PITZ lights the way

The laser room at PITZ with the new photocathode laser

The operators of the European XFEL will once be able to say that their electrons originally came from Zeuthen. This is where a new photocathode laser has recently been installed in the photo injector test facility PITZ. This laser will help to optimise the sophisticated methods for the production of electron beams for the free-electron laser. Within the next months, the new laser will be submitted to extensive tests.

To ensure that the highly intensive X-ray light will reach the experiments in the end, electron beams have to be produced which have an extremely small diameter and do not diverge. Experts call this transverse emittance – the less of it, the better! The trick, again, is light, although in another form: a laser shoots the high-precision light onto a cathode from which the electrons are emitted and accelerated. The better the light pulses, the better the particle beam.

Next to a prototype in the Max Born Institute (MBI) in Berlin, this laser is the first one worldwide to produce these optimal light pulses – called fl at-top pulses – with a time scheme according to the needs of the TESLA-type superconducting accelerators. The laser developed at MBI reaches much shorter rise and fall times than its forerunners and is able to emit various forms of pulses. The whole laser system occupies about five square metres of the new PITZ laser room. The laser was installed during a PITZ shutdown. At the same time, the facility was equipped with a new electron source or “gun”. “First of all, the gun has to undergo conditioning,” says technical coordinator Jürgen Bähr. “It has to get used to high voltages and improve its vacuum properties.”

The new laser system produces ultraviolet flat-top pulses.

One good property is already there: it generates consider-ably less unwanted dark current. The PITZ team assumes that this is thanks to the new cleaning procedure: the vacuum properties of the built-in copper resonator improved notably after being cleaned particle free and with dry ice.