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- 实验方案
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Improving the effects of laser hardening of steels by applying a longitudinally torsional ultrasonic field
摘要： The paper is devoted to the expediency of using ultrasonic treatment in combination with laser hardening for U8, U10, X12M steels and the study of the effect of ultrasonic longitudinal and torsional acoustic vibrations on the intensification of an increase in the concentration of point defects in the crystal structure. The introduction of a longitudinal and torsional ultrasonic field by transforming longitudinal ultrasonic vibrations made it possible to form a highly concentrated effect, which led to an increase in the effects of laser hardening.
关键词： ultrasonic treatment,crystal structure,steels,laser hardening,longitudinal and torsional acoustic vibrations
更新于2025-09-16 10:30:52
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Widely 70-nm wavelength tunability single-frequency erbium laser utilizing multiple-ring architecture
摘要： In this paper, to accomplish the broadly wavelength tunability and single-longitudinal-mode (SLM) operation of erbium-doped fiber (EDF) based laser, the multiple-ring structure is designed and executed. The output power of ?7.3 to 5.1 dBm and optical signal to noise ratio (OSNR) of 31.5 to 36.7 dB/0.06 nm are obtained for the proposed EDF laser over the tuning range of 1520.0–1590.0 nm based on the C-band EDF gain medium. In addition, the Lorentzian linewidth of 14.9 to 20.4 kHz is also attained.
关键词： Wavelength-tunability,Erbium-doped fiber,Single-longitudinal-mode (SLM),Fiber laser,Multiple-ring
更新于2025-09-16 10:30:52
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Stable Single-Longitudinal-Mode Fiber Laser With Ultra-Narrow Linewidth Based on Convex-Shaped Fiber Ring and Sagnac Loop
摘要： In this investigation, a convex-shaped ?ber ring (CSFR)-based single-longitudinal-mode (SLM) erbium-doped ?ber laser (EDFL) is proposed and experimentally veri?ed. The CSFR, composed of only two optical couplers and forming a double-ring architecture, is employed to serve as a high quality mode ?lter to eliminate the dense longitudinal modes of the EDFL. The unpumped erbium-doped ?ber in the Sagnac loop is utilized to produce the ultra-narrowband auto-tracking ?lter effect as a saturable absorber to guarantee the SLM out. The experimental results show that the linewidth of the proposed EDFL is 840 Hz with a high optical signal to noise ratio of 63 dB. In addition, the stability of the EDFL with the maximum output power ?uctuation of 0.01 dB and the maximum central wavelength variation of 0.01 nm, in both the short-term and the long-term observations. Hence, we obtained a SLM EDFL with extremely high stability, ultra-narrow linewidth and high optical signal to noise ratio (OSNR).
关键词： saturable absorber,Single longitudinal mode (SLM),erbium-doped ?ber laser (EDFL)
更新于2025-09-16 10:30:52
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Tailoring the longitudinal electric fields of high-order laser beams and their direct verification in three dimensions
摘要： We demonstrate the tailoring of longitudinal electric fields that arise from tight focusing of spatially phase-shaped high-order laser beams, and verify their spatial distribution in three dimensions. To tailor the three-dimensional (3D) spatial distribution of longitudinal electric fields, we precisely control the relative phase delay between the two lobes of a HG10 laser beam using a spatial light modulator (SLM) before tight focusing. To verify the longitudinal electric fields in the focal volume, we employ 3D microscopic mapping of second-harmonic generation (SHG) from a single semiconductor nanowire that is extremely sensitive to the orientation of the longitudinal electric field. The technique is direct, general and expected to be useful in harnessing and in probing longitudinal electric fields with arbitrary spatial intensity distributions in the 3D focal volume.
