Many properties of condensed matter systems are determined by microscopic processes that occur on femto and picosecond timescales. The development of femtosecond laser systems has provided a unique bench-top tool with which to study and then control ultrafast processes so that the properties of materials can be tuned. We commissioned a new ultrafast optical laboratory in 2005 that today contains 3 separate ultrafast laser systems: a high power mode-locked 100fs, 80 MHz oscillator for time resolved microscopy measurements; a micro-Joule 60 fs regenerative amplifier system with dedicated seed oscillator and optical and infrared optical parametric amplifiers; and a milli-Joule regenerative amplifier system with dedicated seed oscillator. Ancillary apparatus includes autocorrelators, a SPIDER, and beam profiler for pulse characterization, a He gas flow cryostat with room temperature windows, and a photon counting system.

Pump-probe experiment performed with micro-Joule pulses

We perform optical pump-probe experiments in which the sample is 'pumped' by direct optical excitation and the instantaneous state of the sample is ‘probed’ at a later time by a second time delayed optical pulse. By accurately recording the intensity and polarization of the probe pulse we are able to explore transient changes within the electron, phonon and spin populations of the sample. Current and recent projects include the spin dynamics and surface magnetization of Heusler alloys, non-thermal processes within phase change recording materials, optical orientation of linear and angular momentum of electrons within metals, and opto-magnetic switching . We also study other non-linear optical phenomena such as Magnetic Second Harmonic Generation (MSHG).

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