Abstract
We demonstrate a simple method of preparing structured target for enhanced laser-driven proton acceleration under target-normal-sheath-acceleration scheme. A few layers of genetically modified, clinically grown micron sized E. Coli bacteria cell coated on a thin metal foil has resulted in an increase in the maximum proton energy by about 1.5 times and the total proton yield is enhanced by approximately 25 times compared to an unstructured reference foil at a laser intensity of 1019 W/cm2. Particle-in-cell simulations on the system shows that the structures on the target-foil facilitates anharmonic resonance, contributing to enhanced hot electron production which leads to stronger accelerating field. The effect is observed to grow as the number of structures is increased in the focal area of the laser pulse.
Highlights
High intensity laser-plasma based proton acceleration is a rapidly growing research field due to its ability to provide alternative pathways to realize compact table-top ion accelerator,[1,2] which opens up numerous applications in fundamental as well as in applied science such as, cancer therapy,[3] high energy density physics,[4] laboratory astrophysics,[5] nuclear physics,[6] ion driven fast ignition scheme for fusion[7,8] and proton radiography.[9]
The rest of pulse cannot propagate through the plasma electron density gradient until the critical density layer where the plasma frequency (Ωp) becomes equal to the laser frequency (ΩL) and a fraction of the laser energy is transferred to the plasma electrons that drives them to very high energy
Proton emission from the rear side of the target was characterized by a Thomson parabola (TP) spectrometer equipped with a micro-channel-plate (MCP) and a CCD camera
Summary
High intensity laser-plasma based proton acceleration is a rapidly growing research field due to its ability to provide alternative pathways to realize compact table-top ion accelerator,[1,2] which opens up numerous applications in fundamental as well as in applied science such as, cancer therapy,[3] high energy density physics,[4] laboratory astrophysics,[5] nuclear physics,[6] ion driven fast ignition scheme for fusion[7,8] and proton radiography.[9]. In bacteria coated microstructured targets, we have shown that, due to spatially inhomogeneous plasma formation, the self-consistent electrostatic potential (Φ) of the plasma electrons in the laser field becomes highly anharmonic.[30] Unlike the flat solid surface, where the resonance condition is achieved near the critical density layer, in microstructured targets the resonance condition, Ωp[r(t)] = ΩL, can be satisfied in multiple positions (r) within the focal area of the laser pulse following anharmonic resonance.[31,32] In this paper, we demonstrate a novel technique of micro-structuring thin foils for enhanced proton acceleration in the TNSA regime. We have observed approximately 1.5 times boost in the maximum proton energy and almost 25 times increment in the proton yield compared to the reference foil (unstructured)
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