Combining Harmonic Generation and Laser Chirping to Achieve High Spectral Density in Compton Sources

TL;DR

This paper demonstrates that combining laser chirping with harmonic generation in Compton sources enhances spectral density, reduces electron beam energy requirements, and increases photon yield, leading to cost-effective and higher-quality high-intensity photon sources.

Contribution

It introduces a detailed analytical model for line broadening due to energy spread and shows how chirping and harmonics together improve Compton source performance.

Findings

Laser chirping enables higher harmonic use, reducing electron beam energy needs.

Chirping increases photon yield beyond fundamental frequencies.

Analytical models predict line smoothing for different laser pulse envelopes.

Abstract

Recently various laser-chirping schemes have been investigated with the goal of reducing or eliminating ponderomotive line broadening in Compton or Thomson scattering occurring at high laser intensities. As a next level of detail in the spectrum calculations, we have calculated the line smoothing and broadening expected due to incident beam energy spread within a one-dimensional plane wave model for the incident laser pulse, both for compensated (chirped) and unchirped cases. The scattered compensated distributions are treatable analytically within three models for the envelope of the incident laser pulses: Gaussian, Lorentzian, or hyperbolic secant. We use the new results to demonstrate that the laser chirping in Compton sources at high laser intensities: (i) enables the use of higher order harmonics, thereby reducing the required electron beam energies; and (ii) increases the photon yield in a small frequency band beyond that possible with the fundamental without chirping. This combination of chirping and higher harmonics can lead to substantial savings in the design, construction and operational costs of the new Compton sources. This is of particular importance to the the widely popular laser-plasma accelerator based Compton sources, as the improvement in their beam quality enters the regime where chirping is most effective.