The Orion Laser Facility at AWE in the UK consists of ten nanosecond beamlines and two sub-picosecond beamlines. The nanosecond beamlines each nominally deliver 500 J at 351 nm in a 1 ns square temporal profile, but can also deliver a user-definable temporal profile with durations between 0.1 ns and 5 ns. The sub-picosecond beamlines each nominally deliver 500 J at 1053 nm in a 500 fs pulse, with a peak irradiance of greater than 1021 W/cm2. One of the sub-picosecond beamlines can also be frequency-converted to deliver 100 J at 527 nm in a 500 fs pulse, although this is at half the aperture of the 1053 nm beam. Commissioning of all twelve beamlines has been completed, including the 527 nm sub-picosecond option. An overview of the design of the Orion beamlines will be presented, along with a summary of the commissioning and subsequent performance data. The design of Orion was underwritten by running various computer simulations of the beamlines. Work is now underway to validate these simulations against real system data, with the aim of creating predictive models of beamline performance. These predictive models will enable the user’s experimental requirements to be critically assessed ahead of time, and will ultimately be used to determine key system settings and parameters. The facility is now conducting high energy density physics experiments. A capability experiment has already been conducted that demonstrates that Orion can generate plasmas at several million Kelvin and several times solid density. From March 2013 15% of the facility operating time will be given over to external academic users in addition to collaborative experiments with AWE scientists.
The Orion laser facility at AWE in the UK began operations at the start of 2012 to study high energy density physics. It consists of ten nanosecond beam lines and two sub-picosecond beam lines. The nanosecond beam lines each deliver 500 J per beam in 1ns at 351nm with a user-definable pulse shape between 0.1ns and 5ns. The short pulse beams each deliver 500J on target in 500fs with an intensity of greater than 1021 Wcm-2 per beam. All beam lines have been demonstrated, delivering a pulse to target as described. A summary of the design of the facility will be presented, along with its operating performance over the first year of experimental campaigns. The facility has the capability to frequency-double one of the short pulse beams, at sub aperture, to deliver a high contrast short pulse to target with up to 100J. This occurs post-compression and uses a 3mm thick, 300mm aperture KDP crystal. The design and operational performance of this work will be presented. During 2012, the laser performance requirements have been demonstrated and key diagnostics commissioned; progress of this will be presented. Target diagnostics have also been commissioned during this period. Also, there is a development program under way to improve the contrast of the short pulse (at the fundamental) and the operational efficiency of the long pulse. It is intended that, from March 2013, 15% of facility operating time will be made available to external academic users in addition to collaborative experiments with AWE scientists.
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.
This report discusses the design and installation of a phase optic inserted in the near field of the HELEN high power glass laser. The element is designed to shape the intensity distribution at the focal spot of the laser to produce an increase in the peak intensity through correction of static and thermally induced wavefront errors on the beam. A phase element has been fabricated commercially using a magneto-rheological finishing tool. Test data is presented.
This report discusses the design and installation of a static wavefront correction optic on the HELEN laser at AWE. The element is designed to compensate for static phase errors and prompt thermally induced aberrations on the backlighter beam of the laser. Partial compensation of cooling effects is also included in the design. A phase element has been fabricated using a recently developed novel wet etch figuring tool at LLNL. Performance evaluation through comparison of the focal spot pre- and post-installation is provided. The element has been tested on the laser to produce a 2x reduction in focal spot size.
We describe development of passive phase correction elements to compensate for static phase errors and prompt thermally induced aberrations in the HELEN laser at AWE. Partial compensation of cooling effects is also included in the design. Phase elements have been fabricated through two processes, an indirect write lithographic process using amplitude masks generated from measured laser wavefronts and a direct write method using a novel wet etch figuring tool.
We describe development of passive phase correction elements to compensate for static phase errors and prompt thermally induced aberrations in the reconfigured HELEN laser. Partial compensation of cooling effects is also included in the design. Phase elements have been fabricated through lithographic processes using amplitude masks. The masks were generated from measured laser wavefronts. The phase profiles have been measured experimentally and the effect on the HELEN laser wavefront and far field intensity distribution have been calculated by combining these phase profiles with the measured laser wavefronts. The calculations show improvements in Strehl ratio from a factor of 2 up to a factor of 7 depending on the configuration.
