short wavelength spectral response of a SC can be improved if a luminescent down-converting layer is added to the SC structure. We propose the use of a layer containing ZnO nanoparticles (NPs) as a luminescent down-shifter. ZnO is able to absorb efficiently the ultraviolet light (λ < 400 nm), where the SC spectral response is low and to re-emit lower energy photons (longer wavelength photons) for which the SC spectral response is enhanced, thus increasing the total photocurrent. The stoichiometry and crystallinity of ZnO NPs can be controlled and adjusted to obtain the highest visible photoluminescent emission, indicator of an efficient down-shifting. The ratio between the ZnO UV absorption and visible emission is also estimated and from these results we expect the increase of the SC efficiency using ZnO NPs as a down-shifting layer placed on the front side of the SC.

CONTROL OVER THE PERFORMANCE OF MONOCRYSTALLINE SILICON SOLAR CELLS REFERRING TO THE POROUS SILICON LAYER / MONOKRISTALINIO SILICIO SAULĖS ELEMENTŲ CHARAKTERISTIKŲ VALDYMAS AKYTOJO SILICIO SLUOKSNIU

The paper examines the parameters of crystalline silicon solar cells such as fill factor, maximal output power and series resistance forming a porous silicon layer. The obtained results show that introducing the layer into the structure of a solar cell results in a 19 percent enhancement of maximal output power and conversion efficiency. Santrauka Šiame darbe tiriamas akytojo silicio darinių poveikis saulės elementų elektrinėms charakteristikoms: nuosekliajai varžai, voltamperinių charakteristikų formai. Parodyta, kad pagaminus silicio saulės elemente akytojo silicio sluoksnį, galima veikti (valdyti) saulės elementų voltamperines charakteristikas ir elemento nuosekliąją elektrinę varžą. Nustatyta, kad tiriamajame bandinyje suformavus akytojo silicio sluoksnį, apkrovos voltamperinės charakteristikos užpildos rodiklis padidėjo 1,15 karto, o maksimali elemento kuriama ir apkrovos metu atiduodama elektros energijos galia – 1,19 karto. Tiek pat 1,19 karto padidėjo saulės elemento šviesos konversijos į elektros energiją efektyvumas.