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Dipartimento di Fisica - Politecnico di Milano

Ultrafast Photoemission and Optical Spectroscopy (UPhOS)

UPhOS is a facility of the ULTRAS laboratory inside the Physics Department, devoted to the spectroscopy investigations of solids excited by femtosecond laser beams. The laser source provides 50 fs pulses centred at 800 nm (hν = 1.55 eV) with average power of 2 W. Through the use of non-linear optical crystals, laser pulses of 10-13 s in duration, centred at 400, 266 and 200 nm (hν up to 6.2 eV) are achieved, aiming to induce photoemission from solid targets. The ultrashort nature of the laser beam allows us to perform time-resolved spectroscopy with the “pump-probe” technique: the “pump” pulse induces a perturbation in the system under investigation, while the “probe” pulse reveals the effects of the perturbation after a given time-delay. In this way the ultrafast dynamics of the excited states can be observed. The use of largely tunable femtosecond laser pulses opens new, exciting possibilities in the study of electron dynamics in solids within the time-windows typical of scattering phenomena (10-14 s).

The UPhOS facility allows us to perform time-resolved photoemission measurements employing a time-of-flight (ToF) analyzer equipped with a 64 channel MicroChannelPlate detector mounted inside a Mu-metal vacuum chamber. The setup includes an in-situ thin film deposition system. With the same experimental setup, time-resolved reflectivity and magneto-optic Kerr effect measurements can be performed as well.

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