We present an in-depth experimental-computational study of the parameters necessary to optimize a tunable, quasi-monoenergetic, efficient, low-background Compton backscattering (CBS) x-ray source that is based on the self-aligned combination of a laser-plasma accelerator (LPA) and a plasma mirror (PM). The main findings are (1) an LPA driven in the blowout regime by 30 TW, 30 fs laser pulses produce not only a high-quality, tunable, quasi-monoenergetic electron beam, but also a high-quality, relativistically intense (a0 ∼ 1) spent drive pulse that remains stable in profile and intensity over the LPA tuning range. (2) A thin plastic film near the gas jet exit retro-reflects the spent drive pulse efficiently into oncoming electrons to produce CBS x-rays without detectable bremsstrahlung background. Meanwhile, anomalous far-field divergence of the retro-reflected light demonstrates relativistic “denting” of the PM. Exploiting these optimized LPA and PM conditions, we demonstrate quasi-monoenergetic (50% FWHM energy spread), tunable (75–200 KeV) CBS x-rays, characteristics previously achieved only on more powerful laser systems by CBS of a split-off, counter-propagating pulse. Moreover, laser-to-x-ray photon conversion efficiency (∼6 × 10−12) exceeds that of any previous LPA-based quasi-monoenergetic Compton source. Particle-in-cell simulations agree well with the measurements.

Compact tunable Compton x-ray source from laser-plasma accelerator and plasma mirror

We present an in-depth experimental-computational study of the parameters necessary to optimize a tunable, quasi-monoenergetic, efficient, low-background Compton backscattering (CBS) x-ray source that is based on the self-aligned combination of a laser-plasma accelerator (LPA) and a plasma mirror (PM). The main findings are: (1) an LPA driven in the blowout regime by 30 TW, 30 fs laser pulses producesnot only a high-quality, tunable, quasi-monoenergetic electron beam, but also a high-quality, relativistically intense (a0~1) spent drive pulse that remains stable in profile and intensity over the LPA tuning range. (2) A thin plastic film near the gas jet exit retro-reflects the spent drive pulse efficiently into oncoming electrons to produce CBS x-rays without detectable bremsstrahlung background. Meanwhile anomalous far-field divergence of the retro-reflected light demonstrates relativistic "denting" of the PM. Exploiting these optimized LPA and PM conditions, we demonstrate quasi-monoenergetic (50% FWHM energy spread), tunable (75 to 200 KeV) CBS x-rays, characteristics previously achieved only on more powerful laser systems by CBS of a split-off, counter-propagating pulse. Moreover, laser-to-x-ray photon conversion efficiency ~6e12 exceeds that of any previous LPA-based quasi-monoenergetic Compton source. Particle-in-cell simulations agree well with the measurements.

The injection physics in a shock-induced density down-ramp injector was characterized, demonstrating precise control of a laser-plasma accelerator (LPA). Using a jet-blade assembly, experiments systematically varied the shock injector profile, including shock angle, shock position, up-ramp width, and acceleration length. Our work demonstrates that beam energy, energy spread, and pointing can be controlled by adjusting these parameters. As a result, an electron beam that was highly tunable from 25 to 300 MeV with 8% energy spread (ΔEFWHM/E), 1.5 mrad divergence, and 0.35 mrad pointing fluctuation was produced. Particle-in-cell simulation characterized how variation in the shock angle and up-ramp width impacted the injection process. This highly controllable LPA represents a suitable, compact electron beam source for LPA applications such as Thomson sources and free-electron lasers.

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Control of quasi-monoenergetic electron beams from laser-plasma accelerators with adjustable shock density profile

In this paper, biologically-inspired optical imaging systems, including fish eye, bug eye, lobster eye, and RGB color
vision, are discussed as new lensing systems for military and homeland security applications. This new area of interest
includes UV, VIS, IR, and X-ray part of electromagnetic spectrum. In particular, recent progress at Physical Optics
Corporation will be discussed, including such applications as hyperspectral/multi-spectral imagery, video surveillance,
and X-ray inspection.

Animal eyes in homeland security systems

In this report, we demonstrate precise control of a laser plasma accelerator (LPA) through characterization of a shock-induced density downramp injector. Experiments systematically varied the shock injector profile, including shock angle, shock position, up-ramp width, and acceleration length. As a result, an electron beam that was highly tunable from 30 to 300 MeV with 8.5% energy spread, 1.5 mrad divergence and 0.35 mrad pointing fluctuation was produced. We also report the progress of a project focusing on demonstrating the crucial enablers of a compact LPA based MeV Thomson photon source in an integrated experiment and a dedicated 100 TW laser facility built at the Berkeley Lab Laser Accelerator (BELLA) Center, Lawrence Berkeley National Laboratory (LBNL).

Laser-Plasma - Accelerator-Driven Quasi - Monoenergetic MeV Thomson Photon Source and Laser Facility

This paper discusses a new approach to X-ray non-intrusive (NDE) inspection based on hard X-ray imaging optics. A
new X-ray lens, called lobster-eye-lens (LEL) is the transmission lens, based on reflection optics, with grazing-angle
deflection of 0.2° and photon energy of 40-100 keV. The lens reflection-optics is based on large, high-quality X-ray
mirrors with r.m.s. lower than 1 nm. The through-the-wall inspection capability of such a system, based on Compton
back-scattering, can be applied for longer ranges, (up to 100 m in the air), and thick walls (over 2 cm for wood, and over
2 mm for metal). CONOPS examples are given for homeland security applications.

Through-the-wall sensor systems based on hard x-ray imaging optics

A highly productive approach to small systems design and integration (SSDI), and modeling and simulation (M&S),
based on rapid/interactive prototyping has been effectively used at Physical Optics Corporation (POC) to support small
system development of "intellectual products" that cover a broad range of electromagnetic spectra (X-ray, optical,
infrared, and microwave). In particular, the implementation of an accelerated interactive modeling (AIM) environment
produces effective engineering solutions for tackling difficult and complex technical issues for combining 3D
mechanical design and microwave engineering. In addition, using established small systems engineering principles and
the effective use of collaborative input at the start of a development effort that incorporates a diverse range of areas like
optics, mechanics, electronics, software, thermal modeling, electromagnetism, surface chemistry, and manufacturing
plays an important role in the success of future military and homeland security applications.

Richard Koziol

Papers

Through-the-wall sensor systems based on hard x-ray imaging optics

Modeling and simulation for small system integration of military and homeland security applications