Progress Towards Generation of Attosecond Entangled Photons from Two-Photon Decay of Metastable Helium.

Generating attosecond pulses is crucial for measuring electron dynamics of atoms and molecules on the attosecond time scale. Our group is progressing towards a new technique of producing attosecond pulses using entangled photons. We will use entangled biphotons in the extreme-ultraviolet regime generated through two-photon decay of the 1s2s ¹S₀ metastable state in helium to the ground state. The total energy spacing is 20.62eV, resulting in a photon pair correlation time in the attosecond regime. A vacuum chamber and gas cell were designed and constructed, and a 240-nm laser is focused into the gas cell for a direct four-photon excitation of the metastable state. Work is undertaken to detect entangled photons from two-photon decay of metastable helium using a photomultiplier tube. A coincidence measurement setup is also under construction.