Target Area 2 (TA2) receives a beam which is diverted before the final dual beam amplifier of Gemini. After compression, the energy on target is on average 500 mJ in 40 fs (a peak power of 12.5 TW). Focused intensities can reach a few x 1019 Wcm-2. TA2 has a maximum pulse repetition rate of 2 Hz for continuous operation to avoid heating effects in the compressor gratings. Experiments can be performed with gas or solid targets in a range of focusing geometries, and there is a suite of plasma diagnostics available to study the laser-target interactions.
In TA2 we have developed an enhanced optical diagnostic capability for high intensity experiments, such as electron acceleration, photon acceleration, self-focussing and shock wave studies. We use a hollow fibre pulse compressor [1] to provide broad bandwidth (>100nm) pulses compressed to 10fs, enabling scientists to probe inside the main laser pulse (40fs) itself and understand electron dynamics on an ultrafast timescale. Along with this, a commercial tuneable optical parametric amplifier (Topas-White from Light Conversion) generates a probe at a wavelength where detectors are not blinded by the strong emission of harmonic light from the plasma. We also demonstrated the use of an optical Kerr gate within the imaging system to effectively reduce the exposure time of the detector to the length of the gating pulse. Using the hollow fibre, this technique has the potential to create gated imaging and streaked imaging with a resolution of order 10fs [2].
As the first high-power Ti:Sapphire user facility in the UK, TA2 opened up opportunities for plasma physics experiments driven by ultra-short pulses (<40 fs) particularly in electron and ion acceleration and high harmonic generation. In fact we recently celebrated the tenth anniversary of the breakthrough “dream-beam" results on electron acceleration published as three papers in Nature, one of which was the experiment conducted in TA2 [3]. We now provide longer access periods in TA2 than those available in primary CLF target areas in order to allow user groups to explore ideas and techniques that are challenging on short timescales.
[1] J.S. Robinson et al., Appl. Phys. B 85, 525 (2006)
[2] D. R. Symes et al., Appl. Phys. Lett. 96, 011109 (2010)
[3] S. P. D. Mangles et al Nature 431, 535 (2004)
