脉冲功率的工业应用需要紧凑、灵活、稳定的脉冲功率源。高重频LTD是以此为目的发展的新技术,它所代表的脉冲叠加法与传统的脉冲压缩法存在很大的差异。本文介绍基于半导体开关的高重频LTD的基本方法和典型的实验结果。该LTD系统由30个...脉冲功率的工业应用需要紧凑、灵活、稳定的脉冲功率源。高重频LTD是以此为目的发展的新技术,它所代表的脉冲叠加法与传统的脉冲压缩法存在很大的差异。本文介绍基于半导体开关的高重频LTD的基本方法和典型的实验结果。该LTD系统由30个模块构成,每个模块采用24个MOSFET作为开关。实验结果表明：该LTD系统可以产生最高29 k V的输出电压和240 A的输出电流;脉冲宽度在50~170 ns范围内任意可调;控制模块的开关顺序可以方便地组合出不同的波形。LTD的模块化趋势和它的输出波形可调性是其主要优势,而在能量效率上有待进一步改善。展开更多
Modulated electro-hyperthermia (mEHT) is one of the novel oncological treatments with many preclinical and clinical results showing its advantages. The basis of the method is the synergy of thermal and nonthermal effe...Modulated electro-hyperthermia (mEHT) is one of the novel oncological treatments with many preclinical and clinical results showing its advantages. The basis of the method is the synergy of thermal and nonthermal effects, similar to the thermal action of conventional hyperthermia combined with ionizing radiation (radiotherapy). The electric field and the radiofrequency current produced both the thermal and nonthermal processes. The thermal effects produce the elevated temperature as a thermal background to optimize the nonthermal impacts. The low frequency amplitude modulation ensures accurate targeting and promotes immunogenic cell death to develop the tumor specific memory T cells disrupting the malignant cells by immune surveillance. This process (abscopal effect) works like a vaccination. The low frequency amplitude modulation is combined in the new method with the high power pulses for short time, increasing the tumor distortion ability of the electric field. The new modulation combination has much deeper penetration triplicating the active thickness of the effective treatment. The short pulse absorption increases the safety and decreases the thermal toxicity of the treatment, making the treatment safer. The increased power allows for reduced treatment time with the prescribed dose.展开更多
A new spectrum shaping method, based on electro-optic modulation, to alleviate gain narrowing in chirped pulse amplification （CPA） system, is described and numerically simulated. Near-Fourier transform-limited seed ...A new spectrum shaping method, based on electro-optic modulation, to alleviate gain narrowing in chirped pulse amplification （CPA） system, is described and numerically simulated. Near-Fourier transform-limited seed laser pulse is chirped linearly through optical stretcher. Then the chirped laser pulse is coupled into integrated waveguide electro-optic modulator driven by an aperture-coupled-stripline （ACSL） electricalwaveform generator, and the pulse shape and amplitude are shaped in time domain. Because of the direct relationship between frequency interval and time interval of the linearly chirped pulse, the laser pulse spectrum is shaped correspondingly. Spectrum-shaping examples are modeled numerically to determine the spectral resolution of this technique. The phase error introduced in this method is also discussed.展开更多
Based on the modified ramp and fire technique, a novel injection seeding approach with real-time resonance tracking is successfully demonstrated in a single-frequency Nd：YAG pulsed laser. Appling a high-frequency sin...Based on the modified ramp and fire technique, a novel injection seeding approach with real-time resonance tracking is successfully demonstrated in a single-frequency Nd：YAG pulsed laser. Appling a high-frequency sinusoidal modulation voltage to one piezo actuator and an adjustable DC voltage to another piezo actuator for active feedbackm single-mode laser output with high-frequency stability is obtained, and the effect of the piezo hysteresis on the frequency stability can be eliminated for a laser diode pumped @switched Nd：YAG laser at a repetition rate of 400 Hz.展开更多
