Mechanism and Control of High‐Intensity‐Laser‐Driven Proton Acceleration

We discuss the optimization and control of laser‐driven proton beams. Specifically, we report on the dependence of high‐intensity laser accelerated proton beams on the material properties of various thin‐film targets. Evidence of star‐like filaments and beam hollowing (predicted from the electrothermal instability theory) is observed on Radiochromic Film (RCF) and CR‐39 nuclear track detectors. The proton beam spatial profile is found to depend on initial target conductivity and target thickness. For resistive target materials, these structured profiles are explained by the inhibition of current, due to the lack of a return current. The conductors, however, can support large propagating currents due to the substantial cold return current which is composed of free charge carriers in the conduction band to neutralize the plasma from the interaction. The empirical plot shows relationship between the maximum proton energy and the target thickness also supports the return current and target normal sheath acceleration (TNSA) theory. We have also observed filamentary structures in the proton beam like those expected from the Weibel instability in the electron beam. Along with the ion acceleration, a clear electron beam is detected by the RCF along the tangent to the target, which is also the surface direction of target plate. © 2004 American Institute of PhysicsPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87542/2/595_1.pd

Evidence of Ionization Blue Shift Seeding of Forward Raman Scattering

We report on the results of spectroscopic experiments that were conducted by focusing an intense ultra‐short laser pulse onto a helium gas target. The scattered light from the interaction region was measured spectrally and spatially from various directions as a function of laser intensity and plasma density. The experimental data showed that forward Stimulated Raman Scattering (SRS) was sensitive to the focus position of laser relative to the nozzle. Together with the plasma channel that was imaged by a CCD camera, the measurements indicate that SRS is seeded by the ionization blue‐shifted light. The cross‐phase modulation between the SRS and laser beam was also observed in the experiment. © 2004 American Institute of PhysicsPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87541/2/585_1.pd

Computer vision projects with OpenCV and Python 3: six end-to-end projects built using machine learning with OpenCV, Python, and TensorFlow

This book demonstrates techniques to leverage the power of Python, OpenCV, and TensorFlow to solve problems in Computer Vision. This book also shows you how to build an application that can estimate human poses within images. You will also classify images and identify humans in videos, and then develop your own handwritten digit classifier

Compact, Robust Technology for Next-Generation Ultrafast High-Power Fiber Lasers.

Fiber lasers are an attractive alternative to bulk solid-state systems due to their potential for compactness and robustness, as well as their having diffraction-limited output even at high average powers. Combined with the technique of chirped-pulse-amplification (CPA), a new generation of ultrafast lasers can be engineered providing reliable high average power and ultrahigh peak power for applications in high-field research, novel radiation sources, spectroscopy, and materials processing. However, current fiber CPA systems still rely on large stretchers and compressors with free-space bulk diffraction gratings, which are incompatible with fiber laser benefits. Clearly, the bulk diffraction grating stretchers and compressors need to be replaced by much smaller and simpler devices. Chirped volume Bragg gratings (CVBGs) are simple slabs of glass with quasi-periodic indices of refraction that can chirp ultrafast pulses to hundreds of picoseconds and back down to the sub-picosecond level in only a few centimeters of material and with easy alignment. Proof-of-principle experiments using CVBGs for stretchers and compressors in fiber CPA systems have previously been performed, but several issues need to be resolved before they are deployed for mainstream use. This thesis presents a quantitative analysis of the performance of CVBGs at high average powers, which is backed by experimental data wherein the gratings are exposed to a record high 200 W of input power. Due to the grating’s bandwidth and thermal properties, the pulses are recompressible to 350 fs, indicating high fidelity operation. Extrapolation from the model predicts that kW operation, a major goal for all fiber CPA lasers, will be feasible with this technology. Moreover, the fundamental performance of the CVBGs, both spatial and temporal, is characterized. A new fabrication technique has allowed for the elimination of spatial chirp, a previous limitation on the beam quality. Measurements clearly show the new improvement. The fundamental temporal performance is evaluated using numerical and analytical theories, and CVBG stretchers and compressors are shown to have a negligible difference in group delay responses for sub-ps range bandwidths and can be further enhanced through the technique of apodization.Ph.D.Electrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/77798/1/mrever_1.pd

Observation of relativistic cross-phase modulation in high-intensity laser-plasma interactions

A nonlinear optical phenomenon, relativistic cross-phase modulation, is reported. A relativistically intense light beam (I=1.3×1018 W cm-2, λ =1.05 μm) is experimentally observed to cause phase modulation of a lower intensity, copropagating light beam in a plasma. The latter beam is generated when the former undergoes the stimulated Raman forward scattering instability. The bandwidth of the Raman satellite is found to be broadened from 3.8–100 nm when the pump laser power is increased from 0.45–2.4 TW. A signature of relativistic cross-phase modulation, namely, asymmetric spectral broadening of the Raman signal, is observed at a pump power of 2.4 TW. The experimental cross-phase modulated spectra compared well with theoretical calculations. Applications to generation of high-power single-cycle pulses are also discussed

Energy Scaling In A Chirped Volume Bragg Grating Based Yb-Fiber Cpa System

The viability of using chirped volume Bragg gratings for mJ-scale CPA systems is demonstrated. A CVBG-based fiber-CPA system with 0.4mJ amplified and 290μJ recompressed energy from a CVBG compressor is reported. © 2009 Optical Society of America

200 Fs, 50 W Fiber-Cpa System Based On Chirped-Volume-Bragg-Gratings

Record-short pulses of 200fs have been obtained from a power-scalable-Yb-fiber-CPA system that uses chirped-volume-Bragg-gratings for the stretcher and compressor. The power was scaled up to 50W with a corresponding 33W of compressed power. © 2009 Optical Society of America

Power-Scalable, 200 Fs Chirped-Volume-Bragg-Grating Based Fiber-Cpa System

New broadband and spatial-chirp free chirped-volume-Bragg-gratings have been demonstrated to produce 200fs from a 50W Yb-doped fiber based CPA laser system. © 2009 Optical Society of America