Estimates of electron-positron pair production in the interaction of high-power laser radiation with high-Z targets

Abstract

Electron-positron pairs' generation occuring in the interaction of 10 18 -10 20 W/cm 2 laer radiation with high-Z targets are examined. Computational results are presented for the pair production and the positron yield from the target with allowance for the contribution of pair production processes due to electrons and bremsstrahlung photons. Monte-Carlo simulations using the prizma code confirm the estimates obtained. The possible positron yield from high-Z targets irradiated by picosecond lasers of power 10 2 -10 3 TW is estimated to be 10 9 -10 11 .The possibility of electron-positron pair production by relativistic electrons accelerated by a laser field has been discussed since many years [1].It was estimated that the positron production efficiency can be high [2]. The papers cited considered the case of pair production during oscillations of electrons in an electromagnetic wave in the focal region of laser radiation. Here we examine a somewhat different pair production scenario.The interaction of high-power laser radiation with matter results in the production of fast, high-temperature electrons [3]. Relativistic temperatures of fast electrons T f ≈ 1 MeV have been observed in experiments with powerful picosecond lasers [4]. Self-consistent electric fields confine these electrons in the target. When the electrons interact with the matter in a high-Z target, electron-positron pairs are produced [5]. The annihilation photon spectrum can be used for diagnostics of the electron-positron plasma.In the present letter we make estimates of the positron and photon yield as function of the laser power. We have made an assessment of the possibility of using high-power (10 2 -10 3 TW) ultrashort-pulse lasers to produce a highluminosity positron source. Such sources are required for the production of slow (1-10 eV) positrons with an intensity of 10 8 positrons per second. Such positrons find wide applications for the study of Fermi surfaces, defects and surfaces of various materials [6].The interaction of relativistic electrons with matter can lead to electron-positron pair production in the following two processes:In Ref.[7] analytical and numerical calculations of the total cross section of the pair electroproduction process are performed using the differential cross section of Ref. [8]. According to this work the total cross section of the process (i) near the threshold equalswhere r e is the classical electron's radius; α = 1/137; mc 2 is the electron mass, and E 0 is the kinetic energy of the initial electron. At high energies the cross section grows as [9]The approximation formula describes both limits. Fig. 1 shows the points obtained by numerically integrating the exact formulas for the differential section [7], the asymptotic cross sections (2) and (1), and a plot of the approximating function (3).

Copious positron production by femto-second laser via absorption enhancement in a microstructured surface target

“…A tantalum (Ta) plate with thickness of 2 mm, which is placed behind the MST in our scheme, is used as the converter. Because the high-Z converter is thick, the dominant positron generation mechanism is BH process 39 . The electron energy spectrum shown in Fig.…”

Nature of atomic-nuclear processes in intense short laser-matter interaction

“…The process-induced vortical electric field interacts with an electron and does the work precisely equal to the binding energy. the fulfillment of condition (14). It retains during the process of magnetic field transformation from scales l ra /C to atomic scales.…”

“…L1 = L12 a2L2 (14) Thus, the fine structure constant defines the transformation ratio. In this case pe becomes comparable to ionization frequency in order of magnitude.…”

Femtosecond Beam Generation

“…The estimated pair growth rate was of the order of O.l(NA,)/ns at a laser intensity of the order of lo1' W/cm2, where N A~ is the gold atomic density. targets such as Au thin plates with thickness 0.1-1 mm when irradiated with a laser with a power of 102-103 TW [Gryaznykh et al (1998)l. In their estimation, the Bethe-Heilter process is dominant because a thicker target was used.…”