关键词： Second-harmonic generation,Polarization,Longitudinal electric field,3D microscopy,Semiconductor nanowire
更新于2025-09-12 10:27:22
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Effect of Welding Speed on the Prediction Accuracy of Residual Stress in Laser Welded 1.2?mm Thick Dual Phase Steel
摘要： Post-weld residual stress and distortion are significant issues in laser welding as they reduce fatigue strength and toughness. In the present work, cold rolled dual phase steel sheets of 1.2 mm thickness were laser welded in both bead on plate and butt configurations. The optimum heat input was observed to be approximately 25 kJ/m for visually defect free weld with narrow weld bead and through-thickness penetration. A novel attempt was made to increase the welding speed whilst maintaining the optimum heat input. It was observed that, high welding speed led to high residual stress, resulting in longitudinal cracks, whereas the speed at a limiting value of 0.08 m/s was found to be beneficial longitudinal cracks. Literature suggests researchers have for welding without already proposed different mathematical models on keyhole mode laser welding that can predict the residual stress and deformation. However, most of them failed to predict it repetitively, especially for thin sheets. This work tried to find the range of the rationality of this argument. For low-speed condition, residual stress values was substantially wide, making it difficult to predict actual residual stress with the aid of mathematical models. The range of residual stress values was found to be much lower for the optimum heat input and high-speed condition, resulting into better prediction accuracy. Residual stress values were also validated using kernel average misorientation (KAM) study.
关键词： Heat input,Dual phase steel,Kernel average misorientation,Residual stress,Laser welding,Key-hole mode,Welding speed,Weld longitudinal crack
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Low-Jitter, Narrow-Bandwidth, Single Longitudinal Mode Passively Q-Switched Nd:YAG Ring Laser Oscillator with External Feedback
摘要： Fourier-limited, also called single-frequency or single-longitudinal-mode (SLM) nanoseconds lasers at 1 μm are key elements for several applications, such as optical communications, data storage and high-resolution spectroscopy. Some special application such as high spectral resolution LIDAR [1], require very high spectral purity (tens of MHz bandwidth), resulting in long pulse durations in the range of several tens of ns. Microchip lasers with large free spectral range (FSR) comparable to the active medium gain bandwidth (about 160 GHz for Nd:YAG) allow easy SLM selection, but with much shorter pulses. Recently, we demonstrated a Cr:YAG Passively Q-Switched (PQS) Nd:YVO4 ring laser oscillator delivering 50-ns, 80-μJ SLM pulses at 0.1-10 kHz repetition rate employing a specifically designed intracavity etalon to enhance SLM operation [2]. For SLM PQS operations, Nd:YAG offers some advantages if compared to Nd:YVO4. Namely, the higher saturation fluence relaxes the fulfilment of the second PQS threshold condition, the ~2 times longer fluorescence lifetime enhances energy storage and the narrower gain bandwidth favours SLM operation.
关键词： Nd:YAG,single-longitudinal-mode,passively Q-switched,external feedback,ring laser
更新于2025-09-12 10:27:22
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Learning Hemodynamic Effect of Transcranial Infrared Laser Stimulation Using Longitudinal Data Analysis
摘要： Transcranial infrared laser stimulation (TILS) is a promising noninvasive intervention for neurological diseases. Though some experimental work has been done to understand the mechanism of TILS, the reported statistical analysis of data is quite simple and could not provide a comprehensive picture on the effect of TILS. This study learns the effect of TILS on hemodynamics of the human brain from experimental data using longitudinal data analysis methods. Specifically, repeated measures analysis of variance (ANOVA) is first applied to confirm the significance of the TILS effect and its characteristics. Based on that, two parametric mixed-effect models and non-parametric functional mixed-effect model are proposed to model the population-level performance and individual variation of this effect. Interpretations on the fitted models are provided, and comparison of the three proposed models in terms of fitting and prediction performance is made to select the best model. According to the selected model, TILS increases the concentration of oxygenated hemoglobin in the brain and this effect sustains even after the treatment stops. Also, there is considerable variation among individual responses to TILS.
关键词： photobiomodulation,Brain hemodynamics,longitudinal data analysis,functional mixed-effect model
更新于2025-09-11 14:15:04
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Tunable single-longitudinal-mode fiber laser based on a chirped fiber Bragg grating
摘要： In this paper, a tunable single-longitudinal-mode (SLM) fiber laser based on a chirped fiber Bragg grating (CFBG) is proposed and experimentally demonstrated. Multi-sub-cavities formed by a single CFBG inserted inside the laser loop greatly increase the longitudinal mode spacing so that SLM operation can be obtained. The SLM laser output can be tuned in a wide wavelength range from 1535 to 1565 nm by simply adjusting the central wavelength of a tunable optical band-pass filter (TOBF). A side-mode suppression ratio of larger than 50 dB and a linewidth of less than 8.5 kHz have been respectively achieved.
