Generation of monoenergetic ultrashort electron pulses from a fs laser plasma

Ultrashort high-energy electron beams are generated by focusing fs Ti:sapphire laser pulses on a thin metal tape at normal incidence. At laser intensities above 10¹⁶ W/cm² , the fs laser plasma ejects copious amounts of electrons in a direction parallel to the target surface. These electrons are directly detected by means of a backside illuminated X-ray CCD, and their energy spectrum is determined with an electrostatic analyzer. The electrons were observed for two laser polarization directions, parallel and perpendicular to the observation direction. At the maximum applied intensity of 2×10¹⁷ W/cm², the energy distribution peaks at around 35 keV with a hot tail detectable up to about 300 keV. The number of electrons per shot at 35 keV is about 5×10⁸ per sterad per keV. Quasi-monoenergetic electron pulses with a relative energy spread of 1% were produced by using a 50-m slit in the beam path after the analyzer. This approach offers great potential for time-resolved studies of plasma, liquid, and surface structures with atomic-scale spatial resolution. PACS 41.75.Fr; 52.38.Kd; 52.70.Nc     

Generation of a single tunable ultrashort light pulse

A novel system for generating single tunable ultrashort light pulses of high power is described. The pulse train from a mode-locked flashlamp pumped dye laser passes through an amplifier, which is pumped by an N₂ laser. As gain is only available for a few nsec, only one pulse in the train gets amplified. The energy of the resulting single pulse is about 100 μJ.     

激光等离子体加速器的兴起与发展

激光等离子体加速器是近几十年来在世界范围内兴起的一种新型粒子加速器,它在科学研究和日常生活中都有着广泛的应用前景。文章分别从激光电子加速与激光离子加速两方面介绍了它的基本原理与实验发展历程。作为一个新生事物,它取得许多振奋人心的结果,同时也面临着一系列挑战。文章最后对激光等离子体加速器的发展和应用进行了归纳和展望。     

Ion beam parameters of a plasma accelerator

The aim of the present investigation was to determine the dependences of the current density, the energy, and the divergence of the ion beams of an UZDP-type source (a plasma accelerator with closed electron drift in the accelerator channel and an extended zone of ion acceleration) on the parameters which determine its performance, and to establish qualitative relationships between these values.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 20–24, February, 1987.     

Electrode erosion in a pulsed plasma accelerator

There are many papers on cathode phenomena in arcs, but there is no agreed view on the processes near and at the cathode in high-current arcs, in spite of the considerable interest in these phenomena in devices for plasma acceleration [4–7]. Results are presented on cathode damage and cathode spots in plasma accelerators of rail type.     

Generation of long plasma channels in air by focusing ultrashort laser pulses with an axicon

We show that by focusing ultrashort-pulsed laser beams in air with an axicon, relatively long plasma channels can be generated. The axicon generates Bessel-like beams, where the on-axis intensity stays high over distances much longer compared to focusing with conventional lenses. We developed a scheme to detect the presence of the plasma, based on its screening property. Using this scheme, we detected plasma channels longer than 1 m and 3.5 m generated by 8 mJ and 90 mJ input pulse energies, respectively. Our simulations show that axicon focusing can yield self-guided propagation with or without contribution of plasma, depending on the input pulse power.     

The polarization of the plasma cluster in a rail plasma accelerator

In a rail plasma accelerator a polarization of the plasma cluster can occur. The electrons outrun the ions and so a polarization field arises. Some part of energy from the condenser battery corresponds to this field. Simple relations for the maximum polarization length and the polarization energy are derived under conditions of constant cross section area of the plasma cluster and negligible internal magnetic field.     

Generation of high-quality electron beams from a laser-based advanced accelerator

At Shanghai Jiao Tong University (SJTU) we have established a research laboratory for advanced acceleration research based on high-power lasers and plasma technologies. In a primary experiment based on the laser wakefield acceleration (LWFA) scheme, multi-hundred MeV electron beams of reasonable quality are generated using 20-40 TW, 30 femtosecond laser pulses interacting independently with helium, neon, nitrogen and argon gas jet targets. The laser-plasma interaction conditions are optimized for stabilizing the electron beam generation from each type of gas. The electron beam pointing angle stability and divergence angle as well as the energy spectra from each gas jet are measured and compared.     