To meet the future requirements of the AWE plasma physics program, design studies are being conducted for a 100 TW Nd doped glass laser system converted to the third harmonic. The baseline design of the proposed system will be presented. The AWE laser is based on technology developments for the US National Ignition Facility (NIF). The proposal is for a 32 beam laser system which is a sub-set of the 192 beam NIF.
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.
Diffractive optical elements to modify laser beam spatial intensity distributions are described. The elements have been applied to free-space Gaussian to flat-top beam conversion and customization of the modes of a laser resonator. The single pass free space elements demonstrate a high efficiency but result in to much high frequency noise on the beam. The intra-cavity elements significantly altered the TEM00 profile but practical limitations with the positioning of the element within the cavity prevented operation in the design mode.
Scalar and resonance domain diffractive optical elements are proposed for use within high power laser systems. Resonance domain elements are described for beam deflection and polarization selection. Scalar domain elements for harmonic separation filtering and beam shaping in the near- and far- fields are also described. Experimental results are presented for far-field beam shaping and harmonic separation filtering elements.
We report on the measurement of the output beam phase distribution of the high power, 30 cm aperture, Nd:glass laser HELEN using a self referencing cyclic radial shear interferometer. This near field interferometry technique for beam quality measurement is evaluated by comparison with measurements of the far-field intensity distribution. Results are also presented on the evolution of the thermal gradients and their effects on the transmitted wavefront quality through the final disc amplifiers following a laser shot.
This paper reports on the development of several diffractive optical elements (DOE) to fulfill applications on high power Nd glass laser systems. The measured performance for those components realized is discussed. These are focusing beam samplers, beam shapers, and harmonic separation filters (HSF). Designs of more demanding components operating in the resonance domain are also presented. These are linear polarizing elements and beam deflectors.
Preliminary investigations of a potential broad band oscillator for the HELEN laser facility and its proposed upgrade are described. The reasons for the need of broad bandwidth and the choice of commercial technology to achieve it are discussed. The characterization of the device and the diagnostics used for the investigations are described. Small signal amplification of the bandwidth by a glass amplifier was also performed along with investigations of the effect of various bandwidths on the far field beam quality when using random phase plates.
The key to effective utilization and systematic design of resonance domain diffractive elements lies in understanding the way in which the input beam interacts with the structure to produce the output field. This is straightforward in the paraxial, scalar, regime as the diffracted signal can be related directly to the physical parameters of the grating but resonance domain optics provides at least two exciting advantages over conventional optics. The first is the ability to use the wavelength scale structure to produce grating response functions with phase and/or amplitude modulations that cannot be realized conventionally. The second advantage is to use the polarization sensitivity of such devices to increase the functionality of a given element. We report on two novel uses of resonance domain diffractive optics. The first element is a diffractive optic beam deflector intended for high power laser systems, where laser induced damage limits the usefulness of conventional elements. The second element is a reflection grating operating as a polarization beam splitter. In the case of the beam splitter we present a simple model to explain the essential physics behind the operation of the device. This model leads to simple formulae for the design of other polarization sensitive devices.
Binary-phase optics have been used by a number of high-power laser laboratories in order to achieve relatively smooth focal spots. However, the intensity envelopes have in general been of a sinc form rather than `top-hat.' This paper presents work on the production of uniform `top-hat' intensity focal spot profiles obtained from Fresnel binary phase zone plate (PZP) arrays of various designs. Phase plates are used to generate large area smooth focal spots and both theoretical and experimental focal spots are presented. These demonstrate the flexibility of this technique which provides a simple method of generating both uniform `top-hat' intensity profiles and spatially shaped foci, for use with high-power lasers.
Laser damage testing of binary phase diffractive-optic components has been carried out at 1064 nm with 0.5 ns pulses. The surface relief components are produced by etching a fused silica substrate. The results show damage thresholds approaching that of polished fused silica. The design and fabrication of the diffractive-optic components for use with the HELEN multi- terrawatt Nd glass laser system at AWE is briefly described. The components under test were focusing beam samplers and harmonic separation filters.