Gemini is an extension of the front end to make it into a two-beam Petawatt class laser.
The concept of Gemini was developed in 2003-04, and a £3M facility development grant was awarded in 2004. The building of the new facility took three and a half years, and the first experiments were carried out early in 2008.
The output from the front end’s third amplifier is the source beam for Gemini, which consists of a pair of TiS amplifiers, each with its own pump laser and pulse compressor.
The two-beam design of 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.
Each beam will deliver 15 joules to target in a pulse of 30 femtoseconds (i.e. a peak power of 0.5 PW). The maximum focused intensity from one beam is of order 2 x 1021 Wcm-2.
At the start of the project the shot rate was specified as one shot per minute; however, during the course of the project it became possible to upgrade the pump lasers to increase the rate to one shot every 20 seconds. This is an extremely high shot rate for such a facility, and has already led to new experimental approaches to ultra high intensity physics research.
Another unusual feature of Gemini is that the laser room is on the upper floor above the experimental area, so the beams enter the target chamber from above. This provides 360-degree access around the chamber, and allows the beam polarizations to be controlled by the direction they are steered.