关键词： Single-longitudinal-mode (SLM),Fiber laser,Chirped fiber Bragg grating (CFBG)
更新于2025-09-11 14:15:04
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Longitudinal wave propagation in one-dimensional waveguides with sinusoidally varying depth
摘要： In this paper, longitudinal elastic wave propagation in one-dimensional waveguides with sinusoidally varying depth is investigated. Furthermore, different types of such waveguide designs are explored to understand their capability to attenuate the group speeds as well as the velocity amplitudes. The plane waveguide con?gurations with sinusoidally varying depth, of three types, namely Convex, Concave and Full, along with their combinations and variants, whose segmental depth along the length of the waveguide is modeled by a sine function having an amplitude parameter ?? and the half-period p, which leads to a governing differential equation with variable coe?cients, are considered in this study. To study the longitudinal wave propagation in these inhomogenous waveguides, a novel superconvergent ?nite element formulation is developed, which gives an exact stiffness matrix. In addition to the wave propagation analysis, static and free vibration behaviors in these waveguides are also studied. The implemented superconvergent ?nite element formulation for these studies is validated with the commercial ?nite element software Abaqus. In the ?rst part of the wave propagation analysis, abilities of the three plane waveguide con?gurations with sinusoidally varying depth to attenuate high amplitude and frequency waves are investigated for different values of ??. Next, four different waveguides composed of Convex-Concave combinations are studied with an aim to get better attenuation. Following this, the waveguides’ segmental parameters, ?? and p, are varied across the segments along the length of the waveguide, using a sine function and polynomial power law to see if such graded variations give better energy absorption properties compared to the plane waveguides whose parameters are unvarying. In the last part, a developed inhomogenous rod of a certain length is inserted in the middle of a uniform waveguide to study the possibility of changing the longitudinal wave propagation characteristics of the uniform waveguide. The results from the analyses show that the group speed and amplitude of the longitudinal wave in these con?gurations change signi?cantly with space as well as with frequencies, especially for high values of ??. The Concave and Full waveguides delay the propagation of longitudinal waves signi?cantly, which translates into the re?ected waves appearing later in the chosen large time window. The Convex waveguide and its variants reduce the wave amplitudes signi?cantly. Building on these results, some waveguides with notable attenuation characteristics are proposed.
关键词： Sinusoidal depth variation,Superconvergent ?nite element,Convex waveguide,Inhomogenous waveguide,Longitudinal wave propagation,Dispersive waves
更新于2025-09-11 14:15:04
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Time-of-flight electron energy loss spectroscopy by longitudinal phase space manipulation with microwave cavities
摘要： The possibility to perform high-resolution time-resolved electron energy loss spectroscopy has the potential to impact a broad range of research fields. Resolving small energy losses with ultrashort electron pulses, however, is an enormous challenge due to the low average brightness of a pulsed beam. In this paper, we propose to use time-of-flight measurements combined with longitudinal phase space manipulation using resonant microwave cavities. This allows for both an accurate detection of energy losses with a high current throughput and efficient monochromation. First, a proof-of-principle experiment is presented, showing that with the incorporation of a compression cavity the flight time resolution can be improved significantly. Then, it is shown through simulations that by adding a cavity-based monochromation technique, a full-width-at-half-maximum energy resolution of 22 meV can be achieved with 3.1 ps pulses at a beam energy of 30 keV with currently available technology. By combining state-of-the-art energy resolutions with a pulsed electron beam, the technique proposed here opens up the way to detecting short-lived excitations within the regime of highly collective physics.
关键词： electron energy loss spectroscopy,longitudinal phase space manipulation,ultrashort electron pulses,time-of-flight,microwave cavities
更新于2025-09-10 09:29:36