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Accepted: 2021-05-12, 資料番号: PA2210018000

The near field of the probe beam after passing through the gain module is measured. The “streamer effect” is first discovered in the experiment, which is characterized as continuity in the flow direction and non-uniformity in the lateral direction with high spatial frequency. To explain the “streamer effect”, a fluid–solid coupling model and an unstable resonator oscillation model of the direct-liquid-cooled thin-disk laser are established. The simulation results show that the non-uniformity of the coolant along the width of the flow channel gives rise to the streamer effect. A feasible cooling channel to achieve a high uniformity coolant is proposed and experimentally verified. At CW pumping of 9.6 kW, the influence of coolant on the output beam quality can be controlled at β

This paper investigates the rotor cavity positioning and the combination of stator slot and rotor effective slot number on the eddy-current loss for interior permanent-magnet/reluctance machines operating under deep field-weakening conditions. A new closed-form expression for the stator and rotor eddy-current loss is developed. The optimal barrier-positioning for the minimum total loss and the effect on the eddy-current loss of varying the stator slot and rotor effective slot number are investigated for one-, two-, three-, and full-layered rotors.

A direct-liquid-cooled Nd:YLF thin disk laser resonator is presented, which features the use of refractive index matching liquid (RIML) as coolant. Highly uniform pump intensity distribution with rectangular shape is realized by using metallic planar waveguides. Much attention has been paid on the design of the gain module, including how to achieve excellent cooling ability with multi-channel coolers and how to choose the doping levels of the crystals for realizing well-distributed pump absorption. The flow velocity of the coolant is found to be a key parameter for laser performance and optimized to keep it in laminar flow status for dissipating unwanted heat load. A single channel device is used to measure the convective heat transfer coefficient (CHTC) at different flow velocities. Accordingly, the thermal stress in the disk is analyzed numerically and the maximum permissible thermal load is estimated. Experimentally, with ten pieces of a-cut Nd:YLF thin disks of different doping levels, a linear polarized laser with an average output power of 1120 W is achieved at the pump power of 5202 W, corresponding to an optical-optical efficiency of 21.5%, and a slope efficiency of 30.8%. Furthermore, the wavefront aberration of the gain module is measured to be quite weak, with a peak to valley (PV) value of 4.0 μm when it is pumped at 5202 W, which enables the feasibility of its application in an unstable resonator. To the best of our knowledge, this is the first demonstration of kilowatt-level direct-‘refractive index matching liquid’-cooled Nd:YLF thin disk laser resonator.

A large aperture tapered fused silica fiber phase conjugate mirror with a maximum 50.7% stimulated Brillouin scattering (SBS) reflectivity is presented, which is operated with 400 Hz pulse repetition rate and 36.5 mJ input pulse energy. To the best of our knowledge, it is the first time that over 50% SBS reflectivity is achieved by using solid-state phase conjugate mirror under such high pulse repetition rate and high pulse energy. With much higher pulse repetition rate of 500 and 1000 Hz, the maximum SBS reflectivity is 41.2% and 33.3%, respectively. A single-longitudinal-mode Nd:YAG laser is experimentally studied with master oscillator power amplifier (MOPA) scheme using such a tapered fiber as a phase conjugate mirror. A 101 mJ pulse energy is achieved at 400 Hz repetition rate, with a pulse width of 6 ns and a M 2 factor of less than 2. The corresponding peak power reaches 16.8 MW.

A continuous-wave-operation laser amplifier chain consisting of three multi-concentration-doped Yb:YAG slab gain modules (GMs) at room temperature is presented. The output power of 22.3 kW with the beam quality of 3.3 times the diffraction limit is achieved from this chain. To the best of our knowledge, based on a Yb:YAG slab at room temperature, the highest power to date while maintaining excellent beam quality laser output. An extraction efficiency of 36% from the single slab GM is obtained and can be further enhanced to 46% by optimizing the parameters of GM. These results have confirmed that the Yb:YAG slab has an excellent scaling performance and is suitable for the development of high-average-power lasers.

We demonstrate a master oscillator power amplifier (MOPA) architecture based on Yb:YAG amplifiers and adaptive optics (AO) systems with a high power and high beam quality laser output. With two conduction cooled, dual-end-pumped Yb:YAG zigzag-slab amplifiers at room temperature, the fiber laser of 300 W was scaled to 11.9 kW. Moreover, AO system positioned downstream was utilized to correct wavefront of amplified laser. The beam quality β at maximum output power was 2.8 times diffraction limited with closed-loop AO system.

