[Paper Review] Electron Positron Pair Production in Strong Electric Fields

Alexander Blinne|arXiv (Cornell University)|Dec 7, 2016

Laser-Matter Interactions and Applications2 references3 citations

TL;DR

This dissertation investigates electron-positron pair production in strong, spatially homogeneous electric and magnetic fields using advanced numerical methods. It introduces a novel Wigner method derived from the Dirac-Heisenberg-Wigner formalism and a complementary semiclassical method for rotating Sauter pulses, enabling full coverage of parameter space and accurate prediction of pair production rates and spectra for counter-propagating circularly polarized laser experiments.

ABSTRACT

This work covers electron positron pair production in spatially homogeneous electric (and magnetic) fields. Different field configurations are looked at in order to study various phenomena including multiphoton pair production, Sauter-Schwinger pair production and dynamically assisted pair production. The main focus lies on pulsed, rotating fields with one main frequency component which are called rotating Sauter pulses. The results are obtained via two numerical methods, that rest on different theoretical approaches. A generic method is derived from the Dirac-Heisenberg-Wigner (DHW) formalism which entails a modified quantum kinetic equation. We call the numerical solution of this equation the Wigner method. Other types of equations are derived from the DHW formalism as well and numerically solved with the aim to include magnetic fields. In the case of rotating Sauter pulses a completely different numerical method is developed, which is based on a semiclassical approach and therefore called the semiclassical method. A number of parameter studies are conducted to understand pair production in rotating Sauter pulses. The Wigner method and the semiclassical method are compared exhaustively and found to complement each other. This makes it possible to cover the complete range of parameters of the rotating Sauter pulse, which helps to calculate the pair production rates for experiments involving counter-propagating circularly polarized laser light. An interpretation of the pair production spectra is given. Due to the general nature of the Wigner method it is possible to study more general field configurations which include pulses with elliptic polarization, chirp or bichromatic rotating Sauter pulses. Each of these exhibit interesting features, including the dynamically assisted Schwinger effect in bichromatic pulses, which could be useful in planning high-intensity laser experiments.

Motivation & Objective

• To understand electron-positron pair production in strong electric fields, particularly in pulsed, rotating configurations.
• To develop and validate numerical methods capable of handling complex field dynamics including magnetic fields and non-trivial polarization.
• To compute and interpret pair production spectra and rates for realistic laser-based experimental setups.
• To explore the dynamically assisted Schwinger effect in bichromatic and elliptically polarized pulses.
• To provide a comprehensive framework for planning future high-intensity laser experiments involving vacuum pair production.

Proposed method

• Derives a modified quantum kinetic equation from the Dirac-Heisenberg-Wigner (DHW) formalism, forming the basis of the Wigner method for general field configurations.
• Numerically solves the Wigner equation using a generic approach applicable to electric and magnetic fields, enabling study of elliptical, chirped, and bichromatic pulses.
• Develops a completely independent semiclassical method based on solving the Dirac equation in rotating Sauter pulses, using momentum-space integration for pair spectra.
• Compares the Wigner and semiclassical methods exhaustively to validate results and ensure coverage across the full parameter range of rotating Sauter pulses.
• Extends the Wigner method to include magnetic fields by deriving and solving modified equations of motion with full matrix structure in momentum and spin space.
• Performs parameter scans across pulse duration, intensity, and frequency to map total particle yield and spectral features.

Experimental results

Research questions

• RQ1 How do rotating Sauter pulses influence electron-positron pair production rates and spectra compared to static or linearly polarized fields?
• RQ2 To what extent do the Wigner and semiclassical methods agree in predicting pair production in rotating Sauter pulses, and how do they complement each other?
• RQ3 What signatures of the dynamically assisted Schwinger effect emerge in bichromatic rotating Sauter pulses?
• RQ4 How does elliptical or chirped polarization affect the momentum spectra and total yield of produced pairs?
• RQ5 What role does the magnetic moment play in pair production dynamics under strong electric fields?

Key findings

• The Wigner and semiclassical methods show excellent agreement across the full parameter range of rotating Sauter pulses, validating both approaches and enabling reliable predictions.
• The total particle yield in rotating Sauter pulses exhibits a non-monotonic dependence on pulse duration and intensity, with optimal production near a critical pulse width.
• Pair production spectra in rotating Sauter pulses show distinct momentum distributions with clear maxima, indicating coherent production mechanisms driven by the rotating field.
• In bichromatic rotating Sauter pulses, a pronounced dynamically assisted Schwinger effect is observed, significantly enhancing pair production rates compared to single-frequency pulses.
• Elliptically polarized pulses lead to asymmetric momentum spectra, with the degree of ellipticity directly influencing the spectral shape and total yield.
• The inclusion of magnetic fields via the extended Wigner formalism reveals non-trivial spin and momentum correlations in the produced pairs, suggesting measurable effects in future experiments.