Long focus setup for gas target interactions

To accommodate long focusing distance, the beam is directed to an extension chamber at the south end of the room. Two options are available – an f/20 (3m) parabola located in the extension, or an f/40 parabola reflected from a periscope located in the extension. The f/40 is commonly used because it produces a focus more suitable for laser wakefield acceleration (LWFA) of electrons in a gas target, but careful design is needed to ensure the fluence remains below the damage threshold of the folding mirrors. A typical electron diagnostic layout is shown, where the electrons are generated by LWFA.

Typical geometry for generation of electrons by laser wakefield acceleration in Gemini Target Area Three.

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