射频爆磁压缩发生器小型化共形天线

射频爆磁压缩发生器作为一次性电磁脉冲产生和辐射的小型化装置,其辐射天线的结构和性能是其在实用化层面亟待突破的瓶颈。针对这一问题,深入研究了射频爆磁压缩发生器产生和辐射电磁脉冲的机理,并在此基础上,提出了一种适于实际需求的射频爆磁压缩发生器小型化共形天线。此共形天线设计成爆磁压缩发生器本体的一部分,在结构方面保证了该装置的小型化和实用性。CST仿真和实物测试结果表明,此共形天线在0.5 GHz到10.3 GHz的频带上具有良好的辐射特性,在辐射性能方面同样可以满足射频爆磁压缩发生器实用性的需求。     

Pulse compression of difference frequency radiation by liquid crystal phase transparent

The results of theoretical research and numerical simulation of the difference frequency radiation (DFR) pulse generation in 5–25 μm wavelength range in the field of the pumping femtosecond laser pulse are presented. The pulse has the following characteristics: the central wavelength is 2 μm, duration is 34 fs and electric field amplitude is 70.71 MV/m. The pulse propagates in the ZnTe/air periodic structure with the number of periods along the normal to the (110) plane of the ZnTe crystal equal to 13; and the efficiency of the DFR generation is 1.11 × 10^–4. It is shown that the use of the liquid crystal phase transparent, placed in the focal plane of the frequencyspatial shaping system, allows one to realize the DFR pulse compression at which the maximum intensity is increased by a factor of six.     

Pulse compression in dispersion-decreasing-like fibers

Pulse compression characteristics in dispersion-decreasing-like fibers (DDLF) are firstly investigated by employing the second-harmonic generation frequency-resolved optical gating (SHG-FROG) technique, are compared with the numerical results that are obtained using the split-step Fourier method. It is found that the experimental data are consistent with the numerical results. The results show that the pulse compression method is effective. The pulse can be effectively compressed and its spectrum can be broadened in the DDLF. That the pulse compression effect is enhanced with the increase of the input power is in correspondence with the spectrum broadening.     

Pulse compression without chirp control and frequency detuning by high-order coherent Raman scattering in impulsively excited media

It is shown that phase-locked pulses as short as 3 fs can be generated by coherent scattering in impulsively excited Raman media without the necessity of external phase control. The underlying mechanism, temporal characteristics, spectra, phase relations, physical limitations owing to competition processes, and precompensation of dispersion by the hollow waveguide window are studied analytically and numerically without the use of the slowly varying envelope approximation and with a global approach to dispersion. Additionally, the large frequency shifts in both the Stokes and anti-Stokes directions of as much as half the carrier frequency raise the possibility of generating widely tunable ultrashort pulses.     

Pulse compression techniques in ultrasonic non-destructive testing

The development of a pulse compression system applicable to ultrasonic flaw detection is described. The use of pulse compression technique permits a pulse-echo detection system to operate with long transmitted pulses for increased sensitivity, but without sacrificing resolution. The described system is economically implemented using an aluminium strip dispersive delay line. The operating system achieves a time-bandwidth product of 84 and sidelobe levels of —25 dB. Experimental evidence of the system's capabilities is presented.     

Pulse compression in a longitudinally inhomogeneous fiber

A single-mode fiber with a linear or sinusoidal variation in the group-velocity dispersion is fabricated. The nonreciprocal effects and pulse compression due to the longitudinal oscillations of the fiber dispersion are experimentally demonstrated. The periodic modulation of the dispersion can be used to control the pulse dynamics.     

Pulse compression of a high-order harmonic

The fifth harmonic pulses of an intense femtosecond Ti:sapphire laser were experimentally shown to be negatively chirped by using an LiF plate as a positive dispersive medium. The chirp of the harmonic pulse originates from the intensity-dependent atomic dipole phase, which is estimated to be proportional to 25 U_p, where U_p is the ponderomotive energy. Consequently, we have succeeded in compressing the chirped pulses to 13 fs by compensating the intrinsic negative chirp. Chirp effects of the fundamental laser on the pulse width of the fifth harmonic were consistent with the negative chirp of the fifth harmonic.     

Micro-bunch production with radio frequency photoinjectors

In this paper we discuss the generation of ultra-short electron bunches using laser-driven RF guns. The designs are tailored for future plasma accelerators. Second generation plasma accelerators are expected to be very demanding in terms of bunch length, since the accelerated beam is expected to be short with respect to the wavelength of the excited Langmuir space-charge plasma wave. Since the anticipated wavelength ranges from 100 to 300 μm, 10-50 μm-long bunches are required with a bunch population of the order of 10⁸ particles. The laser-driven RF gun is a promising candidate to attain such beams. The rationale for this choice as well as the main limitations in terms of minimum bunch length will be analyzed and discussed in the following. Two possible configurations are evaluated: the direct production at the photocathode surface of ultra-short electron bunches by illumination of the cathode with 160-fs-long laser pulses and the acceleration of a 1-ps electron bunch with further magnetic compression in a wiggler     

超高强度激光脉冲压缩用衍射光栅

衍射光栅是超高强度激光脉冲压缩器的核心元件之一,其高衍射效率、高损伤阈值和大尺寸的苛刻要求是普通商业光栅所远远不能满足的.文章对高强度激光超短脉冲压缩用衍射光栅的基本要求、主要类型、研究现状进行了综述.     

