The oscillator is a commercial product made by Femtolasers. A Titanium doped sapphire (TiS) crystal is pumped by 5.5 Watts of 532 nm green light from a frequency-doubled, diode-pumped neodymium vanadate (Nd:YVO4) laser.

When mode-locked, the oscillator generates pulses of 12 femtoseconds duration with a bandwidth from 750 to 850 nm, at an average power of 550 mW. The repetition rate of the oscillator is 75 megahertz, which corresponds to a train of pulses 13 ns apart, or one every 4 metres. Special dispersion-compensating mirrors are used within the laser cavity to control group velocity dispersion and keep the pulse length short.

The oscillator pulses are stretched to a few picoseconds in a glass block and then sent to the preamplifier. This is a Femtopower Compact Pro, a 9-pass TiS amplifier pumped by a kilohertz frequency-doubled, diode-pumped neodymium YLF laser system (Thales JADE 2). In the preamplifier, one oscillator pulse is amplified every millisecond to an energy of 800mJ; the remaining pulses do not get amplified and are rejected from the pulse train at the next stage.

The train of amplified pulses at 1 kHz repetition rate passes through a pulse selector consisting of a fast Pockels cell and polarizers, which diverts every hundredth pulse into the beam path leading to the Astra laser to make a 10 Hz pulse train that seeds the rest of the amplifier chain.