In this paper, based on the self-reproduction condition of laser wavefront curvature, the influences of disk defocus on laser parameters can be calculated. The laser-pumping overlapping efficiency will decrease by 9%; the magnification will rise to 2.3, and the intra-cavity loss will be high to 30% due to a laser beam size mismatch when each disk has focal length of -100 m in a positive-branch confocal unstable resonator containing four disks with magnification of 1.8. Therefore, the optical conversion efficiency and stability will be reduced significantly. Several methods defocus compensation of are compared, it can be found that inserting variable-focus lens in resonant is useful in large dynamic range. In experiment, the defocus values are measured in different pumping power. A lens group, used for compensate components according to the single pass probe, is carefully designed. Under this compensation, the pulse energy can be maintained in 10 J from 1 Hz to 100 Hz. The output power can be improved 2.33 times compared to non-compensation condition.

This paper describes an analytical approach for calculating the stator iron loss for multiple-barrier interior permanent magnet (IPM) machines with distributed windings, under open and short-circuit (deep field-weakening) conditions. It is based on using a lumped equivalent-circuit model to predict the rotor mmf and then the harmonic components of the airgap flux density. A “filter function” approach is used to calculate the stator tooth and yoke flux densities and hence iron loss components. It provides an insightful means for visualizing the effect of stator and rotor design changes on the stator iron losses. The analytical stator iron loss predictions for four IPM machine configurations are compared with finite element results.

This paper examines the modelling of a 1.6 kW, 3,000 rpm surface permanent magnet machine which was constructed using soft magnetic composites (SMC) stator tooth segments and a bonded rare-earth magnet ring. It was designed for high torque density and efficiency, and low cogging torque. Both 2D and 3D finite-element model results are provided and compared to the experimental measurements of the flux densities, back-EMF, cogging torque, inductance and power losses. Challenges were found in modelling the magnetization of the bonded-ring magnet. The rated efficiency and field-weakening performance are examined by using both measured and finite-element calculated parameters.

A high power multi-pass diode-pumped solid-state MOPA system with large core diameter tapered quartz fiber as phase conjugator is experimentally investigated. The results of the effects of laser longitudinal mode characteristic, laser pulse width and fiber surface optical quality on SBS reflectivity are presented. Maximum SBS reflectivity of 69.7% is obtained with the repetition rate of 1000 Hz, input pulse energy of 38mJ and pulse width of 24 ns. The phase conjugator is made from a taper shaped quartz fiber with the diameter of 1mm at the input end and 0.4mm at the other end. It has good application prospects in improving the beam quality and compressing the pulse width for high power laser system with high repetition rate.

A model for describing laser-induced damage in optical materials by nanosecond laser pulses is investigated. The laser-damage critical fluence is obtained based on calculating the light absorption of nanoabsorbers by using Mie theory and solving the heat equation. Considering a power law distribution of nano-absorbers, we calculated the damage probability at the surface of fused silica including Pt particles. The theoretical results calculated with appropriate parameters are applied to fit the experimental data in order to identify the properties of nanodefects.

The purpose of locomotive load test is to examine and adjust the capability of locomotive often in its non-driving state, and it is a kind of important standard and means to estimate the quality of repairing locomotive in railway locomotive depot. There are two ways of load test at present. One is the water-resistor load test, the other is the dry resistor load test. Because the dry resistor-load test means does not pollute the environment and needs area less, its developing foreground is immense. To solve the difficulty that the current cannot be freely regulated continuously, for the first time, the model of weightier resistor network in digital circuit is applied to the locomotive dry resistor-load test system, which solves the problem of dry resistor-load test theoretically. It is proved by theory and test that the precision of dry resistor means can meet the request of locomotives constant power load test and reach the standard of water-resistor, so it can serve the application of the dry resistor-load test system. During the locomotive load test, the load of locomotive may be regulated so that the locomotive can be adapted run on all kinds of actual work state. According to the characteristic of weightier resistor, the control arithmetic, which is made up of fuzzy algorithm and binary algorithm, realizes the fast and exact regulation on locomotive load. This paperintroduces how to apply fuzzy and binary algorithm to regulate the dry resistor-load and explains the realization of the fuzzy and binary algorithm.

A phase conjugating mirror combining a fused silica rod and an optical fiber is presented. This configuration combines a large diameter fused silica rod with a high laser damage threshold and an optical fiber with a low stimulated Brillouin scattering (SBS) threshold. The composed SBS generator-amplifier construction, similar to the two-cell type makes a forced SBS process, in which the Stokes beam reflected by the fiber is injected into the fused silica rod. Using this combined phase conjugating mirror in a laser-diode-pumped laser master oscillator power amplifier system, we obtained 42% SBS reflectivity at most at 100 Hz repetition rate. At the same time, the inverse beam quality parameter M(2) is reduced from 3 to 1.6, while at 400 Hz repetition rate, M(2) is reduced from 4 to 1.7.

