Nonlinear Compton scattering is a promising source of bright gamma rays. Using readily available intense laser pulses to scatter off the energetic electrons, on the one hand, allows us to significantly increase the total photon yield, but on the other hand, leads to a dramatic spectral broadening of the fundamental emission line as well as its harmonics due to the laser pulse shape induced ponderomotive effects. In this Letter we propose to avoid ponderomotive broadening in harmonics by using the polarization gating technique—a well-known method to construct a laser pulse with temporally varying polarization. We show that by restricting harmonic emission only to the region near the peak of the pulse, where the polarization is linear, it is possible to generate a bright narrow bandwidth comb in the gamma region.

Scattering of intense laser pulses on high-energy electron beams allows one to produce a large number of x and $\gamma$ rays. For temporally pulsed lasers, the resulting spectra are broadband which severely limits practical applications. One could use linearly chirped laser pulses to compensate for that broadening. We show for laser pulses chirped in the spectral domain that there is the optimal chirp parameter at which the spectra have the brightest peak. Additionally, we use catastrophe theory to analytically find this optimal chirp value.

The identification of prospective scenarios for observing quantum vacuum signals in high-intensity laser experiments requires both accurate theoretical predictions and the exploration of high-dimensional parameter spaces. Numerical simulations address the first requirement, while optimization provides an efficient solution for the second one. In the present work, we put forward Bayesian optimization as a new and powerful means to optimize photonic quantum vacuum signals. We demonstrate its great potential on the example of the well-studied case of two-beam collisions. Apart from providing an ideal benchmark case, this immediately gives new physics results. Namely, Bayesian optimization allows us to find the optimal waist sizes for beams with elliptic cross sections, and to identify the specific physical process leading to a discernible signal in a coherent harmonic focusing configuration scenario. Published by the American Physical Society 2024

High-energy radiation can be generated by colliding a relativistic electron bunch with a high-intensity laser pulse—a process known as Thomson scattering. In the nonlinear regime the emitted radiation contains harmonics. For a laser pulse whose length is comparable to its wavelength, the carrier envelope phase changes the behavior of the motion of the electron and therefore the radiation spectrum. Here we show theoretically and numerically the dependency of the spectrum on the intensity of the laser and the carrier envelope phase. Additionally, we also discuss what experimental parameters are required to measure the effects for a beamed pulse.

Quantum reflection is a fascinating signature of the quantum vacuum that emerges from inhomogeneities in the electromagnetic fields. In pursuit of the prospective real-world implementation of quantum reflection in the back-reflection channel, we provide the first numerical estimates for the light-by-light scattering with dipole pulses, which are known to provide the tightest focusing of light possible. For an all-optical setup with a dipole pump and Gaussian probe of the same frequency, we find that the dominant signal signature is related mainly to the back-reflection channel from 4-wave mixing. Focusing on this, we study the particular case of a multiple focusing pulses configuration (belt configuration) as an approximation to the idealized dipole pulse. Using Bayesian optimization methods, we determine optimal parameters that maximize the detectability of a discernible back-reflection signal. Our study indicates that the optimization favors a three-beam collision setup, which we further investigate both numerically and analytically.

Nonlinear Compton scattering is a promising source of bright gamma-rays. Using readily available intense laser pulses to scatter off the energetic electrons on the one hand allows to significantly increase the total photon yield, but on the other hand leads to a dramatic spectral broadening of fundamental emission line as well as its harmonics due to the laser pulse shape induced ponderomotive effects. In this paper we propose to avoid ponderomotive broadening in harmonics by using the polarization gating technique - a well-known method to construct a laser pulse with temporally varying polarization. We show that by restricting harmonic emission only to the region near the peak of the pulse, where the polarization is linear, it is possible to generate a bright narrow bandwidth comb in the gamma region.