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

P L Poole,R R Freeman,N Bourgeois,G E Cochran,P P Rajeev,D Neely,L A Wilson,G G Scott,P S Foster,D W Schumacher,C Hernandez-Gomez,A Krygier,J Bailey

doi:10.1038/srep32041

Abstract

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.

Highlights

We describe the first demonstration of plasma mirrors made using freely suspended, ultra-thin films formed dynamically and in-situ
Presented here are the first experiments demonstrating the utility of freely suspended liquid crystal films as high repetition rate, high quality plasma mirrors for ultra-intense laser experiment and application
The low-field reflectance was measured to be below 0.2%, while the optimum high-field reflectance was above 75%; the resulting contrast enhancement is over two orders of magnitude, comparable to conventional plasma mirrors

Summary

Introduction

We describe the first demonstration of plasma mirrors made using freely suspended, ultra-thin films formed dynamically and in-situ. Pre-pulse light can originate as amplified spontaneous emission from high gain amplifiers, scattered reflections in multipass amplifiers or retro-reflecting optical paths, imperfect phase correction in grating compressors, and as a ramp up to peak intensity due to laser architecture. Though this light may be significantly less intense than the main pulse–10−10 contrast or better is possible in systems designed with pulse cleaning mechanisms–pre-plasma formation sufficient to influence experimental results is commonplace. These include using low-gain optical parametric amplification in the laser front-end[8], using a third order process like cross polarized wave generation (XPW)[9] for pre-pulse reduction before amplification, or the installation of fast Pockels cells and spatial filters to reduce early and incoherent pre-pulses[10]

Methods

Results

Conclusion