Astra Gemini is a high power, ultra-short pulse, high repetition-rate laser. It uses titanium-doped sapphire (TiS) as its active material, and works at 800 nm in the near infra-red part of the spectrum, just outside the region visible to the human eye.
The pulses from Astra Gemini are so short that they are like sheets of light energy thinner than a human hair, which in addition can be focused to a spot a few thousandths of a millimetre across. The energy they contain is thus delivered to a very small target extremely quickly, allowing experimenters to study the way matter behaves under extreme conditions of temperature and pressure.
The two-beam design of Astra Gemini was chosen to maximise the flexibility of the laser system and hence the range of experiments that could be performed. Having two beams allows the possibility of combinations of long and short pulses, different focal lengths, variations in relative timing and mixed polarizations. One of the most important features of Astra Gemini is its high shot repetition rate, which allows users of the facility to scan through wide ranges of laser and target parameters in a relatively short time, and home in on those that give the most useful and interesting results.
Each beam delivers 15 joules to target in a pulse of 40 femtoseconds (i.e. a peak power of 0.5 PW). The maximum focused intensity from one beam is 3x1021 Wcm-2, higher than the 1021 Wcm-2 achieved with the Vulcan Petawatt system.
Laser-plasma interactions under these conditions can produce energetic beams of electrons and protons, high harmonics of the laser frequency and also bright, coherent sources of X-rays. Using the capabilities of Astra Gemini, experimenters can address fundamental questions in astrophysics and plasma physics. Experiments on Astra Gemini have demonstrated the acceleration of electrons in a gas jet to energies comparable with those from large conventional accelerators. There are also possibilities for doing quantum electrodynamics experiments.