For the non-uniform pumping and cooling to the thin disk-type laser medium, the district cooling method for thin disk-type laser medium is proposed and examined both experimentally and theoretically. Based on heat conduction equation, the distributions of temperature and stress in end pumping thin disk-type laser medium with evenly cooling and district cooling are calculated. The results show that the tensile stresses on the edge of gain medium with evenly cooling are changed into the low values of compressive stresses for the case of district cooling, and the distribution of temperature in medium with district cooling is much more uniform than with evenly cooling, the ranges of temperature reduces about 86%, and this result is consistent well with the experimental result. The district cooling method could provide a new way of thermal management for thin disk-type laser.

A large aperture fused silica tapered fiber phase conjugate mirror is presented with a maximum 70% stimulated Brillouin scattering (SBS) reflectivity, which is obtained with 1 kHz repetition rate, 15 ns pulse width and 38 mJ input pulse energy. To the best of our knowledge, this is the highest SBS reflectivity ever reported by using optical fiber as a phase conjugate mirror for such high pulse repetition rate (1 kHz) and several tens of millijoule (mJ) input pulse energy. The influences of fiber end surface quality and pump pulse widths on SBS reflectivity are investigated experimentally. The results show that finer fiber end surface quality and longer input pulse widths are preferred for obtaining higher SBS reflectivity with higher input pulse energy. Double passing amplification experiments are also performed. 52 mJ pulse energy is achieved at 1 kHz repetition rate, with a reflected SBS pulse width of 1.5 ns and a M(2) factor of 2.3. The corresponding peak power reaches 34.6 MW. Obvious beam quality improvement is observed.

A temperature model for a end-pumped thin disk laser with Gaussian beam intensity distribution and single pass absorption performance is built up according to the actual working state. Using infrared thermal image, temperature distribution, temperature variation with time and the temperature difference of the surface laser medium are measured at different pump powers. Experiment on thermal lens focal length of the thin disk laser medium is performed by utilizing Hartmann-Shack wave-front sensor. Considering the fact that thermal lens focal length of the laser medium changes with pump power, the model for analyzing the influence of thermal effect on output power of thin disk laser is presented, according to rate equations. The simulation results obtained in this paper show satisfactory agreement with experimental results. The research has the guiding significance for designing and optimizing thin disk lasers

Perovskite-type BiMnO3, in which ferroelectricity and ferromagnetism co-exist,has potential applications in sensor and information storage. Usually, BiMnO3 is synthesized under high temperature and high pressure in a gold capsule,which restricts its application and development extremely. In this paper, we synthesize the BiMnO3 nanopowders with MnCl2·4H2O,Bi2O3, NaOH,HNO3 and polyglycol at 100 ℃ by the co-precipitation method successfully, in which the conditions of temperature and pressure are reduced, thereby economizing the energy sources and lowering the cost. Their microstructure and magnetic properties are measured by using X-ray diffraction (XRD), transmission electron microscope(TEM) and vibration sample magnetometer(VSM). The effects of synthetical condition and the calcined temperature are also discussed.

A novel combined phase conjugator consisting of a fused silica rod and silica fiber is used in the high repetition laser system to improve the light quality. It has the advantages of higher stimulated Brillouin scattering reflectivity, higher stimulated Brillouin scattering damage threshold and lower stimulated Brillouin scattering threshold. In experiment, under the repetition rate of 100 Hz, maximum 42.05% stimulated Brillouin scattering reflectivity is obtained. According to the coupling wave equations and the boundary conditions of the experiment, the numerical value calculated from this model is in accordance with the experiment result. And the way to improve the working state of this combined phase conjugator is brought forward by our modeling.

The stacking fault in crystals of GaN was studied by high-resolution electron microscope images in combination with image deconvolution. The principle of deconvolution for high-resolution electron microscope images is briefly introduced. It is demonstrated that an image originally does not intuitively reflect the examined crystal structure can be transformed into the structure image. The stacking faults in crystals of GaN were observed with the high-resolution microscope. The image deconvolution was performed for the image, and the atomic configuration in the defect core is seen clearly in the deconvoluted image. Based on this, the type of stacking fault has been determined. Besides, the effectiveness of image deconvolution in studying crystal defects is discussed.