Absolute calibration of optical streak cameras on picosecond time scales using supercontinuum generation.

We report a new method using high-stability, laser-driven supercontinuum generation in a liquid cell to calibrate the absolute photon response of fast optical streak cameras as a function of wavelength when operating at fastest sweep speeds. A stable, pulsed white light source based around the use of self-phase modulation in a salt solution was developed to provide the required brightness on picosecond time scales, enabling streak camera calibration in fully dynamic operation. The measured spectral brightness allowed for absolute photon response calibration over a broad spectral range (425-650 nm). Calibrations performed with two Axis Photonique streak cameras using the Photonis P820PSU streak tube demonstrated responses that qualitatively follow the photocathode response. Peak sensitivities were one photon/count above background. The absolute dynamic sensitivity is less than the static by up to an order of magnitude. We attribute this to the dynamic response of the phosphor being lower.

Low-noise time-resolved optical sensing of electromagnetic pulses from petawatt laser-matter interactions.

We report on the development and deployment of an optical diagnostic for single-shot measurement of the electric-field components of electromagnetic pulses from high-intensity laser-matter interactions in a high-noise environment. The electro-optic Pockels effect in KDP crystals was used to measure transient electric fields using a geometry easily modifiable for magnetic field detection via Faraday rotation. Using dielectric sensors and an optical fibre-based readout ensures minimal field perturbations compared to conductive probes and greatly limits unwanted electrical pickup between probe and recording system. The device was tested at the Vulcan Petawatt facility with 1020 W cm-2 peak intensities, the first time such a diagnostic has been used in this regime. The probe crystals were located ~1.25 m from target and did not require direct view of the source plasma. The measured signals compare favourably with previously reported studies from Vulcan, in terms of the maximum measured intra-crystal field of 10.9 kV/m, signal duration and detected frequency content which was found to match the interaction chamber's horizontal-plane fundamental harmonics of 76 and 101 MHz. Methods for improving the diagnostic for future use are also discussed in detail. Orthogonal optical probes offer a low-noise alternative for direct simultaneous measurement of each vector field component.

Generation of high contrast and high spatial quality idler from a low-gain optical parametric amplifier.

The temporal contrast of a regeneratively amplified, sub-picosecond pulse is enhanced by employing a low-gain optical parametric amplification stage self-pumped by the second harmonic of the pulse. Through careful characterization of the two related nonlinear processes and optimization of the non-collinear geometry, a robust high-contrast idler pulse has been generated, with excellent spatial quality in both the near and far field. The overall energy conversion efficiency exceeds 14%, with 33% intensity conversion efficiency. The temporal cleaning is implemented without any bandwidth losses or spectral shift and produces approximately 20% temporal shortening. These experimental findings are in excellent agreement with numerical calculations.

An in-vacuo optical levitation trap for high-intensity laser interaction experiments with isolated microtargets.

We report on the design, construction, and characterisation of a new class of in-vacuo optical levitation trap optimised for use in high-intensity, high-energy laser interaction experiments. The system uses a focused, vertically propagating continuous wave laser beam to capture and manipulate micro-targets by photon momentum transfer at much longer working distances than commonly used by optical tweezer systems. A high speed (10 kHz) optical imaging and signal acquisition system was implemented for tracking the levitated droplets position and dynamic behaviour under atmospheric and vacuum conditions, with ±5 µm spatial resolution. Optical trapping of 10 ± 4 µm oil droplets in vacuum was demonstrated, over timescales of >1 h at extended distances of ∼40 mm from the final focusing optic. The stability of the levitated droplet was such that it would stay in alignment with a ∼7 µm irradiating beam focal spot for up to 5 min without the need for re-adjustment. The performance of the trap was assessed in a series of high-intensity (10(17) W cm(-2)) laser experiments that measured the X-ray source size and inferred free-electron temperature of a single isolated droplet target, along with a measurement of the emitted radio-frequency pulse. These initial tests demonstrated the use of optically levitated microdroplets as a robust target platform for further high-intensity laser interaction and point source studies.

Multiwavelength interferometry system for the Orion laser facility.

We report on the design and testing of a multiwavelength interferometry system for the Orion laser facility based upon the use of self-path matching Wollaston prisms. The use of UV corrected achromatic optics allows for both easy alignment with an eye-safe light source and small (∼ millimeter) offsets to the focal lengths between different operational wavelengths. Interferograms are demonstrated at wavelengths corresponding to first, second, and fourth harmonics of a 1054 nm Nd:glass probe beam. Example data confirms the broadband achromatic capability of the imaging system with operation from the UV (263 nm) to visible (527 nm) and demonstrates that features as small as 5 µm can be resolved for object sizes of 15 by 10 mm. Results are also shown for an off-harmonic wavelength that will underpin a future capability. The primary optics package is accommodated inside the footprint of a ten-inch manipulator to allow the system to be deployed from a multitude of viewing angles inside the 4 m diameter Orion target chamber.

Monochromatic radiography of high energy density physics experiments on the MAGPIE generator.

A monochromatic X-ray backlighter based on Bragg reflection from a spherically bent quartz crystal has been developed for the MAGPIE pulsed power generator at Imperial College (1.4 MA, 240 ns) [I. H. Mitchell et al., Rev. Sci. Instrum. 67, 1533 (2005)]. This instrument has been used to diagnose high energy density physics experiments with 1.865 keV radiation (Silicon He-α) from a laser plasma source driven by a ∼7 J, 1 ns pulse from the Cerberus laser. The design of the diagnostic, its characterisation and performance, and initial results in which the instrument was used to radiograph a shock physics experiment on MAGPIE are discussed.