Widefield Femtosecond Spin Polarization Imaging via Multiplexed Off-Axis Holography

Understanding and controlling ultrafast spin polarization dynamics in space and time is critical for the development of next generation nanoelectronics devices [1]. Spin-polarized dynamics can be probed on femtosecond timescales through ultrafast circular dichroism (CD) and time-resolved Faraday rotation (FR) spectroscopy, as these pumpprobe techniques exploit the distinct interactions of circularly polarized pulses with spin states. In the presence of an unbalance in spin population induced by a circularly polarized excitation pulse in materials that present strong spin-orbit coupling, CD measures the difference in absorption (resonant response) of left and right circularly polarized light, while FR (often called optical rotatory dispersion, ORD) probes the phase difference between the two circular components (off-resonant response, birefringence).