Particle acceleration in subcycle optical cells

Abstract

A single laser pulse with spot size smaller than half its wavelength (w 0 < λ=2) can provide a net energy gain to ultrarelativistic particles. In this paper, we discuss the properties of an optical cell consisting of N subcycle pulses that propagate in the direction perpendicular to the electron motion. We show that the energy gain produced by the cell is proportional to N and it is sizable even for Oð1 TWÞ pulses. DOI: 10.1103/PhysRevSTAB.17.071301 PACS numbers: 41.75.Jv Modern conventional accelerators transfer only a small amount of energy to particles per unit cell. Large energy gradients are achieved combining the cells in periodic structures and phase locking the particle motion to the rf cavities. On the other hand, phase slippage is difficult to be avoided in laser-based accelerators and acceleration is achieved by a few beam-pulse interactions but, in this case, the energy transfer per pulse can be very large due to the huge electric fields available in lasers. Unlike rf-based accelerators, the interaction time τ of the particle with the laser is much longer that the period T of the laser fields. Such a long interaction time causes several drawbacks. Plasma-based accelerators [1] tend to be prone to instabilities when τ ≫ T. This difficulty has been overcome by the development of high-power sub-ps lasers and resulted into large energy gains and beams of unprecedented quality [2]. Similarly, laser accelerators in vacuum [3,4] require special geometrical configurations of the laser pulse to bypass the limitations imposed by the Lawson-Woodward theorem [5] and reach a finite energy gain even if τ ≫ T [6]. These challenges have not been overcome yet, and vacuum-based techniques are much less developed than laser-plasma accelerators. As discussed in this paper, however, the impressive progresses in subcycle laser technology achieved in the past decade could boost vacuum acceleration in a way similar to what sub-ps lasers have done in the past for plasma-based accelerators.Attosecond optics allows for the focusing of pulses to spot sizes significantly smaller than λ [7], and for creation [8,9], manipulation and regeneration of isolated subcycle pulses [10]. In addition, accelerators based on subcycle pulses can be operated in the τ < T regime: particles that are injected nearly perpendicularly with respect to the pulse propagation axis (see Fig. 1) will experience only a fraction of the oscillating electric field and, if properly phased, they will acquire a net energy gain when they cross the focus of the pulse. A set of N subcycle pulses can be employed to transfer a fixed amount of energy to the particles through N beam-pulse interactions. If the overall energy gain is constant and the beam is stable in phase space, then the N-pulse optical lattice acts as a single accelerating unit (optical cell) with a well defined transfer function. Particles crossing an optical cell will experience an energy gain that, in general, will depend on the initial position of the particle; moreover, the particles will be d...

Relativistic Classical and Quantum Nonlinear Phenomena in the Induced Processes on Free Electrons

“…On the other hand, the spectrum of direct acceleration mechanisms of charged particles by a single laser pulse is very restricted, since one should use the laser beams focused to subwavelength waist radii, or use subcycle laser pulses, or use radially polarized lasers, violating the plane character of a coherent laser pulse for particles acceleration by a single wave-pulse in vacuum without the third body. All these scenarios with different field configurations have been investigated both theoretically and experimentally in the works [38,[69][70][71][72][73][74][75][76][77][78][79][80][81][82][83][84][85]. Note that beside the focusing of a laser pulse to subwavelength waist radii we can get nonplane laser beam by terminating the field, either by reflection, absorption, or diffraction [86].…”

The dynamics of compact laser pulses

“…Lower intensity pulses have also been used as diagnostic tools for exploring the structure of plasmas in various states [3,4]. In order to interpret experimental data involving classical laser interactions with both charged and neutral matter, theoretical models [5][6][7][8] rely crucially on parameterizations of the electromagnetic fields in laser pulses, particularly in situations where traditional formulations using monochromatic or paraxial-beam approximations have limitations [9][10][11]. Such theoretical models may not be compact in all spatial dimensions and the role of a laser pulse as a classical probe is further limited by the scales that it is designed to resolve.…”

Production of high energy-solid density electron bunches and hardγ-quanta and positron fluxes by ultrarelativistic lasers in solid-plasma targets

“…The spectrum of direct acceleration mechanisms of charged particles by a single laser pulse is very restricted, since one should use the laser beams focused to subwavelength waist radii, or use subcycle laser pulses, or use radially polarized lasers. All these scenarios with different field configurations have been investigated both theoretically and experimentally [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28]. The Lawson-Woodward theorem can also be bypassed by terminating the field, either by reflection, absorption, or diffraction [29].…”