Laser driven proton acceleration is an active field of research due to its high potential in reducing the size and cost of conventional accelerators. The acceleration scheme consists of a very high intensity (), high contrast () laser pulse[
High Power Laser Science and Engineering, Volume. 2, Issue 2, 02000e15(2014)
Density measurements of laser interaction with ordered structured ‘snow’ targets
This paper presents a new method to control the position of a micro-column snow target. This target enables the measurement of the mean electron density of the pre-plasma created by a pre-pulse with different time delays. This research will allow a better understanding of the generation of fast protons from the interaction between a structured pre-plasma and a high intensity laser.
Laser driven proton acceleration is an active field of research due to its high potential in reducing the size and cost of conventional accelerators. The acceleration scheme consists of a very high intensity (), high contrast () laser pulse[
Recently, we demonstrated that by using frozen micro-column targets, which were grown on a sapphire substrate, significantly improved absorption of the laser energy by the micro-column target took place. This study showed that more than 90% of the incident energy was absorbed by the target[
Characterization and control of the morphology of the micro-structured targets is necessary to gain a better understanding of the interaction process and for optimization of the proton acceleration. As a first step, we present here a method to control the position of the micro-columns which is based on seeding of nucleation centers on the sapphire substrate. The nucleation centers were implanted on the sapphire substrate by spattering of aluminum. The size and shape of the seeding dots were determined by laser writing lithography. Selective growth of the micro-columns on the nucleation centers was achieved. The obtained structured target is characterized by enhanced order of each micro-column. The detailed shape of the column is determined by the growth parameters, which will be described elsewhere. Scanning electron microscopy (SEM) and optical images of the structured target are shown in Figure
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Previous experiments and PIC simulations have shown the important role of the pre-plasma on the proton acceleration mechanism[
The experiments were performed at the Hebrew University High Intensity Laser facility (HUJI). A schematic representation of the experimental setup is shown in Figure
In Figure
The mean electron density was calculated using[
Although the mean density agrees with our estimates, a better spatial description of the plasma cloud is sought. We are currently in the process of developing a system in which spatial measurements of the plasma cloud can be measured. It should be noted that these measurements are not trivial as the average density is low but the gradients are not. This measurement will contribute to a better understanding of the interaction of a high intensity laser with our targets. The spatial electron density measured will be integrated into our PIC code and will allow a better understanding of the acceleration mechanism.
In conclusion, we have achieved the manufacture of ordered snow micro-column targets using nucleation sites deposited on a sapphire substrate. This target allowed the measurement of the plasma density generated by the pre-pulse for different time delays after the interaction between the pre-pulse and the snow column target. This research will allow a better understanding of the generation of fast protons from the interaction between structured pre-plasma and high intensity lasers.
[7] T. Plachan, S. Pecker, Z. Henis, S. Eisenmann, A. Zigler. Appl. Phys. Lett., 90(2007).
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E. Schleifer, M. Botton, E. Nahum, S. Eisenman, A. Zigler, and Z. Henis. Density measurements of laser interaction with ordered structured ‘snow’ targets[J]. High Power Laser Science and Engineering, 2014, 2(2): 02000e15
Special Issue: HIGH INTENSITY LASER AND ATTOSECOND
Received: Mar. 28, 2014
Accepted: Apr. 24, 2014
Published Online: Jun. 4, 2014
The Author Email: E. Schleifer (elad.schleifer@mail.huji.ac.il)