Development Of Third Harmonic Generation As A Short Pulse Probe Of Shock Heated Material

We are studying high-pressure laser produced shock waves in silicon (100). To examine the material dynamics, we are performing pump-probe style experiments utilizing 600 ps and 40 fs laser pulses from a Ti:sapphire laser. Two-dimensional interferometry reveals information about the shock breakout, while third harmonic light generated at the rear surface is used to infer the crystalline state of the material as a function of time. Sustained third harmonic generation (THG) during a similar to 100 kbar shock breakout indicate that the rear surface remains crystalline for at least 3 ns. However, a decrease in THG during a similar to 300 kbar shock breakout suggests a different behavior, which could include a change in crystalline structure.Mechanical Engineerin

Laser wakefield excitation and measurement on a femtosecond time scale: Theory and experiment. Progress report, September 1, 1994--August 31, 1995

A brief discussion was given for each of the following topics: superluminous wake excitation; photon frequency-shift (photon accelerator) spectroscopy; focusing, diffraction and 2D spectral shift; Raman self-modulation effects; optical preaccelerator; accelerator physics developments; experimental facilities; experimental results--pressure-tunable harmonic generation; experiments in progress--time-domain Rayleigh interferometry; Russian collaboration; and technology transfer

Multi-GeV Electron Generation Using Texas Petawatt Laser

We present simulation results and experimental setup for multi-GeV electron generation by a laser plasma wake field accelerator (LWFA) driven by the Texas Petawatt (TPW) laser. Simulations show that, in plasma of density n(e) = 2 - 4 x cm(-3), the TPW laser pulse (1.1 PW, 170 fs) can self-guide over 5 Rayleigh ranges, while electrons self-injected into the LWFA can accelerate up to 7 GeV. Optical diagnostic methods employed to observe the laser beam self-guiding, electron trapping and plasma bubble formation and evolution are discussed. Electron beam diagnostics, including optical transition radiation (OTR) and electron gamma ray shower (EGS) generation, are discussed as well.Physic

Using arts‐based methods to develop service user led learning materials for social work education

Theories transmitted to students about professional practice in health and social care come traditionally from the perspective of practitioners, often as a heroic narrative, inevitably casting the service‐user in a passive role (Wiltshire, 2006). Post‐modern theorists like Foucault (1973) call this the authoritative 'gaze' that objectifies the user of public services, generating a power relationship between the professional and the service user. New perspectives are needed to redress this imbalance, drawing on the narratives of the service‐users themselves (Greenhalgh, 2006). Since 2007, a project led by service‐users at London South Bank University has been experimenting with new approaches to developing learning and teaching materials for social work education using opportunities afforded by the recent accreditation of awards within the General Social Care Council’s new Post Qualifying Framework. This paper outlines some of our experiences to date of experimenting with creative arts‐based approaches to facilitate the development of learning materials as ‘inherently creative acts’ (Sagan, 2007). This paper documents the experiences of a small group of service users and academics as we have all worked in different ways to co‐produce it using different mediums and media in order to contribute our views

Femtosecond Thermionic Emission in the Space-Charge Limited Regime

We study femtosecond-laser-pulse-induced electron emission from W(100), Al(110), and Ag(lll) in the sub-damage regime (1–44 mJ/cm2 fluence) by simultaneously measuring the incident-light reflectivity, total electron yield, and electron-energy distribution curves of the emitted electrons. The total-yield results are compared with a space-charge-limited extension of the Richardson-Dushman equation for short-time-scale thermionic emission and with particle-in-a-cell computer simulations of femtosecond-pulsed-induced thermionic emission. Quantitative agreement between the experimental results and two calculated temperature-dependent yields is obtained and shows that the yield varies linearly with temperature beginning at a threshold electron temperature of ~0.25 eV The particle-in-a-cell simulations also reproduce the experimental electron-energy distribution curves. Taken together, the experimental results, the theoretical calculations, and the results of the simulations indicate that thermionic emission from nonequilibrium electron heating provides the dominant source of the emitted electrons. Furthermore, the results demonstrate that a quantitative theory of space-charge-limited femtosecond-pulse-induced electron emission is possible

Ultrafast Radial Transport In A Micron‐Scale Aluminum Plasma Excited At Relativistic Intensity

Using femtosecond microscopy, we observe a thermal/ionization front expand radially at ∼108cm/s from a λ2‐size spot of an aluminum target excited at >1018W/cm2. Numerical modeling shows transport is predominantly radiative and may be initially nonlocal. © 2004 American Institute of PhysicsPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87543/2/609_1.pd

High quality implementation of 4Rs + MTP increases classroom emotional support and reduces absenteeism

School-based social and emotional learning (SEL) programs are associated with improvements in children’s SEL and academic outcomes, and the quality of classroom interactions. The magnitude of these effects increases at high levels of program implementation quality. This study aimed to (1) identify teachers’ profiles of quality of implementation, (2) explore teachers and classroom characteristics contributing to their propensity to comply with high quality of implementation, and (3) examine the relations between school assignment to an SEL program, quality of classroom interactions, and child SEL and academic outcomes at different levels of teachers’ compliance propensity. This study drew upon data from a cluster-randomized controlled trial evaluating the efficacy of 4Rs + MTP, a literacy-based SEL program, on third and fourth grade teachers (n = 330) and their students (n = 5,081) across 60 New York City public elementary schools. Latent profile analysis indicated that measures of teacher responsiveness and amount of exposure to implementation supports contributed to the differentiation of profiles of high and low quality of implementation. Random forest analysis showed that more experienced teachers with low levels of professional burnout had high propensity to comply with high quality of implementation. Multilevel moderated mediation analysis indicated that 4Rs + MTP teachers with high compliance propensity were associated with higher classroom emotional support and lower children’s school absences than their counterparts in the control group. These findings may inform debates in policy research about the importance of providing the supports teachers need to implement SEL school programs with high quality