Pulse compression by use of deformable mirrors

An electrostatically deformable, gold-coated, silicon nitride membrane mirror was used as a phase modulator to compress pulses from 92 to 15 fs. Both an iterative genetic algorithm and single-step dispersion compensation based on frequency-resolved optical gating calibration of the mirror were used to compress pulses to within 10% of the transform limit. Frequency-resolved optical gating was used to characterize the pulses and to test the range of the deformable-mirror-based compressor.     

Verification of surface WGM in radio frequency band

The ideas of generating surface whispering gallery mode (SWGM) through coating a microresonator with a layer of metamaterials is proposed in our previous work. In this paper, we verify the SWGM with a square resonator based on two-dimensional LC network in radio frequency band. The equivalent node voltage distribution matrix of this resonator is derived. Results show that node voltage can be amplified when the square resonator is covered with a layer of double negative metamaterials. The performance of the metamaterial resonator as a dielectric sensor with excellent sensitivity has been demonstrated. This work may put a great step toward the realization of SWGM sensors using metamaterials.     

Pulse compression during second-harmonic generation in aperiodic quasi-phase-matching gratings

We propose a simple means for compressing optical pulses with second-harmonic generation. Aperiodic quasi-phase-matching gratings impart a frequency-dependent phase shift on the second-harmonic pulse relative to the fundamental pulse and can be engineered to correct for arbitrary phase distortions. The mechanism is discussed, and a detailed analysis of the compression of quadratic phase (linear frequency) chirped pulses is presented.     

Pulse compression at 1.06 microm in dispersion-decreasing holey fibers

We report compression of low-power femtosecond pulses at 1.06 microm in a dispersion-decreasing holey fiber. Near-adiabatic compression of 130 fs pulses down to 60 fs has been observed. Measured spectra and pulse shapes agree well with numerical simulations. Compression factors of ten are possible in optimized fibers.     

Efficiency of sequential resonance compression of radio pulses

A study is made of the efficiency of forming high-power wide-band and ultrawide-band radio pulses by a sequence of resonance compression steps. An analysis is made of the compression of radio pulses with a rectangular envelope in a chain consisting of two or three compressors, and also in a chain where the output signal from the first stage has an exponential trailing edge and the other stages have rectangular envelopes. The maximum energy storage efficiency is determined for a cavity excited by a signal with an exponential trailing edge. Zh. Tekh. Fiz. 69, 131–133 (April 1999)     

Gamma-electron dynamics and radio frequency capacitive sheathdiagnostics

Time-resolved measurements of gamma-electrons energy spectra in low-pressure capacitively coupled RF discharge are presented. Time dependence of the sheath voltage is calculated from experimental results and compared with theoretical predictions. Good quantitative agreement is observed for collisional sheath. In low pressure discharge sheath voltage time dependence is close to [1+cos(ωτ)], which qualitatively corresponds to the theoretical results. Asymmetry of electron energy spectra for increasing and decreasing sheath voltage is observed and explained by divergence and convergence of electron trajectories in plasma (klystron-effect)     

石墨烯射频器件研究进展

石墨烯因具有优良的电学特性,在半导体行业中受到广泛关注,特别因其具有超薄的结构和极高的载流子迁移率,为解决短沟道效应提供了可能,并且在高速电子领域具有应用前景.近年来,使用石墨烯作为沟道材料制备射频晶体管及射频电路是发挥石墨烯材料优势的一个重要研究方向.制造高性能的射频器件,首先要制备出高性能的石墨烯材料.在金属衬底上沉积均匀的单层石墨烯材料或者在绝缘衬底上外延生长单层、双层石墨烯材料都是获得高质量石墨烯材料的常用方法.器件结构及工艺流程的设计也是提升晶体管射频性能的重要因素,多指栅结构、T型栅结构、埋栅结构以及自对准工艺的发展能够有效改善石墨烯射频晶体管的截止频率及最大振荡频率.石墨烯晶体管独特的电学特性使得其除了可以构造与其他半导体材料电路相似的射频电路结构,还可以构造出功能完整并且结构更加简单的新型射频电路结构.     

An improved radio frequency heavy ion source

Abstract

An improved r.f. heavy ion source, which can operate with gases, liquids and solids is described. The operating temperature of the ion source may reach 1000°C. It can therefore, generate ion beams of a considerable number of elements. including metallic ions. At present, ion beams of S⁺, Al⁺, As⁺. Zn⁺, Mg⁺, Cd⁺, Ag⁺, Sm⁺, Te⁺, Se⁺, Sn⁺, In⁺, Hg⁺, etc. have been extracted. The extracted total beam current ranges from several hundred microamperes to the order of milliampere. The useful fraction of ion in the total beam is 70–90%. Life span of the source ranges from 40 hours to more than 100 hours. The emittance of the source is 3 × 10^?6 cm rad. Structure and operating characteristics of this ion source are discussed.     

Sheath motion in a capacitively coupled radio frequency discharge

The sheath motion in a capacitively coupled RF discharge is highly nonlinear. The voltage waveform on a cylindrical probe placed in the sheath region is measured as a function of position and time. A circuit model of the probe-discharge system relates the observed probe voltage to the sheath motion. The equations derived from this circuit model are solved numerically with varying nonlinear sheath motions; the resulting waveforms are compared with the experimental observations to determine the actual sheath motion. The time-varying plasma potential is also determined, indirectly, from the comparison. The authors also report observation of oscillations related to the plasma frequency, whose peak harmonic component can be calculated from a single plasma model. These oscillations can be a useful plasma diagnostic for determining plasma density. The presence of these high-frequency oscillations may significantly enhance the rate of stochastic heating of electrons