Experiments using the full power Gemini beams are conducted in Target Area 3 (TA3). Since being commissioned in 2007, Gemini has seen successful campaigns addressing a wide range of topics in fundamental physics and the optimisation of laser-driven secondary sources. The highest intensity achievable is of order 2 x 10²¹ Wcm^-2 making Gemini one of the most intense lasers in the world. The extreme temperatures, pressures and magnetic fields generated in plasma create exotic conditions comparable to those found in astrophysical objects. It should even be possible to observe quantum electrodynamic effects by studying the effect of the focussed laser on vacuum. These laser-plasma interactions also produce bright beams of electrons, ions and coherent x-rays. Because Gemini is a compact and high repetition rate laser it is ideally suited for providing these secondary sources with the ultimate aim of application in industrial and commercial environments.

​TA3 is a versatile area with a large target chamber that can be configured for the various beam arrangements required. The North and South beams enter the area from above and are steered onto either f/20 (3m focal length) or f/2 (30cm focal length) parabolic mirrors with the smallest focal spot being about 2 microns (see D. R. Symes et al., CLF Ann. Rep. 2012-13).

Light arriving before the main pulse is an inherent feature of all chirped pulse amplification lasers and to mitigate for this the North beam has the option of a passing through a double plasma mirror system. This consists of a pair of anti-reflection coated substrates which suddenly become highly reflective once the laser becomes intense enough to ionise the glass. In this way, the leading edge of the laser pulse is cleaned up allowing interactions with ultra-thin target foils of only 10nm thickness without the target being destroyed before the peak intensity of the laser.

Solid targets, provided by the CLF Target Fabrication facility, are mounted in arrays held on a wheel enabling hundreds of shots to be taken in vacuum without cycling the chamber. Gas targets are irradiated by focussing either through a plume from a high pressure gas jet or through a capillary guiding structure. A range of plasma diagnostics is available for experimental users including ion and electron spectrometers, x-ray crystal and flat-field spectrometers and pinhole cameras. Optical spectrometers and pulse length diagnostics are used to characterise the pulses reflected and transmitted by the target. Pick off beamlets can be used to backlight the plasma for time-resolved shadowgraphic and interferometric probing. In addition, specialised diagnostics purchased or constructed by university groups are often used for specific experiments.

Because of the generation of energetic particles and radiation, the entire area is surrounded by a 1m thick concrete shielding wall with the entrance being blocked by a thick lead door. The visiting user groups conduct the experiment from an external control room which also has on-shot diagnostic information provided on the performance of the laser. The maximum repetition rate of Gemini is one shot every 20 seconds enabling scientists to undertake multiple parameter scans to obtain comprehensive data sets.