Thomas H. Bett

Binary-phase zone plate arrays for the generation of uniform focal profiles

The generation of uniform focal intensity profiles is important for a number of applications, including laser-plasma interaction experiments. We report on a focusing system that uses a novel binary-phase optic capable of producing efficient two-dimensional uniform top-hat intensity optical and x-ray profiles.

Binary phase zone-plate arrays for laser-beam spatial-intensity distribution conversion

We report on the theory and development of a diffractive element composed of a binary phase zone-plate array. This component conditions the intensity distribution in the focal plane of a conventional refractive lens to generate efficiently (82%) a flattop intensity envelope on target. Analysis of the design indicates that manufacturing tolerances are not critical. Experimental performances on target from x-ray emission and shock-breakout measurements are also presented.

Overview of laser systems for the Orion facility at the AWE

The commissioning of the Orion laser facility at the Atomic Weapons Establishment (AWE) in the UK has recently been completed. The facility is a twelve beam Nd:glass-based system for studying high energy density physics. It consists of ten frequency-tripled beam-lines operating with nanosecond pulses, synchronized with two beam-lines with subpicosecond pulses, each capable of delivering 500 J to target. One of the short pulse beams has the option of frequency doubling, at reduced aperture, to yield up to 100 J at 527 nm in a subpicosecond pulse with high temporal contrast. An extensive array of target diagnostics is provided. This article describes the laser design and commissioning and presents key performance data of the facilitys laser systems.

Multipass reconfiguration of the HELEN Nd:glass laser at the Atomic Weapons Establishment

The HELEN high-power Nd:glass laser has been rebuilt in a new multipass configuration that requires fewer components to maintain existing performance. This is expected to lead to greater system availability and reduced running costs. We describe the new design, discuss some of the key issues that had to be addressed, and present operational results.

Comprehensive description of the Orion laser facility

The Orion laser facility at the atomic weapons establishment (AWE) in the UK has been operational since April 2013, fielding experiments that require both its long and short pulse capability. This paper provides a full description of the facility in terms of laser performance, target systems and diagnostics currently available. Inevitably, this is a snapshot of current capability—the available diagnostics and the laser capability are evolving continuously. The laser systems consist of ten beams, optimised around 1 ns pulse duration, which each provide a nominal 500 J at a wavelength of 351 nm. There are also two short pulse beams, which each provide 500 J in 0.5 ps at 1054 nm. There are options for frequency doubling one short pulse beam to enhance the pulse temporal contrast. More recently, further contrast enhancement, based on optical parametric amplification (OPA) in the front end with a pump pulse duration of a few ps, has been installed. An extensive suite of diagnostics are available for users, probing the optical emission, x-rays and particles produced in laser-target interactions. Optical probe diagnostics are also available. A description of the diagnostics is provided.

Ultrahigh contrast from a frequency-doubled chirped-pulse-amplification beamline

This paper describes frequency-doubled operation of a high-energy chirped-pulse-amplification beamline. Efficient type-I second-harmonic generation was achieved using a 3 mm thick 320 mm aperture KDP crystal. Shots were fired at a range of energies achieving more than 100 J in a subpicosecond, 527 nm laser pulse with a power contrast of 10(14).

Diffractive optical elements for intra-cavity beam-shaping of laser modes

Abstract Diffractive optical elements (DOE) are applied as intra-cavity mode selection devices for customizing the fundamental mode of laser resonators for high power laser systems. Using a phase-conjugating mode selecting element (MSE) in a laser oscillator, we are able to produce a good approximation to a super-Gaussian mode with a near flat intensity profile. This offers higher energy extraction from any following laser amplifiers compared to an unmodified Gaussian TEM00 mode. Two different designs for operation in a 1 m cavity length Nd:YAG master oscillator are presented. Both designs are surface relief phase elements fabricated in fused silica using photolithography with reactive-ion etching to produce 16 level elements for use in transmission. One element is designed to replace the cavity end mirror, while the other stands off an arbitrary distance from the end mirror. A novel iterated design for these transmissive elements is introduced. Numerical results and experimental measurements are presented and discussed.

Contrast enhancements to petawatt lasers using short pulse optical parametric amplifiers and frequency doubling

This paper describes the integration of a short pulse optical parametric amplifier into the chirped pulse amplification beam lines of the Orion laser facility. This enables Orion to generate petawatt laser pulses at 1054 nm with a nanosecond contrast of >10(10). By combining this with frequency-doubling post compression, we can generate 100 J, 500 fs laser pulses with a nanosecond contrast calculated to be ∼10(18).

Overview of Project Orion

Project Orion will provide a facility for performing high energy density plasma physics experiments at AWE. The laser consists of ten, nanosecond beam lines delivering a total of 5kJ with 0.1-5ns temporally shaped pulses and two short pulse beam lines, each producing 500J in 0.5ps with intensity > 10^21 W/cm^2. The performance of the Orion laser is reported as the first phase of commissioning (one short and one long pulse beam) concludes. Target shots with all beam lines will begin in 2012.

Diffractive beam samplers for large-aperture beam diagnostics

Diffractive beam samplers have been employed for some time on the HELEN laser at AWE. The phase gratings combine two functions viz. sampling and focusing in one element. The weak phase modulation generates low power diagnostic beams from which energy measurements have been made. This paper reports on further beam characterization measurements of the imaging properties of these components by recording far field and near field intensity distributions of beams up to 200mm diameter.