Terahertz pump Terahertz probe spectroscopy is used to follow the dynamic evolution of the far infra-red absorption spectroscopy of a sample following excitation by a high-field femtosecond THz pulse. The excitation pulse is generated by focussing 800 nm radiation onto a lithium niobate crystal. The probe pulse is generated by focussing 800 nm radiation onto a gallium phosphide crystal. The two THz beams are coupled by way of a wire grid polariser. Off-axis parabolic mirrors are then used to steer and focus the resulting THz radiation onto the sample being studied. The output THz beam is focused onto a zinc telluride detection crystal along with a further 800 nm pulse. The resulting THz response is split in a Wollaston prism and detected using a photodiode and two lock-in amplifiers. This technique allows us to study such properties as spin dynamics in quantum materials on a femtosecond timescale.
The Thz Pump Thz Probe experiment is serviced by two linear delay stages with a travel of 150 mm and a 2 micron accuracy, leading to a 1 nanosecond temporal window and resolution of 7 fs in each case.