Polarimetric microscopy for optical control and high precision measurement of valley polarization.

Two-dimensional transition metal dichalcogenides (2D TMDCs) have two degenerate energy valleys in their Brillouin zone, and these two separate valleys can be used as an information carrier in optoelectronic devices. Circularly polarized optical pumping can selectively populate a single valley, resulting in direct band transitions at the populated valley and associated circularly polarized photoluminescence (PL) emission. However, the birefringence and linear dichroism in optical microscopes can not only distort the circular polarization states of optical pumping but also contaminate experimentally derived information about the polarization states of valley-polarized PL signals. To solve this problem, we suggest a polarimetric microscopy method that manipulates the valley population by optical pumping and measures the polarized PL emission of 2D TMDCs; pumping beam polarization can be precisely controlled by the polarization correction unit, and the original polarization state of the emitted PL signal can be recovered using the Mueller matrix inherent to the optical experimental setup. Using our method, errors when measuring the degree of circular polarization in PL signals can be reduced from 19% to 6%, enabling accurate estimation of exciton lifetimes. Our result offers an accurate and reliable way to process information in valley-based optoelectronic devices.