Coherent instabilities in the booster and collider of the heavy ion accelerator complex NICA

In the first part some knowledge about the coherent instabilities in cyclic accelerators and storage rings necessary for the analysis of the collective effects in the heavy ion collider NICA is given. The second part discusses the possibilities for arising of coherent instabilities in the booster and in the collider of the NICA complex. Both coupling impedances and instability thresholds and growth rates have been estimated for single and coupled bunches. Parameters of the beam feedback system for damping of the instabilities have been analyzed. The investigation has been performed at the Veksler and Baldin Laboratory of High Energy Physics, JINR.     

Application of fiber laser for a Higgs factory

This paper proposes a medium size (～ 6?km) circular Higgs factory based on a photon collider. The recent breakthrough in fiber laser technology by means of a coherent amplifier network makes such a collider feasible and probably also affordable.     

Single laser beam fiber optic trap

Optical forces acting on a sphere were experimentally analyzed to investigate the single-beam fiber optic trap using a cleaved optical fiber or a lensed optical fiber. A stable optical trap could be created at the point where the x-directed (horizontal) optical forces were precisely balanced, and the vector sum of axial and transverse forces acting on a sphere gave a restoring force directed back to the stable point. As compared with other embodiments, such as a single-beam gradient trap (optical tweezers) and dual-beam fiber optical traps, this single-beam fiber optic trapping was most economical, much simpler to operate, and required relatively low optical power to capture an object. Furthermore, a lensed optical fiber could easily trap and manipulate a micro object in comparison with a cleaved optical fiber because of the strong transverse optical confinement.     

Instabilities in compensated electron ring beams

An analysis is performed of the coherent instabilities which can develop in electron ring beams when an ion component is present in the beam. Increments of the instabilities are introduced, and it is shown that the compensation of an electron beam by ions results in a weakening of the instabilities characteristic of purely electron beams. The most rapidly growing coherent instabilities are determined, and possible methods are pointed out for their stabilization.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 37–53, January, 1978.     

Fiber-optic synthesizer of controlled sequences of ultrashort light pulses for single-beam coherent anti-Stokes Raman scattering microspectroscopy

A photonic-crystal fiber operated in the regime of modulation instability is shown to simultaneously enable efficient spectral transformation and pulse shaping of laser fields, synthesizing optimal field waveforms for single-beam coherent anti-Stokes Raman scattering and coherence-controlled excitation of molecular systems.     

Optical damage control via the Fe2+/Fe3+ ratio in proton-exchanged LiNbO3 waveguides

Intensity thresholds for the onset of optical damage in alpha-phase proton-exchanged waveguides on undoped LiNbO(3) have been increased from the substrate value to a factor 500 greater. This has been achieved by increasing the exchange time, which in turn increases the [Fe(2+)]/[Fe(3+)] ratio in the guide. Intensity thresholds have been measured with a single-beam configuration, while [Fe(2+)]/[Fe(3+)] ratios have been determined from decay measurements during optical erasure of photorefractive gratings. In heavily Fe-doped guides, thresholds are too small to be measured, but the dependence of the Fe(2+) absorption on the exchange time appears similar to undoped samples.     

Pulse shaping by modulation instability in a photonic-crystal fiber for coherence control and single-beam coherent anti-Stokes Raman-scattering microspectroscopy

Modulation instability in a highly nonlinear photonic-crystal fiber is shown to allow the generation of optimally pulse-shaped field waveforms that are ideally suited for coherence-controlled nonlinear Raman scattering, including single-beam coherent anti-Stokes Raman-scattering microspectroscopy. This approach enables the integration of the efficient spectral transformation and pulse-shaping operations needed for the realization of nonlinear Raman techniques in a single fiber-format component.     

Long range forces and limits on unparticle interactions

Couplings between standard model particles and unparticles from a nontrivial scale invariant sector can lead to long range forces. If the forces couple to quantities such as baryon or lepton (electron) number, stringent limits result from tests of the gravitational inverse square law. These limits are much stronger than from collider phenomenology and astrophysics.     

Stability of nonlinear Fabry-Perot resonators

The stability of folded Fabry-Perot resonators is investigated for the case where the resonator contains a medium with a dispersive third-order nonlinearity. Positive-branch instabilities of Ikeda type are found, with thresholds comparable to optical bistability thresholds. In the unstable region, the internal field is apparently chaotic, though oscillatory behaviour is found in a special case.     

ON THE AVERAGE LUMINOSITY OF ELECTRON POSITRON COLLIDER AND POSITRON-PRODUING ENERGY

In this paper, the average luminosity of linac injected electron positron collider is investigated from the positron-producing energy point of view. When the energy of the linac injector is fixed to be less than the operating energy of the storage ring, it has been found that there exists a positron-producing energy to give optimum average luminosity. Two cases have been studied, one for an ideal storage ring with no single-beam instability and the other for practical storage ring with fast head-tail instability. The result indicates that there is a positron-producing energy corresponding to the minimum injection time, but this does not correspond to the optimum average luminosity for the practical storage rings. For Beijing Electron Positron Collider (BEPC), the positron-producing energy corresponding to the optimum average luminosity is about one tenth of the total injector energy.     