Driven by pulse modulated radio-frequency plasma in capacitively coupled discharge are studied by source, the behavior of SiH4/N2/02 using a one-dimensional fluid model. Totally, 48 different species （electrons, ions...Driven by pulse modulated radio-frequency plasma in capacitively coupled discharge are studied by source, the behavior of SiH4/N2/02 using a one-dimensional fluid model. Totally, 48 different species （electrons, ions, neutrals, radicals and excited species） are involved in this simulation. Time evolution of the particle densities and electron temperature with different duty cycles are obtained, as well as the electronegativity nsiH-3 /ne of the main negative ion （Sill3 ）. The results show that, by reducing the duty cycle, higher electron temperature and particle density can be achieved for the same average dissipated power, and the ion energy can also be effectively reduced, which will offer evident improvement in plasma deposition processes compared with the case of continuous wave discharge.展开更多
The behavior of a RF-excited waveguide CO2 laser in the pulse regime is studied theoretically. The output pulse evolution is studied by applying three types of pulses namely the square, sine and the triangular ones as...The behavior of a RF-excited waveguide CO2 laser in the pulse regime is studied theoretically. The output pulse evolution is studied by applying three types of pulses namely the square, sine and the triangular ones as the excitation pulses. The frequency dependence behavior of the output pulse is also presented.展开更多
High-peak-power transform-limited narrow-linewidth nanosecond all-fiber lasers are desired in a range of applications.However,their linewidths will be broadened by self-phase modulation(SPM).We propose a novel concept...High-peak-power transform-limited narrow-linewidth nanosecond all-fiber lasers are desired in a range of applications.However,their linewidths will be broadened by self-phase modulation(SPM).We propose a novel concept that generates transform-limited laser pulses by temporally shaping the pulse seed.The impact of the pulse shape on SPM-induced spectral broadening was studied numerically and experimentally.It was found theoretically that the square-shape pulsed laser is immune to SPM-induced spectral broadening.Based on this principle,we built a high-peak-power,linearly polarized,square-shape nanosecond all-fiber laser in a master oscillator power amplifier(MOPA)configuration.Stimulated Brillouin scattering(SBS)limited peak powers of 4.02 kW,5.06 kW,6.52 kW and 9.30 kW were obtained at pulse widths of 8 ns,7 ns,6 ns and 5 ns.Thanks to the square-shape pulsed seed,the linewidths at maximum peak power remained at 129.5 MHz,137.6 MHz,156.2 MHz and 200.1 MHz,respectively,close to the transform-limited values of110.8 MHz,126.6 MHz,147.7 MHz and 177.3 MHz.展开更多
文摘脉冲功率的工业应用需要紧凑、灵活、稳定的脉冲功率源。高重频LTD是以此为目的发展的新技术,它所代表的脉冲叠加法与传统的脉冲压缩法存在很大的差异。本文介绍基于半导体开关的高重频LTD的基本方法和典型的实验结果。该LTD系统由30个模块构成,每个模块采用24个MOSFET作为开关。实验结果表明：该LTD系统可以产生最高29 k V的输出电压和240 A的输出电流;脉冲宽度在50~170 ns范围内任意可调;控制模块的开关顺序可以方便地组合出不同的波形。LTD的模块化趋势和它的输出波形可调性是其主要优势,而在能量效率上有待进一步改善。
文摘Modulated electro-hyperthermia (mEHT) is one of the novel oncological treatments with many preclinical and clinical results showing its advantages. The basis of the method is the synergy of thermal and nonthermal effects, similar to the thermal action of conventional hyperthermia combined with ionizing radiation (radiotherapy). The electric field and the radiofrequency current produced both the thermal and nonthermal processes. The thermal effects produce the elevated temperature as a thermal background to optimize the nonthermal impacts. The low frequency amplitude modulation ensures accurate targeting and promotes immunogenic cell death to develop the tumor specific memory T cells disrupting the malignant cells by immune surveillance. This process (abscopal effect) works like a vaccination. The low frequency amplitude modulation is combined in the new method with the high power pulses for short time, increasing the tumor distortion ability of the electric field. The new modulation combination has much deeper penetration triplicating the active thickness of the effective treatment. The short pulse absorption increases the safety and decreases the thermal toxicity of the treatment, making the treatment safer. The increased power allows for reduced treatment time with the prescribed dose.
