Enhanced brightness of a laser-driven x-ray and particle source by microstructured surfaces of silicon targets

Abstract

The production of intense x-ray and particle sources is one of the most remarkable aspects of high energy laser interaction with a solid target. Wide application of these laser-driven secondary sources requires a high yield, which is partially limited by the amount of laser energy absorbed by the target. Here, we report on the enhancement of laser absorption and x-ray and particle flux by target surface modifications. In comparison to targets with flat front surfaces, our experiments show exceptional laser-to-target performance for our novel cone-shaped silicon microstructures. The structures are manufactured via laser-induced surface structuring. Spectral and spatial studies of reflectance and x-ray generation reveal significant increases of the silicon K a line and a boost of the overall x-ray intensity, while the amount of reflected light decreases. Also, the proton and electron yields are enhanced, but both temperatures remain comparable to those of flat foil targets. We support the experimental findings with 2D particle in cell simulations to identify the mechanisms responsible for the strong enhancement. Our results demonstrate how custom surface structures can be used to engineer high power laser-plasma sources for future applications.

Targets with cone-shaped microstructures from various materials for enhanced high-intensity laser–matter interaction

“…To find the optimal geometry for a specific laser configuration, parameter scans can be performed by fabricating microstructures with varying geometries and dimensions, which is within reasonable effort as most of the processing parameters can be easily modified. Previous studies [10,25] discussed that the influence of the microstructures on the energy transfer between laser and target not only depends on the properties of the target, such as the material, cone geometry and distribution, but also on the laser parameters, among which pulse length and contrast are key factors. Depending on the amount of energy deposited before the main pulse, the microstructures will retain their overall geometry or dissolve.…”

“…There are several methods available for fabrication including etching, twophoton polymerisation, laser processing, pulsed laser depo-sition and various moulding techniques [7,8] . Recently, coneshaped microstructures have attracted the interest of the community [9,10] . Her et al [11] discovered the formation of such conical needles on silicon wafer surfaces after exposing them to a series of ultrashort laser pulses.…”

Target Characteristics Used in Laser-Plasma Acceleration of Protons Based on the TNSA Mechanism

“…In order to maximize the protons flux obtained from a target and not rely solely on its inherent surface contaminants rich in H atoms, including here water vapours or other compounds (e.g., One of the first results which stood several years as a record for proton energy at 58 MeV was obtained using a 100 μm foil made of PS [1]. In Figure 3 we present results obtained with targets made of different plastic foils: PS [1-3, 24, 60, 61], Mylar [32,[62][63][64][65][66][67], PMP [50], Kapton [68], SiN [65,69], amorphous Carbon [70], synthetic diamond (CVD) [38], liquid crystals-8CB [71], and a pure Si substrate [72].…”

“…A paradigm shift has been seen in the last years in the target morphology, from simple flat foils to micro-and nano-structured targets presented in several reports, in order to highlight the benefit of the latests. Targets consisting of nanowires [88], micropillars and microtubes [51,72,89], nanochannels [59], nanoholes [90], flat foils embedded with nanoparticles [91] or with nanospheres [66,69,92], double layers made of different materials [38,93], a combination of double-layer and embedded nanospheres [67], foams [94][95][96] and flat foil with grooves or micro-gratings [28,69,97,98] have already been tested. The results reported with these types of targets are presented also in Figure 4.…”

Quality Improvement of Laser-Induced Periodic Ripple Structures on Silicon Using a Bismuth-Indium Alloy Film

“…Silicon wafers with patterned surface structures have important applications in many fields [18][19][20][21]. In the past few decades, numerous investigations and promising results of LIPSSs on silicon have been made.…”