We investigate proton acceleration by a laser pulse obliquely incident on a double layer target via 3D PIC simulations. It is found that the proton beam energy spread changes by the laser irradiation position and it reaches a minimum at certain position. This provides a way to control the proton energy spectrum. We show that by appropriately adjusting the size and position of the second proton layer that high energy protons with much smaller energy spread can be obtained.
The use of ultrathin solid foils offers optimal conditions for accelerating protons from laser-matter interactions. When the target is thin enough that relativistic self-induced transparency (RSIT) sets in, all of the target electrons get heated to high energies by the laser, which maximizes the accelerating electric field and therefore the final ion energy. In this work, we first investigate how ion acceleration by ultraintense femtosecond laser pulses in transparent CH$_2$ solid foils is modified when turning from normal to oblique ($45^\circ$) incidence. Due to stronger electron heating, we…
It is well known that Brunel's vacuum heating mechanism is operative for laser energy absorption when the target plasma density rises sharply. For non-relativistic laser intensities and planar targets it is also necessary that the laser should strike the target at oblique incidence. The laser electric field at oblique incidence has a component normal to the surface to extract electrons from the target in the vacuum region for Brunel's mechanism to be operative. At relativistic laser intensities, oblique incidence is not necessarily required as the J x B force is significant and can extract ele…
The basic understanding of high-intensity femtosecond laser absorption in a solid is crucial for high-energy-density science. This multidimensional problem has many variables like laser parameters, solid target material, and geometry of the excitation. This is important for a basic understanding of intense laser-matter interaction as well for applications such as `plasma mirror'. Here, we have experimentally observed high-intensity, high-contrast femtosecond laser absorption by an optically polished fused silica target at near-relativistic laser intensities ($\sim$10$^{18}$ W/cm$^2$). The lase…
Formation of femtosecond sawtooth pulses by high harmonic generation from relativistic oscillating mirrors is studied. For oblique incidence of $p$-polarized laser pulse, one can efficiently control the intensity of the first few harmonics by modifying the plasma density gradient at the plasma-vacuum interface. With appropriate choice of the laser amplitude and incidence angle, the generated harmonics can form a millijoule femtosecond sawtooth pulse. The scheme does not rely on phase manipulation and/or pulse synchronization as in the state-of-art methods. It is also shown that such a sawtooth…
Laser-solid interaction can lead to the acceleration of protons to tens of MeV. Here, we show that a strong enhancement of this acceleration can be achieved by splitting the laser pulse to two parts of equal energy and opposite incidence angles. Through the use of two- and three-dimensional Particle-In-Cell simulations, we find that the multi-pulse interaction leads to a standing wave pattern at the front side of the target, with an enhanced electric field and a substantial modification of the hot electron generation process. This in turn leads to significant improvement of the proton spectra,…
It is conjectured that all perturbative approaches to quantum electrodynamics (QED) break down in the collision of a high-energy electron beam with an intense laser, when the laser fields are boosted to `supercritical' strengths far greater than the critical field of QED. As field strengths increase toward this regime, cascades of photon emission and electron-positron pair creation are expected, as well as the onset of substantial radiative corrections. Here we identify the important role played by the collision angle in mitigating energy losses to photon emission that would otherwise prevent …
We develop an analytical model for ultraintense attosecond pulse emission in the highly relativistic laser-plasma interaction. In this model, the attosecond pulse is emitted by a strongly compressed electron layer around the instant when the layer transverse current changes the sign and its longitudinal velocity approaches the maximum. The emitted attosecond pulse has a broadband exponential spectrum and a stabilized constant spectral phase $ψ(ω)=\pmπ/2-ψ_{A_m}$. The waveform of the attosecond pulse is also given explicitly, to our knowledge, for the first time. We validate the analytical mode…