文摘A new spectrum shaping method, based on electro-optic modulation, to alleviate gain narrowing in chirped pulse amplification （CPA） system, is described and numerically simulated. Near-Fourier transform-limited seed laser pulse is chirped linearly through optical stretcher. Then the chirped laser pulse is coupled into integrated waveguide electro-optic modulator driven by an aperture-coupled-stripline （ACSL） electricalwaveform generator, and the pulse shape and amplitude are shaped in time domain. Because of the direct relationship between frequency interval and time interval of the linearly chirped pulse, the laser pulse spectrum is shaped correspondingly. Spectrum-shaping examples are modeled numerically to determine the spectral resolution of this technique. The phase error introduced in this method is also discussed.
文摘Based on the modified ramp and fire technique, a novel injection seeding approach with real-time resonance tracking is successfully demonstrated in a single-frequency Nd：YAG pulsed laser. Appling a high-frequency sinusoidal modulation voltage to one piezo actuator and an adjustable DC voltage to another piezo actuator for active feedbackm single-mode laser output with high-frequency stability is obtained, and the effect of the piezo hysteresis on the frequency stability can be eliminated for a laser diode pumped @switched Nd：YAG laser at a repetition rate of 400 Hz.
基金supported by National Natural Science Foundation of China (No.10775025)Important National Science & Technology Specific Project of China (No.2011ZX02403-001)Program for New Century Excellent Talents in University of China (NCET-08-0073)
文摘Driven by pulse modulated radio-frequency plasma in capacitively coupled discharge are studied by source, the behavior of SiH4/N2/02 using a one-dimensional fluid model. Totally, 48 different species （electrons, ions, neutrals, radicals and excited species） are involved in this simulation. Time evolution of the particle densities and electron temperature with different duty cycles are obtained, as well as the electronegativity nsiH-3 /ne of the main negative ion （Sill3 ）. The results show that, by reducing the duty cycle, higher electron temperature and particle density can be achieved for the same average dissipated power, and the ion energy can also be effectively reduced, which will offer evident improvement in plasma deposition processes compared with the case of continuous wave discharge.
文摘The behavior of a RF-excited waveguide CO2 laser in the pulse regime is studied theoretically. The output pulse evolution is studied by applying three types of pulses namely the square, sine and the triangular ones as the excitation pulses. The frequency dependence behavior of the output pulse is also presented.
基金supported by the National Natural Science Foundation of China(Nos.61705265 and 61705264)the National Key R&D Programme of China(No.2017YFF0104603)the China Postdoctoral Science Foundation(No.2017M620070)
文摘High-peak-power transform-limited narrow-linewidth nanosecond all-fiber lasers are desired in a range of applications.However,their linewidths will be broadened by self-phase modulation(SPM).We propose a novel concept that generates transform-limited laser pulses by temporally shaping the pulse seed.The impact of the pulse shape on SPM-induced spectral broadening was studied numerically and experimentally.It was found theoretically that the square-shape pulsed laser is immune to SPM-induced spectral broadening.Based on this principle,we built a high-peak-power,linearly polarized,square-shape nanosecond all-fiber laser in a master oscillator power amplifier(MOPA)configuration.Stimulated Brillouin scattering(SBS)limited peak powers of 4.02 kW,5.06 kW,6.52 kW and 9.30 kW were obtained at pulse widths of 8 ns,7 ns,6 ns and 5 ns.Thanks to the square-shape pulsed seed,the linewidths at maximum peak power remained at 129.5 MHz,137.6 MHz,156.2 MHz and 200.1 MHz,respectively,close to the transform-limited values of110.8 MHz,126.6 MHz,147.7 MHz and 177.3 MHz.
