Experiment and simulation of novel liquid crystal plasma mirrors for high contrast, intense laser pulses.

We describe the first demonstration of plasma mirrors made using freely suspended, ultra-thin films formed dynamically and in-situ. We also present novel particle-in-cell simulations that for the first time incorporate multiphoton ionization and dielectric models that are necessary for describing plasma mirrors. Dielectric plasma mirrors are a crucial component for high intensity laser applications such as ion acceleration and solid target high harmonic generation because they greatly improve pulse contrast. We use the liquid crystal 8CB and introduce an innovative dynamic film formation device that can tune the film thickness so that it acts as its own antireflection coating. Films can be formed at a prolonged, high repetition rate without the need for subsequent realignment. High intensity reflectance above 75% and low-field reflectance below 0.2% are demonstrated, as well as initial ion acceleration experimental results that demonstrate increased ion energy and yield on shots cleaned with these plasma mirrors.

Experimental capabilities of 0.4 PW, 1 shot/min Scarlet laser facility for high energy density science.

We report on the recently completed 400 TW upgrade to the Scarlet laser at The Ohio State University. Scarlet is a Ti:sapphire-based ultrashort pulse system that delivers >10 J in 30 fs pulses to a 2 µm full width at half-maximum focal spot, resulting in intensities exceeding 5×1021 W/cm2. The laser fires at a repetition rate of once per minute and is equipped with a suite of on-demand and on-shot diagnostics detailed here, allowing for rapid collection of experimental statistics. As part of the upgrade, the entire laser system has been redesigned to facilitate consistent, characterized high intensity data collection at high repetition rates. The design and functionality of the laser and target chambers are described along with initial data from commissioning experimental shots.

Microengineering Laser Plasma Interactions at Relativistic Intensities.

We report on the first successful proof-of-principle experiment to manipulate laser-matter interactions on microscales using highly ordered Si microwire arrays. The interaction of a high-contrast short-pulse laser with a flat target via periodic Si microwires yields a substantial enhancement in both the total and cutoff energies of the produced electron beam. The self-generated electric and magnetic fields behave as an electromagnetic lens that confines and guides electrons between the microwires as they acquire relativistic energies via direct laser acceleration.

Effects of front-surface target structures on properties of relativistic laser-plasma electrons.

We report the results of a study of the role of prescribed geometrical structures on the front of a target in determining the energy and spatial distribution of relativistic laser-plasma electrons. Our three-dimensional particle-in-cell simulation studies apply to short-pulse, high-intensity laser pulses, and indicate that a judicious choice of target front-surface geometry provides the realistic possibility of greatly enhancing the yield of high-energy electrons while simultaneously confining the emission to narrow (<5°) angular cones.

Effects of preplasma scale length and laser intensity on the divergence of laser-generated hot electrons.

We report on a numerical study of the effects of preplasma scale length and laser intensity on the hot-electron (≥1 MeV) divergence angle using full-scale 2D3V (two dimensional in space, three dimensional in velocity) simulations including a self-consistent laser-plasma interaction and photoionization using the particle-in-cell code LSP. Our simulations show that the fast-electron divergence angle increases approximately linearly with the preplasma scale length for a fixed laser intensity. On the other hand, for a fixed preplasma scale length, the laser intensity has little effect on the divergence angle in the range between 10(18) and 10(21) W/cm(2). These findings have important implications for the interpretation of experimental results.

Time dependence of fast electron beam divergence in ultraintense laser-plasma interactions.

We report on the measurement and computer simulation of the divergence of fast electrons generated in an ultraintense laser-plasma interaction (LPI) and the subsequent propagation in a nonrefluxing target. We show that, at Iλ(2) of 10(20) Wcm(-2)µm(2), the time-integrated electron beam full divergence angle is (60±5)°. However, our time-resolved 2D particle-in-cell simulations show the initial beam divergence to be much smaller (≤30°). Our simulations show the divergence to monotonically increase with time, reaching a final value of (68±7)° after the passage of the laser pulse, consistent with the experimental time-integrated measurements. By revealing the time-dependent nature of the LPI, we find that a substantial fraction of the laser energy (~7%) is transported up to 100 µm with a divergence of 32°.