Generation of high-quality electron beams from a laser-based advanced accelerator

At Shanghai Jiao Tong University (SJTU) we have established a research laboratory for advanced acceleration research based on high-power lasers and plasma technologies. In a primary experiment based on the laser wakefield acceleration (LWFA) scheme, multi-hundred MeV electron beams of reasonable quality are generated using 20-40 TW, 30 femtosecond laser pulses interacting independently with helium, neon, nitrogen and argon gas jet targets. The laser-plasma interaction conditions are optimized for stabilizing the electron beam generation from each type of gas. The electron beam pointing angle stability and divergence angle as well as the energy spectra from each gas jet are measured and compared.     

Macroscopic model of plasma accelerator

A simple macroscopic model of plasma accelerator, well describing the process of the plasma cluster acceleration in the accelerator and being directly derived from the physical principles of activity of the accelerator performance, is presented in the present paper.     

Dynamics of a current bridge in a coaxial plasma accelerator

The pioneering investigation of the behavior of a current bridge in a coaxial accelerator with pulsed delivery of a working gas liberated from titanium hydride by an electrical discharge is reported. A new method to trace the motion of the current bridge using LEDs is suggested. The behavior of the current bridge in accelerators with axial and radial gas injection is studied. The parameters of an accelerator generating a pure plasma jet with a high kinetic energy (such as the size and polarity of electrodes, gas flow direction, and time delay between the delivery of the gas to the accelerator and its ionization) are optimized. The applicability of an electrodynamic model to this type of accelerator is discussed. Good agreement between experimental data and calculation results is obtained.     

Reflection and transmission of an ultrashort electromagnetic pulse incident normal to a flat plasma layer

The process of reflection and transmission of ultrashort pulses incident normal to a flat plasma layer of finite thickness and on a step barrier is calculated within an exact mathematical approach for various parameters (barrier width and duration and carrier frequency of a corrected Gaussian pulse) of the problem.     

Generation of phase-locked and tunable continuous-wave radiation in the terahertz regime

Broadly tunable phase-stable single-frequency terahertz radiation is generated with an optical heterodyne photomixer. The photomixer is excited by two near-infrared CW diode lasers that are phase locked to the stabilized optical frequency comb of a femtosecond titanium:sapphire laser. The terahertz radiation emitted by the photomixer is downconverted into RF frequencies with a waveguide harmonic mixer and measurement-limited linewidths at the Hertz level are demonstrated.     

Generation of ultrashort microwave pulses based on cyclotronsuperradiance

We have theoretically and experimentally investigated the superradiance from a bunch of electrons rotating in a homogeneous magnetic field. A RADAN-303B modulator equipped with a subnanosecond pulse slicer has been used to generate high current subnanosecond electron bunches (250 kV, 0.1-1 kA, 0.3-0.5 ns). Transverse momentum was imparted to the electrons by a kicker. It is shown that for the experimental observation of cyclotron superradiance from high current electron bunches the optimum conditions are the conditions of group synchronism, when the translational velocity of the bunch coincides with the group velocity of the radiation propagating in the waveguide. In the 35 GHz range microwave pulses with record short duration, down to 0.4 ns, with a peak power level up to 200 kW, have been obtained     

Measurement of plasma parameters of a quasistationary plasma accelerator from self-absorbed spectral lines

Translated from Zhurnal Priklladnoi Spektroskopii, Vol. 56, No. 3, pp. 451–455, March, 1992.     

Generation of ultrashort pulses in solid media with a large gain coefficient

Lebedev Physics Institute, Academy of Sciences of the USSR. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 32, No. 3, pp. 369–379, March, 1989.     

Generation and propagation of pulse trains with ultrashort pulse separation

We investigate the nonlinear Schrödinger equation with variable coefficients by employing perturbation method. The analysis solution of the harmonic form is presented. The solution is one of forms to describe pulse trains with ultrashort pulse separation, which is about two orders of magnitude shorter than one of sech-type solitons considered before. And we could systematically adjust the perturbation parameter to obtain different pulse separation. As an example, we consider a nonlinear dispersive system with spatial parameter variations, and the results show that, the pulse train with ultrashort pulse separation presented by analysis solution may keep its shape even if the velocity is changed. The stability of the solution is discussed numerically, and the results reveal that the finite initial perturbations, such as white noise could not influence the main character of the solution. In addition, the stability of the solution is also discussed under more general conditions.