Undepleted direct laser acceleration.

Intense lasers enable generating high-energy particle beams in university-scale laboratories. With the direct laser acceleration (DLA) method, the leading part of the laser pulse ionizes the target material and forms a positively charged ion plasma channel into which electrons are injected and accelerated. The high energy conversion efficiency of DLA makes it ideal for generating large numbers of photonuclear reactions. In this work, we reveal that, for efficient DLA to prevail, a target material of sufficiently high atomic number is required to maintain the injection of ionization electrons at the peak intensity of the pulse when the DLA channel is already formed. We demonstrate experimentally and numerically that, when the atomic number is too low, the target is depleted of its ionization electrons prematurely. Applying this understanding to multi-petawatt laser experiments is expected to result in increased neutron yields, a perquisite for a wide range of research and applications

Spectral detuning of relativistic surface harmonics

Relativistic surface harmonics driven by high-intensity lasers are considered a promising future light source, as their bandwidth and brightness are scalable with the driving laser power. Typically, the emission frequencies of these sources are limited to integer multiples of the laser fundamental frequency. In this Letter, we describe how the generation dynamics of these harmonics may enable spectral detuning of their frequencies. A dent in the plasma surface driven by the radiation pressure of the laser field grows during the interaction and varies the harmonic beam divergence. When a temporal chirp is added to the driving laser pulse, different instantaneous fundamental frequencies drive the harmonic beam to different cone angles, resulting in an overall spectral detuning of the high harmonics beam. We present experimental measurements of the dependence of the spectral detuning on the temporal chirp of the driving pulse. We show how these results are reproduced by our model, and conclude with its predictions for higher intensity laser systems

Spectrally and temporally resolved mid-infrared imaging by Adiabatic Sum Frequency upconversion

We introduce a broadband mid-infrared upconversion imaging scheme based on adiabatic frequency conversion. Contrary to state-of-the-art upconversion imaging limited by phase matching, our method does not require serial acquisitions to cover a large spectrum.</jats:p