基于单光束Z-scan技术的非线性测量技术的发展

介绍了由Sheik-Bahae等人提出的、用于测量材料三阶非线性的单光束Z-scan技术。该技术能同时测量材料的非线性折射和非线性吸收,并能给出非线性折射的符号。介绍了以该技术为基础并经改进的几种测量技术:遮挡Z-scan,I-scan和微分Z-scan。引出了近10年来新发展的相位4f相干成像技术,并对其基本原理进行了阐述,分析了其应用特点。该技术具有使用单脉冲进行测量,光路简单,测量灵敏度高,无样品移动等特点。     

White-light parametric instabilities in plasmas

Parametric instabilities driven by partially coherent radiation in plasmas are described by a generalized statistical Wigner-Moyal set of equations, formally equivalent to the full wave equation, coupled to the plasma fluid equations. A generalized dispersion relation for stimulated Raman scattering driven by a partially coherent pump field is derived, revealing a growth rate dependence, with the coherence width sigma of the radiation field, scaling with 1/sigma for backscattering (three-wave process), and with 1/sigma1/2 for direct forward scattering (four-wave process). Our results demonstrate the possibility to control the growth rates of these instabilities by properly using broadband pump radiation fields.     

Highly sensitive single-beam heterodyne coherent anti-Stokes Raman scattering

Single-beam coherent anti-Stokes Raman-scattering (CARS) microspectroscopy achieves a complete CARS scheme with a femtosecond laser. Here, we introduce heterodyne detection in a simple experimental extension: the optical fields driving the CARS process and the local oscillator used for heterodyning are derived from a single beam of ultrashort laser pulses by pulse shaping. The heterodyne signal is amplified by more than 3 orders of magnitude and is linearly dependent on the concentration of Raman scatterers. This dramatically increases the sensitivity of chemically selective detection at microscopic resolution while maintaining the simplicity of the single-beam setup.     

Stable massive particles at colliders

We review the theoretical motivations and experimental status of searches for stable massive particles (SMPs) which could be sufficiently long-lived as to be directly detected at collider experiments. The discovery of such particles would address a number of important questions in modern physics including the origin and composition of dark matter in the universe and the unification of the fundamental forces. This review describes the techniques used in SMP-searches at collider experiments and the limits so far obtained on the production of SMPs which possess various colour, electric and magnetic charge quantum numbers. We also describe theoretical scenarios which predict SMPs along with the phenomenology needed to model their production at colliders and interactions with matter. In addition, the interplay between collider searches and open questions in cosmology such as dark matter composition is addressed.     

Modified temperature-anisotropy instability thresholds in the solar wind

The proton and electron temperature anisotropies in the solar wind are constrained by the instability thresholds for temperature-anisotropy-driven kinetic plasma instabilities. The modifications to the marginal instability conditions from accounting for the influence of damping connected with the collisional effects in the solar wind plasma are calculated for right- and left-handed polarized parallel propagating Alfvén waves and mirror and firehose fluctuations. These modifications provide tighter threshold constraints compared to the marginal thresholds but do not fully explain the observations at small values of the parallel plasma beta.     

Instabilities Propagated Along the External Magnetic Field in Magnetized Active Plasmas

The conditions for spontaneous onset of instabilities propagated along the external (stationary or quasi-stationary) magnetic field in cold and magnetized active plasmas are considered in collisionless approximation. Attention is given to non-resonant cases, i.e. to situations in which the modal frequencies of the wave significantly differ from the frequency of coherent electromagnetic radiation arising due to the active particles. It is shown that instabilities are also possible in these non-resonant cases and that, under certain specified conditions, they develop only in a very narrow wavelength band. The pertaining amplitude increments are evaluated.     

Experimental demonstration of colliding-beam-lifetime improvement by electron lenses

We report the successful application of space-charge forces of a low-energy electron beam for improvement of particle lifetime determined by beam-beam interaction at a high-energy collider. In our experiments, an electron lens, a novel instrument developed for the beam-beam compensation, was set on a 980-GeV proton bunch at the Fermilab Tevatron proton-antiproton collider. The proton-bunch losses due to its interaction with the antiproton beam were reduced by a factor of 2 when the electron lens was operating. We describe the principle of electron lens operation and present experimental results.     

Actively shaped supercontinuum from a photonic crystal fiber for nonlinear coherent microspectroscopy

The combination of broadband pulses from a photonic crystal fiber (PCF) pumped by a standard 100 fs oscillator and pulse shaping is successfully employed for coherently controlled nonlinear spectroscopy. The pulse shaper manages not only to compress the PCF supercontinuum in a closed-loop optimization scheme but also to manipulate the phase at the same time for quantum control applications. This approach is demonstrated by single-beam coherent anti-Stokes Raman microspectroscopy and should be, due to its simplicity, well suited for general applications in nonlinear microscopy.     

Maximum overlap,atomic coherent states and the generator coordinate method

A version of the maximum overlap approach is presented, based on the generator coordinate method. Recourse is made to techniques developed with reference to atomic coherent states. Shape instabilities in quasi-spin two-level models are studied.