抄録
Vortex beams, which include phase or polarization singularities, have attracted attention and provided
new approaches to spectroscopic studies. We demonstrate in this paper the application of vortex pulses
to four-wave-mixing (FWM) spectroscopy which is a major technique to investigate the coherent
dynamics of excitons in semiconductors. The measurements provide some unique properties of GaN
excitons: FWM using optical vortex demonstrates the coherent orbital angular momentum dynamics
significantly exceeds the exciton dephasing time and its decay reflects inhomogeneity of rotational phase
gradient; FWM using polarization vortex realizes a snap-shot measurement of optical anisotropies in
GaN films, allowing us to evaluate the uniaxial strain energies and the spin-exchange interaction
constant with high accuracy and sensitivity.
