arXiv subjects

D. W. Schumacher

Publications and source records attributed to D. W. Schumacher.

9 recordsLinked to original sources

arXiv2026

Stability and optical quality of "windmill"-formed 8CB liquid crystal films for replenishable plasma mirrors

Liquid crystal (LC) film plasma mirrors (PMs) based on 4-octyl-4'-cyanobiphenyl (8CB) are an enabling technology for reflecting high-fluence laser pulses. These freestanding LC films can achieve high optical quality and are well-suited for rep-rated applications, as motorized devices continuously replenish films over an aperture following each destructive laser shot. However, a systematic characterization of film quality as a function of seminal operating conditions had not yet been performed for the LC "windmill" version of the device, which aims to match the repetition rate of an existing "spinning disk" (SDI) version and the angular stability of the "linear slider" (LSTI) version. We determined the 8CB film quality using low-power wavefront measurements, and studied the film-to-film wavefront stability and formation reliability. The film-formation reliability of 8CB LC films demonstrated >97% formation success at 2.7 mm/s film-forming speeds, but decreased to 45% at 10.8 mm/s. These reliability numbers will inform future designs to reach Hz-level repetition rates and beyond. Depending on area-of-interest within the 10 mm diameter film, the added wavefront root-mean-squared (RMS) variation was as small as 12 nm for a 2 mm diameter region, and <50 nm for a 3 mm diameter region. Within the optimal 21-22 degrees C operating regime, pointing fluctuations remained at or below 0.5 mrad. With a maximum effective film formation frequency of approximately 0.25 Hz, these results establish windmill-formed 8CB films as promising candidates to pursue next-iteration improvements towards rep-rated plasma-mirror operation.

physics.optics↗

arXiv2017

Study of accelerated ion energy and spatial distribution with variable thickness liquid crystal targets

We report on laser-based ion acceleration using freely suspended liquid crystal film targets, formed with thicknesses varying from 100 $nm$ to 2 $μm$ for this experiment. Optimization of Target Normal Sheath Acceleration (TNSA) of protons is shown using a 1 $\times$ $10^{20}$ $W/cm^2$, 30 fs laser with intensity contrast better than $10^{-7}:1$. The optimum thickness was near 700 $nm$, resulting in a proton energy maximum of 24 $MeV$. Radiochromic film (RCF) was employed on both the laser and target normal axes, revealing minimal laser axis signal but a striking ring distribution in the low energy target normal ion signature that varies with liquid crystal thickness. Discussion of this phenomenon and a comparison to similar observations on other laser systems is included.

physics.plasm-ph↗

arXiv2017

Direct Testing against Experiment of a Fundamental Ultrashort Pulse Laser Damage Simulation Technique with Utility for the Modeling of Nanostructure Formation

We have developed the first laser damage simulation algorithm capable of determining crater and surface modification morphology from microscopic physics. Rapid progress in the field of high intensity ultrafast lasers has enabled its utility in a myriad of applications. Simulation plays an important role in this research by allowing for closer analysis of the physical mechanisms involved, but current techniques struggle to meet both the spatial scope or resolution requirements for modeling such dynamics, typically specializing in one or the other. Consequently, it is difficult to extract the physical form of the laser induced surface modification, hampering direct comparison of simulation to experimental results. Our algorithm offers a compromise to existing simulation techniques and enables the production of a complete density profile in addition to the simulation of intermediate dynamics. We use this capability to directly test our simulation against experimentally produced copper craters. Additionally, we show how our algorithm can be used to model the formation of surface roughness and nanoparticles.

physics.comp-ph↗

arXiv2015

Microengineering laser plasma interactions at relativistic intensities

We report on the first successful proof-of-principle experiment to manipulate laser-matter interactions on the microscale 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 total and cut-off 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 (DLA).

physics.plasm-ph↗

arXiv2015

In-situ, variable thickness, liquid crystal film target inserter for moderate repetition rate intense laser applications

Liquid crystal films have recently been demonstrated as variable thickness, planar targets for ultra-intense laser matter experiments and applications such as ion acceleration. By controlling the parameters of film formation, including liquid crystal temperature and volume, their thickness can be varied on-demand from 10 $nm$ to above 10 $μm$. This thickness range enables for the first time real-time selection and optimization of various ion acceleration mechanisms using low cost, high quality targets. Our previous work employed these targets in single shot configuration, requiring chamber cycling after the pre-made films were expended. Presented here is a film formation device capable of drawing films from a bulk liquid crystal source volume to any thickness in the aforementioned range. This device will form films under vacuum within 2 $μm$ of the same location each time, well within the Rayleigh range of even tight $F/ \#$ systems. The repetition rate of the device exceeds 0.1 $Hz$ for sub-100 $nm$ films, enabling inexpensive, moderate repetition rate plasma target insertion for state of the art lasers currently in use or under development. Characterization tests of the device performed at the Scarlet laser facility at Ohio State will be presented.

physics.plasm-ph↗

arXiv2014

Liquid crystal films as on-demand, variable thickness (50-5000 nm) targets for intense lasers

We have developed a new type of target for intense laser-matter experiments that offers significant advantages over those currently in use. The targets consist of a liquid crystal film freely suspended within a metal frame. They can be formed rapidly on-demand with thicknesses ranging from nanometers to micrometers, where the particular value is determined by the liquid crystal temperature and initial volume as well as by the frame geometry. The liquid crystal used for this work, 8CB (4'-octyl-4-cyanobiphenyl), has a vapor pressure below $10^{-6}$ Torr, so films made at atmospheric pressure maintain their initial thickness after pumping to high vacuum. Additionally, the volume per film is such that each target costs significantly less than one cent to produce. The mechanism of film formation and relevant physics of liquid crystals are described, as well as ion acceleration data from the first shots on liquid crystal film targets at the Ohio State University Scarlet laser facility.

physics.plasm-ph↗

arXiv2014

Enhancing Bremsstrahlung Production From Ultraintense Laser-Solid Interactions With Front Surface Structures

We report the results of a combined study of particle-in-cell and Monte Carlo modeling that investigates the production of Bremsstrahlung radiation produced when an ultraintense laser interacts with a tower-structured target. These targets are found to significantly narrow the electron angular distribution as well as produce significantly higher energies. These features combine to create a significant enhancement in directionality and energy of the Bremstrahlung radiation produced by a high-Z converter target. These studies employ short-pulse, high intensity laser pulses, and indicate that novel target design has potential to greatly enhance the yield and narrow the directionality of high energy electrons and $γ$-rays. We find that the peak $γ$-ray brightness for this source is 6.0$\times$10$^{19}$ ${\rm s^{-1}mm^{-2}mrad^{-2}}$ at 10MeV and 1.4$\times$10$^{19}$ ${\rm s^{-1}mm^{-2}mrad^{-2}}$ at 100MeV (0.1$\%$ bandwidth).

physics.plasm-ph↗

arXiv2014

On The Origin of Super-Hot Electrons from Intense Laser Interactions with Solid Targets having Moderate Scale Length Preformed Plasmas

We use PIC modeling to identify the acceleration mechanism responsible for the observed generation of super-hot electrons in ultra-intense laser-plasma interactions with solid targets with pre-formed plasma. We identify several features of direct laser acceleration (DLA) that drive the generation of super-hot electrons. We find that, in this regime, electrons that become super-hot are primarily injected by a looping mechanism that we call loop-injected direct acceleration (LIDA).

physics.plasm-ph↗

arXiv2013

The 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 3D PIC 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 degree) angular cones.

physics.plasm-ph↗